Mercurial > hg > mpdl-xml-content
view texts/XML/echo/fr/Voltaire_1738_1FP6HWGK.xml @ 13:facea8c79160
DE Specs Version 2.1.1 Autumn 2011
| author | Klaus Thoden <kthoden@mpiwg-berlin.mpg.de> |
|---|---|
| date | Thu, 02 May 2013 11:29:00 +0200 |
| parents | 22d6a63640c6 |
| children |
line wrap: on
line source
<?xml version="1.0" encoding="utf-8"?><echo xmlns="http://www.mpiwg-berlin.mpg.de/ns/echo/1.0/" xmlns:de="http://www.mpiwg-berlin.mpg.de/ns/de/1.0/" xmlns:dcterms="http://purl.org/dc/terms" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:echo="http://www.mpiwg-berlin.mpg.de/ns/echo/1.0/" xmlns:xhtml="http://www.w3.org/1999/xhtml" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" version="1.0RC"> <metadata> <dcterms:identifier>ECHO:1FP6HWGK.xml</dcterms:identifier> <dcterms:creator identifier="GND:118627813">Voltaire</dcterms:creator> <dcterms:title xml:lang="fr">Elémens de la philosophie de Neuton : mis à la portée de tout le monde</dcterms:title> <dcterms:date xsi:type="dcterms:W3CDTF">1738</dcterms:date> <dcterms:language xsi:type="dcterms:ISO639-3">fra</dcterms:language> <dcterms:rights>CC-BY-SA</dcterms:rights> <dcterms:license xlink:href="http://creativecommons.org/licenses/by-sa/3.0/">CC-BY-SA</dcterms:license> <dcterms:rightsHolder xlink:href="http://www.mpiwg-berlin.mpg.de">Max Planck Institute for the History of Science, Library</dcterms:rightsHolder> </metadata> <text xml:lang="fr" type="free"> <div xml:id="echoid-div1" type="section" level="1" n="1"><pb file="0001" n="1"/> <pb file="0002" n="2"/> <p> <s xml:id="echoid-s1" xml:space="preserve">T <lb/>No. </s> <s xml:id="echoid-s2" xml:space="preserve">122.</s> <s xml:id="echoid-s3" xml:space="preserve"/> </p> <pb file="0003" n="3"/> <handwritten/> <pb file="0004" n="4"/> <handwritten/> <handwritten/> <handwritten/> <pb file="0005" n="5"/> </div> <div xml:id="echoid-div2" type="section" level="1" n="2"> <head xml:id="echoid-head1" xml:space="preserve">ELEMENS <lb/>DE LA <lb/>PHILOSOPHIE <lb/>DE NEUTON.</head> <pb file="0006" n="6"/> <pb file="0007" n="7"/> <figure> <image file="0007-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0007-01"/> </figure> <pb file="0008" n="8"/> <pb file="0009" n="9"/> <figure> <image file="0009-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0009-01"/> </figure> <pb file="0010" n="10"/> <pb file="0011" n="11"/> </div> <div xml:id="echoid-div3" type="section" level="1" n="3"> <head xml:id="echoid-head2" xml:space="preserve"><emph style="red">ELÉMENS</emph></head> <head xml:id="echoid-head3" xml:space="preserve">DELA</head> <head xml:id="echoid-head4" xml:space="preserve">PHILOSOPHIE</head> <head xml:id="echoid-head5" xml:space="preserve"><emph style="red">DE NEUTON,</emph></head> <p> <s xml:id="echoid-s4" xml:space="preserve">Mis à la portée de tout le monde.</s> <s xml:id="echoid-s5" xml:space="preserve"/> </p> </div> <div xml:id="echoid-div4" type="section" level="1" n="4"> <head xml:id="echoid-head6" xml:space="preserve"><emph style="red">Par M<emph style="super">R</emph>. DE VOLTAIRE.</emph></head> <figure> <image file="0011-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0011-01"/> </figure> </div> <div xml:id="echoid-div5" type="section" level="1" n="5"> <head xml:id="echoid-head7" xml:space="preserve"><emph style="red">A AMSTERDAM,</emph></head> <p> <s xml:id="echoid-s6" xml:space="preserve">Chez <emph style="sc">Etienne</emph> <emph style="sc">Ledet</emph> & </s> <s xml:id="echoid-s7" xml:space="preserve">Compagnie.</s> <s xml:id="echoid-s8" xml:space="preserve"/> </p> </div> <div xml:id="echoid-div6" type="section" level="1" n="6"> <head xml:id="echoid-head8" xml:space="preserve"><emph style="red">M. DCC. XXXVIII.</emph></head> <pb file="0012" n="12"/> <pb file="0013" n="13"/> <figure> <image file="0013-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0013-01"/> </figure> </div> <div xml:id="echoid-div7" type="section" level="1" n="7"> <head xml:id="echoid-head9" xml:space="preserve">A MADAME <lb/>LA <lb/>MARQUISE DU CH.**</head> <p> <s xml:id="echoid-s9" xml:space="preserve">TU m’appelles à toi vaſte & </s> <s xml:id="echoid-s10" xml:space="preserve">puiſſant Génie, <lb/>Minerve de la France, immortelle Emilie, <lb/>Diſciple de Neuton, & </s> <s xml:id="echoid-s11" xml:space="preserve">de la Vérité, <lb/>Tu pénétres mes ſens des feux de ta clarté, <pb o="4" file="0014" n="14" rhead="ELEMENS"/> Je renonce aux lauriers, que long-tems au Théâtre <lb/>Chercha d’un vain plaiſir mon eſprit idolâtre. <lb/></s> <s xml:id="echoid-s12" xml:space="preserve">De ces triomphes vains mon cœur n’eſt plus touché. </s> <s xml:id="echoid-s13" xml:space="preserve"><lb/>Que le jaloux Rufus à la terre attaché, <lb/>Traîne au bord du tombeau la fureur inſenſée, <lb/>D’enfermer dans un vers un fauſſe penſée, <lb/>Qu’il arme contre moi ſes languiſſantes mains <lb/>Des traits qu’il deſtinoit au reſte des humains. </s> <s xml:id="echoid-s14" xml:space="preserve"><lb/>Que quatre fois par mois un ignorant Zoile, <lb/>Eleve en fremiſſant une voix imbécile. </s> <s xml:id="echoid-s15" xml:space="preserve"><lb/>Je n’entends point leurs cris que la haine à formez. </s> <s xml:id="echoid-s16" xml:space="preserve"><lb/>Je ne vois point leurs pas dans la fange imprimez. </s> <s xml:id="echoid-s17" xml:space="preserve"><lb/>Le charme tout-puiſſant de la Philoſophie <lb/>Eleve un eſprit ſage au-deſſus de l’envie. </s> <s xml:id="echoid-s18" xml:space="preserve"><lb/>Tranquille au haut des Cieux que Neuton s’eſt ſou-<lb/>mis, <lb/>Il ignore en effet s’il a des Ennemis. </s> <s xml:id="echoid-s19" xml:space="preserve"><lb/>Je ne les connois plus. </s> <s xml:id="echoid-s20" xml:space="preserve">Déja de la carriere <lb/>L’auguſte Vérité vient m’ouvrir la barriere. </s> <s xml:id="echoid-s21" xml:space="preserve"><lb/>Déja ces tourbillons l’un par l’autre preſſez, <lb/>Se mouvant ſans eſpace, & </s> <s xml:id="echoid-s22" xml:space="preserve">ſans règle entaſſez, <lb/>Ces fantômes ſavants à mes yeux diſparaiſſent.</s> <s xml:id="echoid-s23" xml:space="preserve"> <pb o="5" file="0015" n="15" rhead="DE NEUTON."/> Un jour plus pur me luit; </s> <s xml:id="echoid-s24" xml:space="preserve">les mouvements renaiſ-<lb/>ſent. <lb/></s> <s xml:id="echoid-s25" xml:space="preserve">L’eſpace qui de Dieu contient l’immenſité, <lb/>Voit rouler dans ſon ſein l’Univers limité, <lb/>Cet Univers ſi vaſte à notre faible vûe, <lb/>Et qui n’eſt qu’un atome, un point dans l’éten-<lb/>due.</s> <s xml:id="echoid-s26" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s27" xml:space="preserve">Dieu parle, & </s> <s xml:id="echoid-s28" xml:space="preserve">le Chaos ſe diſſipe à ſa voix; <lb/></s> <s xml:id="echoid-s29" xml:space="preserve">Vers un centre commun tout gravite à la fois, <lb/>Ce reſſort ſi puiſſant l’ame de la Nature, <lb/>Etoit enſéveli dans une nuit obſcure, <lb/>Le compas de Neuton meſurant l’Univers, <lb/>Leve enfin ce grand voile & </s> <s xml:id="echoid-s30" xml:space="preserve">les Cieux ſont ou-<lb/>verts.</s> <s xml:id="echoid-s31" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s32" xml:space="preserve">Il déploye à mes yeux par une main ſavante, <lb/>De l’Aſtre des Saiſons la robe étincelante. <lb/></s> <s xml:id="echoid-s33" xml:space="preserve">L’Emeraude, l’azur, le pourpre, le rubis, <lb/>Sont l’immortel tiſſu dont brillent ſes habits. </s> <s xml:id="echoid-s34" xml:space="preserve"><lb/>Chacun de ſes rayons dans ſa ſubſtance pure, <lb/>Porte en ſoi les couleurs dont ſe peint la Nature, <lb/>Et confondus enſemble, ils éclairent nos yeux, <pb o="6" file="0016" n="16" rhead="ELEMENS"/> Ils animent le Monde, ils empliſſent les Cieux.</s> <s xml:id="echoid-s35" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s36" xml:space="preserve">Confidens du Très Haut, Subſtances éternelles, <lb/>Qui brûlés de ſes feux, qui couvrez de vos aîles <lb/>Le Trône où votre Maître eſt aſſis parmi vous, <lb/>Parlez, du grand Neuton n’étiez-vous point ja-<lb/>loux?</s> <s xml:id="echoid-s37" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s38" xml:space="preserve">La Mer entend ſa voix. </s> <s xml:id="echoid-s39" xml:space="preserve">Je vois l’humide Em-<lb/>pire, <lb/>S’élever, s’avancer, vers le Ciel qui l’attire, <lb/>Mais un pouvoir central arrête ſes efforts, <lb/>La Mer tombe, s’affaiſſe, & </s> <s xml:id="echoid-s40" xml:space="preserve">roule vers ſes bords.</s> <s xml:id="echoid-s41" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s42" xml:space="preserve">Cometes que l’on craint à l’égal du tonnerre, <lb/>Ceſſez dépouvanter les Peuples de la Terre, <lb/>Dans une ellipſe immenſe achevez votre cours, <lb/>Remontez, deſcendez près de l’Aſtre des jours, <lb/>Lancez vos feux, volez, & </s> <s xml:id="echoid-s43" xml:space="preserve">revenant ſans ceſſe, <lb/>Des Mondes épuiſez ranimez la vieilleſſe.</s> <s xml:id="echoid-s44" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s45" xml:space="preserve">Et toi Sœur du Soleil, Aſtre, qui dans les Cieux, <lb/>Des ſages éblouï<unsure/>s trompois les faibles yeux, <lb/>Neuton de ta carriere a marqué les limites, <pb o="7" file="0017" n="17" rhead="DE NEUTON."/> Marche, éclaire les nuits; </s> <s xml:id="echoid-s46" xml:space="preserve">tes bornes ſont preſcri-<lb/>tes.</s> <s xml:id="echoid-s47" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s48" xml:space="preserve">Terre change de forme, & </s> <s xml:id="echoid-s49" xml:space="preserve">que la peſanteur, <lb/>En abaiſſant le Pole, éleve l’Equateur. <lb/></s> <s xml:id="echoid-s50" xml:space="preserve">Pole immobile aux yeux, ſi lent dans votre courſe, <lb/>Fuyez le char glacé de ſept Aſtres de l’Ourſe, <lb/>Einbraſſez dans le cours de vos longs mouve-<lb/>ments, <lb/>Deux cens ſiècles entiers par delà ſix mille ans.</s> <s xml:id="echoid-s51" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s52" xml:space="preserve">Que ces objets ſont beaux! que notre ame épurée <lb/>Vole à ces vérités dont elle eſt éclairée! <lb/>Oui dans le ſein de Dieu, loin de ce corps mortel, <lb/>L’eſprit ſemble écouter la voix de l’Eternel.</s> <s xml:id="echoid-s53" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s54" xml:space="preserve">Vous à qui cette voix ſe fait ſi bien entendre <lb/>Comment avez-vous pu, dans un âge encor tendre, <lb/>Malgré les vains plaiſirs ces écueils des beaux <lb/>jours, <lb/>Prendre un vol ſi hardi, ſuivre un ſi vaſte cours, <lb/>Marcher après Neuton dans cette route obſcure <lb/>Du labyrinthe immenſe, où ſe perd la Nature? <lb/></s> <s xml:id="echoid-s55" xml:space="preserve">Puiſſai je auprès de vous, dans ce Temple écarté, <pb o="8" file="0018" n="18" rhead="ELEMENS DE NEUTON."/> Aux regards des Français montrer la Vérité. <lb/></s> <s xml:id="echoid-s56" xml:space="preserve">Tandis <anchor type="note" xlink:href="" symbol="(a)"/> qu’Algaroti, ſûr d’inſtruire & </s> <s xml:id="echoid-s57" xml:space="preserve">de plaire, Vers le Tibre étonné conduit cette Etrangere, <lb/>Que de nouvelles fleurs il orne ſes atraits, <lb/>Le Compas à la main j’en tracerai les traits, <lb/>De mes crayons groſſiers je peindrai l’Immortelle. <lb/></s> <s xml:id="echoid-s58" xml:space="preserve">Cherchant à l’embellir je la rendrais moins belle, <lb/>Elle eſt ainſi que vous, noble, ſimple & </s> <s xml:id="echoid-s59" xml:space="preserve">ſans fard, <lb/>Au-deſſus de l’éloge, au-deſſus de mon Art.</s> <s xml:id="echoid-s60" xml:space="preserve"/> </p> <note symbol="(a)" position="foot" xml:space="preserve">Mr. Algaroti jeune Vénitien fait imprimer actuelle-<lb/>ment à Veniſe un Traité ſur la lumiere dans lequel il ex-<lb/>plique l’attraction.</note> <figure> <image file="0018-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0018-01"/> </figure> <pb file="0019" n="19"/> <figure> <image file="0019-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0019-01"/> </figure> </div> <div xml:id="echoid-div8" type="section" level="1" n="8"> <head xml:id="echoid-head10" xml:space="preserve">AMADAME <lb/>LA <lb/>MARQUISE DU CH**</head> <head xml:id="echoid-head11" style="it" xml:space="preserve">AVANT PROPOS.</head> <p> <s xml:id="echoid-s61" xml:space="preserve">MADAME,</s> </p> <p> <s xml:id="echoid-s62" xml:space="preserve">Cen’eſt point ici une Marquiſe, ni une <lb/>Philoſophie imaginaire. </s> <s xml:id="echoid-s63" xml:space="preserve">L’étude ſolide que <pb o="10" file="0020" n="20" rhead="DE LA PHILOSOPHIE"/> vous avez faite de pluſieurs nouvelles vé-<lb/>rités & </s> <s xml:id="echoid-s64" xml:space="preserve">le fruit d’un travail reſpectable, ſont <lb/>ce que j’offre au Public pour votre gloire, <lb/>pour celle de votre Sexe, & </s> <s xml:id="echoid-s65" xml:space="preserve">pour l’utilité de <lb/>quiconque voudra cultiver ſa raiſon & </s> <s xml:id="echoid-s66" xml:space="preserve">jouï<unsure/>r <lb/>ſans peine de vos recherches. </s> <s xml:id="echoid-s67" xml:space="preserve">Il ne faut <lb/>pas s’attendre à trouver ici des agrémens. <lb/></s> <s xml:id="echoid-s68" xml:space="preserve">Toutes les mains ne ſavent pas couvrir de <lb/>fleurs les épines des Sciences; </s> <s xml:id="echoid-s69" xml:space="preserve">je dois me <lb/>borner à tâcher de bien concevoir quelques <lb/>Vérités & </s> <s xml:id="echoid-s70" xml:space="preserve">à les faire voir avec ordre & </s> <s xml:id="echoid-s71" xml:space="preserve"><lb/>clarté. </s> <s xml:id="echoid-s72" xml:space="preserve">Ce ſeroit à vous de leur préter des <lb/>ornemens.</s> <s xml:id="echoid-s73" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s74" xml:space="preserve">Ce nom de Nouvelle Philoſophie ne ſe-<lb/>roit que le titre d’un Roman nouveau, s’il <lb/>n’annonçoit que les conjectures d’un Mo-<lb/>derne, oppoſées aux fantaiſies des Anciens. <lb/></s> <s xml:id="echoid-s75" xml:space="preserve">Une Philoſophie qui ne ſeroit établie que <lb/>ſur des explications hazardées, ne mériteroit <lb/>pas en rigueur le moindre examen. </s> <s xml:id="echoid-s76" xml:space="preserve">Car il <lb/>y a un nombre innombrable de manieres <lb/>d’arriver à l’Erreur, il n’y a qu’une ſeule rou-<lb/>te vers la Vérité: </s> <s xml:id="echoid-s77" xml:space="preserve">il y a donc l’infini con-<lb/>tre un à parier, qu’un Philoſophe qui ne <lb/>s’appuiera que ſur des Hypothèſes ne dira <lb/>que des chiméres. </s> <s xml:id="echoid-s78" xml:space="preserve">Voilà pourquoi tous les <pb o="11" file="0021" n="21" rhead="DE NEUTON."/> Anciens qui ont raifonné ſur la Phyſique ſans <lb/>avoir le flambeau de l’expérience, n’ont <lb/>été que des aveugles, qui expliquoient la <lb/>nature des couleurs à d’autres aveugles.</s> <s xml:id="echoid-s79" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s80" xml:space="preserve">Cet Ecrit ne ſera point un cours de Phyſi-<lb/>que complet. </s> <s xml:id="echoid-s81" xml:space="preserve">S’il étoit tel, il ſeroit immen-<lb/>ſe; </s> <s xml:id="echoid-s82" xml:space="preserve">une ſeule partie de la Phyſique occupe <lb/>la vie de pluſieurs hommes, & </s> <s xml:id="echoid-s83" xml:space="preserve">les laiſſe ſou-<lb/>vent mourir dans l’incertitude.</s> <s xml:id="echoid-s84" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s85" xml:space="preserve">Vous-vous bornez dans cette étude, dont <lb/>je rends compte, à vous faire ſeulement une <lb/>idée nette de ces Reſſorts ſi déliez & </s> <s xml:id="echoid-s86" xml:space="preserve">ſi puiſ-<lb/>ſants, de ces Loix primitives de la Nature, <lb/>que Neuton a découvertes; </s> <s xml:id="echoid-s87" xml:space="preserve">à examiner <lb/>juſqu’où il s’eſt arrêté. </s> <s xml:id="echoid-s88" xml:space="preserve">Nous commence-<lb/>rons, comme lui, par la lumiere: </s> <s xml:id="echoid-s89" xml:space="preserve">c’eſt de <lb/>tous les corps qui ſe font ſentir à nous le <lb/>plus délié, le plus approchant de l’infini en <lb/>petit, c’eſt pourtant celui que nous con-<lb/>noiſſons davantage. </s> <s xml:id="echoid-s90" xml:space="preserve">On l’a ſuivi dans ſes <lb/>mouvemens, dans ſes effets; </s> <s xml:id="echoid-s91" xml:space="preserve">on eſt par-<lb/>venu à l’anatomiſer, à le ſéparer en toutes <lb/>ſes parties poſſibles. </s> <s xml:id="echoid-s92" xml:space="preserve">C’eſt celui de tous les <lb/>corps dont la nature intime eſt le plus dé- <pb o="12" file="0022" n="22" rhead="DE LA PHILOSOPHIE"/> veloppée. </s> <s xml:id="echoid-s93" xml:space="preserve">C’eſt celui qui nous approche de <lb/>plus près des premiers Reſſorts de la Na-<lb/>ture.</s> <s xml:id="echoid-s94" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s95" xml:space="preserve">On tâchera de mettre ces Elémens, à la <lb/>portée de ceux qui ne connaiſſent de <lb/>Neuton & </s> <s xml:id="echoid-s96" xml:space="preserve">de la Philoſophie que le nom <lb/>ſeul. </s> <s xml:id="echoid-s97" xml:space="preserve">La Science de la Nature eſt un bien <lb/>qui appartient à tous les hommes. </s> <s xml:id="echoid-s98" xml:space="preserve">Tous <lb/>voudroient avoir connaiſſance de leur bien, <lb/>peu ont le tems ou la patience de le calcu-<lb/>ler; </s> <s xml:id="echoid-s99" xml:space="preserve">Neuton a compté pour eux. </s> <s xml:id="echoid-s100" xml:space="preserve">Il faudra <lb/>ici ſe contenter quelquefois de la ſomme de <lb/>ces calculs. </s> <s xml:id="echoid-s101" xml:space="preserve">Tous les jours un homme pu-<lb/>blic, un Miniſtre, ſe forme une idée juſte <lb/>du réſultat des opérations que lui-même n’a <lb/>pu faire; </s> <s xml:id="echoid-s102" xml:space="preserve">d’autres yeux ont vu pour lui, d’au-<lb/>tres mains ont travaillé, & </s> <s xml:id="echoid-s103" xml:space="preserve">le mettent en <lb/>état par un compte fidèle de porter ſon ju-<lb/>gement. </s> <s xml:id="echoid-s104" xml:space="preserve">Tout homme d’eſprit ſera à peu <lb/>près dans le cas de ce Miniſtre.</s> <s xml:id="echoid-s105" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s106" xml:space="preserve">La Philoſophie de Neuton a ſemblé juſ-<lb/>qu’à préſent à beaucoup de perſonnes auſſi <lb/>inintelligible que celle des Anciens: </s> <s xml:id="echoid-s107" xml:space="preserve">mais <lb/>l’obſcurité des Grecs venoit de ce qu’en ef-<lb/>fet ils n’avoient point de lumiere; </s> <s xml:id="echoid-s108" xml:space="preserve">& </s> <s xml:id="echoid-s109" xml:space="preserve">les té- <pb o="13" file="0023" n="23" rhead="DE NEUTON."/> nèbres de Neuton viennent de ce que ſa <lb/>lumiere étoit trop loin de nos yeux. </s> <s xml:id="echoid-s110" xml:space="preserve">Il a <lb/>trouvé des vérités: </s> <s xml:id="echoid-s111" xml:space="preserve">mais ils les a cherchées <lb/>& </s> <s xml:id="echoid-s112" xml:space="preserve">placées dans un abîme, il faut y deſcen-<lb/>dre & </s> <s xml:id="echoid-s113" xml:space="preserve">les apporter au grand jour.</s> <s xml:id="echoid-s114" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s115" xml:space="preserve">On trouvera ici toutes celles qui condui-<lb/>ſent à établir la nouvelle proprieté de la <lb/>matiere découverte par Neuton. </s> <s xml:id="echoid-s116" xml:space="preserve">On ſera <lb/>obligé de parler de quelques ſingularités, <lb/>qui ſe ſont trouvées ſur la route dans cette <lb/>carriere; </s> <s xml:id="echoid-s117" xml:space="preserve">mais on ne s’écartera point <lb/>du but.</s> <s xml:id="echoid-s118" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s119" xml:space="preserve">Ceux qui voudront s’inſtruire davantage, <lb/>liront les excellentes Phyſiques des Grave-<lb/>ſandes, des Keils, des Muſchenbroeks, des <lb/>Pembertons & </s> <s xml:id="echoid-s120" xml:space="preserve">s’approcheront de Neuton <lb/>par degrez.</s> <s xml:id="echoid-s121" xml:space="preserve"/> </p> <figure> <image file="0023-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0023-01"/> </figure> <pb file="0024" n="24"/> <figure> <image file="0024-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0024-01"/> </figure> </div> <div xml:id="echoid-div9" type="section" level="1" n="9"> <head xml:id="echoid-head12" xml:space="preserve">CHAPITRE PREMIER.</head> <head xml:id="echoid-head13" style="it" xml:space="preserve">Ce que c’eſt que la Lumiere & comment elle <lb/>vient à nous.</head> <p> <s xml:id="echoid-s122" xml:space="preserve">LES GRECS & </s> <s xml:id="echoid-s123" xml:space="preserve">enſuite tous les Peu-<lb/> <anchor type="note" xlink:label="note-0024-01a" xlink:href="note-0024-01"/> ples Barbares, qui ont appris d’eux à <lb/>raiſonner & </s> <s xml:id="echoid-s124" xml:space="preserve">à ſe tromper, ont dit de Siè-<lb/>cleen Siècle: </s> <s xml:id="echoid-s125" xml:space="preserve">„La Lumiere eſt un accident, <lb/>& </s> <s xml:id="echoid-s126" xml:space="preserve">cet accident eſt l’acte du tranſparent <lb/>entant que tranſparent, les couleurs ſont ce <lb/>qui meut les corps tranſparens. </s> <s xml:id="echoid-s127" xml:space="preserve">Les corps <lb/>lumineux & </s> <s xml:id="echoid-s128" xml:space="preserve">colorez ont des qualités ſem- <pb o="15" file="0025" n="25" rhead="DE NEUTON."/> blables à celles qu’ils excitent en nous <lb/>par la grande raiſon que rien ne donne <lb/>ce qu’il n’a pas. </s> <s xml:id="echoid-s129" xml:space="preserve">Enfin, la lumiere & </s> <s xml:id="echoid-s130" xml:space="preserve">les <lb/>couleurs ſont un mêlange du chaud, du <lb/>froid, du ſec, & </s> <s xml:id="echoid-s131" xml:space="preserve">de l’humide; </s> <s xml:id="echoid-s132" xml:space="preserve">car l’humi-<lb/>de, le ſec, le froid, & </s> <s xml:id="echoid-s133" xml:space="preserve">le chaud, étant <lb/>les Principes de tout, il faut bien que les <lb/>couleurs en ſoient un compoſé”.</s> <s xml:id="echoid-s134" xml:space="preserve"/> </p> <div xml:id="echoid-div9" type="float" level="2" n="1"> <note position="left" xlink:label="note-0024-01" xlink:href="note-0024-01a" xml:space="preserve">Défini-<lb/>tion ſin-<lb/>guliére <lb/>par les <lb/>Péri-<lb/>patéti-<lb/>ciens.</note> </div> <p> <s xml:id="echoid-s135" xml:space="preserve">C’eſt cet abſurde galimatias que des <lb/>Maîtres d’ignorance, payez par le Public, <lb/>ont fait reſpecter à la crédulité humaine <lb/>pendant tant d’années: </s> <s xml:id="echoid-s136" xml:space="preserve">c’eſt ainſi qu’on a <lb/>raiſonné preſque ſur-tout, juſqu’aux tems <lb/>des Galilées & </s> <s xml:id="echoid-s137" xml:space="preserve">des Deſcartes. </s> <s xml:id="echoid-s138" xml:space="preserve">Long-tems mê-<lb/>me après eux ce Jargon, qui deshonore l’En-<lb/>tendement humain, a ſubſiſté dans pluſieurs <lb/>Ecoles. </s> <s xml:id="echoid-s139" xml:space="preserve">J’oſe dire que la Raiſon de l’hom-<lb/>me, ainſi obſcurcie, eſt bien au-deſſous de <lb/>ces connaiſſances ſi bornées, mais ſi ſûres, <lb/>que nous appellons Inſtinct dans les Brutes. <lb/></s> <s xml:id="echoid-s140" xml:space="preserve">Ainſi nous ne pouvons trop nous féliciter <lb/>d’être nez dans un tems & </s> <s xml:id="echoid-s141" xml:space="preserve">chez un Peu-<lb/>ple, où l’on commence à ouvrir les yeux, <lb/>& </s> <s xml:id="echoid-s142" xml:space="preserve">à jouïr du plus bel appanage de l’Humani-<lb/>té, l’uſage de la Raiſon.</s> <s xml:id="echoid-s143" xml:space="preserve"/> </p> <pb o="16" file="0026" n="26" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s144" xml:space="preserve">Tous les prétendus Philoſophes ayant <lb/>donc deviné au hazard, à travers le voile <lb/>qui couvroit la Nature, Deſcartes eſt ve-<lb/>nu qui a découvert un coin de ce grand <lb/>voile. </s> <s xml:id="echoid-s145" xml:space="preserve">Il a dit: </s> <s xml:id="echoid-s146" xml:space="preserve">la Lumiere eſt une matiere <lb/>fine & </s> <s xml:id="echoid-s147" xml:space="preserve">déliée, qui eſt répandue par-tout, & </s> <s xml:id="echoid-s148" xml:space="preserve"><lb/>qui frappe nos yeux. </s> <s xml:id="echoid-s149" xml:space="preserve">Les couleurs ſont les <lb/>ſenſations que Dieu excite en nous, ſelon <lb/>les divers mouvemens qui portent cette <lb/>Matiere à nos organes. </s> <s xml:id="echoid-s150" xml:space="preserve">Juſques-là Deſcar-<lb/>tes a eu raiſon, il falloit, ou qu’il s’en tint <lb/>là, ou qu’en allant plus loin, l’expérience <lb/>fût ſon guide. </s> <s xml:id="echoid-s151" xml:space="preserve">Mais il étoit poſſédé de l’en-<lb/> <anchor type="note" xlink:label="note-0026-01a" xlink:href="note-0026-01"/> vie d’établir un Syſtême. </s> <s xml:id="echoid-s152" xml:space="preserve">Cette paſſion fit <lb/>dans ce grand Homme ce que font les paſ-<lb/>ſions dans tous les hommes; </s> <s xml:id="echoid-s153" xml:space="preserve">elles les en-<lb/>traînent au-delà de leurs Principes.</s> <s xml:id="echoid-s154" xml:space="preserve"/> </p> <div xml:id="echoid-div10" type="float" level="2" n="2"> <note position="left" xlink:label="note-0026-01" xlink:href="note-0026-01a" xml:space="preserve">L’Eſprit <lb/>Syſté-<lb/>matique <lb/>a égaré <lb/>Deſear-<lb/>tes.</note> </div> <p> <s xml:id="echoid-s155" xml:space="preserve">Il avoit poſé pour premier fondement de <lb/>ſa Philoſophie, qu’il ne falloit rien croi-<lb/>re ſans évidence; </s> <s xml:id="echoid-s156" xml:space="preserve">& </s> <s xml:id="echoid-s157" xml:space="preserve">cependant au mépris <lb/>de ſa propre Règle, il imagine trois Elé-<lb/>mens formez des cubes prétendus qu’il ſup-<lb/>poſe avoir été faits par le Créateur, & </s> <s xml:id="echoid-s158" xml:space="preserve">s’ê-<lb/>tre briſez en tournant ſur eux-mêmes, lorſ-<lb/>qu’ils ſortirent des mains de Dieu. </s> <s xml:id="echoid-s159" xml:space="preserve">Ces trois <lb/>Elémens imaginaires ſont, comme on ſait:</s> <s xml:id="echoid-s160" xml:space="preserve"/> </p> <pb o="17" file="0027" n="27" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s161" xml:space="preserve">1<emph style="super">0</emph>. </s> <s xml:id="echoid-s162" xml:space="preserve">La partie la plus épaiſſe de ces cubes, <lb/>& </s> <s xml:id="echoid-s163" xml:space="preserve">c’eſt cet Elément groſſier dont ſe forme-<lb/> <anchor type="note" xlink:label="note-0027-01a" xlink:href="note-0027-01"/> rent ſelon lui les corps ſolides des Planetes, <lb/>les Mers, l’Air même.</s> <s xml:id="echoid-s164" xml:space="preserve"/> </p> <div xml:id="echoid-div11" type="float" level="2" n="3"> <note position="right" xlink:label="note-0027-01" xlink:href="note-0027-01a" xml:space="preserve">Son <lb/>Syſtê-<lb/>me.</note> </div> <p> <s xml:id="echoid-s165" xml:space="preserve">2<emph style="super">0</emph>. </s> <s xml:id="echoid-s166" xml:space="preserve">La pouſſiere impalpable que le briſe-<lb/>ment de ces dés avoit produite, & </s> <s xml:id="echoid-s167" xml:space="preserve">qui rem-<lb/>plit à l’infini les interſtices de l’Univers in-<lb/>fini dans lequel il ne ſuppoſe aucun vuide.</s> <s xml:id="echoid-s168" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s169" xml:space="preserve">3<emph style="super">0</emph>. </s> <s xml:id="echoid-s170" xml:space="preserve">Les milieux de ces prétendus dés bri-<lb/>ſés, attenués également de tous côtés, & </s> <s xml:id="echoid-s171" xml:space="preserve">en-<lb/>fin arondis en boules, dont il lui plaît de fai-<lb/>re la lumiere, & </s> <s xml:id="echoid-s172" xml:space="preserve">qu’il répand gratuitement <lb/>dans l’Univers.</s> <s xml:id="echoid-s173" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s174" xml:space="preserve">Plus ce Syſtême étoit ingénieuſement ima-<lb/> <anchor type="note" xlink:label="note-0027-02a" xlink:href="note-0027-02"/> giné, plus vous ſentez qu’il étoit indigne <lb/>d’un Philoſophe. </s> <s xml:id="echoid-s175" xml:space="preserve">Car, puiſque rien de tout <lb/>cela n’eſt prouvé, autant valloit adopter le <lb/>froid & </s> <s xml:id="echoid-s176" xml:space="preserve">le chaud, le ſec & </s> <s xml:id="echoid-s177" xml:space="preserve">l’humide. </s> <s xml:id="echoid-s178" xml:space="preserve">Erreur <lb/>pour erreur qu’importe laquelle domine! <lb/>Ne perdons point de tems à combattre cette <lb/>création des cubes & </s> <s xml:id="echoid-s179" xml:space="preserve">des trois Elémens, ou <lb/>plutôt ce Chaos. </s> <s xml:id="echoid-s180" xml:space="preserve">Contentons-nous de voir ici <lb/>ſeulement les erreurs Philoſophiques dans <lb/>leſquelles l’eſprit Syſtématique a entraîné <lb/>le génie ſublime de Deſcartes; </s> <s xml:id="echoid-s181" xml:space="preserve">& </s> <s xml:id="echoid-s182" xml:space="preserve">ne réfu-<lb/>tons ſur-tout que ces ſortes d’erreurs qui, <pb o="18" file="0028" n="28" rhead="DE LA PHILOSOPHIE"/> ayant l’air de la vérité.</s> <s xml:id="echoid-s183" xml:space="preserve">, ſembloient reſpecta-<lb/>bles, & </s> <s xml:id="echoid-s184" xml:space="preserve">méritoient d’être relevées.</s> <s xml:id="echoid-s185" xml:space="preserve"/> </p> <div xml:id="echoid-div12" type="float" level="2" n="4"> <note position="right" xlink:label="note-0027-02" xlink:href="note-0027-02a" xml:space="preserve">Faux<unsure/></note> </div> <p> <s xml:id="echoid-s186" xml:space="preserve">Selon Deſcartes la lumiere ne vient point <lb/>à nos yeux du Soleil, mais c’eſt une matiere <lb/>globuleuſe répandue par-tout, que le Soleil <lb/>pouſſe, & </s> <s xml:id="echoid-s187" xml:space="preserve">qui preſſe nos yeux comme un bâ-<lb/>ton pouſſé par un bout preſſe à l’inſtant à l’au-<lb/>tre bout. </s> <s xml:id="echoid-s188" xml:space="preserve">Cela paroiſſoit plauſible, mais cela <lb/>n’en eſt pas moins faux: </s> <s xml:id="echoid-s189" xml:space="preserve">cependant Deſcar-<lb/>tes étoit tellement perſuadé de ce Syſtême <lb/>que dans ſa dix-ſeptième Lettre du troiſiè-<lb/>me Tome, il dit & </s> <s xml:id="echoid-s190" xml:space="preserve">répète poſitivement: <lb/></s> <s xml:id="echoid-s191" xml:space="preserve">F’avoue que je ne ſai rien en Pbiloſopbie ſi la <lb/>lumiere du Soleil n’eſt pas transmiſe à nos yeux <lb/>en un inſtant. </s> <s xml:id="echoid-s192" xml:space="preserve">En effet, il faut avouer que, <lb/>tout grand génie qu’il étoit, il ſavoit enco-<lb/>re peu de choſe en vraye Philoſophie; </s> <s xml:id="echoid-s193" xml:space="preserve">il lui <lb/>manquoit l’expérience du Siècle qui l’a ſui-<lb/>vi. </s> <s xml:id="echoid-s194" xml:space="preserve">Ce Siècle eſt autant ſupérieur à Deſcar-<lb/>tes, que Deſcartes l’étoit à l’Antiquité.</s> <s xml:id="echoid-s195" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s196" xml:space="preserve">10. </s> <s xml:id="echoid-s197" xml:space="preserve">Si la lumiere étoit toujours répandue, <lb/> <anchor type="note" xlink:label="note-0028-01a" xlink:href="note-0028-01"/> toujours exiſtante dans l’air, nous verrions <lb/>clair la nuit comme le jour, puiſque le Soleil <lb/>ſous l’Hemisphére pouſſeroit toujours les glo-<lb/>bules en tout ſens, & </s> <s xml:id="echoid-s198" xml:space="preserve">que l’impreſſion en vien-<lb/>droit également à nos yeux.</s> <s xml:id="echoid-s199" xml:space="preserve"/> </p> <div xml:id="echoid-div13" type="float" level="2" n="5"> <note position="left" xlink:label="note-0028-01" xlink:href="note-0028-01a" xml:space="preserve">Du <lb/>mouve-<lb/>ment <lb/>progreſ-<lb/>ſif de <lb/>la lu-<lb/>miere.</note> </div> <pb o="19" file="0029" n="29" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s200" xml:space="preserve">20. </s> <s xml:id="echoid-s201" xml:space="preserve">Il eſt démontré que la lumiere émane <lb/>du Soleil, & </s> <s xml:id="echoid-s202" xml:space="preserve">on ſait que c’eſt à peu près en <lb/>ſept ou huit minutes de tems qu’elle fait ce <lb/>chemin immenſe, qu’un boulet de Canon <lb/>conſervant ſa vîteſſe ne feroit pas en vingt-<lb/>cinq années.</s> <s xml:id="echoid-s203" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s204" xml:space="preserve">L’Auteur du Spectacle de la Nature, Ou-<lb/> <anchor type="note" xlink:label="note-0029-01a" xlink:href="note-0029-01"/> vrage très - eſtimable, eſt tombé ici dans <lb/>une petite mépriſe qu’il corrigera ſans dou-<lb/>te à la premiere Edition de ſon Livre. </s> <s xml:id="echoid-s205" xml:space="preserve">Il dit <lb/>que la lumiere vient en ſept minutes <lb/>des Etoiles, ſelon Neuton; </s> <s xml:id="echoid-s206" xml:space="preserve">il a pris les Etoiles <lb/>pour le Soleil. </s> <s xml:id="echoid-s207" xml:space="preserve">La lumiere émane des Etoi-<lb/>les les plus prochaines en ſix mois, ſelon un <lb/>certain calcul fondé ſur des expériences très-<lb/>délicates & </s> <s xml:id="echoid-s208" xml:space="preserve">très - fautives. </s> <s xml:id="echoid-s209" xml:space="preserve">Ce n’eſt point <lb/>Neuton, c’eſt Hugens & </s> <s xml:id="echoid-s210" xml:space="preserve">Hartſoeker, qui <lb/>ont fait cette ſuppoſition. </s> <s xml:id="echoid-s211" xml:space="preserve">Il dit encore, pour <lb/>prouver que Dieu créa la lumiere avant le <lb/>Soleil, que la lumiere eſt répandue par toute la <lb/>Nature, & </s> <s xml:id="echoid-s212" xml:space="preserve">qu’ elle ſe fait ſentir, quand les Aſtres <lb/>lumineux la pouſſent; </s> <s xml:id="echoid-s213" xml:space="preserve">mais il eſt démontré <lb/>qu’elle arrive des Etoiles fixes en un <lb/>tems très-long. </s> <s xml:id="echoid-s214" xml:space="preserve">Or, ſi elle fait ce chemin, el-<lb/>le n’étoit donc point répandue auparavant. <lb/></s> <s xml:id="echoid-s215" xml:space="preserve">Il eſt bon de ſe précautionner contre ces <pb o="20" file="0030" n="30" rhead="DE LA PHILOSOPHIE"/> erreurs, que l’on répète tous les jours dans <lb/>beaucoup de Livres qui ſont l’écho les uns <lb/>des autres.</s> <s xml:id="echoid-s216" xml:space="preserve"/> </p> <div xml:id="echoid-div14" type="float" level="2" n="6"> <note position="right" xlink:label="note-0029-01" xlink:href="note-0029-01a" xml:space="preserve">Erreur <lb/>du Spec-<lb/>tacle de <lb/>la Natu-<lb/>re.</note> </div> <p> <s xml:id="echoid-s217" xml:space="preserve">Voici en peu de mots la ſubſtance de la <lb/>Démonſtration ſenſible de Romer, que la <lb/>lumiere employe ſept à huit minutes dans <lb/>ſon chemin du Soleil à la Terre.</s> <s xml:id="echoid-s218" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s219" xml:space="preserve">On obferve de la Terre en C. </s> <s xml:id="echoid-s220" xml:space="preserve">ce Satellite de <lb/> <anchor type="note" xlink:label="note-0030-01a" xlink:href="note-0030-01"/> Jupiter, qui s’éclipſe réguliérement une fois <lb/>en quarante-deux heures & </s> <s xml:id="echoid-s221" xml:space="preserve">demie. </s> <s xml:id="echoid-s222" xml:space="preserve">Si la Ter-<lb/>re étoit immobile, l’Obſervateur en C. </s> <s xml:id="echoid-s223" xml:space="preserve">verroit <lb/>en trente fois quarante-deux heures & </s> <s xml:id="echoid-s224" xml:space="preserve">demie, <lb/>trente émerſions de ce Satellite, mais au <lb/>bout de ce tems, la Terre ſe trouve en D. <lb/></s> <s xml:id="echoid-s225" xml:space="preserve">alors l’Obſervateur ne voit plus cette émer-<lb/>ſion préciſément au bout de trente fois qua-<lb/>rante-deux heures & </s> <s xml:id="echoid-s226" xml:space="preserve">demie, mais il faut a-<lb/>jouter le tems que la lumiere met à ſe mou-<lb/>voir de C. </s> <s xml:id="echoid-s227" xml:space="preserve">en D. </s> <s xml:id="echoid-s228" xml:space="preserve">& </s> <s xml:id="echoid-s229" xml:space="preserve">ce tems eſt ſenſible-<lb/>ment conſidérable. </s> <s xml:id="echoid-s230" xml:space="preserve">Mais cet eſpace C. </s> <s xml:id="echoid-s231" xml:space="preserve">D. </s> <s xml:id="echoid-s232" xml:space="preserve"><lb/>eſt encore moins grand que l’eſpace G. </s> <s xml:id="echoid-s233" xml:space="preserve">H. </s> <s xml:id="echoid-s234" xml:space="preserve"><lb/>car C. </s> <s xml:id="echoid-s235" xml:space="preserve">D. </s> <s xml:id="echoid-s236" xml:space="preserve">eſt corde du Cercle, & </s> <s xml:id="echoid-s237" xml:space="preserve">G. </s> <s xml:id="echoid-s238" xml:space="preserve">H. </s> <s xml:id="echoid-s239" xml:space="preserve"><lb/>eſt le Diametre du Cercle. </s> <s xml:id="echoid-s240" xml:space="preserve">Ce Cercle eſt <lb/>le grand Orbe que décrit la Terre, le So-<lb/>leil eſt au milieu; </s> <s xml:id="echoid-s241" xml:space="preserve">la lumiere en venant <pb file="0031" n="31"/> <anchor type="figure" xlink:label="fig-0031-01a" xlink:href="fig-0031-01"/> <pb file="0032" n="32"/> <pb o="21" file="0033" n="33" rhead="DE NEUTON."/> du Satellite de Jupiter, traverſe C. </s> <s xml:id="echoid-s242" xml:space="preserve">D. </s> <s xml:id="echoid-s243" xml:space="preserve">en <lb/>dix minutes, & </s> <s xml:id="echoid-s244" xml:space="preserve">G. </s> <s xml:id="echoid-s245" xml:space="preserve">H. </s> <s xml:id="echoid-s246" xml:space="preserve">en 15. </s> <s xml:id="echoid-s247" xml:space="preserve">ou 16. </s> <s xml:id="echoid-s248" xml:space="preserve">mi-<lb/>nutes. </s> <s xml:id="echoid-s249" xml:space="preserve">Le Soleil eſt entre G. </s> <s xml:id="echoid-s250" xml:space="preserve">& </s> <s xml:id="echoid-s251" xml:space="preserve">H. </s> <s xml:id="echoid-s252" xml:space="preserve">donc <lb/>la lumiere vient du Soleil en 7 ou 8 minutes.</s> <s xml:id="echoid-s253" xml:space="preserve"/> </p> <div xml:id="echoid-div15" type="float" level="2" n="7"> <note position="left" xlink:label="note-0030-01" xlink:href="note-0030-01a" xml:space="preserve">Dé-<lb/>monſ-<lb/>tration <lb/>du mou-<lb/>vement <lb/>de la lu-<lb/>miere.</note> <figure xlink:label="fig-0031-01" xlink:href="fig-0031-01a"> <image file="0031-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0031-01"/> </figure> </div> <p> <s xml:id="echoid-s254" xml:space="preserve">Mr. </s> <s xml:id="echoid-s255" xml:space="preserve">Broadley, en dernier lieu, a obſervé <lb/>par des expériences réïtérées & </s> <s xml:id="echoid-s256" xml:space="preserve">ſûres, que <lb/>pluſieurs Etoiles, vues en différens tems, pa-<lb/>roiſſoient tantôt un peu plus vers le Nord, <lb/>tantôt un peu plus vers le Sud; </s> <s xml:id="echoid-s257" xml:space="preserve">il a prouvé <lb/>que cette différence ne pouvoit venir que <lb/>du mouvement annuel de la Terre, & </s> <s xml:id="echoid-s258" xml:space="preserve">de la <lb/>progreſſion de la lumiere. </s> <s xml:id="echoid-s259" xml:space="preserve">Il a obſervé que <lb/>ſi ces Etoiles ont une parallaxe, cette pa-<lb/>rallaxe n’eſt que d’une ſeconde.</s> <s xml:id="echoid-s260" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s261" xml:space="preserve">Or cela préſupoſé, voici le raiſonnement <lb/>que je fais: </s> <s xml:id="echoid-s262" xml:space="preserve">Un Aſtre, qui n’a qu’une ſe-<lb/>conde de parallaxe annuelle, eſt quatre cens <lb/>mille fois plus loin de nous que le Soleil; <lb/></s> <s xml:id="echoid-s263" xml:space="preserve">ſi la lumiere nous vient du Soleil en S<unsure/>. </s> <s xml:id="echoid-s264" xml:space="preserve"><lb/>minutes, comme le croit Mr. </s> <s xml:id="echoid-s265" xml:space="preserve">Broadley, <lb/>elle nous viendra donc de ces Etoiles en <lb/>6. </s> <s xml:id="echoid-s266" xml:space="preserve">années & </s> <s xml:id="echoid-s267" xml:space="preserve">plus d’un mois. </s> <s xml:id="echoid-s268" xml:space="preserve">Mais ce n’eſt <lb/>pas tout. </s> <s xml:id="echoid-s269" xml:space="preserve">Ces Etoiles ſont de la premiere <lb/>grandeur, donc les Etoiles de la ſixième <lb/>grandeur, étant ſix fois plus éloignées, ne <pb o="22" file="0034" n="34" rhead="DE LA PHILOSOPHIE"/> font parvenir leur lumiere à nous qu’en <lb/>plus de 36. </s> <s xml:id="echoid-s270" xml:space="preserve">ans & </s> <s xml:id="echoid-s271" xml:space="preserve">demi.</s> <s xml:id="echoid-s272" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s273" xml:space="preserve">3. </s> <s xml:id="echoid-s274" xml:space="preserve">Les rayons qu’on détourne par un <lb/>Priſme, & </s> <s xml:id="echoid-s275" xml:space="preserve">qu’on force de prendre un nou-<lb/>veau chemin, démontrent que la lumiere ſe <lb/>meut effectivement, & </s> <s xml:id="echoid-s276" xml:space="preserve">n’eſt pas un amas <lb/>de globules ſimplement preſſe.</s> <s xml:id="echoid-s277" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s278" xml:space="preserve">4<emph style="super">0</emph>. </s> <s xml:id="echoid-s279" xml:space="preserve">Si la lumiere étoit un amas de globu-<lb/>les exiſtans dans l’air & </s> <s xml:id="echoid-s280" xml:space="preserve">en tous lieux, un <lb/>petit trou qu’on pratique dans une cham-<lb/>bre obſcure devroit l’illuminer toute entié-<lb/>re: </s> <s xml:id="echoid-s281" xml:space="preserve">car la lumiere, pouſſée alors en tout ſens <lb/>par ce petit trou, agiroit en tout ſens, com-<lb/>me des boules d’yvoire rangées en rond, ou <lb/>en quarré, s’écarteroient toutes, ſiune ſeu-<lb/>le d’elles étoit fortement preſſée; </s> <s xml:id="echoid-s282" xml:space="preserve">mais il <lb/>arrive tout le contraire. </s> <s xml:id="echoid-s283" xml:space="preserve">La lumiere reçue <lb/>par un petit orifice, lequel ne laiſſe paſſer <lb/>que peu de rayons, éclaire à peine un de-<lb/>mi-pied de l’endroit qu’elle frappe.</s> <s xml:id="echoid-s284" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s285" xml:space="preserve">5<emph style="super">0</emph>. </s> <s xml:id="echoid-s286" xml:space="preserve">La lumiere entre toujours par un <lb/>trou en ligne droite, en quelque ſens <lb/>que l’on puiſſe imaginer, mais ſi des glo-<lb/>bules étoient ſimplement preſſés, il ſe-<lb/>roit impoſſible que cette preſſion ſe fît en <lb/>ligne droite. </s> <s xml:id="echoid-s287" xml:space="preserve">Il eſt donc démontré que <lb/>Deſcartes s’eſt trompé & </s> <s xml:id="echoid-s288" xml:space="preserve">ſur la nature de <pb o="23" file="0035" n="35" rhead="DE NEUTON."/> la lumiere & </s> <s xml:id="echoid-s289" xml:space="preserve">ſur la maniere dont elle nous <lb/>eſt tranſmiſe.</s> <s xml:id="echoid-s290" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s291" xml:space="preserve">Le Pere Mallebranche, génie plus ſubtil <lb/> <anchor type="note" xlink:label="note-0035-01a" xlink:href="note-0035-01"/> que vrai, qui conſulta toujours ſes médita-<lb/>tions, mais non toujours le Nature, adopta <lb/>ſans preuve les trois Elémens de Deſcar-<lb/>tes; </s> <s xml:id="echoid-s292" xml:space="preserve">mais il changea beaucoup de choſes à <lb/>ce Château enchanté. </s> <s xml:id="echoid-s293" xml:space="preserve">Il imagina ſans autre <lb/>preuve une autre explication de la lumiere.</s> <s xml:id="echoid-s294" xml:space="preserve"/> </p> <div xml:id="echoid-div16" type="float" level="2" n="8"> <note position="right" xlink:label="note-0035-01" xlink:href="note-0035-01a" xml:space="preserve">Erreur <lb/>du Pere <lb/>Malle-<lb/>bran-<lb/>che.</note> </div> <p> <s xml:id="echoid-s295" xml:space="preserve">Des vibrations du Corps lumineux impri-<lb/>ment, ſelon lui, des ſecouſſes à de petits <lb/>tourbillons mous, capables de compreſſion, <lb/>& </s> <s xml:id="echoid-s296" xml:space="preserve">tout compoſés de matiere ſubtile. </s> <s xml:id="echoid-s297" xml:space="preserve">Mais <lb/>ſi on avoit demandé à Mallebranche com-<lb/>ment ces petits tourbillons mous auroient <lb/>tranſmis à nos yeux la lumiere, comment <lb/>l’action du Soleil pourroit paſſer en un inſ-<lb/>tant à travers tant de petits corps compri-<lb/>més les uns par les autres, & </s> <s xml:id="echoid-s298" xml:space="preserve">dont un très-<lb/>petit nombre ſuffiroit pour amortir cette <lb/>action, comment enfin ſes tourbillons mous, <lb/>ne ſe ſeroient point mêlez en tournant les <lb/>uns ſur les autres, qu’auroit répondu le Pe-<lb/>re Mallebranche? </s> <s xml:id="echoid-s299" xml:space="preserve">Sur quel fondement po-<lb/>ſoit-il cet édifice imaginaire? </s> <s xml:id="echoid-s300" xml:space="preserve">Faut-il que <pb o="24" file="0036" n="36" rhead="DE LA PHILOSOPHIE"/> des hommes qui ne parloient que de véritê <lb/>n’ayent écrit que des Romans!</s> </p> <p> <s xml:id="echoid-s301" xml:space="preserve">Qu’eſt-ce donc enfin que la lumiere? </s> <s xml:id="echoid-s302" xml:space="preserve">C’eſt <lb/> <anchor type="note" xlink:label="note-0036-01a" xlink:href="note-0036-01"/> le feu lui-même, lequel brûle à une petite diſ-<lb/>tance, lorſque ſes parties ſont moins tenuës, <lb/>ou plus rapides, ou plus réunies; </s> <s xml:id="echoid-s303" xml:space="preserve">& </s> <s xml:id="echoid-s304" xml:space="preserve">qui <lb/>éclaire doucement nos yeux, quand il agit <lb/>de plus loin, quand ſes particules ſont plus fi-<lb/>nes, & </s> <s xml:id="echoid-s305" xml:space="preserve">moins rapides, & </s> <s xml:id="echoid-s306" xml:space="preserve">moins réunies.</s> <s xml:id="echoid-s307" xml:space="preserve"/> </p> <div xml:id="echoid-div17" type="float" level="2" n="9"> <note position="left" xlink:label="note-0036-01" xlink:href="note-0036-01a" xml:space="preserve">Déſini-<lb/>tion de <lb/>la lu-<lb/>miere.</note> </div> <p> <s xml:id="echoid-s308" xml:space="preserve">Ainſi une bougie allumée brûleroit l’œil <lb/>qui ne ſeroit qu’à quelques lignes d’elle, & </s> <s xml:id="echoid-s309" xml:space="preserve"><lb/>éclaire l’œil qui en eſt à quelques pouces. <lb/></s> <s xml:id="echoid-s310" xml:space="preserve">Ainſi les rayons du Soleil, épars dans l’eſpace <lb/>de l’air, illuminent les objets, & </s> <s xml:id="echoid-s311" xml:space="preserve">réunis dans <lb/>un verre ardent fondent le plomb & </s> <s xml:id="echoid-s312" xml:space="preserve">l’or.</s> <s xml:id="echoid-s313" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s314" xml:space="preserve">Ce feu eſt dardé en tout ſens du point <lb/>rayonnant: </s> <s xml:id="echoid-s315" xml:space="preserve">c’eſt ce qui fait qu’il eſt apper-<lb/>çu de tous les côtez; </s> <s xml:id="echoid-s316" xml:space="preserve">il faut donc toujours <lb/>le conſidérer comme des lignes partant d’un <lb/>centre à la circonférence. </s> <s xml:id="echoid-s317" xml:space="preserve">Ainſi tout faiſ-<lb/>ceau, tout amas, tout trait de rayons, ve-<lb/>nant du Soleil ou d’un feu quelconque, doit <lb/>être conſidéré comme un cone, dont la baſe <lb/>eſt ſur notre prunelle, & </s> <s xml:id="echoid-s318" xml:space="preserve">dont la pointe eſt <lb/>dans le feu qui le darde.</s> <s xml:id="echoid-s319" xml:space="preserve"/> </p> <pb o="25" file="0037" n="37" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s320" xml:space="preserve">Cette matiere de feu s’élance du Soleil <lb/>juſqu’à nous & </s> <s xml:id="echoid-s321" xml:space="preserve">juſqu’à Saturne, &</s> <s xml:id="echoid-s322" xml:space="preserve">c. </s> <s xml:id="echoid-s323" xml:space="preserve">avec <lb/>une rapidité qui épouvante l’imagination.</s> <s xml:id="echoid-s324" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s325" xml:space="preserve">Le calcul apprend que, ſi le Soleil eſt à <lb/>vingt quatre mille demi-diametres de la Ter-<lb/>re, il s’enſuit que la lumiere parcourt de cet <lb/>Aſtre à nous, (en nombres ronds) mille mil-<lb/>lions de pieds par ſeconde. </s> <s xml:id="echoid-s326" xml:space="preserve">Or un boulet <lb/>d’une livre de bale, pouſſé par une demi-li-<lb/>vre de poudre, ne fait en une ſeconde que <lb/>600. </s> <s xml:id="echoid-s327" xml:space="preserve">pieds; </s> <s xml:id="echoid-s328" xml:space="preserve">ainſi donc la rapidité d’un rayon <lb/>du Soleil eſt, en nombres ronds, ſeize cens <lb/>ſoixante & </s> <s xml:id="echoid-s329" xml:space="preserve">ſix mille ſix cens fois plus forte <lb/>que celle d’un boulet de Canon.</s> <s xml:id="echoid-s330" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s331" xml:space="preserve">Je n’entrerai point ici dans la fameu-<lb/> <anchor type="note" xlink:label="note-0037-01a" xlink:href="note-0037-01"/> ſe diſpute des forces vives; </s> <s xml:id="echoid-s332" xml:space="preserve">je renvoye <lb/>ſur cela le Lecteur au Mémoire plein de <lb/>ſageſſe & </s> <s xml:id="echoid-s333" xml:space="preserve">de profondeur qu’a donné Mr. </s> <s xml:id="echoid-s334" xml:space="preserve">de <lb/>Mairan.</s> <s xml:id="echoid-s335" xml:space="preserve"/> </p> <div xml:id="echoid-div18" type="float" level="2" n="10"> <note position="right" xlink:label="note-0037-01" xlink:href="note-0037-01a" xml:space="preserve">Voyez <lb/>Memoi-<lb/>res de <lb/>l’Acadé-<lb/>mie <lb/>1728.</note> </div> <p> <s xml:id="echoid-s336" xml:space="preserve">J’eſpére que ce Philoſophe & </s> <s xml:id="echoid-s337" xml:space="preserve">ceux qui <lb/>ſont le plus oppoſés aux forces vives, per-<lb/>mettront qu’on avance en toute rigueur <lb/>cette Propoſition ſuivante:</s> <s xml:id="echoid-s338" xml:space="preserve"/> </p> <pb o="26" file="0038" n="38" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s339" xml:space="preserve">L’effet que produit la force d’un corps <lb/>dans un monvement, du moins uniforme-<lb/>ment accéléré, eſt le produit de ſa maſſe <lb/>par le quarré de ſa viteſſe; </s> <s xml:id="echoid-s340" xml:space="preserve">c’<unsure/>eſt-à-dire <lb/>qu’un corps, s’il a dix degrez de vîteſſe, <lb/>fera, toutes choſes égales, cent fois autant <lb/>d’impreſſion, que s’il n’avoit qu’un degré <lb/>de vîteſſe.</s> <s xml:id="echoid-s341" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s342" xml:space="preserve">Si donc une ſeule particule de lumiere <lb/>agit en raiſon du quarré de ſa vîteſſe, & </s> <s xml:id="echoid-s343" xml:space="preserve">ſi <lb/>cette vîteſſe eſt environ ſeize cens mille <lb/>par rapport à celle du boulet, ce quarré ſera <lb/>2560000000000; </s> <s xml:id="echoid-s344" xml:space="preserve">il ſera donc vrai que, ſi cet <lb/>atome n’eſt que deux miliaſſes cinq cens <lb/>ſoixante miliards moins gros qu’une livre, il <lb/>fera encore le même effet qu’un boulet de Ca-<lb/>non. </s> <s xml:id="echoid-s345" xml:space="preserve">Suppoſez cet atome mille miliards plus <lb/> <anchor type="note" xlink:label="note-0038-01a" xlink:href="note-0038-01"/> petit encore; </s> <s xml:id="echoid-s346" xml:space="preserve">un moment d’émanation de <lb/>lumiere détruiroit tout ce qui vegète ſur la <lb/>ſurface de la Terre. </s> <s xml:id="echoid-s347" xml:space="preserve">Concevez qu’elle doit <lb/>être la petiteſſe d’une particule de lumiere, <lb/>qui paſſe ſi librement à-travers d’un verre; <lb/></s> <s xml:id="echoid-s348" xml:space="preserve">& </s> <s xml:id="echoid-s349" xml:space="preserve">pour avoir quelque idée de l’infini, con-<lb/>cevez ce que doit être une matiere un mil-<lb/>lion de fois plus ſubtile encore, qui paſſe en-<lb/>tre les pores de l’Or & </s> <s xml:id="echoid-s350" xml:space="preserve">de l’Aimant, & </s> <s xml:id="echoid-s351" xml:space="preserve">qui <pb o="27" file="0039" n="39" rhead="DE NEUTON."/> pénétre les Rochers & </s> <s xml:id="echoid-s352" xml:space="preserve">les entrailles de la <lb/>Terre.</s> <s xml:id="echoid-s353" xml:space="preserve"/> </p> <div xml:id="echoid-div19" type="float" level="2" n="11"> <note position="left" xlink:label="note-0038-01" xlink:href="note-0038-01a" xml:space="preserve">Extrê-<lb/>me peti-<lb/>teſſe du <lb/>corps de <lb/>la lu-<lb/>miere.</note> </div> <p> <s xml:id="echoid-s354" xml:space="preserve">Le Soleil qui nous darde cette matiere <lb/>lumineuſe en ſept ou huit minutes, & </s> <s xml:id="echoid-s355" xml:space="preserve">les <lb/>Etoiles, ces autres Soleils, qui nous l’en-<lb/>voyent en pluſieurs années, en fourniſ-<lb/>ſent éternellement, ſans paraître s’épuiſer, à <lb/>peu près comme le Muſc élance ſans ceſſe <lb/>autour de lui des corps odoriférants, ſans <lb/>rien perdre ſenſiblement de ſon poids.</s> <s xml:id="echoid-s356" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s357" xml:space="preserve">Enfin, la rapidité avec laquelle le Soleil <lb/>darde ſes rayons eſt en proportion avec <lb/>ſa groſſeur, qui ſurpaſſe environ un million <lb/>de fois celle de la Terre, & </s> <s xml:id="echoid-s358" xml:space="preserve">avec la vîteſſe <lb/>dont ce Corps de feu immenſe roule ſur lui-<lb/>même en vingt-cinq jours & </s> <s xml:id="echoid-s359" xml:space="preserve">demi.</s> <s xml:id="echoid-s360" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s361" xml:space="preserve">La force, l’illumination, l’intenſité, la den-<lb/>ſité de toute lumiere, eſt calculée Il ſe trou-<lb/>ve par un calcul ſingulier que cette force eſt <lb/>préciſément en même raiſon, que la for-<lb/>ce avec laquelle les corps tombent, & </s> <s xml:id="echoid-s362" xml:space="preserve"><lb/>avec laquelle Mr. </s> <s xml:id="echoid-s363" xml:space="preserve">Neuton fait voir que tous <lb/>les Globes céleſtes s’attirent. </s> <s xml:id="echoid-s364" xml:space="preserve">Cette pro-<lb/>portion eſt ce qu’on appelle la raiſon in- <pb o="28" file="0040" n="40" rhead="DE LA PHILOSOPHIE"/> verſe du quarré des diſtances. </s> <s xml:id="echoid-s365" xml:space="preserve">Il faut ſe fa-<lb/>miliariſer avec cette expreſſion. </s> <s xml:id="echoid-s366" xml:space="preserve">Elle ſignifie <lb/>une choſe ſimple & </s> <s xml:id="echoid-s367" xml:space="preserve">intelligible: </s> <s xml:id="echoid-s368" xml:space="preserve">c’eſt qu’un <lb/>corps qui ſera expoſé à quatre pieds d’un <lb/> <anchor type="note" xlink:label="note-0040-01a" xlink:href="note-0040-01"/> feu quelconque, ſera ſeize fois moins é-<lb/>clairé & </s> <s xml:id="echoid-s369" xml:space="preserve">moins échauffé, recevra ſeize fois <lb/>moins de rayons que le corps qui ſera à un <lb/>pied; </s> <s xml:id="echoid-s370" xml:space="preserve">ſeize eſt le quarré de quatre. </s> <s xml:id="echoid-s371" xml:space="preserve">Or qua-<lb/>tre eſt la diſtance où eſt le corps moins <lb/>éclairé, donc la lumiere envoye à ce corps <lb/>diſtant de quatre pieds, non pas quatre fois <lb/>moins de rayons, mais ſeize fois moins de <lb/>rayons. </s> <s xml:id="echoid-s372" xml:space="preserve">Voilà ce qu’on appelle la raiſon in-<lb/>verſe du quarré des diſtances, ce qu’il faut <lb/>bien entendre; </s> <s xml:id="echoid-s373" xml:space="preserve">car cette proportion ſera un <lb/>des fondemens de la Nouvelle Philoſophie <lb/>que nous tâchons de rendre familiere.</s> <s xml:id="echoid-s374" xml:space="preserve"/> </p> <div xml:id="echoid-div20" type="float" level="2" n="12"> <note position="left" xlink:label="note-0040-01" xlink:href="note-0040-01a" xml:space="preserve">Propor-<lb/>tion <lb/>dans la-<lb/>quelle <lb/>toute <lb/>lumiere <lb/>agit.</note> </div> <p> <s xml:id="echoid-s375" xml:space="preserve">Nous pouvons en paſſant conclure de la <lb/> <anchor type="note" xlink:label="note-0040-02a" xlink:href="note-0040-02"/> célérité avec laquelle la ſubſtance du Soleil <lb/>s’échappe ainſi vers nous en ligne droite, <lb/>combien le plein de Deſcartes eſt chiméri-<lb/>que. </s> <s xml:id="echoid-s376" xml:space="preserve">Car 10. </s> <s xml:id="echoid-s377" xml:space="preserve">comment une ligne droite <lb/>pourroit-elle parvenir à nous, à travers <lb/>tant de millions de couches de matiere <lb/>mues en ligne courbe, & </s> <s xml:id="echoid-s378" xml:space="preserve">à travers tant de <lb/>mouvemens divers? </s> <s xml:id="echoid-s379" xml:space="preserve">20. </s> <s xml:id="echoid-s380" xml:space="preserve">Comment un corps <pb o="29" file="0041" n="41" rhead="DE NEUTON."/> ſi délié pourroit-il en ſept ou huit minutes <lb/>parcourir l’eſpace de trente millions de nos <lb/>lieues, qui eſt entre le Soleil & </s> <s xml:id="echoid-s381" xml:space="preserve">nous, s’il a-<lb/>voit à pénétrer dans cet eſpace une ma-<lb/>tiére réſiſtante? </s> <s xml:id="echoid-s382" xml:space="preserve">Il faudroit que chaque ra-<lb/>yon, dérangeât en un moment trente mil-<lb/>lions de lieues de matiére ſubtile. </s> <s xml:id="echoid-s383" xml:space="preserve">Remar-<lb/>quez encore que cette prétendue matiére <lb/>ſubtile réſiſteroit dans le plein abſolu, au-<lb/>tant que la matiére la plus compacte. </s> <s xml:id="echoid-s384" xml:space="preserve">Car <lb/>une livre de poudre d’or, preſſée dans une <lb/>boëte, réſiſte autant qu’un morceau d’or <lb/>peſant une livre. </s> <s xml:id="echoid-s385" xml:space="preserve">Ainſi un rayon du Soleil <lb/>auroit bien plus d’effort à faire, que s’il avoit <lb/>à percer un cone d’or, dont l’axe ſeroit <lb/>trente millions de lieues.</s> <s xml:id="echoid-s386" xml:space="preserve"/> </p> <div xml:id="echoid-div21" type="float" level="2" n="13"> <note position="left" xlink:label="note-0040-02" xlink:href="note-0040-02a" xml:space="preserve">Pro-<lb/>greſſion <lb/>de la lu-<lb/>miere. <lb/>Preuve <lb/>de l’im-<lb/>poſſibi-<lb/>lité du <lb/>plein.</note> </div> <p> <s xml:id="echoid-s387" xml:space="preserve">Il y a plus. </s> <s xml:id="echoid-s388" xml:space="preserve">L’expérience, ce vrai <lb/>Maître de Philoſophie, nous apprend que <lb/>la lumiere en venant d’un Elément dans un <lb/>autre Elément, d’un milieu dans un autre <lb/>milieu, n’y paſſe pas toute entiere, comme <lb/>nous le dirons: </s> <s xml:id="echoid-s389" xml:space="preserve">une grande partie eſt ré-<lb/>flechie, l’air en fait rejaillir plus qu’il n’en <lb/>transmet; </s> <s xml:id="echoid-s390" xml:space="preserve">ainſi il ſeroit impoſſible qu’il nous <lb/>vint aucune lumiere des Etoiles, elle ſeroit <lb/>toute abſorbée, toute répercutée, avant <pb o="30" file="0042" n="42" rhead="DE LA PHILOSOPHIE"/> qu’un ſeul rayon pût ſeulement venir à <lb/>moitié de notre atmoſphére. </s> <s xml:id="echoid-s391" xml:space="preserve">Mais dans <lb/>les Chapitres, où nous expliquerons <lb/>les principes de la gravitation, nous ver-<lb/>rons une foule d’arguments, qui prou-<lb/>vent que ce plein prétendu étoit un Ro-<lb/>man.</s> <s xml:id="echoid-s392" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s393" xml:space="preserve">Arrêtons-nous ici un moment pour voir <lb/>combien la Vérité s’établit lentement chez <lb/>les hommes.</s> <s xml:id="echoid-s394" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s395" xml:space="preserve">Il y a près de cinquante ans que Romer <lb/>avoit démontré par les obſervations ſur les <lb/>Eclipſes des Satellites de Jupiter, que la lu-<lb/>miere émane du Soleil à la Terre en ſept <lb/>minutes & </s> <s xml:id="echoid-s396" xml:space="preserve">demie ou environ, cependant <lb/>non-ſeulement on ſoutient encore le con-<lb/>traire dans pluſieurs Livres de Phyſique; <lb/></s> <s xml:id="echoid-s397" xml:space="preserve">mais voici comme on parle dans un Recueil <lb/>en trois Volumes, tiré des obſervations de <lb/>toutes les Académies de l’Europe, imprimé <lb/>en 1730. </s> <s xml:id="echoid-s398" xml:space="preserve">page 35. </s> <s xml:id="echoid-s399" xml:space="preserve">Volume. </s> <s xml:id="echoid-s400" xml:space="preserve">1.</s> <s xml:id="echoid-s401" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s402" xml:space="preserve">Quelques-uns ont prétendu que d’un <lb/>Corps lumineux, comme le Soleil, il ſe fait <lb/>un écoulement continuel d’une infinité de <pb o="31" file="0043" n="43" rhead="DE NEUTON."/> petites parties inſenſibles, qui portent <lb/>la lumiere juſqu’a nos yeux; </s> <s xml:id="echoid-s403" xml:space="preserve">mais cette <lb/>opinion, qui ſe reſſent encore un peu de la <lb/>vieille Philoſophie, n’eſt pas ſoutenable.</s> </p> <p> <s xml:id="echoid-s404" xml:space="preserve">Cette opinion eſt pourtant démontrée de <lb/>plus d’une façon: </s> <s xml:id="echoid-s405" xml:space="preserve">& </s> <s xml:id="echoid-s406" xml:space="preserve">loin de reſſentir la <lb/>vieille Philoſophie, elle y eſt directement <lb/>contraire; </s> <s xml:id="echoid-s407" xml:space="preserve">car quoi de plus contraire à des <lb/>mots vuides de ſens, que des meſures, des <lb/>calculs, & </s> <s xml:id="echoid-s408" xml:space="preserve">des expériences?</s> <s xml:id="echoid-s409" xml:space="preserve"/> </p> <figure> <image file="0043-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0043-01"/> </figure> <pb file="0044" n="44"/> <figure> <image file="0044-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0044-01"/> </figure> </div> <div xml:id="echoid-div23" type="section" level="1" n="10"> <head xml:id="echoid-head14" xml:space="preserve">CHAPITRE DEUX.</head> <head xml:id="echoid-head15" style="it" xml:space="preserve">La proprietè que la lumiere a de ſe réflecbi@ <lb/>n’étoit pas véritablement connue. Elle n’eſt <lb/>point réflechie par les parties ſoli-<lb/>des des corps, comme on <lb/>le croioit.</head> <p> <s xml:id="echoid-s410" xml:space="preserve">AYANT ſu ce que c’eſt que la lumie-<lb/>re, d’où elle nous vient, comment & </s> <s xml:id="echoid-s411" xml:space="preserve">en <lb/>quel tems elle arrive à nous; </s> <s xml:id="echoid-s412" xml:space="preserve">voyons ſes <lb/>proprietés, & </s> <s xml:id="echoid-s413" xml:space="preserve">ſes effets ignorés juſqu’à <lb/>nos jours. </s> <s xml:id="echoid-s414" xml:space="preserve">Le premier de ſes effets eſt <lb/>qu’elle ſemble rejaillir de la ſurface ſolide <lb/>de tous les objets, pour en apporter dans nos <lb/>yeux les images.</s> <s xml:id="echoid-s415" xml:space="preserve"/> </p> <pb o="33" file="0045" n="45" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s416" xml:space="preserve">Tous les hommes, tous les Philoſophes, & </s> <s xml:id="echoid-s417" xml:space="preserve"><lb/>les Deſcartes & </s> <s xml:id="echoid-s418" xml:space="preserve">les Mallebranches, & </s> <s xml:id="echoid-s419" xml:space="preserve">ceux <lb/>qui ſe ſont éloignez le plus des penſées vul-<lb/>gaires, ont également cru qu’en effet ce <lb/>ſont les ſurfaces ſolides des corps qui nous <lb/>renvoyent les rayons. </s> <s xml:id="echoid-s420" xml:space="preserve">Plus une ſurface eſt <lb/>unie & </s> <s xml:id="echoid-s421" xml:space="preserve">ſolide, plus elle fait, dit-on, re-<lb/>jaillir de lumiere; </s> <s xml:id="echoid-s422" xml:space="preserve">plus un corps a de pores <lb/>larges & </s> <s xml:id="echoid-s423" xml:space="preserve">droits, plus il transmet de rayons <lb/>à travers ſa ſubſtance. </s> <s xml:id="echoid-s424" xml:space="preserve">Ainſi le miroir poli <lb/>dont le fond eſt convert d’une ſurface de <lb/>vif argent, nous renvoye tous les rayons; <lb/></s> <s xml:id="echoid-s425" xml:space="preserve">ainſi ce même miroir ſans vif argent ayant <lb/>des pores droits & </s> <s xml:id="echoid-s426" xml:space="preserve">larges & </s> <s xml:id="echoid-s427" xml:space="preserve">en grand <lb/>nombre, laiſſe paſſer une grande partie des <lb/>rayons. </s> <s xml:id="echoid-s428" xml:space="preserve">Plus un corps a de pores larges <lb/>& </s> <s xml:id="echoid-s429" xml:space="preserve">droits, plus il eſt diaphane: </s> <s xml:id="echoid-s430" xml:space="preserve">tel eſt, di-<lb/>ſoit-on, le diamant, telle eſt l’eau elle-mê-<lb/>me; </s> <s xml:id="echoid-s431" xml:space="preserve">voilà les idées généralement reçues, <lb/>& </s> <s xml:id="echoid-s432" xml:space="preserve">que perſonne ne révoquoit en doute.</s> <s xml:id="echoid-s433" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s434" xml:space="preserve">Cependant toutes ces idées ſont entiére-<lb/>ment fauſſes, tant ce qui eſt vraiſemblable, <lb/>eſt ſouvent ce qui eſt le plus éloigné de la <lb/>vérité. </s> <s xml:id="echoid-s435" xml:space="preserve">Les Philoſophes ſe ſont jettez en <lb/>cela dans l’erreur, de la même maniere que <pb o="34" file="0046" n="46" rhead="DE LA PHILOSOPHIE"/> le Vulgaire y eſt tout porté, quand il penſe <lb/>que le Soleil n’eſt pas plus grand qu’il le <lb/>paroît aux yeux. </s> <s xml:id="echoid-s436" xml:space="preserve">Voici en quoi conſiſtoit <lb/>cette erreur des Philoſophes.</s> <s xml:id="echoid-s437" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s438" xml:space="preserve">Il n’y a aucun corps dont nous puiſſions <lb/>unir véritablement la ſurface. </s> <s xml:id="echoid-s439" xml:space="preserve">Cependant <lb/>beaucoup de ſurfaces nous paraiſſent unies <lb/>& </s> <s xml:id="echoid-s440" xml:space="preserve">d’un poli parfait. </s> <s xml:id="echoid-s441" xml:space="preserve">Pourquoi voyons nous <lb/>uni & </s> <s xml:id="echoid-s442" xml:space="preserve">égal ce qui ne l’eſt pas? </s> <s xml:id="echoid-s443" xml:space="preserve">La ſuperfi-<lb/>cie la plus égale, n’eſt par rapport aux pe-<lb/> <anchor type="note" xlink:label="note-0046-01a" xlink:href="note-0046-01"/> tits corps qui compoſent la lumiere, qu’un <lb/>amas de montagnes, de cavitez & </s> <s xml:id="echoid-s444" xml:space="preserve">d’inter-<lb/>vales, de même que la pointe de l’éguille <lb/>la plus fine eſt hériſſée en effet d’émi-<lb/>nences & </s> <s xml:id="echoid-s445" xml:space="preserve">d’aſpérités que le Microſcope dé-<lb/>couvre.</s> <s xml:id="echoid-s446" xml:space="preserve"/> </p> <div xml:id="echoid-div23" type="float" level="2" n="1"> <note position="left" xlink:label="note-0046-01" xlink:href="note-0046-01a" xml:space="preserve">Aucun <lb/>corps <lb/>uni.</note> </div> <p> <s xml:id="echoid-s447" xml:space="preserve">Tous les faiſceaux des rayons de lumic-<lb/>re qui tomberoient ſur ces inégalités, ſe ré-<lb/>flechiroient ſelon qu’ils y ſeroient tombez; <lb/></s> <s xml:id="echoid-s448" xml:space="preserve">donc étant inégalement tombez ils ne ſe ré-<lb/>flechiroient jamais réguliérement, donc on <lb/>ne pourroit jamais ſe voir dans une glace.</s> <s xml:id="echoid-s449" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s450" xml:space="preserve">La lumiere qui nous apporte notre ima-<lb/>ge de deſſus un miroir, ne vient donc point <pb o="35" file="0047" n="47" rhead="DE NEUTON."/> certainement des parties ſolides de la ſuper-<lb/>ficie de ce miroir; </s> <s xml:id="echoid-s451" xml:space="preserve">elle ne vient point non <lb/> <anchor type="note" xlink:label="note-0047-01a" xlink:href="note-0047-01"/> plus des parties ſolides de mercure & </s> <s xml:id="echoid-s452" xml:space="preserve">d’é-<lb/>tain étendues derriere cette glace. </s> <s xml:id="echoid-s453" xml:space="preserve">Ces <lb/>parties ne ſont pas plus planes, pas <lb/>plus unies, que la glace même. </s> <s xml:id="echoid-s454" xml:space="preserve">Les <lb/>parties ſolides de l’étain & </s> <s xml:id="echoid-s455" xml:space="preserve">du mercure <lb/>ſont incomparablement plus grandes, <lb/>plus larges, que les parties ſolides conſ-<lb/>tituantes de la lumiere; </s> <s xml:id="echoid-s456" xml:space="preserve">donc ſi les petites <lb/>particules de lumiere tombent ſur ces groſ-<lb/>ſes parties de mercure, elle s’éparpilleront <lb/>de tous côtés comme des grains de plomb <lb/>tombant ſur des platras. </s> <s xml:id="echoid-s457" xml:space="preserve">Quel pouvoir in-<lb/>connu fait donc rejaillir vers nous la lumie-<lb/>re réguliérement? </s> <s xml:id="echoid-s458" xml:space="preserve">Il paroît déja que ce ne <lb/>ſont pas les corps qui nous la renvoyent <lb/>ainſi. </s> <s xml:id="echoid-s459" xml:space="preserve">Ce qui ſembloit le plus connu le <lb/>plus inconteſtable chez les hommes, de-<lb/>vient un myſtère plus grand que ne l’étoit <lb/>autrefois la peſanteur de l’air. </s> <s xml:id="echoid-s460" xml:space="preserve">Examinons <lb/>ce Problême de la Nature, notre étonnement <lb/>redoublera. </s> <s xml:id="echoid-s461" xml:space="preserve">On ne peut s’inſtruire ici qu’avec <lb/>ſurpriſe.</s> <s xml:id="echoid-s462" xml:space="preserve"/> </p> <div xml:id="echoid-div24" type="float" level="2" n="2"> <note position="right" xlink:label="note-0047-01" xlink:href="note-0047-01a" xml:space="preserve">Lumie-<lb/>re non <lb/>réfle-<lb/>chie par <lb/>les par-<lb/>ties ſo-<lb/>lides.</note> </div> <p> <s xml:id="echoid-s463" xml:space="preserve">Prenez un morceau, un cube de criſtal, <lb/>par exemple; </s> <s xml:id="echoid-s464" xml:space="preserve">voici tout ce qui arrive aux <pb o="36" file="0048" n="48" rhead="DE LA PHILOSOPHIE"/> rayons du Soleil qui tombent ſur ce corps <lb/>ſolide & </s> <s xml:id="echoid-s465" xml:space="preserve">tranſparent.</s> <s xml:id="echoid-s466" xml:space="preserve"/> </p> <figure> <image file="0048-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0048-01"/> </figure> <p> <s xml:id="echoid-s467" xml:space="preserve">1<emph style="super">0</emph>. </s> <s xml:id="echoid-s468" xml:space="preserve">Une petite partie des rayons rebon-<lb/>diſſent à vos yeux de ſa premiere ſurface <lb/>A. </s> <s xml:id="echoid-s469" xml:space="preserve">ſans toucher même à cette ſurface, <lb/>comme il ſera plus amplement prouvé.</s> <s xml:id="echoid-s470" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s471" xml:space="preserve">2<emph style="super">0</emph>. </s> <s xml:id="echoid-s472" xml:space="preserve">Une partie des rayons eſt reçue dans <lb/>la ſubſtance de ce corps, elle s’y joue, s’y <lb/>perd & </s> <s xml:id="echoid-s473" xml:space="preserve">s’y éteint.</s> <s xml:id="echoid-s474" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s475" xml:space="preserve">3<emph style="super">0</emph>. </s> <s xml:id="echoid-s476" xml:space="preserve">Une troiſième partie parvient à l’in-<lb/>térieur C. </s> <s xml:id="echoid-s477" xml:space="preserve">de la ſurface B. </s> <s xml:id="echoid-s478" xml:space="preserve">& </s> <s xml:id="echoid-s479" xml:space="preserve">d’auprès de <lb/>cette ſurface B. </s> <s xml:id="echoid-s480" xml:space="preserve">elle retourne en A. </s> <s xml:id="echoid-s481" xml:space="preserve">& </s> <s xml:id="echoid-s482" xml:space="preserve">quel-<lb/>ques rayons en viennent à vos yeux.</s> <s xml:id="echoid-s483" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s484" xml:space="preserve">4<emph style="super">0</emph>. </s> <s xml:id="echoid-s485" xml:space="preserve">Une quatrième partie paſſe dans l’air.</s> <s xml:id="echoid-s486" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s487" xml:space="preserve">5<emph style="super">0</emph>. </s> <s xml:id="echoid-s488" xml:space="preserve">Une cinquième partie qui eſt la plus <lb/>conſidérable revient d’au-delà de la ſurface <lb/>ultérieure B. </s> <s xml:id="echoid-s489" xml:space="preserve">dans le criſtal, y repaſſe, & </s> <s xml:id="echoid-s490" xml:space="preserve"><lb/>vient ſe réflechir à vos yeux. </s> <s xml:id="echoid-s491" xml:space="preserve">N’examinons <pb o="37" file="0049" n="49" rhead="DE NEUTON."/> ici que ces derniers rayons qui, s’échappant <lb/>de la ſurface ultérieure B. </s> <s xml:id="echoid-s492" xml:space="preserve">& </s> <s xml:id="echoid-s493" xml:space="preserve">ayant trou-<lb/>vé l’air, rejailliſſent de deſſus cet air vers <lb/>nous en rentrant à travers le criſtal. </s> <s xml:id="echoid-s494" xml:space="preserve">Cer-<lb/>tainement ils n’ont pas rencontré dans cet <lb/>air des parties ſolides ſur leſquelles ils <lb/>ayent rebondi, car ſi au lieu d’air ils ren-<lb/>contrent de l’eau à cette ſurface B. </s> <s xml:id="echoid-s495" xml:space="preserve">peu <lb/>reviennent alors, ils entrent dans cette <lb/>eau, ils la pénétrent en grand nombre. </s> <s xml:id="echoid-s496" xml:space="preserve">Or <lb/>l’eau eſt environ huit cens fois plus peſan-<lb/>te, plus ſolide, moins rare que l’air. </s> <s xml:id="echoid-s497" xml:space="preserve">Ce-<lb/>pendant ces rayons ne rejailliſſent point de <lb/>deſſus cette eau, & </s> <s xml:id="echoid-s498" xml:space="preserve">rejailliſſent de deſſus <lb/>cet air dans ce verre, donc ce n’eſt point <lb/>des parties ſolides des corps que la lumiere <lb/>eſt réflechie.</s> <s xml:id="echoid-s499" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s500" xml:space="preserve">Voici une obſervation plus ſinguliere & </s> <s xml:id="echoid-s501" xml:space="preserve"><lb/>plus déciſive: </s> <s xml:id="echoid-s502" xml:space="preserve">Expoſez dans une chambre <lb/>obſcure ce criſtal A. </s> <s xml:id="echoid-s503" xml:space="preserve">B. </s> <s xml:id="echoid-s504" xml:space="preserve">aux rayons du So-<lb/>leil de façon, que les traits de lumiere par-<lb/>venus à ſa ſuperficie B. </s> <s xml:id="echoid-s505" xml:space="preserve">faſſent un angle de <lb/>plus de 40. </s> <s xml:id="echoid-s506" xml:space="preserve">degrez avec la perpendicule.</s> <s xml:id="echoid-s507" xml:space="preserve"/> </p> <pb o="38" file="0050" n="50" rhead="DE LA PHILOSOPHIE"/> <figure> <image file="0050-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0050-01"/> </figure> <note position="left" xml:space="preserve">Expé-<lb/>riences <lb/>déciſi-<lb/>ves.</note> <p> <s xml:id="echoid-s508" xml:space="preserve">La plûpart de ces rayons alors ne pénétre <lb/>plus dans l’air, ils rentrent tous dans ce <lb/>criſtal à l’inſtant même qu’ils en ſortent, <lb/>ils reviennent, comme vous voyez, mais <lb/>cette courbure eſt inſenſible.</s> <s xml:id="echoid-s509" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s510" xml:space="preserve">Certainement ce n’eſt pas la ſurface ſoli-<lb/>de de l’air qui les a repouſſés dans ce verre, <lb/>pluſieurs de ces rayons entroient dans l’air <lb/>auparavant, quand ils tomboient moins o-<lb/>bliquement; </s> <s xml:id="echoid-s511" xml:space="preserve">pourquoi donc à une obli-<lb/>quité de 40 degrez dix - neuf minutes, la <lb/>plûpart de ces rayons n’y paſſe-t-elle plus? <lb/></s> <s xml:id="echoid-s512" xml:space="preserve">trouvent-ils à ce degré plus de réſiſtance, <lb/>plus de matiere dans cet air, qu’ils n’en <lb/>trouvent dans ce criſtal qu’ils avoient pé-<lb/>nétré? </s> <s xml:id="echoid-s513" xml:space="preserve">trouvent - ils plus de parties ſolides, <pb o="39" file="0051" n="51" rhead="DE NEUTON."/> dans l’air à quarante degrés & </s> <s xml:id="echoid-s514" xml:space="preserve">un tiers qu’à <lb/>40? </s> <s xml:id="echoid-s515" xml:space="preserve">l’air eſt à peu près deux mille quatre cens <lb/>fois plus rare, moins peſant, moins ſolide, <lb/>que le criſtal, donc ces rayons devoient paſſer <lb/>dans l’air avec deux mille quatre cens fois plus <lb/>de facilité, qu’ils n’ont pénétré l’épaiſſeur du <lb/>criſtal. </s> <s xml:id="echoid-s516" xml:space="preserve">Cependant, malgré cette prodigieu-<lb/>ſe apparence de facilité, ils ſont repouſſez; <lb/></s> <s xml:id="echoid-s517" xml:space="preserve">ils le ſont donc par une force qui eſt ici deux <lb/>mille quatre cens fois plus puiſſante que l’air, <lb/>ils ne ſont donc point repouſſez par l’air; </s> <s xml:id="echoid-s518" xml:space="preserve">les <lb/>rayons encore une fois ne ſont donc point <lb/>réflechis à nos yeux par les parties ſolides <lb/>de la matiere. </s> <s xml:id="echoid-s519" xml:space="preserve">La lumiere rejaillit ſi peu <lb/>deſſus les parties ſolides des corps, que <lb/>c’eſt en effet du vuide qu’elle rejaillit.</s> <s xml:id="echoid-s520" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s521" xml:space="preserve">Vous venez de voir que la lumiere tom-<lb/>bant à un angle de 40. </s> <s xml:id="echoid-s522" xml:space="preserve">degrez 19. </s> <s xml:id="echoid-s523" xml:space="preserve">minutes <lb/>ſur du criſtal, rejaillit preſque toute entiere <lb/>de deſſus l’air quelle rencontre à la ſurface <lb/>ultérieure de ce criſtal. </s> <s xml:id="echoid-s524" xml:space="preserve">Que la lumiere y <lb/>tombe à un angle moindre d’une ſeule mi-<lb/>nute, il en paſſe encore moins hors de <lb/>cette ſurface dans l’air. </s> <s xml:id="echoid-s525" xml:space="preserve">Qu’on ôte l’air, <lb/>il ne paſſera plus de rayons du tout. </s> <s xml:id="echoid-s526" xml:space="preserve">C’eſt <lb/>une choſe démontrée.</s> <s xml:id="echoid-s527" xml:space="preserve"/> </p> <pb o="40" file="0052" n="52" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s528" xml:space="preserve">Or quand il y a de l’eau à cette ſurface, <lb/>beaucoup de rayons entrent dans cette eau <lb/>au lieu de rejaillir. </s> <s xml:id="echoid-s529" xml:space="preserve">Quand il n’y a que de <lb/>l’air, bien moins de rayons entrent dans cet <lb/>air. </s> <s xml:id="echoid-s530" xml:space="preserve">Quand il n’y a plus d’air, aucun rayon <lb/>ne paſſe; </s> <s xml:id="echoid-s531" xml:space="preserve">donc c’eſt du vuide en effet que <lb/>la lumiere rejaillit.</s> <s xml:id="echoid-s532" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s533" xml:space="preserve">Voilà donc des preuves indubitables que <lb/>ce n’eſt point une ſuperficie ſolide qui nous <lb/>renvoye la lumiere: </s> <s xml:id="echoid-s534" xml:space="preserve">il y a bien d’autres <lb/>preuves encore de cette nouvelle vérité; </s> <s xml:id="echoid-s535" xml:space="preserve">en <lb/>voici une que nous expliquerons à ſa place. <lb/></s> <s xml:id="echoid-s536" xml:space="preserve">Tout corps opaque réduit en lame mince, <lb/>laiſſe paſſer à travers ſa ſubſtance des rayons <lb/>d’une certaine eſpèce, & </s> <s xml:id="echoid-s537" xml:space="preserve">réflechit les autres <lb/>rayons: </s> <s xml:id="echoid-s538" xml:space="preserve">or, ſi la lumiere étoit renvoyée par <lb/>les corps, tous les rayons qui tomberoient <lb/>ſur ces lames, ſeroient réflechis ſur ces la-<lb/>mes. </s> <s xml:id="echoid-s539" xml:space="preserve">Enfin nous verrons que jamais ſi é-<lb/>tonnant paradoxe n’a été prouvé en plus de <lb/>manieres. </s> <s xml:id="echoid-s540" xml:space="preserve">Commençons donc par nous fa-<lb/>miliariſer avec ces Vérités.</s> <s xml:id="echoid-s541" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s542" xml:space="preserve">1<emph style="super">0</emph>. </s> <s xml:id="echoid-s543" xml:space="preserve">Cette lumiere qu’on croit réflechie par <lb/>la ſurface ſolide des corps, rejaillit en effet <pb o="41" file="0053" n="53" rhead="DE NEUTON."/> fans avoir touché à cette ſurface.</s> <s xml:id="echoid-s544" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s545" xml:space="preserve">2<emph style="super">0</emph>. </s> <s xml:id="echoid-s546" xml:space="preserve">La lumiere n’eſt point renvoyée de <lb/>derriere un miroir par la ſurface ſolide du <lb/>vif argent; </s> <s xml:id="echoid-s547" xml:space="preserve">mais elle eſt renvoyée du ſein des <lb/>pores du miroir, & </s> <s xml:id="echoid-s548" xml:space="preserve">des pores du vif argent <lb/>même.</s> <s xml:id="echoid-s549" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s550" xml:space="preserve">3<emph style="super">0</emph>. </s> <s xml:id="echoid-s551" xml:space="preserve">Il ne faut point, comme on l’a penſé <lb/>juſques à préſent, que les pores de ce vif ar-<lb/>gent ſoient très-petits pour réflechir la lu-<lb/>miere, au contraire il faut qu’ils ſoient <lb/>larges.</s> <s xml:id="echoid-s552" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s553" xml:space="preserve">Ce ſera encore un nouveau ſujet de ſur-<lb/> <anchor type="note" xlink:label="note-0053-01a" xlink:href="note-0053-01"/> priſe pour ceux qui n’ont pas étudié <lb/>cette Philoſophie, d’entendre dire que <lb/>le ſecret de rendre un corps opaque, eſt <lb/>ſouvent d’élargir ſes pores, & </s> <s xml:id="echoid-s554" xml:space="preserve">que le moyen <lb/>de le rendre tranſparent eſt de les étrecir. <lb/></s> <s xml:id="echoid-s555" xml:space="preserve">L’ordre de la Nature paraitra tout changé: </s> <s xml:id="echoid-s556" xml:space="preserve"><lb/>ce qui ſembloit devoir faire l’opacité, eſt <lb/>préciſément ce qui opérera la tranſparence; </s> <s xml:id="echoid-s557" xml:space="preserve"><lb/>& </s> <s xml:id="echoid-s558" xml:space="preserve">ce qui paraiſſoit rendre les corps tranſ-<lb/>parens, ſera ce qui les rendra opaques. </s> <s xml:id="echoid-s559" xml:space="preserve">Ce-<lb/>pendant rien n’eſt ſi vrai, & </s> <s xml:id="echoid-s560" xml:space="preserve">l’expérience <lb/>la plus groſſiére le démontre.</s> <s xml:id="echoid-s561" xml:space="preserve"/> </p> <div xml:id="echoid-div25" type="float" level="2" n="3"> <note position="right" xlink:label="note-0053-01" xlink:href="note-0053-01a" xml:space="preserve">Plus les <lb/>pores <lb/>ſont pe-<lb/>tits plus <lb/>la lumie-<lb/>re paſſe.</note> </div> <p> <s xml:id="echoid-s562" xml:space="preserve">Un papier ſec, dont les pores ſont très- <pb o="42" file="0054" n="54" rhead="DE LA PHILOSOPHIE"/> larges, eſt opaque, nul rayon de lumiere <lb/>ne le traverſe: </s> <s xml:id="echoid-s563" xml:space="preserve">étreciſſez ſes pores en l’im-<lb/>bibant, ou d’eau ou d’huile, il devient <lb/>tranſparent; </s> <s xml:id="echoid-s564" xml:space="preserve">la même choſe arrive au lin-<lb/>ge, au ſel, &</s> <s xml:id="echoid-s565" xml:space="preserve">c.</s> <s xml:id="echoid-s566" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s567" xml:space="preserve">Il y a donc des principes ignorés qui opé-<lb/>rent ces merveilles, des cauſes qui font re-<lb/>jaillir la lumiere, avant qu’elle ait touché <lb/>une ſurface, qui la renvoyent des pores du <lb/>corps tranſparent, qui la ramenent du mi-<lb/>lieu même du vuide; </s> <s xml:id="echoid-s568" xml:space="preserve">nous ſommes invinci-<lb/>blement obligés d’admettre ces faits, quelle <lb/>qu’en puiſſe être la cauſe.</s> <s xml:id="echoid-s569" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s570" xml:space="preserve">Etudions donc les autres myſtères de la <lb/>lumiere, & </s> <s xml:id="echoid-s571" xml:space="preserve">voyons ſi de ces effets ſurpre-<lb/>nans, on remonte juſqu’à quelque Principe <lb/>inconteſtable, qu’il faille admettre auſſi-<lb/>bien que ces effets même.</s> <s xml:id="echoid-s572" xml:space="preserve"/> </p> <figure> <image file="0054-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0054-01"/> </figure> <pb file="0055" n="55"/> <figure> <image file="0055-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0055-01"/> </figure> </div> <div xml:id="echoid-div27" type="section" level="1" n="11"> <head xml:id="echoid-head16" xml:space="preserve">CHAPITRE TROIS.</head> <p style="it"> <s xml:id="echoid-s573" xml:space="preserve">De la proprieté que la lumiere a de ſe briſer <lb/>en paſſant d’une ſubſtance dans une autre, <lb/>& </s> <s xml:id="echoid-s574" xml:space="preserve">de prendre un nouveau chemin.</s> <s xml:id="echoid-s575" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s576" xml:space="preserve">LA SECONDE proprieté des rayons <lb/>de la lumiere qu’il faut bien examiner, <lb/>eſt celle de ſe détourner de leur chemin en <lb/>paſſant du Soleil dans l’air, de l’air dans le <lb/>verre, du verre dans l’eau, &</s> <s xml:id="echoid-s577" xml:space="preserve">c. </s> <s xml:id="echoid-s578" xml:space="preserve">C’eſt cette <lb/>nouvelle direction dans ces différens mi-<lb/>lieux, c’eſt ce briſement de la lumiere qu’on <pb o="44" file="0056" n="56" rhead="DE LA PHILOSOPHIE"/> appelle réfraction, c’eft par cette proprie-<lb/>té qu’une rame plongée dans l’eau parait <lb/>courbée au Matelot qui la manie; </s> <s xml:id="echoid-s579" xml:space="preserve">c’eſt ce <lb/>qui fait que dans une jatte nous ap-<lb/>percevrons, en y jettant de l’eau, l’objet que <lb/>nous n’appercevions pas auparavant en nous <lb/>tenant à la même place.</s> <s xml:id="echoid-s580" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s581" xml:space="preserve">Enfin c’eſt par le moyen de cette réfrac-<lb/>tion que nos yeux jouïſſent de la vûe. </s> <s xml:id="echoid-s582" xml:space="preserve">Les <lb/>fecrets admirables de la réfraction étoient <lb/>ignorés de l’Antiquité, qui cependant l’avoit <lb/>ſous les yeux, & </s> <s xml:id="echoid-s583" xml:space="preserve">dont on faiſoit uſage tous <lb/>les jours, ſans qu’il ſoit reſté un ſeul Ecrit, <lb/>qui puiſſe faire croire qu’on en eût deviné <lb/>la raiſon. </s> <s xml:id="echoid-s584" xml:space="preserve">Ainſi encore aujourd’hui nous igno-<lb/>rons la cauſe des mouvemens même de no-<lb/>tre corps, & </s> <s xml:id="echoid-s585" xml:space="preserve">des penſè<unsure/>es de notre ame; <lb/></s> <s xml:id="echoid-s586" xml:space="preserve">mais cette ignorance eſt différente. </s> <s xml:id="echoid-s587" xml:space="preserve">Nous <lb/>n’avons & </s> <s xml:id="echoid-s588" xml:space="preserve">nous n’aurons jamais d’Inſtru-<lb/>ment aſſez fin pour voir les premiers reſſorts <lb/>de nous - mêmes; </s> <s xml:id="echoid-s589" xml:space="preserve">mais l’induſtrie hurnai-<lb/>ne s’eſt faite de nouveaux yeux, qui B<unsure/>ous <lb/>ont fait appercevoir ſur les effets de la lu-<lb/>miere, preſque tout ce qu’il eſt permis aux <lb/>hommes d’en ſavoir.</s> <s xml:id="echoid-s590" xml:space="preserve"/> </p> <pb o="45" file="0057" n="57" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s591" xml:space="preserve">Il ſaut ſe faire ici une idée nette d’une <lb/> <anchor type="note" xlink:label="note-0057-01a" xlink:href="note-0057-01"/> expérience três-commune. </s> <s xml:id="echoid-s592" xml:space="preserve">Une pièce d’or <lb/>eſt dans ce baſſin: </s> <s xml:id="echoid-s593" xml:space="preserve">votre œil eſt placé au <lb/>bord du baſſin à telle diſtance, que vous <lb/>ne voyez point cette pièce:</s> <s xml:id="echoid-s594" xml:space="preserve"/> </p> <div xml:id="echoid-div27" type="float" level="2" n="1"> <note position="right" xlink:label="note-0057-01" xlink:href="note-0057-01a" xml:space="preserve">Com-<lb/>ment <lb/>la lu-<lb/>miere <lb/>ſe bri-<lb/>ſe.</note> </div> <figure> <image file="0057-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0057-01"/> </figure> <p> <s xml:id="echoid-s595" xml:space="preserve">Qu’on y verſe de l’eau, vous ne l’apper-<lb/>perceviez point d’abord où elle étoit: </s> <s xml:id="echoid-s596" xml:space="preserve">main-<lb/>tenant vous la voyez où elle n’eſt pas; <lb/></s> <s xml:id="echoid-s597" xml:space="preserve">qu’eſt-il arrivé?</s> <s xml:id="echoid-s598" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s599" xml:space="preserve">L’objet A. </s> <s xml:id="echoid-s600" xml:space="preserve">réflechit un rayon qui vient <lb/>frapper contre le bord du baſſin, & </s> <s xml:id="echoid-s601" xml:space="preserve">qui <lb/>n’arrivera jamais à votre œil: </s> <s xml:id="echoid-s602" xml:space="preserve">il réflechit <lb/>auſſi ce rayon A. </s> <s xml:id="echoid-s603" xml:space="preserve">B. </s> <s xml:id="echoid-s604" xml:space="preserve">qui paſſe par-deſſus <pb o="46" file="0058" n="58" rhead="DE LA PHILOSOPHIE"/> votre œil: </s> <s xml:id="echoid-s605" xml:space="preserve">or à préſent vous recevez ce <lb/>rayon A. </s> <s xml:id="echoid-s606" xml:space="preserve">B. </s> <s xml:id="echoid-s607" xml:space="preserve">C. </s> <s xml:id="echoid-s608" xml:space="preserve">ce n’eſt point votre œil qui a <lb/>changé de place, c’eſt donc le rayon A. </s> <s xml:id="echoid-s609" xml:space="preserve">B.</s> <s xml:id="echoid-s610" xml:space="preserve">; <lb/>il s’eſt manifeſtement detourné au bord de <lb/>ce baſſin en paſſant de l’eau dans l’air, ainſi <lb/>il frappe votre œil en C.</s> <s xml:id="echoid-s611" xml:space="preserve"/> </p> <figure> <image file="0058-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0058-01"/> </figure> <p> <s xml:id="echoid-s612" xml:space="preserve">Mais vous voyez toujours les objets en li-<lb/>gne droite, donc vous voyez l’objet ſuivant <lb/>la ligne droite C. </s> <s xml:id="echoid-s613" xml:space="preserve">D. </s> <s xml:id="echoid-s614" xml:space="preserve">donc vous voyez l’ob-<lb/>jet au point D. </s> <s xml:id="echoid-s615" xml:space="preserve">au - deſſus du lieu où il eſt <lb/>en effet.</s> <s xml:id="echoid-s616" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s617" xml:space="preserve">Si ce rayon ſe briſe en un ſens, quand il <lb/>paſſe de l’eau dans l’air, il doit ſe briſer en <lb/>un ſens contraire, quand il entre de l’air <lb/>dans l’eau.</s> <s xml:id="echoid-s618" xml:space="preserve"/> </p> <pb o="47" file="0059" n="59" rhead="DE NEUTON."/> <figure> <image file="0059-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0059-01"/> </figure> <p> <s xml:id="echoid-s619" xml:space="preserve">J’élève ſur cette eau une perpendiculaire, <lb/>le rayon A. </s> <s xml:id="echoid-s620" xml:space="preserve">qui partant du point lumineux <lb/>ſe briſe au point B. </s> <s xml:id="echoid-s621" xml:space="preserve">& </s> <s xml:id="echoid-s622" xml:space="preserve">s’approche dans l’eau <lb/>de cette perpendiculaire en ſuivant le che-<lb/>min B. </s> <s xml:id="echoid-s623" xml:space="preserve">D. </s> <s xml:id="echoid-s624" xml:space="preserve">& </s> <s xml:id="echoid-s625" xml:space="preserve">ce même rayon D. </s> <s xml:id="echoid-s626" xml:space="preserve">B. </s> <s xml:id="echoid-s627" xml:space="preserve">en paſ-<lb/>ſant de l’eau dans l’air, ſe briſe en allant <lb/>vers A.</s> <s xml:id="echoid-s628" xml:space="preserve">, & </s> <s xml:id="echoid-s629" xml:space="preserve">en s’éloignant de cette même <lb/>perpendiculaire; </s> <s xml:id="echoid-s630" xml:space="preserve">la lumiere ſe réfracte donc <lb/>ſelon les milieux qu’elle traverſe. </s> <s xml:id="echoid-s631" xml:space="preserve">C’eſt ſur <lb/>ce Principe que la Nature a diſpoſé les hu-<lb/>meurs différentes qui ſont dans nos yeux, <lb/>afin que les traits de lumiere, qui paſſent à <lb/>travers ces humeurs, ſe briſent de façon <lb/>qu’ils ſe réuniſſent après dans un point ſur <lb/>notre rétine: </s> <s xml:id="echoid-s632" xml:space="preserve">c’eſt enfin ſur ce Principe que <pb o="48" file="0060" n="60" rhead="DE LA PHILOSOPHIE"/> nous fabriquons les Lunettes dont les ver-<lb/>res éprouvent des réfractions encore plus <lb/>grandes qu’il ne s’en fait dans nos yeux, & </s> <s xml:id="echoid-s633" xml:space="preserve"><lb/>qui, apportant ainſi plus de rayons réunis, <lb/>peuvent étendre, juſqu’à deux cens fois, <lb/>la force de notre vûe; </s> <s xml:id="echoid-s634" xml:space="preserve">de même que l’in-<lb/>vention des leviers a donné une nouvelle <lb/>force à nos bras, qui ſont des leviers natu-<lb/>rels. </s> <s xml:id="echoid-s635" xml:space="preserve">Nous allions expliquer la raiſon que <lb/>Neuton a trouvée de cette proprieté de la <lb/>lumiere; </s> <s xml:id="echoid-s636" xml:space="preserve">mais vous voulez voir auparavant <lb/>comment cette réfraction agit dans nos <lb/>yeux, & </s> <s xml:id="echoid-s637" xml:space="preserve">comment le ſens de la vûe, le <lb/>plus étendu de tous nos Sens, doit ſon exiſ-<lb/>tence à la réfraction. </s> <s xml:id="echoid-s638" xml:space="preserve">Quelque connue que <lb/>ſoit cette matiere, il eſt bon de fortifier <lb/>par un nouvel examen les idées que vous en <lb/>avez. </s> <s xml:id="echoid-s639" xml:space="preserve">Les perſonnes qui pourront lire ce <lb/>petit Ouvrage, ſeront bien-aiſes de ne point <lb/>chercher ailleurs ce qu’elles deſireroient ſa-<lb/>voir touchant la vûe.</s> <s xml:id="echoid-s640" xml:space="preserve"/> </p> <figure> <image file="0060-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0060-01"/> </figure> <pb file="0061" n="61"/> <figure> <image file="0061-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0061-01"/> </figure> </div> <div xml:id="echoid-div29" type="section" level="1" n="12"> <head xml:id="echoid-head17" xml:space="preserve"><emph style="bf">CHAPITRE QUATRE.</emph></head> <head xml:id="echoid-head18" style="it" xml:space="preserve">De la conformation de nos yeux, comment la <lb/>lumiere entre & agit dans cet organe.</head> <p> <s xml:id="echoid-s641" xml:space="preserve">POur connaitre l’œil de l’homme en phy-<lb/>ſicien qui ne conſidere que la viſion, il <lb/> <anchor type="note" xlink:label="note-0061-01a" xlink:href="note-0061-01"/> faut d’abord ſavoir que la premiere enve-<lb/>loppe blanche, le rempart & </s> <s xml:id="echoid-s642" xml:space="preserve">l’ornement de <lb/>l’œil, ne tranſmet aucun rayon. </s> <s xml:id="echoid-s643" xml:space="preserve">Plus ce <lb/>blanc de l’œil eſt fort & </s> <s xml:id="echoid-s644" xml:space="preserve">uni, plus il ré-<lb/>flechit de lumiere; </s> <s xml:id="echoid-s645" xml:space="preserve">& </s> <s xml:id="echoid-s646" xml:space="preserve">lorſque quelque paſ-<lb/>ſion vive porte au viſage de nouveaux <lb/>eſprits, qui viennent encore tendre & </s> <s xml:id="echoid-s647" xml:space="preserve">ébran- <pb o="50" file="0062" n="62" rhead="DE LA PHILOSOPHIE"/> ler cette tunique, alors des étincelles ſem-<lb/>blent en ſortir.</s> <s xml:id="echoid-s648" xml:space="preserve"/> </p> <div xml:id="echoid-div29" type="float" level="2" n="1"> <note position="right" xlink:label="note-0061-01" xlink:href="note-0061-01a" xml:space="preserve">Deſcrip-<lb/>tion de <lb/>l’œil.</note> </div> <p> <s xml:id="echoid-s649" xml:space="preserve">Au milieu de cette membrane s’éleve un <lb/>peu la cornée, mince, dure & </s> <s xml:id="echoid-s650" xml:space="preserve">tranſparen-<lb/>te, telle précifément que le verre de votre <lb/>montre que vous placeriéz en cette façon <lb/>ſur une boule.</s> <s xml:id="echoid-s651" xml:space="preserve"/> </p> <figure> <image file="0062-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0062-01"/> </figure> <p> <s xml:id="echoid-s652" xml:space="preserve">Sous cette cornée, eſt l’iris, autre membrane, <lb/>qui, colorée par elle-même, répand ſes cou-<lb/>leurs ſur cette cornée transparente qui la cou-<lb/>vre; </s> <s xml:id="echoid-s653" xml:space="preserve">c’eſt cette iris tantôt brune, tantôt bleue, <lb/>qui rend les yeux bleus ou noirs. </s> <s xml:id="echoid-s654" xml:space="preserve">Elle eſt <lb/>percée dans ſon milieu, qui ainſi paroît tou-<lb/>jours noir; </s> <s xml:id="echoid-s655" xml:space="preserve">& </s> <s xml:id="echoid-s656" xml:space="preserve">ce milieu eſt la prunelle de <lb/>l’œil. </s> <s xml:id="echoid-s657" xml:space="preserve">C’eſt par cette ouverture que ſont <lb/>introduits les rayons de la lumiere: </s> <s xml:id="echoid-s658" xml:space="preserve">elle s’a-<lb/>grandit par un mouvement involontaire <lb/>dans les endroits obſcurs, pour recevoir plus <pb o="51" file="0063" n="63" rhead="DE NEUTON."/> de rayons; </s> <s xml:id="echoid-s659" xml:space="preserve">elle ſe reſſerre enſuite, lorſqu’u-<lb/>ne grande clarté l’offenſe.</s> <s xml:id="echoid-s660" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s661" xml:space="preserve">Les rayons admis par cette prunelle ont <lb/>déja ſouffert une réfraction aſſez forte en <lb/>paſſant à travers la cornée dont elle eſt cou-<lb/>verte. </s> <s xml:id="echoid-s662" xml:space="preserve">Imaginez cette cornée comme le ver-<lb/>re de votre montre, il eſt convexe en de-<lb/>hors, & </s> <s xml:id="echoid-s663" xml:space="preserve">concave en dedans: </s> <s xml:id="echoid-s664" xml:space="preserve">tous les <lb/>rayons obliques ſe ſont briſés dans l’épaiſ-<lb/>ſeur de ce verre; </s> <s xml:id="echoid-s665" xml:space="preserve">mais enſuite ſa concavité <lb/>rétablit ce que ſa convéxité a briſé. </s> <s xml:id="echoid-s666" xml:space="preserve">La <lb/>méme choſe arrive dans notre cornée. </s> <s xml:id="echoid-s667" xml:space="preserve">Les <lb/>rayons ainſi rompus & </s> <s xml:id="echoid-s668" xml:space="preserve">briſés, trouvent a-<lb/>près avoir franchi la cornée, une hu-<lb/>meur transparente dans laquelle ils paſſent. <lb/></s> <s xml:id="echoid-s669" xml:space="preserve">Cette eau eſt nommée l’humeur aqueuſe. </s> <s xml:id="echoid-s670" xml:space="preserve"><lb/>Les Anatomiſtes ne s’accordent point en-<lb/>core entr’eux ſur la forme de ce petit ré-<lb/>ſervoir. </s> <s xml:id="echoid-s671" xml:space="preserve">Mais, quelle que ſoit ſa figu-<lb/>re, la Nature ſemble avoir placé là cette <lb/>humeur claire & </s> <s xml:id="echoid-s672" xml:space="preserve">limpide, pour opérer des <lb/>réfractions, pour transmettre purement la <lb/>lumiere, pour que le criſtallin, qui eſt der-<lb/>riere, puiſſe s’avancer ſans effort, & </s> <s xml:id="echoid-s673" xml:space="preserve">changer <lb/>librement de figure, pour que l’humidité <lb/>néceſſaire s’entretienne, &</s> <s xml:id="echoid-s674" xml:space="preserve">c.</s> <s xml:id="echoid-s675" xml:space="preserve"/> </p> <pb o="52" file="0064" n="64" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s676" xml:space="preserve">Enfin, les rayons étant ſortis de cette eau <lb/>trouvent une eſpèce de diamant liquide, <lb/>taillé en lentille, & </s> <s xml:id="echoid-s677" xml:space="preserve">enchaſſé dans une <lb/>membrane déliée & </s> <s xml:id="echoid-s678" xml:space="preserve">diaphane elle-même. <lb/></s> <s xml:id="echoid-s679" xml:space="preserve">Ce diamant eſt le criſtallin, c’eſt lui <lb/>qui rompt tous les rayons obliques, c’eſt <lb/>un principal organe de la réfraction & </s> <s xml:id="echoid-s680" xml:space="preserve"><lb/>de la vûe; </s> <s xml:id="echoid-s681" xml:space="preserve">parfaitement ſemblable en cela <lb/>à un Verre lenticulaire de Lunette. </s> <s xml:id="echoid-s682" xml:space="preserve">Soit <lb/>ce criſtallin ou ce Verre lenticulaire.</s> <s xml:id="echoid-s683" xml:space="preserve"/> </p> <figure> <image file="0064-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0064-01"/> </figure> <p> <s xml:id="echoid-s684" xml:space="preserve">Le rayon perpendiculaire A. </s> <s xml:id="echoid-s685" xml:space="preserve">le pénétre, <lb/>ſans ſe détourner; </s> <s xml:id="echoid-s686" xml:space="preserve">mais les rayons obliques <pb o="53" file="0065" n="65" rhead="DE NEUTON."/> B. </s> <s xml:id="echoid-s687" xml:space="preserve">A. </s> <s xml:id="echoid-s688" xml:space="preserve">C. </s> <s xml:id="echoid-s689" xml:space="preserve">ſe détournent dans l’épaiſſeur du <lb/>Verre en s’approchant des perpendiculai-<lb/>res, qu’on tireroit ſur les endroits où ils tom-<lb/>bent. </s> <s xml:id="echoid-s690" xml:space="preserve">Enſuite quand ils ſortent du Verre <lb/>pour paſſer dans l’air, ils ſe briſent encore en <lb/>s’éloignant du perpendicule; </s> <s xml:id="echoid-s691" xml:space="preserve">ce nouveau <lb/>briſement eſt préciſément ce qui les fait <lb/>converger en D. </s> <s xml:id="echoid-s692" xml:space="preserve">foyer du Verre lenticu-<lb/>laire.</s> <s xml:id="echoid-s693" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s694" xml:space="preserve">Or la rétine, cette membrane legére, cet-<lb/>te expanſion du nerf optique, qui tapiſſe <lb/>le fond de notre œil, eſt le foyer du criſtal-<lb/>lin: </s> <s xml:id="echoid-s695" xml:space="preserve">c’eſt à cette rétine que les rayons abou-<lb/>tiſſent: </s> <s xml:id="echoid-s696" xml:space="preserve">mais avant d’y parvenir, ils ren-<lb/>contrent encore un nouveau milieu qu’ils <lb/>traverſent; </s> <s xml:id="echoid-s697" xml:space="preserve">ce nouveau milieu eſt l’humeur <lb/>vitrée, moins ſolide que le criſtallin, moins <lb/>fluide que l’humeur aqueuſe.</s> <s xml:id="echoid-s698" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s699" xml:space="preserve">C’eſt dans cette humeur vitrée que les <lb/>rayons ont le tems de s’aſſembler, avant de <lb/>venir faire leur derniere réunion ſur les <lb/>points du fond de notre œil. </s> <s xml:id="echoid-s700" xml:space="preserve">Figurez-vous <lb/>donc ſous cette lentille du criſtallin, cette <lb/>humeur vitrée ſur laquelle le criſtallin s’ap-<lb/>puye; </s> <s xml:id="echoid-s701" xml:space="preserve">cette humeur tient le criſtallin dans <pb o="54" file="0066" n="66" rhead="DE LA PHILOSOPHIE"/> ſa concavité, & </s> <s xml:id="echoid-s702" xml:space="preserve">eſt arondie vers la rétine.</s> <s xml:id="echoid-s703" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s704" xml:space="preserve">Les rayons en s’échapant de cette der-<lb/>niere humeur achevent donc de converger. <lb/></s> <s xml:id="echoid-s705" xml:space="preserve">Chaque faiſceau de rayons parti d’un point <lb/>de l’objet vient fraper un point de notre <lb/>rétine.</s> <s xml:id="echoid-s706" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s707" xml:space="preserve">Une figure, où chaque partie de l’œil <lb/>ſe voit ſous ſon propre nom, expliquera <lb/>mieux tout cet artifice, que ne pourroient <lb/>faire des lignes, des A. </s> <s xml:id="echoid-s708" xml:space="preserve">& </s> <s xml:id="echoid-s709" xml:space="preserve">des B. </s> <s xml:id="echoid-s710" xml:space="preserve">La ſtruc-<lb/>ture des yeux ainſi développée, on peut con-<lb/>naitre aiſément pourquoi on à ſi ſouvent <lb/>beſoin du ſecours d’un Verre, & </s> <s xml:id="echoid-s711" xml:space="preserve">quel eſt <lb/>l’uſage des Lunettes.</s> <s xml:id="echoid-s712" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s713" xml:space="preserve">Souvent un œil ſera trop plat, ſoit par <lb/> <anchor type="note" xlink:label="note-0066-01a" xlink:href="note-0066-01"/> la conformation de ſa cornée, ſoit par ſon <lb/>criſtallin, que l’âge ou la maladie aura deſſe-<lb/>ché; </s> <s xml:id="echoid-s714" xml:space="preserve">alors les réfractions ſeront plus fai-<lb/>bles & </s> <s xml:id="echoid-s715" xml:space="preserve">en moindre quantité, les rayons ne <lb/>ſe raſſembleront plus ſur la rétine. </s> <s xml:id="echoid-s716" xml:space="preserve">Conſi-<lb/>dérez cet œil trop plat que l’on nomme œil <lb/>de presbite.</s> <s xml:id="echoid-s717" xml:space="preserve"/> </p> <div xml:id="echoid-div30" type="float" level="2" n="2"> <note position="left" xlink:label="note-0066-01" xlink:href="note-0066-01a" xml:space="preserve">Oeil <lb/>presbi-<lb/>te.</note> </div> <p> <s xml:id="echoid-s718" xml:space="preserve">Ne regardons, pour plus de facilité, que <pb file="0067" n="67"/> <anchor type="figure" xlink:label="fig-0067-01a" xlink:href="fig-0067-01"/> <pb file="0068" n="68"/> <pb file="0069" n="69"/> <pb file="0070" n="70"/> <anchor type="figure" xlink:label="fig-0070-01a" xlink:href="fig-0070-01"/> <pb o="55" file="0071" n="71" rhead="DE NEUTON."/> trois faiſceaux, trois cones des rayons, qui <lb/>de l’objet tombent ſur cet œil, ils ſe réuni-<lb/>ront aux points A. </s> <s xml:id="echoid-s719" xml:space="preserve">A. </s> <s xml:id="echoid-s720" xml:space="preserve">A. </s> <s xml:id="echoid-s721" xml:space="preserve">par delà la rétine, <lb/>il verra les objets confus.</s> <s xml:id="echoid-s722" xml:space="preserve"/> </p> <div xml:id="echoid-div31" type="float" level="2" n="3"> <figure xlink:label="fig-0067-01" xlink:href="fig-0067-01a"> <image file="0067-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0067-01"/> </figure> <figure xlink:label="fig-0070-01" xlink:href="fig-0070-01a"> <image file="0070-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0070-01"/> </figure> </div> <p> <s xml:id="echoid-s723" xml:space="preserve">La Nature a fourni un ſecours contre <lb/>cet inconvénient, par la force qu’elle a <lb/>donnée aux muſcles de l’œil d’allonger, ou <lb/>d’aplatir l’œil, de l’approcher ou de le re-<lb/>culer de la rétine. </s> <s xml:id="echoid-s724" xml:space="preserve">Ainſi dans cet œil de <lb/>Vieillard, ou dans cet œil malade, le criſtal-<lb/>lin a la faculté de s’avancer un peu, & </s> <s xml:id="echoid-s725" xml:space="preserve">d’aller <lb/>en D. </s> <s xml:id="echoid-s726" xml:space="preserve">D.</s> <s xml:id="echoid-s727" xml:space="preserve">: alors l’eſpace entre le criſtallin & </s> <s xml:id="echoid-s728" xml:space="preserve"><lb/>le fond de la rétine deviennent plus grands, <lb/>les rayons ont le tems de venir ſe réunir ſur <lb/>la rétine, au lieu d’aller au-delà; </s> <s xml:id="echoid-s729" xml:space="preserve">mais lorſ-<lb/>que cette force eſt perdue, l’induſtrie hu-<lb/>maine y ſupplée, un verre lenticulaire eſt <lb/>mis entre l’objet & </s> <s xml:id="echoid-s730" xml:space="preserve">l’œil affaibli. </s> <s xml:id="echoid-s731" xml:space="preserve">L’effet de <lb/>ce verre eſt de rapprocher les rayons qu’il <lb/>a reçus, l’œil les reçoit donc & </s> <s xml:id="echoid-s732" xml:space="preserve">plus raſſem-<lb/>blés & </s> <s xml:id="echoid-s733" xml:space="preserve">en plus grand nombre: </s> <s xml:id="echoid-s734" xml:space="preserve">ils vien-<lb/>nent aboutir à un point de la rétine comme <lb/>il le faut; </s> <s xml:id="echoid-s735" xml:space="preserve">alors la vûe eſt nette & </s> <s xml:id="echoid-s736" xml:space="preserve">diſ-<lb/>tincte.</s> <s xml:id="echoid-s737" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s738" xml:space="preserve">Regardez cet autre œil, qui a une mala- <pb o="56" file="0072" n="72" rhead="DE LA PHIL OSOPHIE"/> die contraire, il eſt trop rond: </s> <s xml:id="echoid-s739" xml:space="preserve">les rayons ſe <lb/>réuniſſent trop tôt, comme vous le voyez <lb/>au point B. </s> <s xml:id="echoid-s740" xml:space="preserve">ils ſe croiſent trop vîte, ils ſe <lb/>ſéparent en B. </s> <s xml:id="echoid-s741" xml:space="preserve">& </s> <s xml:id="echoid-s742" xml:space="preserve">vont faire une tache ſur <lb/>la rétine. </s> <s xml:id="echoid-s743" xml:space="preserve">C’eſt-là ce qu’on appelle un œil <lb/> <anchor type="note" xlink:label="note-0072-01a" xlink:href="note-0072-01"/> myope. </s> <s xml:id="echoid-s744" xml:space="preserve">Cet inconvénient diminue à me-<lb/>ſure que l’âge en amene d’autres, qui ſont <lb/>la ſéchereſſe & </s> <s xml:id="echoid-s745" xml:space="preserve">la faibleſſe: </s> <s xml:id="echoid-s746" xml:space="preserve">elles aplatiſ-<lb/>ſent inſenſiblement cet œil trop rond; </s> <s xml:id="echoid-s747" xml:space="preserve">& </s> <s xml:id="echoid-s748" xml:space="preserve"><lb/>voilà pourquoi on dit que les vûes courtes <lb/>durent plus long-tems. </s> <s xml:id="echoid-s749" xml:space="preserve">Ce n’eſt pas qu’en <lb/>effet elles durent plus que les autres, mais <lb/>c’eſt qu’à un certain âge, l’œil deſſeché s’a-<lb/>platit: </s> <s xml:id="echoid-s750" xml:space="preserve">alors celui qui étoit obligé aupara-<lb/>vant d’approcher ſon Livre à trois ou qua-<lb/>tre pouces de ſon œil, peut lire quelquefois <lb/>à un pied de diſtance: </s> <s xml:id="echoid-s751" xml:space="preserve">mais auſſi ſa vûe de-<lb/>vient bien-tôt trouble & </s> <s xml:id="echoid-s752" xml:space="preserve">confuſe, il ne <lb/>peut voir les objets éloignés; </s> <s xml:id="echoid-s753" xml:space="preserve">telle eſt no-<lb/>tre condition, qu’un défaut ne ſe répare <lb/>presque jamais que par un autre.</s> <s xml:id="echoid-s754" xml:space="preserve"/> </p> <div xml:id="echoid-div32" type="float" level="2" n="4"> <note position="left" xlink:label="note-0072-01" xlink:href="note-0072-01a" xml:space="preserve">Oeil <lb/>myope.</note> </div> <p> <s xml:id="echoid-s755" xml:space="preserve">Or, tandis que cet œil eſt trop rond, il lui <lb/>faut un Verre qui empêche les rayons de ſe <lb/>réunir ſi vîte. </s> <s xml:id="echoid-s756" xml:space="preserve">Ce Verre fera le contraire du <lb/>premier, au lieu d’être convexe des deux cô-<lb/>tés, il ſera un peu concave des deux cô- <pb file="0073" n="73"/> <anchor type="figure" xlink:label="fig-0073-01a" xlink:href="fig-0073-01"/> <pb file="0074" n="74"/> <pb o="57" file="0075" n="75" rhead="DE NEUTON."/> tés, & </s> <s xml:id="echoid-s757" xml:space="preserve">les rayons divergeront dans celui-<lb/>ci, au lieu qu’ils convergeroient dans l’au-<lb/>tre. </s> <s xml:id="echoid-s758" xml:space="preserve">Ils viendront par conſéquent ſe réu-<lb/>nir plus loin, qu’ils ne faiſoient auparavant <lb/>dans l’œil, & </s> <s xml:id="echoid-s759" xml:space="preserve">alors cet œil jouïra d’une <lb/>vûe parfaite. </s> <s xml:id="echoid-s760" xml:space="preserve">On proportionne la convéxité <lb/>& </s> <s xml:id="echoid-s761" xml:space="preserve">la concavité des Verres aux défauts de <lb/>nos yeux: </s> <s xml:id="echoid-s762" xml:space="preserve">c’eſt ce qui fait que les mêmes <lb/>Lunettes qui rendent la vûe nette à un <lb/>Vieillard, ne ſeront d’aucun ſecours à un <lb/>autre; </s> <s xml:id="echoid-s763" xml:space="preserve">car il n’y a ni deux maladies, ni <lb/>deux hommes, ni deux choſes au monde <lb/>égales.</s> <s xml:id="echoid-s764" xml:space="preserve"/> </p> <div xml:id="echoid-div33" type="float" level="2" n="5"> <figure xlink:label="fig-0073-01" xlink:href="fig-0073-01a"> <image file="0073-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0073-01"/> </figure> </div> <p> <s xml:id="echoid-s765" xml:space="preserve">L’Antiquité ne connaiſſoit point ces Lu-<lb/>nettes. </s> <s xml:id="echoid-s766" xml:space="preserve">Cependant elle connaiſſoit les Mi-<lb/>roirs ardents; </s> <s xml:id="echoid-s767" xml:space="preserve">une vérité découverte n’eſt <lb/>pas toujours une raiſon pour qu’on décou-<lb/>vre les autres véritéz qui y tiennent. </s> <s xml:id="echoid-s768" xml:space="preserve">L’at-<lb/>traction de. </s> <s xml:id="echoid-s769" xml:space="preserve">l’Aimant étoit connue, & </s> <s xml:id="echoid-s770" xml:space="preserve">ſa <lb/>direction échapoit aux yeux. </s> <s xml:id="echoid-s771" xml:space="preserve">La démons-<lb/>tration de la circulation du ſang étoit dans <lb/>la ſaignée même que pratiquoient tous les <lb/>Médecins Grecs, & </s> <s xml:id="echoid-s772" xml:space="preserve">cependant perſonne <lb/>ne ſe doutoit que le ſang circulât.</s> <s xml:id="echoid-s773" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s774" xml:space="preserve">Il y a grande apparence que c’eſt du tems <pb o="58" file="0076" n="76" rhead="DE LA PHIL OSOPHIE"/> de Roger Bacon au XIII. </s> <s xml:id="echoid-s775" xml:space="preserve">Siècle que l’on <lb/>trouva ces lunettes appellées beſicles, & </s> <s xml:id="echoid-s776" xml:space="preserve"><lb/>les loupes qui donnent de nouveaux yeux <lb/>aux Vieillards; </s> <s xml:id="echoid-s777" xml:space="preserve">car il eſt le premier qui en <lb/>parle.</s> <s xml:id="echoid-s778" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s779" xml:space="preserve">Vous venez de voir les effets que la ré-<lb/>fraction fait dans vos yeux, ſoit que les <lb/>rayons arrivent ſans ſecours intermédiaire, <lb/>ſoit qu’ils ayent traverſé des criſtaux: </s> <s xml:id="echoid-s780" xml:space="preserve">vous <lb/>concevez que ſans cette réfraction opérée <lb/>dans nos yeux, & </s> <s xml:id="echoid-s781" xml:space="preserve">ſans cette réflexion des <lb/>rayons de deſſus les ſurfaces des corps vers <lb/>nous, les organes de la vûe nous ſeroient <lb/>inutiles. </s> <s xml:id="echoid-s782" xml:space="preserve">Les moyens que la Nature employe <lb/>pour faire cette réfraction, les loix qu’el-<lb/>le ſuit, ſont des myſtères que nous allons <lb/>déveloper. </s> <s xml:id="echoid-s783" xml:space="preserve">Il faut auparavant achever ce <lb/>que nous avons à dire touchant la vûe, il <lb/>faut ſatisfaire à ces queſtions ſi naturelles: <lb/></s> <s xml:id="echoid-s784" xml:space="preserve">Pourquoi nous voyons les objets au - delà <lb/>d’un Miroir, & </s> <s xml:id="echoid-s785" xml:space="preserve">non ſur le Miroir même? </s> <s xml:id="echoid-s786" xml:space="preserve"><lb/>Pourquoi un Miroir concave rend l’objet <lb/>plus grand? </s> <s xml:id="echoid-s787" xml:space="preserve">Pourquoi le Miroir convexe <lb/>rend l’objet plus petit? </s> <s xml:id="echoid-s788" xml:space="preserve">Pourquoi les Teleſ-<lb/>copes rapprochent & </s> <s xml:id="echoid-s789" xml:space="preserve">agrandiſſent les cho-<lb/>ſes? </s> <s xml:id="echoid-s790" xml:space="preserve">Par quel artifice la Nature nous fait <pb o="59" file="0077" n="77" rhead="DE NEUTON."/> connaitre les grandeurs, les diſtances, les <lb/>ſituations? </s> <s xml:id="echoid-s791" xml:space="preserve">Quelle eſt enfin la véritable rai-<lb/>ſon, qui fait que nous voyons les objets tels <lb/>qu’ils ſont, quoique dans nos yeux ils ſe <lb/>peignent renverſez? </s> <s xml:id="echoid-s792" xml:space="preserve">Il n’y a rien là qui ne <lb/>mérite la curioſité de tout Etre penſant; <lb/></s> <s xml:id="echoid-s793" xml:space="preserve">mais nous ne nous étendrions pas ſur ces <lb/>ſujets que tant d’illuſtres Ecrivains ont <lb/>traités, & </s> <s xml:id="echoid-s794" xml:space="preserve">nous renverrions à eux, ſi nous <lb/>n’avions pas à faire connaitre quelques vé-<lb/>rités aſſez nouvelles, & </s> <s xml:id="echoid-s795" xml:space="preserve">curieuſes pour un <lb/>petit nombre de Lecteurs.</s> <s xml:id="echoid-s796" xml:space="preserve"/> </p> <figure> <image file="0077-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0077-01"/> </figure> <pb file="0078" n="78"/> <figure> <image file="0078-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0078-01"/> </figure> </div> <div xml:id="echoid-div35" type="section" level="1" n="13"> <head xml:id="echoid-head19" xml:space="preserve">CHAPITRE CINQ.</head> <head xml:id="echoid-head20" style="it" xml:space="preserve">Des Miroirs, des Teleſcopes: des Raiſons que <lb/>les Matbématiques donnent des myſtè-<lb/>res de la viſion; que ces raiſons ne <lb/>ſont point du tout ſuffiſantes.</head> <p> <s xml:id="echoid-s797" xml:space="preserve">LES RAYONS qu’une Puiſſance, juſ-<lb/>qu’à nos jours inconnue, fait rejailli@ <lb/>à vos yeux de deſſus la ſurface d’un Miroir, <lb/>ſans toucher à cette ſurface, & </s> <s xml:id="echoid-s798" xml:space="preserve">des pores de <lb/>ce Miroir, ſans toucher aux parties ſolides; <lb/></s> <s xml:id="echoid-s799" xml:space="preserve">ces rayons, dis-je, retournent à vos yeux <pb o="61" file="0079" n="79" rhead="DE NEUTON."/> dans le même ſens qu’ils ſont arrivés à ce <lb/>Miroir. </s> <s xml:id="echoid-s800" xml:space="preserve">Si c’eſt votre viſage que vous re-<lb/>gardez, les rayons partis de votre viſage <lb/>parallèlement & </s> <s xml:id="echoid-s801" xml:space="preserve">en perpendiculaire ſur le <lb/>Miroir, y retournent de même qu’une bal-<lb/>le qui rebondit perpendiculairement ſur le <lb/>plancher.</s> <s xml:id="echoid-s802" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s803" xml:space="preserve">Si vous regardez dans ce Miroir M. </s> <s xml:id="echoid-s804" xml:space="preserve">un <lb/> <anchor type="note" xlink:label="note-0079-01a" xlink:href="note-0079-01"/> objet qui eſt à côté de vous comme A. </s> <s xml:id="echoid-s805" xml:space="preserve">il <lb/>arrive aux rayons partis de cet objet la mê-<lb/>me choſe qu’à une balle, qui rebondiroit <lb/>en B. </s> <s xml:id="echoid-s806" xml:space="preserve">où eſt votre œil. </s> <s xml:id="echoid-s807" xml:space="preserve">C’eſt ce qu’on ap-<lb/>pelle l’angle d’incidence égal à l’angle de <lb/>réflexion.</s> <s xml:id="echoid-s808" xml:space="preserve"/> </p> <div xml:id="echoid-div35" type="float" level="2" n="1"> <note position="right" xlink:label="note-0079-01" xlink:href="note-0079-01a" xml:space="preserve">Miroir <lb/>plan.</note> </div> <figure> <image file="0079-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0079-01"/> </figure> <pb o="62" file="0080" n="80" rhead="DE LA PHIL OSOPHIE"/> <figure> <image file="0080-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0080-01"/> </figure> <p> <s xml:id="echoid-s809" xml:space="preserve">La ligne A. </s> <s xml:id="echoid-s810" xml:space="preserve">C. </s> <s xml:id="echoid-s811" xml:space="preserve">eſt la ligne d’incidence, la <lb/>ligne C. </s> <s xml:id="echoid-s812" xml:space="preserve">B. </s> <s xml:id="echoid-s813" xml:space="preserve">eſt la ligne de réflexion. </s> <s xml:id="echoid-s814" xml:space="preserve">On <lb/>ſait aſſez, & </s> <s xml:id="echoid-s815" xml:space="preserve">le ſeul énoncé le démontre, <lb/>que ces lignes forment des angles égaux ſur <lb/>la ſurface de la glace; </s> <s xml:id="echoid-s816" xml:space="preserve">maintenant pour-<lb/>quoi ne vois-je l’objet ni en A. </s> <s xml:id="echoid-s817" xml:space="preserve">où il eſt, <lb/>ni dans C. </s> <s xml:id="echoid-s818" xml:space="preserve">dont viennent à mes yeux les <lb/>rayons, mais en D. </s> <s xml:id="echoid-s819" xml:space="preserve">derriere le Miroir <lb/>même?</s> <s xml:id="echoid-s820" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s821" xml:space="preserve">La Géométrie vous dira: </s> <s xml:id="echoid-s822" xml:space="preserve">c’eſt que l’angle <pb o="63" file="0081" n="81" rhead="DE NEUTON."/> d’incidence eſt égal à l’angle de réflexion: <lb/></s> <s xml:id="echoid-s823" xml:space="preserve">c’eſt que votre œil en B. </s> <s xml:id="echoid-s824" xml:space="preserve">rapporte l’objet <lb/>en D.</s> <s xml:id="echoid-s825" xml:space="preserve">; c’eſt que les objets ne peuvent agir <lb/>ſur vous qu’en ligne droite, & </s> <s xml:id="echoid-s826" xml:space="preserve">que la ligne <lb/>droite continuée dans votre œil B. </s> <s xml:id="echoid-s827" xml:space="preserve">juſques <lb/>derriere le miroir en D. </s> <s xml:id="echoid-s828" xml:space="preserve">eſt auſſi longue que <lb/>la ligne A C. </s> <s xml:id="echoid-s829" xml:space="preserve">& </s> <s xml:id="echoid-s830" xml:space="preserve">la ligne C B. </s> <s xml:id="echoid-s831" xml:space="preserve">priſes en-<lb/>ſemble.</s> <s xml:id="echoid-s832" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s833" xml:space="preserve">Enfin elle vous dira encore: </s> <s xml:id="echoid-s834" xml:space="preserve">vous ne <lb/>voyez jamais les objets que du point oû les <lb/>rayons commencent à diverger. </s> <s xml:id="echoid-s835" xml:space="preserve">Soit ce <lb/>Miroir M. </s> <s xml:id="echoid-s836" xml:space="preserve">I.</s> <s xml:id="echoid-s837" xml:space="preserve"/> </p> <figure> <image file="0081-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0081-01"/> </figure> <pb o="64" file="0082" n="82" rhead="DE LA PHILOSOPHIE"/> <figure> <image file="0082-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0082-01"/> </figure> <p> <s xml:id="echoid-s838" xml:space="preserve">Les faiſceaux de rayons qui partent <lb/>de chaque point de l’objet A, commen-<lb/>cent à diverger dès l’inſtant qu’ils par-<lb/>tent de l’objet; </s> <s xml:id="echoid-s839" xml:space="preserve">ils arrivent ſur la ſur-<lb/>face du Miroir: </s> <s xml:id="echoid-s840" xml:space="preserve">là chacun de ces rayons <lb/> <anchor type="note" xlink:label="note-0082-01a" xlink:href="note-0082-01"/> tombe, s’écarte, & </s> <s xml:id="echoid-s841" xml:space="preserve">ſe réflechit vers l’œil. <lb/></s> <s xml:id="echoid-s842" xml:space="preserve">Cet œil les rapporte aux points D. </s> <s xml:id="echoid-s843" xml:space="preserve">D. </s> <s xml:id="echoid-s844" xml:space="preserve">au <lb/>bout des lignes droites, où ces mêmes rayons <lb/>ſe rencontreroient; </s> <s xml:id="echoid-s845" xml:space="preserve">mais en ſe rencontrant <lb/>aux points D. </s> <s xml:id="echoid-s846" xml:space="preserve">D. </s> <s xml:id="echoid-s847" xml:space="preserve">ces rayons feroient la mê-<lb/>me choſe qu’aux points A. </s> <s xml:id="echoid-s848" xml:space="preserve">A. </s> <s xml:id="echoid-s849" xml:space="preserve">ils commen- <pb o="65" file="0083" n="83" rhead="DE NEUTON."/> ceroient à diverger; </s> <s xml:id="echoid-s850" xml:space="preserve">donc vous voyez l’ob-<lb/>jet A. </s> <s xml:id="echoid-s851" xml:space="preserve">A. </s> <s xml:id="echoid-s852" xml:space="preserve">aux points D. </s> <s xml:id="echoid-s853" xml:space="preserve">D.</s> <s xml:id="echoid-s854" xml:space="preserve"/> </p> <div xml:id="echoid-div36" type="float" level="2" n="2"> <note position="left" xlink:label="note-0082-01" xlink:href="note-0082-01a" xml:space="preserve">Miroir <lb/>plan.</note> </div> <p> <s xml:id="echoid-s855" xml:space="preserve">Ces angles & </s> <s xml:id="echoid-s856" xml:space="preserve">ces lignes ſervent, ſans <lb/>doute, à vous donner une intelligence de <lb/>cet artifice de la Nature; </s> <s xml:id="echoid-s857" xml:space="preserve">mais il s’en faut <lb/>beaucoup qu’elles puiſſent vous apprendre <lb/>la raiſon Phyſique efficiente, pourquoi votre <lb/>ame rapporte ſans héſiter l’objet au-delà du <lb/>Miroir à la même diſtance qu’il eſt au deçà. <lb/></s> <s xml:id="echoid-s858" xml:space="preserve">Ces lignes vous repréſentent ce qui arrive, <lb/>mais elles ne vous apprennent point pour-<lb/>quoi cela arrive.</s> <s xml:id="echoid-s859" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s860" xml:space="preserve">Si vous voulez ſavoir comment un Miroir <lb/>convexe diminue les objets, & </s> <s xml:id="echoid-s861" xml:space="preserve">comment un <lb/>Miroir concave les augmente, ces lignes <lb/>d’incidence & </s> <s xml:id="echoid-s862" xml:space="preserve">de réflexion vous en rendront <lb/>la même raiſon.</s> <s xml:id="echoid-s863" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s864" xml:space="preserve">On vous dit: </s> <s xml:id="echoid-s865" xml:space="preserve">Ce cone de rayons qui di-<lb/> <anchor type="note" xlink:label="note-0083-01a" xlink:href="note-0083-01"/> verge du point A. </s> <s xml:id="echoid-s866" xml:space="preserve">& </s> <s xml:id="echoid-s867" xml:space="preserve">qui tombe ſur ce Mi-<lb/>roir convexe, y fait des angles d’incidence <lb/>égaux aux angles de réflexion, dont les li-<lb/>gnes vont dans notre œil. </s> <s xml:id="echoid-s868" xml:space="preserve">Or ces angles <lb/>ſont plus petits que s’ils étoient tombés ſur <lb/>une ſurface plane, donc s’ils ſont ſuppoſés <pb o="66" file="0084" n="84" rhead="DE LA PHILOSOPHIE"/> paſſer en B. </s> <s xml:id="echoid-s869" xml:space="preserve">ils y convergeront bien plutôt, <lb/>donc l’objet qui ſeroit en B. </s> <s xml:id="echoid-s870" xml:space="preserve">B. </s> <s xml:id="echoid-s871" xml:space="preserve">ſeroit plus <lb/>petit.</s> <s xml:id="echoid-s872" xml:space="preserve"/> </p> <div xml:id="echoid-div37" type="float" level="2" n="3"> <note position="right" xlink:label="note-0083-01" xlink:href="note-0083-01a" xml:space="preserve">Miroir <lb/>con-<lb/>vexe.</note> </div> <figure> <image file="0084-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0084-01"/> </figure> <p> <s xml:id="echoid-s873" xml:space="preserve">Or votre œil rapporte l’objet en B. </s> <s xml:id="echoid-s874" xml:space="preserve">B. <lb/></s> <s xml:id="echoid-s875" xml:space="preserve">aux points d’où les rayons commence-<lb/>roient à diverger, donc l’objet doit vous pa-<lb/>raitre plus petit, comme il l’eſt en effet dans <lb/>cette figure. </s> <s xml:id="echoid-s876" xml:space="preserve">Par la même raiſon qu’il pa-<lb/>rait plus petit, il vous parait plus près, <lb/>puiſqu’en effet les points où aboutiroient les <lb/>rayons B. </s> <s xml:id="echoid-s877" xml:space="preserve">B. </s> <s xml:id="echoid-s878" xml:space="preserve">ſont plus près du Miroir que <lb/>ne le ſont les rayons A. </s> <s xml:id="echoid-s879" xml:space="preserve">A.</s> <s xml:id="echoid-s880" xml:space="preserve"/> </p> <pb o="67" file="0085" n="85" rhead="DE NEUTON."/> <figure> <image file="0085-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0085-01"/> </figure> <p> <s xml:id="echoid-s881" xml:space="preserve">Par la raiſon des contraires, vous devez <lb/>voir les objets plus grands & </s> <s xml:id="echoid-s882" xml:space="preserve">plus éloignés <lb/>dans un Miroir concave, en plaçant l’ob-<lb/>jet aſſez près du Miroir.</s> <s xml:id="echoid-s883" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s884" xml:space="preserve">Car les cones des rayons A. </s> <s xml:id="echoid-s885" xml:space="preserve">A. </s> <s xml:id="echoid-s886" xml:space="preserve">venant <lb/>à diverger ſur le Miroir aux points où ces <lb/>rayons tombent, s’ils ſe réflechiſſoient à <lb/>travers ce Miroir, ils ne ſe réuniroient qu’en <lb/>B. </s> <s xml:id="echoid-s887" xml:space="preserve">B. </s> <s xml:id="echoid-s888" xml:space="preserve">donc c’eſt en B. </s> <s xml:id="echoid-s889" xml:space="preserve">B. </s> <s xml:id="echoid-s890" xml:space="preserve">que vous les <pb o="68" file="0086" n="86" rhead="DE LA PHILOSOPHIE"/> voyez. </s> <s xml:id="echoid-s891" xml:space="preserve">Or B. </s> <s xml:id="echoid-s892" xml:space="preserve">B. </s> <s xml:id="echoid-s893" xml:space="preserve">eſt plus grand & </s> <s xml:id="echoid-s894" xml:space="preserve">plus <lb/>éloigné du Miroir que n’eſt A. </s> <s xml:id="echoid-s895" xml:space="preserve">A. </s> <s xml:id="echoid-s896" xml:space="preserve">donc <lb/>vous verrez l’objet plus grand, & </s> <s xml:id="echoid-s897" xml:space="preserve">plus loin.</s> <s xml:id="echoid-s898" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s899" xml:space="preserve">Voilà en général ce qui ſe paſſe dans les <lb/>rayons réflechis à vos yeux, & </s> <s xml:id="echoid-s900" xml:space="preserve">ce ſeul Prin-<lb/>cipe, que l’angle d’incidence eſt toujours <lb/>égal à l’angle de réflexion, eſt le premier <lb/>fondement de tous les myſtères de la Catop-<lb/>trique.</s> <s xml:id="echoid-s901" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s902" xml:space="preserve">MAINTENANT il s’agit de ſavoir, <lb/>comment les lunettes augmentent ces gran-<lb/>deurs & </s> <s xml:id="echoid-s903" xml:space="preserve">raprochent ces diſtances. </s> <s xml:id="echoid-s904" xml:space="preserve">Enfin <lb/>pourquoi les objets ſe peignant renverſés <lb/>dans vos yeux, vous les voyez cependant <lb/>comme ils ſont.</s> <s xml:id="echoid-s905" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s906" xml:space="preserve">A l’égard des grandeurs & </s> <s xml:id="echoid-s907" xml:space="preserve">des diſtan-<lb/>ces, voici ce que les Mathématiques vous <lb/>en apprendront. </s> <s xml:id="echoid-s908" xml:space="preserve">Plus un objet fera dans <lb/>votre œil un grand angle, plus l’objet vous <lb/>paraitra grand: </s> <s xml:id="echoid-s909" xml:space="preserve">rien n’eſt plus ſimple. <lb/></s> <s xml:id="echoid-s910" xml:space="preserve"> <anchor type="note" xlink:label="note-0086-01a" xlink:href="note-0086-01"/> Cette ligne H. </s> <s xml:id="echoid-s911" xml:space="preserve">K. </s> <s xml:id="echoid-s912" xml:space="preserve">que vous voyez, à cent <lb/>pas, trace un angle dans l’œil A. </s> <s xml:id="echoid-s913" xml:space="preserve">(figure <lb/>premiere); </s> <s xml:id="echoid-s914" xml:space="preserve">à deux cens pas, elle trace un <lb/>angle la moitié plus petit dans l’œil B.</s> <s xml:id="echoid-s915" xml:space="preserve"> <pb file="0087" n="87"/> <pb file="0088" n="88"/> <anchor type="figure" xlink:label="fig-0088-01a" xlink:href="fig-0088-01"/> <pb o="69" file="0089" n="89" rhead="DE NEUTON."/> (figure ſeconde). </s> <s xml:id="echoid-s916" xml:space="preserve">Or l’angle qui ſe forme <lb/>dans votre rétine & </s> <s xml:id="echoid-s917" xml:space="preserve">dont votre rétine eſt <lb/>la baze, eſt comme l’angle dont l’objet eſt <lb/>la baze. </s> <s xml:id="echoid-s918" xml:space="preserve">Ce ſont des angles oppoſez au ſom-<lb/>met: </s> <s xml:id="echoid-s919" xml:space="preserve">donc par les premieres notions des E-<lb/>lémens de la Géométrie ils ſont égaux; </s> <s xml:id="echoid-s920" xml:space="preserve">donc <lb/>ſi l’angle formé dans l’œil A. </s> <s xml:id="echoid-s921" xml:space="preserve">eſt double de <lb/>l’angle formé dans l’œil B.</s> <s xml:id="echoid-s922" xml:space="preserve">, cet objet paraitra <lb/>une fois plus grand à l’œil A. </s> <s xml:id="echoid-s923" xml:space="preserve">qu’à l’œil B.</s> <s xml:id="echoid-s924" xml:space="preserve"/> </p> <div xml:id="echoid-div38" type="float" level="2" n="4"> <note position="left" xlink:label="note-0086-01" xlink:href="note-0086-01a" xml:space="preserve">Expli-<lb/>cations <lb/>géomé-<lb/>triques <lb/>de la vi-<lb/>ſion.</note> <figure xlink:label="fig-0088-01" xlink:href="fig-0088-01a"> <image file="0088-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0088-01"/> </figure> </div> <p> <s xml:id="echoid-s925" xml:space="preserve">Maintenant pour que l’œil étant en B. <lb/></s> <s xml:id="echoid-s926" xml:space="preserve">voye l’objet auſſi grand, que le voit l’œil en <lb/>A.</s> <s xml:id="echoid-s927" xml:space="preserve">, il faut faire en ſorte que cet œil B. </s> <s xml:id="echoid-s928" xml:space="preserve">re-<lb/>çoive un angle auſſi grand que celui de l’œil <lb/>A. </s> <s xml:id="echoid-s929" xml:space="preserve">qui eſt une fois plus près. </s> <s xml:id="echoid-s930" xml:space="preserve">Le<unsure/>s verres <lb/>d’un téleſcope feront cet effet.</s> <s xml:id="echoid-s931" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s932" xml:space="preserve">Ne mettons ici qu’un ſeul verre pour plus <lb/>de facilité, & </s> <s xml:id="echoid-s933" xml:space="preserve">faiſons abſtraction des autres <lb/>effets de pluſieurs verres. </s> <s xml:id="echoid-s934" xml:space="preserve">L’objet H. </s> <s xml:id="echoid-s935" xml:space="preserve">K. <lb/></s> <s xml:id="echoid-s936" xml:space="preserve">(troiſième figure) envoye ſes rayons à <lb/>ce verre. </s> <s xml:id="echoid-s937" xml:space="preserve">Ils ſe réuniſſent à quelque diſtance <lb/>du verre. </s> <s xml:id="echoid-s938" xml:space="preserve">Concevons un verre taillé de <lb/>ſorte, que ces rayons ſe croiſent pour aller <lb/>former dans l’œil en C. </s> <s xml:id="echoid-s939" xml:space="preserve">un angle auſſi grand <lb/>que celui de l’œil en A. </s> <s xml:id="echoid-s940" xml:space="preserve">alors l’œil, nous <lb/>dit-on, juge par cet angle. </s> <s xml:id="echoid-s941" xml:space="preserve">Il voit donc <pb o="70" file="0090" n="90" rhead="DE LA PHILOSOPHIE"/> alors l’objet de la même grandeur, que le <lb/>voit l’œil en A. </s> <s xml:id="echoid-s942" xml:space="preserve">Mais en A. </s> <s xml:id="echoid-s943" xml:space="preserve">il le voit à <lb/>cent pas de diſtance: </s> <s xml:id="echoid-s944" xml:space="preserve">donc en C. </s> <s xml:id="echoid-s945" xml:space="preserve">recevant <lb/>le même angle, il le verra encore à cent <lb/>pas de diſtance. </s> <s xml:id="echoid-s946" xml:space="preserve">Tout l’effet des verres de <lb/>lunettes multipliez, & </s> <s xml:id="echoid-s947" xml:space="preserve">des téleſcopes divers, <lb/>& </s> <s xml:id="echoid-s948" xml:space="preserve">des microſcopes qui agrandiſſent les ob-<lb/>jets, conſiſte donc à faire voir les choſes <lb/>ſous un plus grand angle. </s> <s xml:id="echoid-s949" xml:space="preserve">L’objet A. </s> <s xml:id="echoid-s950" xml:space="preserve">B. <lb/></s> <s xml:id="echoid-s951" xml:space="preserve">eſt vu par le moyen de ce verre ſous l’an-<lb/>gle D, C, D. </s> <s xml:id="echoid-s952" xml:space="preserve">qui eſt bien plus grand que <lb/>l’angle A, C, B.</s> <s xml:id="echoid-s953" xml:space="preserve"/> </p> <figure> <image file="0090-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0090-01"/> </figure> <p> <s xml:id="echoid-s954" xml:space="preserve">Vous demandez encore aux règles d’op-<lb/>tique, pourquoi vous voyez les objets dans <pb o="71" file="0091" n="91" rhead="DE NEUTON."/> leur ſituation, quoiqu’ils ſe peignent ren-<lb/>verſez ſur notre rétine?</s> <s xml:id="echoid-s955" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s956" xml:space="preserve">Le rayon qui part de la tête de cet hom-<lb/>me A.</s> <s xml:id="echoid-s957" xml:space="preserve">, vient au point inférieur de votre <lb/>rétine A. </s> <s xml:id="echoid-s958" xml:space="preserve">ſes pieds B. </s> <s xml:id="echoid-s959" xml:space="preserve">ſont vus par les rayons <lb/>B. </s> <s xml:id="echoid-s960" xml:space="preserve">B. </s> <s xml:id="echoid-s961" xml:space="preserve">au point ſupérieur de votre rétine B. <lb/></s> <s xml:id="echoid-s962" xml:space="preserve">Ainſi cet homme<unsure/> eſt peint reellement la tê-<lb/>te en bas & </s> <s xml:id="echoid-s963" xml:space="preserve">les pieds en haut au fond de <lb/>vos yeux. </s> <s xml:id="echoid-s964" xml:space="preserve">Pourquoi donc ne voyez-vous <lb/>pas cet homme renverſé, mais droit, & </s> <s xml:id="echoid-s965" xml:space="preserve">tel <lb/>qu’il eſt?</s> <s xml:id="echoid-s966" xml:space="preserve"/> </p> <figure> <image file="0091-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0091-01"/> </figure> <p> <s xml:id="echoid-s967" xml:space="preserve">Pour réſoudre cette queſtion, on ſe ſert de <lb/>la comparaiſon de l’aveugle, qui tient dans <lb/>ſes mains deux bâtons croiſez avec leſquels <lb/>il devine très-bien la poſition des objets.</s> <s xml:id="echoid-s968" xml:space="preserve"/> </p> <pb o="72" file="0092" n="92" rhead="DE LA PHILOSOPHIE"/> <figure> <image file="0092-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0092-01"/> </figure> <p> <s xml:id="echoid-s969" xml:space="preserve">Car le point A.</s> <s xml:id="echoid-s970" xml:space="preserve">, qui eſt à gauche, é-<lb/>tant ſenti par la main droite à l’aide du bâ-<lb/>ton, il le juge auſſi-tôt à gauche; </s> <s xml:id="echoid-s971" xml:space="preserve">& </s> <s xml:id="echoid-s972" xml:space="preserve">le point <lb/>B. </s> <s xml:id="echoid-s973" xml:space="preserve">que ſa main gauche a ſenti par l’entre-<lb/>miſe de l’autre bâton, il le juge à droite <lb/>ſans ſe tromper.</s> <s xml:id="echoid-s974" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s975" xml:space="preserve">Tous les Maîtres d’optique nous diſent <lb/>donc, que la partie inférieure de l’œil rap-<lb/>portetout d’un coup ſa ſenſation à la partie <lb/>ſupérieure A. </s> <s xml:id="echoid-s976" xml:space="preserve">de l’objet, & </s> <s xml:id="echoid-s977" xml:space="preserve">que la partie <lb/>ſupérieure de la rétine rapporte auſſi natu-<lb/>rellement la ſenſation à la partie inférieure <lb/>B.</s> <s xml:id="echoid-s978" xml:space="preserve">; ainſi on voit l’objet dans ſa ſituation <lb/>véritable.</s> <s xml:id="echoid-s979" xml:space="preserve"/> </p> <pb o="73" file="0093" n="93" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s980" xml:space="preserve">Quand vous aurez connu parfaitement <lb/> <anchor type="note" xlink:label="note-0093-01a" xlink:href="note-0093-01"/> tous ces angles, & </s> <s xml:id="echoid-s981" xml:space="preserve">toutes ces lignes Mathé-<lb/>matiques, par leſquelles on ſuit le chemin <lb/>de la lumiere juſqu’au fond de l’œil, ne <lb/>croyez pas pour cela ſavoir comment vous <lb/>appercevez les grandeurs, les diſtances, les <lb/>ſituations des choſes. </s> <s xml:id="echoid-s982" xml:space="preserve">Les proportions géo-<lb/>métriques de ces angles & </s> <s xml:id="echoid-s983" xml:space="preserve">de ces lignes ſont <lb/>juſtes, il eſt vrai; </s> <s xml:id="echoid-s984" xml:space="preserve">mais il n’y a pas plus de <lb/>rapport entr’elles & </s> <s xml:id="echoid-s985" xml:space="preserve">nos ſenſations, qu’en-<lb/>tre le ſon que nous entendons & </s> <s xml:id="echoid-s986" xml:space="preserve">la gran-<lb/>deur, la diſtance, la ſituation de la choſe <lb/>entendue. </s> <s xml:id="echoid-s987" xml:space="preserve">Par le ſon, mon oreille eſt frap-<lb/>pée; </s> <s xml:id="echoid-s988" xml:space="preserve">j’entends des tons & </s> <s xml:id="echoid-s989" xml:space="preserve">rien de plus. </s> <s xml:id="echoid-s990" xml:space="preserve">Par <lb/>la vûe, mon œil eſt ébranlé; </s> <s xml:id="echoid-s991" xml:space="preserve">je vois des <lb/>couleurs & </s> <s xml:id="echoid-s992" xml:space="preserve">rien de plus. </s> <s xml:id="echoid-s993" xml:space="preserve">Non-ſeulement <lb/>les proportions de ces angles, & </s> <s xml:id="echoid-s994" xml:space="preserve">de ces li-<lb/>gnes, ne peuvent en aucune maniere être <lb/>la cauſe immédiate du jugement que je for-<lb/>me des objets; </s> <s xml:id="echoid-s995" xml:space="preserve">mais en pluſieurs cas ces <lb/>proportions ne s’accordent point du tout <lb/>avec la façon dont nous voyons les objets.</s> <s xml:id="echoid-s996" xml:space="preserve"/> </p> <div xml:id="echoid-div39" type="float" level="2" n="5"> <note position="right" xlink:label="note-0093-01" xlink:href="note-0093-01a" xml:space="preserve">Nul rap-<lb/>port im-<lb/>médiat <lb/>entre les <lb/>règles <lb/>d’opti-<lb/>que & <lb/>nos ſen-<lb/>ſations.</note> </div> <p> <s xml:id="echoid-s997" xml:space="preserve">Par exemple, un homme vu à quatre pas, <lb/> <anchor type="note" xlink:label="note-0093-02a" xlink:href="note-0093-02"/> & </s> <s xml:id="echoid-s998" xml:space="preserve">à huit pas, eſt vu de même grandeur. <lb/></s> <s xml:id="echoid-s999" xml:space="preserve">Cependant l’image de cet homme, à huit <pb o="74" file="0094" n="94" rhead="DE LA PHILOSOPHIE"/> pas, eſt préciſément double dans votre œil, <lb/>de celle qu’il y trace à quatre pas. </s> <s xml:id="echoid-s1000" xml:space="preserve">Les an-<lb/>gles ſont différens, & </s> <s xml:id="echoid-s1001" xml:space="preserve">vous voyez l’objet <lb/>toujours également grand; </s> <s xml:id="echoid-s1002" xml:space="preserve">donc il eſt évi-<lb/>dent par ce ſeul exemple, choiſi entre plu-<lb/>ſieurs, que ces angles & </s> <s xml:id="echoid-s1003" xml:space="preserve">ces lignes ne ſont <lb/>point du tout la cauſe immédiate de la ma-<lb/>niere dont nous voyons.</s> <s xml:id="echoid-s1004" xml:space="preserve"/> </p> <div xml:id="echoid-div40" type="float" level="2" n="6"> <note position="right" xlink:label="note-0093-02" xlink:href="note-0093-02a" xml:space="preserve">Exem-<lb/>ple en <lb/>preuve.</note> </div> <p> <s xml:id="echoid-s1005" xml:space="preserve">Avant donc de continuer les recherches <lb/>que nous avons commencées ſur la lumiere, <lb/>& </s> <s xml:id="echoid-s1006" xml:space="preserve">ſur les loix mécaniques de la Nature, <lb/>vous m’ordonnez de dire ici comment les <lb/>idées des diſtances, des grandeurs, des ſi-<lb/>tuations, des objets, ſont reçues dans notre <lb/>ame. </s> <s xml:id="echoid-s1007" xml:space="preserve">Cet examen nous fournira quelque <lb/>choſe de nouveau & </s> <s xml:id="echoid-s1008" xml:space="preserve">de vrai, c’eſt la ſeule <lb/>excuſe d’un Livre.</s> <s xml:id="echoid-s1009" xml:space="preserve"/> </p> <figure> <image file="0094-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0094-01"/> </figure> <pb file="0095" n="95"/> <figure> <image file="0095-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0095-01"/> </figure> </div> <div xml:id="echoid-div42" type="section" level="1" n="14"> <head xml:id="echoid-head21" xml:space="preserve">CHAPITRE SIXIEME.</head> <head xml:id="echoid-head22" style="it" xml:space="preserve">Comment nous connaiſſons les diſtances, les <lb/>grandeurs, les figures, les ſituations.</head> <p> <s xml:id="echoid-s1010" xml:space="preserve">CCOMMENÇONS par la diſtance. <lb/></s> <s xml:id="echoid-s1011" xml:space="preserve"> <anchor type="note" xlink:label="note-0095-01a" xlink:href="note-0095-01"/> Il eſt clair qu’elle ne peut être apper-<lb/>çue immédiatement par elle-méme; </s> <s xml:id="echoid-s1012" xml:space="preserve">car la <lb/>diſtance n’eſt qu’une ligne de l’objet à nous. <lb/></s> <s xml:id="echoid-s1013" xml:space="preserve">Cette ligne ſe termine à un point, nous ne <lb/>ſentons donc que ce point; </s> <s xml:id="echoid-s1014" xml:space="preserve">& </s> <s xml:id="echoid-s1015" xml:space="preserve">ſoit que l’ob-<lb/>jet exiſte à mille lieues, ou qu’il ſoit à un <lb/>pied, ce point eſt toujours le même.</s> <s xml:id="echoid-s1016" xml:space="preserve"/> </p> <div xml:id="echoid-div42" type="float" level="2" n="1"> <note position="right" xlink:label="note-0095-01" xlink:href="note-0095-01a" xml:space="preserve">Les an-<lb/>gles, ni <lb/>les li-<lb/>gnes op-<lb/>tiques, <lb/>ne peu-<lb/>vent <lb/>nous <lb/>faire <lb/>connai-<lb/>tre les <lb/>diſtan-<lb/>ces.</note> </div> <pb o="76" file="0096" n="96" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s1017" xml:space="preserve">Nous n’avons donc aucun moyen im-<lb/>médiat, pour appercevoir tout d’un coup la <lb/>diſtance, comme nous en avons, pour ſen-<lb/>tir par l’attouchement, ſi un corps eſt dur <lb/>ou mou; </s> <s xml:id="echoid-s1018" xml:space="preserve">par le goût, s’il eſt doux ou amer; <lb/></s> <s xml:id="echoid-s1019" xml:space="preserve">par l’ouïe, ſi de deux ſons l’un eſt grave <lb/>& </s> <s xml:id="echoid-s1020" xml:space="preserve">l’autre aigu. </s> <s xml:id="echoid-s1021" xml:space="preserve">Il faut donc que l’idée de <lb/>la diſtance nous vienne par le moyen d’une <lb/>autre idée intermédiaire: </s> <s xml:id="echoid-s1022" xml:space="preserve">mais il faut au <lb/>moins que j’apperçoive cette intermédiaire; </s> <s xml:id="echoid-s1023" xml:space="preserve"><lb/>car une idée que je n’aurai point, ne ſer-<lb/>vira certainement pas à m’en faire avoir <lb/>une autre. </s> <s xml:id="echoid-s1024" xml:space="preserve">Je dis qu’une telle maiſon eſt à <lb/>un mille d’une telle riviére; </s> <s xml:id="echoid-s1025" xml:space="preserve">mais ſi je ne <lb/>ſai pas où eſt cette riviére, je ne fai cer-<lb/>tainement pas où eſt cette maiſon. </s> <s xml:id="echoid-s1026" xml:space="preserve">Un corps <lb/>cède aiſément à l’impreſſion de ma main; </s> <s xml:id="echoid-s1027" xml:space="preserve">je <lb/>conclus immédiatement ſa molleſſe. </s> <s xml:id="echoid-s1028" xml:space="preserve">Un au-<lb/>tre réſiſte, je fens immédiatement ſa dure-<lb/>té; </s> <s xml:id="echoid-s1029" xml:space="preserve">il faudroit donc que je ſentiſſe les angles <lb/>formés dans mon œil, pour en conclure im-<lb/>médiatement les diſtances des objets. </s> <s xml:id="echoid-s1030" xml:space="preserve">Mais <lb/>perſonne ne s’aviſe de ſonger à ces angles <lb/>quand il regarde un objet. </s> <s xml:id="echoid-s1031" xml:space="preserve">La plûpart des <lb/>hommes ne ſavent pas même ſi ces angles <lb/>exiſtent: </s> <s xml:id="echoid-s1032" xml:space="preserve">donc il eſt évident que ces an- <pb o="77" file="0097" n="97" rhead="DE NEUTON."/> gles ne peuvent être la cauſe immédiate de <lb/>ce que vous connaiſſez les diſtances.</s> <s xml:id="echoid-s1033" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1034" xml:space="preserve">Celui qui, pour la premiere fois de ſa vie, <lb/> <anchor type="note" xlink:label="note-0097-01a" xlink:href="note-0097-01"/> entendroit le bruit du Canon, ou le ſon d’un <lb/>Concert, ne pourroit juger ſi on tire ce ca-<lb/>non, ou ſi on exécute ce concert à une <lb/>lieue, ou à trente pas. </s> <s xml:id="echoid-s1035" xml:space="preserve">Il n’y a que l’ex-<lb/>périence qui puiſſe l’accoutumer à juger de <lb/>la diſtance qui eſt entre lui & </s> <s xml:id="echoid-s1036" xml:space="preserve">l’endroit d’où <lb/>part ce bruit. </s> <s xml:id="echoid-s1037" xml:space="preserve">Les vibrations, les ondula-<lb/>tions de l’air, portent un ſon à ſes oreilles, <lb/>ou plutôt à ſon ame; </s> <s xml:id="echoid-s1038" xml:space="preserve">mais ce bruit n’aver-<lb/>tit pas plus ſon ame de l’endroit où le bruit <lb/>commence, qu’il ne lui apprend la forme <lb/>du canon ou des inſtrumens de Muſique.</s> <s xml:id="echoid-s1039" xml:space="preserve"/> </p> <div xml:id="echoid-div43" type="float" level="2" n="2"> <note position="right" xlink:label="note-0097-01" xlink:href="note-0097-01a" xml:space="preserve">Exem-<lb/>ple en <lb/>preu-<lb/>ve.</note> </div> <p> <s xml:id="echoid-s1040" xml:space="preserve">C’eſt la même choſe préciſément par rap-<lb/>port aux rayons de lumiere qui partent d’un <lb/>objet, ils ne nous apprennent point du tout <lb/>où eſt cet objet.</s> <s xml:id="echoid-s1041" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1042" xml:space="preserve">Ils ne nous font pas connaitre davanta-<lb/> <anchor type="note" xlink:label="note-0097-02a" xlink:href="note-0097-02"/> ge les grandeurs ni même les figures.</s> <s xml:id="echoid-s1043" xml:space="preserve"/> </p> <div xml:id="echoid-div44" type="float" level="2" n="3"> <note position="right" xlink:label="note-0097-02" xlink:href="note-0097-02a" xml:space="preserve">Ces li-<lb/>gnes op-<lb/>tiques <lb/>ne font <lb/>connai-<lb/>tre ni les <lb/>gran-<lb/>deurs ni <lb/>les figu-<lb/>res.</note> </div> <p> <s xml:id="echoid-s1044" xml:space="preserve">Je vois de loin une eſpèce de petite Tout. <lb/></s> <s xml:id="echoid-s1045" xml:space="preserve">J’avance, j’apperçois, & </s> <s xml:id="echoid-s1046" xml:space="preserve">je touche un grand <pb o="78" file="0098" n="98" rhead="DE LA PHILOSOPHIE"/> Bâtiment quadrangulaire. </s> <s xml:id="echoid-s1047" xml:space="preserve">Certainement ce <lb/>que je vois & </s> <s xml:id="echoid-s1048" xml:space="preserve">ce que je touche, n’eſt pas <lb/>ce que je voiois. </s> <s xml:id="echoid-s1049" xml:space="preserve">Ce petit objet rond qui <lb/>étoit dans mes yeux, n’eſt point ce grand <lb/>Bâtiment quarré.</s> <s xml:id="echoid-s1050" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1051" xml:space="preserve">Autre choſe eſt donc l’objet meſurable <lb/>& </s> <s xml:id="echoid-s1052" xml:space="preserve">tangible, autre choſe eſt l’objet viſible. <lb/></s> <s xml:id="echoid-s1053" xml:space="preserve">J’entends de ma chambre le bruit d’un ca-<lb/> <anchor type="note" xlink:label="note-0098-01a" xlink:href="note-0098-01"/> roſſe: </s> <s xml:id="echoid-s1054" xml:space="preserve">j’ouvre la fenêtre & </s> <s xml:id="echoid-s1055" xml:space="preserve">je le vois; </s> <s xml:id="echoid-s1056" xml:space="preserve">je <lb/>deſcends & </s> <s xml:id="echoid-s1057" xml:space="preserve">j’entre dedans. </s> <s xml:id="echoid-s1058" xml:space="preserve">Or ce caroſſe <lb/>que j’ai entendu, ce caroſſe que j’ai vu, ce <lb/>caroſſe que j’ai touché, ſont trois objets ab-<lb/>ſolument divers de trois de mes ſens, qui <lb/>n’ont aucun rapport immédiat les uns avec <lb/>les autres.</s> <s xml:id="echoid-s1059" xml:space="preserve"/> </p> <div xml:id="echoid-div45" type="float" level="2" n="4"> <note position="left" xlink:label="note-0098-01" xlink:href="note-0098-01a" xml:space="preserve">Exem-<lb/>ple en <lb/>preu-<lb/>ve.</note> </div> <p> <s xml:id="echoid-s1060" xml:space="preserve">Il y a bien plus: </s> <s xml:id="echoid-s1061" xml:space="preserve">il eſt démontré, com-<lb/>me je l’ai dit, qu’il ſe forme dans mon <lb/>œil un angle une fois plus grand, quand je <lb/>vois un homme à quatre pieds de moi, <lb/>que quand je vois le même homme à deux <lb/>pieds de moi. </s> <s xml:id="echoid-s1062" xml:space="preserve">Cependant je vois toujours <lb/>cet homme de la même grandeur: </s> <s xml:id="echoid-s1063" xml:space="preserve">comment <lb/>mon ſentiment contredit - il ainſi le méca-<lb/>niſme de mes organes? </s> <s xml:id="echoid-s1064" xml:space="preserve">L’objet eſt réelle-<lb/>ment une fois plus petit dans mes yeux, &</s> <s xml:id="echoid-s1065" xml:space="preserve"> <pb o="79" file="0099" n="99" rhead="DE NEUTON."/> je le vois une fois plus grand. </s> <s xml:id="echoid-s1066" xml:space="preserve">C’eſt en <lb/>vain qu’on veut expliquer ce myſtère par <lb/>le chemin, ou par la forme que prend le criſ-<lb/>tallin dans nos yeux. </s> <s xml:id="echoid-s1067" xml:space="preserve">Quelque ſuppoſition <lb/>que l’on faſſe, l’angle ſous lequel je vois un <lb/>homme à quatre pieds de moi, eſt toujours <lb/>double de l’angle ſous lequel je le vois à <lb/>deux pieds; </s> <s xml:id="echoid-s1068" xml:space="preserve">& </s> <s xml:id="echoid-s1069" xml:space="preserve">la Géométrie ne réſoudra <lb/>jamais ce Problême.</s> <s xml:id="echoid-s1070" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1071" xml:space="preserve">Ces lignes & </s> <s xml:id="echoid-s1072" xml:space="preserve">ces angles géométriques ne <lb/> <anchor type="note" xlink:label="note-0099-01a" xlink:href="note-0099-01"/> ſont pas plus réellement la cauſe de ce que <lb/>nous voyons les objets à leur place, que <lb/>de ce que nous les voyons de telles gran-<lb/>deurs, & </s> <s xml:id="echoid-s1073" xml:space="preserve">à telle diſtance.</s> <s xml:id="echoid-s1074" xml:space="preserve"/> </p> <div xml:id="echoid-div46" type="float" level="2" n="5"> <note position="right" xlink:label="note-0099-01" xlink:href="note-0099-01a" xml:space="preserve">Ni la ſi-<lb/>tuation <lb/>des ob-<lb/>jets.</note> </div> <p> <s xml:id="echoid-s1075" xml:space="preserve">L’ame ne conſidere pas ſi telle partie <lb/>va ſe peindre au bas de l’œil, elle ne <lb/>rapporte rien à des lignes qu’elle ne voit <lb/>point. </s> <s xml:id="echoid-s1076" xml:space="preserve">L’œil ſe baiſſe ſeulement, pour voir <lb/>ce qui eſt près de la terre, & </s> <s xml:id="echoid-s1077" xml:space="preserve">ſe relève pour <lb/>voir ce qui eſt au-deſſus de la terre.</s> <s xml:id="echoid-s1078" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1079" xml:space="preserve">Tout celane pouvoit être éclairci, & </s> <s xml:id="echoid-s1080" xml:space="preserve">mis <lb/>hors de toute conteſtation, que par quel-<lb/>qu’aveugle - né, à qui on auroit donné le <lb/>ſens de la vûe. </s> <s xml:id="echoid-s1081" xml:space="preserve">Car ſi cet aveugle, au mo- <pb o="80" file="0100" n="100" rhead="DE LA PHILOSOPHIE"/> ment qu’il eût ouvert les yeux, eût jugé <lb/>des diſtances, des grandeurs & </s> <s xml:id="echoid-s1082" xml:space="preserve">des ſitua-<lb/>tions, il eut été vrai que les angles optiques, <lb/>formez tout d’un coup dans ſa rétine, euſ-<lb/>ſent été les cauſes immédiates de ſes ſenti-<lb/>mens. </s> <s xml:id="echoid-s1083" xml:space="preserve">Auſſi le Docteur Barclay aſſûroit a-<lb/>près Mr. </s> <s xml:id="echoid-s1084" xml:space="preserve">Loke (& </s> <s xml:id="echoid-s1085" xml:space="preserve">allant même en cela plus <lb/>loin que Loke) que ni ſituation, ni gran-<lb/>deur, ni diſtance, ni figure, ne ſeroit au-<lb/>cunement diſcernée par cet aveugle, dont <lb/>les yeux recevroient tout d’un coup la lu-<lb/>miere.</s> <s xml:id="echoid-s1086" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1087" xml:space="preserve">Mais où trouver l’aveugle, dont dépen-<lb/> <anchor type="note" xlink:label="note-0100-01a" xlink:href="note-0100-01"/> doit la déciſion indubitable de cette queſ-<lb/>tion? </s> <s xml:id="echoid-s1088" xml:space="preserve">Enfin en 1729. </s> <s xml:id="echoid-s1089" xml:space="preserve">Mr. </s> <s xml:id="echoid-s1090" xml:space="preserve">Chiſelden, un <lb/>de ces fameux Chirurgiens, qui joignent l’ad-<lb/>dreſſe de la main aux plus grandes lumieres <lb/>de l’eſprit, ayant imaginé qu’on pouvoit <lb/>donner la vûe à un aveugle-né, en lui ab-<lb/>baiſſant ce qu’on appelle des cataractes, qu’il <lb/>ſoupçonnoit formées dans ſes yeux, preſ-<lb/>qu’au moment de ſa naiſſance, il propoſa <lb/>l’opération. </s> <s xml:id="echoid-s1091" xml:space="preserve">L’aveugle eut de la peine à y <lb/>conſentir. </s> <s xml:id="echoid-s1092" xml:space="preserve">Il ne concevoit pas trop, que <lb/>le ſens de la vûe pût beaucoup augmenter <lb/>ſes plaiſirs. </s> <s xml:id="echoid-s1093" xml:space="preserve">Sans l’envie qu’on lui inſpira <pb o="81" file="0101" n="101" rhead="DE NEUTON."/> d’apprendre à lire & </s> <s xml:id="echoid-s1094" xml:space="preserve">à écrire, il n’eût point <lb/>deſiré de voir. </s> <s xml:id="echoid-s1095" xml:space="preserve">Il vérifioit par cette indif-<lb/>férence, qu’il eſt impoſſible d’être malbeureúx, <lb/>par la privation des biens dont on n’a pas d’i-<lb/>dée: </s> <s xml:id="echoid-s1096" xml:space="preserve">vérité bien importante. </s> <s xml:id="echoid-s1097" xml:space="preserve">Quoi qu’il en <lb/>ſoit, l’opération fut faite & </s> <s xml:id="echoid-s1098" xml:space="preserve">réuſſit. </s> <s xml:id="echoid-s1099" xml:space="preserve">Ce <lb/>jeune homme d’environ quatorze ans, vit <lb/>la lumiere pour la premiere fois. </s> <s xml:id="echoid-s1100" xml:space="preserve">Son <lb/>expérience confirma tout ce que Loke & </s> <s xml:id="echoid-s1101" xml:space="preserve"><lb/>Barclay avoient ſi bien prévu. </s> <s xml:id="echoid-s1102" xml:space="preserve">Il ne diſtin-<lb/>gua de long-tems ni grandeur, ni diſtance, <lb/>ni ſituation, ni méme figure. </s> <s xml:id="echoid-s1103" xml:space="preserve">Un objet <lb/>d’un pouce, mis devant ſon œil, & </s> <s xml:id="echoid-s1104" xml:space="preserve">qui lui <lb/>cachoit une maiſon, lui paraiſſoit auſſi <lb/>grand que la maiſon. </s> <s xml:id="echoid-s1105" xml:space="preserve">Tout ce qu’il <lb/>voioit, lui ſembloit d’abord être ſur ſes <lb/>yeux, & </s> <s xml:id="echoid-s1106" xml:space="preserve">les toucher comme les objets du <lb/>tact touchent la peau. </s> <s xml:id="echoid-s1107" xml:space="preserve">Il ne pouvoit diſ-<lb/>tinguer ce qu’il avoit jugé rond à l’aide de <lb/>ſes mains, d’avec ce qu’il avoit jugé angu-<lb/>laire, ni diſcerner avec ſes yeux, ſi ce <lb/>que ſes mains avoient ſenti être en haut <lb/>ou en bas, étoit en effet en haut ou en <lb/>bas. </s> <s xml:id="echoid-s1108" xml:space="preserve">Il étoit ſi loin de connaitre les gran-<lb/>deurs, qu’après avoir enfin conçu par la <lb/>vûe, que ſa maiſon étoit plus grande que <lb/>ſa chambre, il ne concevoit pas comment <pb o="82" file="0102" n="102" rhead="DE LA PHILOSOPHIE"/> la vûe pouvoit donner cette idée. </s> <s xml:id="echoid-s1109" xml:space="preserve">Ce ne <lb/>fut qu’au bout de deux mois d’expérience, <lb/>qu’il put appercevoir que les tableaux re-<lb/>préſentoient des corps ſolides: </s> <s xml:id="echoid-s1110" xml:space="preserve">& </s> <s xml:id="echoid-s1111" xml:space="preserve">lorſqu’a-<lb/>près ce long tatonnement d’un ſens nouveau <lb/>en lui, il eut ſenti que des corps, & </s> <s xml:id="echoid-s1112" xml:space="preserve">non <lb/>des ſurfaces ſeules, étoient peints dans les <lb/>tableaux; </s> <s xml:id="echoid-s1113" xml:space="preserve">il y porta la main, & </s> <s xml:id="echoid-s1114" xml:space="preserve">fut étonné <lb/>de ne point trouver avec ſes mains ces <lb/>corps ſolides, dont il commençoit à apper-<lb/>cevoir les repréſentations. </s> <s xml:id="echoid-s1115" xml:space="preserve">Il demandoit <lb/>quel étoit le trompeur, du ſens du toucher, <lb/>ou du ſens de la vûe.</s> <s xml:id="echoid-s1116" xml:space="preserve"/> </p> <div xml:id="echoid-div47" type="float" level="2" n="6"> <note position="left" xlink:label="note-0100-01" xlink:href="note-0100-01a" xml:space="preserve">Preuve <lb/>par l’ex-<lb/>périen-<lb/>ce de <lb/>l’aveu-<lb/>gle-né <lb/>guéri <lb/>par Chi-<lb/>ſelden.</note> </div> <p> <s xml:id="echoid-s1117" xml:space="preserve">Ce fut donc une déciſion irrévocable, <lb/>que la maniere dont nous voyons les cho-<lb/>ſes, n’eſt point du tout la ſuite immédia-<lb/>te des angles formés dans nos yeux; </s> <s xml:id="echoid-s1118" xml:space="preserve">car <lb/>ces angles Mathématiques étoient dans les <lb/>yeux de cet homme, comme dans les nô-<lb/>tres, & </s> <s xml:id="echoid-s1119" xml:space="preserve">ne lui ſervoient de rien ſans les ſe-<lb/>cours de l’expérience & </s> <s xml:id="echoid-s1120" xml:space="preserve">des autres ſens.</s> <s xml:id="echoid-s1121" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1122" xml:space="preserve">Comment nous repréſentons-nous donc <lb/>les grandeurs & </s> <s xml:id="echoid-s1123" xml:space="preserve">les diſtances? </s> <s xml:id="echoid-s1124" xml:space="preserve">De la même <lb/>façon dont nous imaginons les paſſions des <lb/>hommes, par les couleurs qu’elles peignent <pb o="83" file="0103" n="103" rhead="DE NEUTON."/> ſur leurs viſages, & </s> <s xml:id="echoid-s1125" xml:space="preserve">par l’altération qu’elles <lb/>portent dans leurs traits. </s> <s xml:id="echoid-s1126" xml:space="preserve">Il n’y a perſon-<lb/> <anchor type="note" xlink:label="note-0103-01a" xlink:href="note-0103-01"/> ne, qui ne liſe tout d’un coup ſur le front <lb/>d’un autre, la honte, ou la colére. </s> <s xml:id="echoid-s1127" xml:space="preserve">C’eſt la <lb/>Langue que la Nature parle à tous les yeux; <lb/></s> <s xml:id="echoid-s1128" xml:space="preserve">mais l’expérience ſeule apprend ce langa-<lb/>ge. </s> <s xml:id="echoid-s1129" xml:space="preserve">Auſſi l’expérience ſeule nous apprend, <lb/>que quand un objet eſt trop loin, nous le <lb/>voyons confuſément & </s> <s xml:id="echoid-s1130" xml:space="preserve">faiblement. </s> <s xml:id="echoid-s1131" xml:space="preserve">Delà <lb/>nous formons des idées, qui enſuite accom-<lb/>pagnent toujours la ſenſation de la vûe. </s> <s xml:id="echoid-s1132" xml:space="preserve"><lb/>Ainſi tout homme qui, à dix pas, aura vu <lb/>ſon cheval haut de cinq pieds, s’il voit, <lb/>quelques minutes après, ce cheval comme <lb/>un mouton, ſon ame, par un jugement <lb/>involontaire, conclud à l’inſtant que ce che-<lb/>val eſt très-loin.</s> <s xml:id="echoid-s1133" xml:space="preserve"/> </p> <div xml:id="echoid-div48" type="float" level="2" n="7"> <note position="right" xlink:label="note-0103-01" xlink:href="note-0103-01a" xml:space="preserve">Com-<lb/>ment <lb/>nous <lb/>connaiſ-<lb/>ſons les <lb/>diſtan-<lb/>ces & <lb/>les gran-<lb/>deurs.</note> </div> <p> <s xml:id="echoid-s1134" xml:space="preserve">Il eſt bien vrai que, quand je vois mon <lb/>cheval gros comme un mouton, il ſe for-<lb/>me alors dans mon œil une peinture plus pe-<lb/>tite, un angle plus aigu; </s> <s xml:id="echoid-s1135" xml:space="preserve">mais c’eſt-là ce <lb/>qui accompagne, non ce qui cauſe mon <lb/>ſentiment. </s> <s xml:id="echoid-s1136" xml:space="preserve">De même il ſe fait un autre é-<lb/>branlement dans mon cerveau, quand je <lb/>vois un homme rougir de honte, que quand <lb/>je le vois rougir de colére; </s> <s xml:id="echoid-s1137" xml:space="preserve">mais ces diffé- <pb o="84" file="0104" n="104" rhead="DE LA PHILOSOPHIE"/> rentes impreſſions ne m’apprendroient rien <lb/>de ce qui ſe paſſe dans l’ame de cet hom-<lb/>me, ſans l’expérience dont la voix ſeule ſe <lb/>fait entendre.</s> <s xml:id="echoid-s1138" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1139" xml:space="preserve">Loin que cet angle ſoit la cauſe immé-<lb/>diate de ce que je juge qu’un grand che-<lb/>val eſt très-loin, quand je vois ce cheval <lb/>fort petit; </s> <s xml:id="echoid-s1140" xml:space="preserve">il arrive au contraire, à tous les <lb/>momens, que je vois ce même cheval éga-<lb/>lement grand, à dix pas, à vingt, à trente <lb/>pas, quoique l’angle à dix pas ſoit double, <lb/>triple, quadruple.</s> <s xml:id="echoid-s1141" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1142" xml:space="preserve">Je regarde de fort loin, par un petit <lb/> <anchor type="note" xlink:label="note-0104-01a" xlink:href="note-0104-01"/> trou, un homme poſté ſur un toit, le loin-<lb/>tain & </s> <s xml:id="echoid-s1143" xml:space="preserve">le peu de rayons m’empêchent d’a-<lb/>bord de diſtinguer ſi c’eſt un homme: </s> <s xml:id="echoid-s1144" xml:space="preserve">l’ob-<lb/>jet me parait très - petit, je crois voir une <lb/>ſtatue de deux pieds tout au plus: </s> <s xml:id="echoid-s1145" xml:space="preserve">l’ob-<lb/>jet ſe remue, je juge que c’eſt un hom-<lb/>me, & </s> <s xml:id="echoid-s1146" xml:space="preserve">dès ce même inſtant cet homme <lb/>me parait de la grandeur ordinaire; </s> <s xml:id="echoid-s1147" xml:space="preserve">d’où <lb/>viennent ces deux jugemens ſi différens?</s> <s xml:id="echoid-s1148" xml:space="preserve"/> </p> <div xml:id="echoid-div49" type="float" level="2" n="8"> <note position="left" xlink:label="note-0104-01" xlink:href="note-0104-01a" xml:space="preserve">Exem-<lb/>ple.</note> </div> <p> <s xml:id="echoid-s1149" xml:space="preserve">Quand j’ai cru voir une ſtatue, je l’ai <lb/>imaginée de deux pieds, parce que je la <pb o="85" file="0105" n="105" rhead="DE NEUTON."/> voiois ſous un tel angle: </s> <s xml:id="echoid-s1150" xml:space="preserve">nulle expérien-<lb/>ce ne plioit mon ame à démentir les traits <lb/>imprimés dans ma rétine; </s> <s xml:id="echoid-s1151" xml:space="preserve">mais dès que j’ai <lb/>jugé que c’étoit un homme, la liaiſon miſe <lb/>par l’expérience, dans mon cerveau, entre <lb/>l’idée d’un homme & </s> <s xml:id="echoid-s1152" xml:space="preserve">l’idée de la hauteur <lb/>de cinq à ſix pieds, me force, ſans que j’y <lb/>penſe, à imaginer, par un jugement ſoudain, <lb/>que je vois un homme de telle hauteur, <lb/>& </s> <s xml:id="echoid-s1153" xml:space="preserve">à voir une telle hauteur en effet.</s> <s xml:id="echoid-s1154" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1155" xml:space="preserve">Il faut abſolument conclure de tout ce-<lb/> <anchor type="note" xlink:label="note-0105-01a" xlink:href="note-0105-01"/> ci, que les diſtances, les grandeurs, les <lb/>ſituations, ne ſont pas, à proprement par-<lb/>ler, des choſes viſibles, c’eſt-à-dire, ne <lb/>ſont pas les objets propres & </s> <s xml:id="echoid-s1156" xml:space="preserve">immédiats de <lb/>la vûe. </s> <s xml:id="echoid-s1157" xml:space="preserve">L’objet propre & </s> <s xml:id="echoid-s1158" xml:space="preserve">immédiat de la <lb/>vûe, n’eſt autre choſe que la lumiere colo-<lb/>rée: </s> <s xml:id="echoid-s1159" xml:space="preserve">tout le reſte, nous ne le ſentons qu’à <lb/>la longue & </s> <s xml:id="echoid-s1160" xml:space="preserve">par expérience. </s> <s xml:id="echoid-s1161" xml:space="preserve">Nous appre-<lb/>nons à voir, préciſément comme nous ap-<lb/>prenons à parler & </s> <s xml:id="echoid-s1162" xml:space="preserve">à lire. </s> <s xml:id="echoid-s1163" xml:space="preserve">La différence <lb/>eſt, que l’art de voir eſt plus facile, & </s> <s xml:id="echoid-s1164" xml:space="preserve">que la <lb/>Nature eſt également à tous notre Maî-<lb/>tre.</s> <s xml:id="echoid-s1165" xml:space="preserve"/> </p> <div xml:id="echoid-div50" type="float" level="2" n="9"> <note position="right" xlink:label="note-0105-01" xlink:href="note-0105-01a" xml:space="preserve">Nous <lb/>appre-<lb/>nons à <lb/>voir <lb/>comme <lb/>à lire.</note> </div> <p> <s xml:id="echoid-s1166" xml:space="preserve">Les jugemens ſoudains, preſque unifor- <pb o="86" file="0106" n="106" rhead="DE LA PHILOSOPHIE"/> mes, que toutes nos ames, à un certain â-<lb/> <anchor type="note" xlink:label="note-0106-01a" xlink:href="note-0106-01"/> ge, portent des diſtances, des grandeurs, <lb/>des ſituations, nous font penſer, qu’il n’y <lb/>a qu’à ouvrir les yeux, pour voir de la ma-<lb/>niere dont nous voyons. </s> <s xml:id="echoid-s1167" xml:space="preserve">On ſe trompe; <lb/></s> <s xml:id="echoid-s1168" xml:space="preserve">il y faut le ſecours des autres ſens. </s> <s xml:id="echoid-s1169" xml:space="preserve">Si les <lb/>hommes n’avoient que le ſens de la vûe, ils <lb/>n’auroient aucun moyen pour connaitre l’é-<lb/>tendue, en longueur, largeur, & </s> <s xml:id="echoid-s1170" xml:space="preserve">profondeur; </s> <s xml:id="echoid-s1171" xml:space="preserve"><lb/>& </s> <s xml:id="echoid-s1172" xml:space="preserve">un pur Eſprit ne pourroit jamais la con-<lb/>naitre, à moins que Dieu ne la lui revelât. </s> <s xml:id="echoid-s1173" xml:space="preserve"><lb/>Il eſt très-difficile de ſéparer dans notre en-<lb/>tendement l’extenſion d’un objet d’avec les <lb/>couleurs de cet objet. </s> <s xml:id="echoid-s1174" xml:space="preserve">Nous ne voyons <lb/>jamais rien que d’étendu, & </s> <s xml:id="echoid-s1175" xml:space="preserve">de-là nous <lb/>ſommes tout portez à croire, que nous <lb/>voyons en effet l’étendue. </s> <s xml:id="echoid-s1176" xml:space="preserve">Nous ne pou-<lb/>vons guère diſtinguer dans notre ame ce <lb/>jaune que nous voyons dans un Louïs d’or, <lb/>d’avec ce Louïs d’or dont nous voyons le jau-<lb/>ne. </s> <s xml:id="echoid-s1177" xml:space="preserve">C’eſt comme, lorſque nous entendons <lb/>prononcer ce mot Louïs d’or, nous ne pou-<lb/>vons nous empêcher d’attacher, malgré <lb/>nous, l’idée de cette monnoye au ſon que <lb/>nous entendons prononcer.</s> <s xml:id="echoid-s1178" xml:space="preserve"/> </p> <div xml:id="echoid-div51" type="float" level="2" n="10"> <note position="left" xlink:label="note-0106-01" xlink:href="note-0106-01a" xml:space="preserve">La vûe <lb/>ne peut <lb/>faire <lb/>connai-<lb/>tre l’é-<lb/>tendue.</note> </div> <p> <s xml:id="echoid-s1179" xml:space="preserve">Si tous les hommes parloient la même <pb o="87" file="0107" n="107" rhead="DE NEUTON."/> Langue, nous ſerions toujours prêts à croi-<lb/>re, qu’il y auroit une connexion néceſſai-<lb/>re entre les mots & </s> <s xml:id="echoid-s1180" xml:space="preserve">les idées. </s> <s xml:id="echoid-s1181" xml:space="preserve">Or tous les <lb/>hommes ont ici le même langage, en fait <lb/>d’imagination. </s> <s xml:id="echoid-s1182" xml:space="preserve">La Nature leur dit à tous: <lb/></s> <s xml:id="echoid-s1183" xml:space="preserve">Quand vous aurez vu des couleurs pendant <lb/>un certain tems, votre imagination vous <lb/>repréſentera à tous, de la même façon, les <lb/>corps auxquels ces couleurs ſemblent atta-<lb/>chées. </s> <s xml:id="echoid-s1184" xml:space="preserve">Ce jugement prompt & </s> <s xml:id="echoid-s1185" xml:space="preserve">involontai-<lb/>re que vous ſormerez, vous ſera utile dans <lb/>le cours de votre vie; </s> <s xml:id="echoid-s1186" xml:space="preserve">car s’il falloit atten-<lb/>dre pour eſtimer les diſtances, les grandeurs, <lb/>les ſituations, de tout ce qui vous environ-<lb/>ne, que vous euſſiez examiné des angles & </s> <s xml:id="echoid-s1187" xml:space="preserve"><lb/>des rayons viſuels; </s> <s xml:id="echoid-s1188" xml:space="preserve">vous ſeriez morts avant <lb/>de ſavoir, ſi les choſes dont vous avez be-<lb/>ſoin, ſont à dix pas de vous, ou à cent mil-<lb/>lions des lieues, & </s> <s xml:id="echoid-s1189" xml:space="preserve">ſi elles ſont de la groſſeur <lb/>d’un ciron, ou d’une montagne. </s> <s xml:id="echoid-s1190" xml:space="preserve">Il vaudroit <lb/>beaucoup mieux pour vous être nés aveu-<lb/>gles.</s> <s xml:id="echoid-s1191" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1192" xml:space="preserve">Nous avons donc très-grand tort quand <lb/>nous diſons que nos Sens nous trompent. <lb/></s> <s xml:id="echoid-s1193" xml:space="preserve">Chacun de nos ſens fait la fonction à laquel-<lb/>le la Nature l’a deſtiné. </s> <s xml:id="echoid-s1194" xml:space="preserve">Ils s’aident mu- <pb o="88" file="0108" n="108" rhead="DE LA PHILOSOPHIE"/> tuellement pour envoyer à notre ame, par <lb/>les mains de l’expérience, la meſure des <lb/>connaiſſances que notre état comporte. <lb/></s> <s xml:id="echoid-s1195" xml:space="preserve">Nous demandons à nos Sens, ce qu’ils ne <lb/>ſont point faits pour nous donner. </s> <s xml:id="echoid-s1196" xml:space="preserve">Nous <lb/>voudrions que nos yeux nous fiſſent con-<lb/>naitre la ſolidité, la grandeur, la diſtance, <lb/>&</s> <s xml:id="echoid-s1197" xml:space="preserve">c.</s> <s xml:id="echoid-s1198" xml:space="preserve">: mais il faut que le toucher s’accorde <lb/>en cela avec la vûe, & </s> <s xml:id="echoid-s1199" xml:space="preserve">que l’expérience <lb/>les ſeconde. </s> <s xml:id="echoid-s1200" xml:space="preserve">Si le Pere Mallebranche avoit <lb/>enviſagé la Nature par ce côté, il eût at-<lb/>tribué moins d’erreurs à nos Sens qui ſont <lb/>les ſeules ſources de toutes nos idées.</s> <s xml:id="echoid-s1201" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1202" xml:space="preserve">Il eſt tems de reprendre le fil des dé-<lb/>couvertes de Neuton, & </s> <s xml:id="echoid-s1203" xml:space="preserve">de rentrer dans <lb/>l’examen Phyſique & </s> <s xml:id="echoid-s1204" xml:space="preserve">Mathématique des <lb/>choſes.</s> <s xml:id="echoid-s1205" xml:space="preserve"/> </p> <figure> <image file="0108-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0108-01"/> </figure> <pb file="0109" n="109"/> <figure> <image file="0109-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0109-01"/> </figure> </div> <div xml:id="echoid-div53" type="section" level="1" n="15"> <head xml:id="echoid-head23" xml:space="preserve">CHAPITRE SEPT.</head> <head xml:id="echoid-head24" style="it" xml:space="preserve">De la cauſe qui fait briſer les rayons de la lu-<lb/>miere en paſſant d’une ſubſtance dans une <lb/>autre; que cette cauſe eſt une loi générale de <lb/>la Nature inconnue avant Neuton; que l’in-<lb/>flexion de la lumiere eſt encore un effet de <lb/>cette cauſe, &c.</head> <p> <s xml:id="echoid-s1206" xml:space="preserve">NOUS avons déja vu l’artifice preſque <lb/>incompréhenſible de la réflexion de <lb/>la lumiere, que l’impulſion connue ne peut <lb/>cauſer. </s> <s xml:id="echoid-s1207" xml:space="preserve">Celui de la réfraction dont nous <pb o="90" file="0110" n="110" rhead="DE LA PHILOSOPHIE"/> allons reprendre l’examen n’eſt pas moins <lb/>ſurprenant.</s> <s xml:id="echoid-s1208" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1209" xml:space="preserve">Commençons par nous bien affermir <lb/> <anchor type="note" xlink:label="note-0110-01a" xlink:href="note-0110-01"/> dans une idée nette de la choſe qu’il faut <lb/>expliquer. </s> <s xml:id="echoid-s1210" xml:space="preserve">Souvenons - nous bien, que <lb/>quand la lumiere tombe d’une ſubſtance <lb/>plus rare, plus legére comme l’air, dans <lb/>une ſubſtance plus peſante, plus denſe <lb/>comme l’eau, & </s> <s xml:id="echoid-s1211" xml:space="preserve">qui ſemble lui devoir réſiſ-<lb/>ter davantage, la lumiere alors quitte ſon <lb/>chemin & </s> <s xml:id="echoid-s1212" xml:space="preserve">ſe briſe en s’approchant d’une <lb/>perpendicule, qu’on éleveroit ſur la ſurfa-<lb/>ce de cette eau.</s> <s xml:id="echoid-s1213" xml:space="preserve"/> </p> <div xml:id="echoid-div53" type="float" level="2" n="1"> <note position="left" xlink:label="note-0110-01" xlink:href="note-0110-01a" xml:space="preserve">Ce que <lb/>c’eſt <lb/>que ré-<lb/>fraction.</note> </div> <p> <s xml:id="echoid-s1214" xml:space="preserve">Mr. </s> <s xml:id="echoid-s1215" xml:space="preserve">Le Clerc, dans ſa Phyſique, a dit tout <lb/>le contraire faute d’attention. </s> <s xml:id="echoid-s1216" xml:space="preserve">En ſon Li-<lb/>vre cinq, chapitre huit: </s> <s xml:id="echoid-s1217" xml:space="preserve">„ Plus la réſiſtan-<lb/>ce des corps eſt grande, dit-il, plus la <lb/>lumiere qui tombe dans eux s’éloigne de <lb/>la perpendicule. </s> <s xml:id="echoid-s1218" xml:space="preserve">Ainſi le rayon s’éloi-<lb/>gne de la perpendicule en paſſant de l’air <lb/>dans l’eau”. </s> <s xml:id="echoid-s1219" xml:space="preserve">Ce n’eſt pas la ſeule mépriſe <lb/>qui ſoit dans le Clerc, & </s> <s xml:id="echoid-s1220" xml:space="preserve">un homme qui au-<lb/>roit le malheur d’étudier la Phyſique dans <lb/>les Ecrits de cet Auteur, n’auroit guère <lb/>que des idées fauſſes ou confuſes.</s> <s xml:id="echoid-s1221" xml:space="preserve"/> </p> <pb o="91" file="0111" n="111" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s1222" xml:space="preserve">Pour avoir une idée bien nette de cette <lb/>vérité, regardez ce rayon qui tombe de <lb/>l’air dans ce criſtal.</s> <s xml:id="echoid-s1223" xml:space="preserve"/> </p> <figure> <image file="0111-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0111-01"/> </figure> <p> <s xml:id="echoid-s1224" xml:space="preserve">Vous ſavez comme il ſe briſe. </s> <s xml:id="echoid-s1225" xml:space="preserve">Ce rayon <lb/>A E. </s> <s xml:id="echoid-s1226" xml:space="preserve">fait un angle avec cette perpendiculaire <lb/>B E. </s> <s xml:id="echoid-s1227" xml:space="preserve">en tombant ſur la ſurface de ce criſtal. <lb/></s> <s xml:id="echoid-s1228" xml:space="preserve">Ce même rayon réſracté dans ce criſtal, <lb/>fait un autre angle avec cette même per-<lb/>pendiculaire qui régle ſa réfraction. </s> <s xml:id="echoid-s1229" xml:space="preserve">Il fal-<lb/>lut méſurer cette incidence & </s> <s xml:id="echoid-s1230" xml:space="preserve">ce briſement <lb/>de la lumiere. </s> <s xml:id="echoid-s1231" xml:space="preserve">Snellius trouva le premier <lb/>la proportion conſtante, ſuivant laquelle <lb/>les rayons ſe rompent dans ces différens <pb o="92" file="0112" n="112" rhead="DE LA PHILOSOPHIE"/> milieux. </s> <s xml:id="echoid-s1232" xml:space="preserve">On en fit l’honneur à Deſcartes. <lb/></s> <s xml:id="echoid-s1233" xml:space="preserve">On attribue toujours au Philoſophe le plus <lb/>accrédité les découvertes qu’il rend publi-<lb/>ques: </s> <s xml:id="echoid-s1234" xml:space="preserve">il profite des travaux obſcurs d’au-<lb/>trui, & </s> <s xml:id="echoid-s1235" xml:space="preserve">il augmente ſa gloire de leurs re-<lb/>cherches. </s> <s xml:id="echoid-s1236" xml:space="preserve">La découverte de Snellius étoit <lb/>alors un Chef-d’œuvre de ſagacité. </s> <s xml:id="echoid-s1237" xml:space="preserve">Cette <lb/>proportion découverte par Snellius eſt très-<lb/>aiſée à entendre.</s> <s xml:id="echoid-s1238" xml:space="preserve"/> </p> <figure> <image file="0112-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0112-01"/> </figure> <p> <s xml:id="echoid-s1239" xml:space="preserve">Plus la ligne A. </s> <s xml:id="echoid-s1240" xml:space="preserve">B. </s> <s xml:id="echoid-s1241" xml:space="preserve">que vous voyez, eſt <lb/>grande, plus la ligne C. </s> <s xml:id="echoid-s1242" xml:space="preserve">D. </s> <s xml:id="echoid-s1243" xml:space="preserve">ſera grande <lb/> <anchor type="note" xlink:label="note-0112-01a" xlink:href="note-0112-01"/> auſſi. </s> <s xml:id="echoid-s1244" xml:space="preserve">Cette ligne A. </s> <s xml:id="echoid-s1245" xml:space="preserve">B. </s> <s xml:id="echoid-s1246" xml:space="preserve">eſt ce qu’on ap-<lb/>pelle ſinus d’incidence. </s> <s xml:id="echoid-s1247" xml:space="preserve">Cette ligne C. </s> <s xml:id="echoid-s1248" xml:space="preserve">D. <lb/></s> <s xml:id="echoid-s1249" xml:space="preserve">eſt le ſinus de la réfraction. </s> <s xml:id="echoid-s1250" xml:space="preserve">Ce n’eſt pas <pb o="93" file="0113" n="113" rhead="DE NEUTON."/> lci le lieu d’expliquer en général ce que <lb/>c’eſt qu’un ſinus. </s> <s xml:id="echoid-s1251" xml:space="preserve">Ceux qui ont étudié la <lb/>Géométrie le ſavent aſſez. </s> <s xml:id="echoid-s1252" xml:space="preserve">Les autres <lb/>pourroient être un peu embaraſſez de la <lb/>définition. </s> <s xml:id="echoid-s1253" xml:space="preserve">Il ſuffit de bien ſavoir que ces <lb/>deux ſinus, de quelque grandeur qu’ils <lb/>ſoient, ſont toujours en proportion dans <lb/>un milieu donné. </s> <s xml:id="echoid-s1254" xml:space="preserve">Or cette proportion eſt <lb/>différente, quand la réfraction ſe fait dans <lb/>un milieu différent.</s> <s xml:id="echoid-s1255" xml:space="preserve"/> </p> <div xml:id="echoid-div54" type="float" level="2" n="2"> <note position="left" xlink:label="note-0112-01" xlink:href="note-0112-01a" xml:space="preserve">Ce que <lb/>c’eſt que <lb/>ſinus de <lb/>réfrac-<lb/>tion.</note> </div> <p> <s xml:id="echoid-s1256" xml:space="preserve">La lumiere qui tombe obliquement de <lb/>l’air dans du criſtal, s’y briſe de façon, que <lb/>le ſinus de réfraction C. </s> <s xml:id="echoid-s1257" xml:space="preserve">D. </s> <s xml:id="echoid-s1258" xml:space="preserve">eſt au ſinus d’in-<lb/>cidence A. </s> <s xml:id="echoid-s1259" xml:space="preserve">B. </s> <s xml:id="echoid-s1260" xml:space="preserve">comme 2. </s> <s xml:id="echoid-s1261" xml:space="preserve">à 3. </s> <s xml:id="echoid-s1262" xml:space="preserve">ce qui ne veut <lb/>dire autre choſe, ſinon que cette ligne A. <lb/></s> <s xml:id="echoid-s1263" xml:space="preserve">B. </s> <s xml:id="echoid-s1264" xml:space="preserve">eſt un tiers plus grande dans l’air, en ce <lb/>cas, que la ligne C. </s> <s xml:id="echoid-s1265" xml:space="preserve">D. </s> <s xml:id="echoid-s1266" xml:space="preserve">dans ce criſtal.</s> <s xml:id="echoid-s1267" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1268" xml:space="preserve">Dans l’eau cette proportion eſt de 3. </s> <s xml:id="echoid-s1269" xml:space="preserve">à 4. <lb/></s> <s xml:id="echoid-s1270" xml:space="preserve">Ainſi il eſt palpable que le criſtal réfracte, <lb/>briſe la lumiere d’un neuvième plus forte-<lb/>ment que l’eau. </s> <s xml:id="echoid-s1271" xml:space="preserve">Il faut donc ſavoir que <lb/>danstous les cas, & </s> <s xml:id="echoid-s1272" xml:space="preserve">dans toutes les obliqui-<lb/>tés d’incidence poſſibles, le criſtal ſera plus <lb/>refringent que l’eau d’un neuvième. </s> <s xml:id="echoid-s1273" xml:space="preserve">Il s’a-<lb/>git de ſavoir non - ſeulement la cauſe de <pb o="94" file="0114" n="114" rhead="DE LA PHILOSOPHIE"/> la réfraction, mais la cauſe de ces réfrac-<lb/>tions différentes.</s> <s xml:id="echoid-s1274" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1275" xml:space="preserve">Deſcartes a trouvé, à ſon ordinaire, des <lb/> <anchor type="note" xlink:label="note-0114-01a" xlink:href="note-0114-01"/> raiſons ingénieuſes & </s> <s xml:id="echoid-s1276" xml:space="preserve">plauſibles de cette <lb/>proprieté de la lumiere; </s> <s xml:id="echoid-s1277" xml:space="preserve">mais là, comme en <lb/>tout le reſte, mettant ſon eſprit à la place <lb/>des choſes, il a donné des conjectures pour <lb/>des vérités. </s> <s xml:id="echoid-s1278" xml:space="preserve">Il a feint que la lumiere, en <lb/>paſſant de l’air dans un milieu nouveau, plus <lb/>épais, plus compact, y paſſe plus libre-<lb/>ment, y eſt moins retardée dans ſa ten-<lb/>dance prétendue au mouvement, & </s> <s xml:id="echoid-s1279" xml:space="preserve">moins re-<lb/>tardée, diſoit-il, moins troublée dans un mi-<lb/>lieu denſe, comme le verre, que dans un milieu <lb/>moins épais, comme l’eau. </s> <s xml:id="echoid-s1280" xml:space="preserve">Nous avons déja <lb/>vu combien il s’abuſe en aſſûrant que la <lb/>lumiere n’a qu’une tendance au mouvement. <lb/></s> <s xml:id="echoid-s1281" xml:space="preserve">Nous avons vu que les rayons ſe meuvent <lb/>en effet, puiſqu’ils changent de place à nos <lb/>yeux dans leurs réfractions. </s> <s xml:id="echoid-s1282" xml:space="preserve">Mais ſon er-<lb/>reur ici eſt encore aſſez importante: </s> <s xml:id="echoid-s1283" xml:space="preserve">il ſe <lb/>trompe en croyant que les corps les plus <lb/> <anchor type="note" xlink:label="note-0114-02a" xlink:href="note-0114-02"/> ſolides ſont toujours ceux qui briſent le plus <lb/>la lumiere, & </s> <s xml:id="echoid-s1284" xml:space="preserve">qui lui ouvrent en la briſant <lb/>un chemin plus facile. </s> <s xml:id="echoid-s1285" xml:space="preserve">Il n’eſt pas vrai que <lb/>tous les corps ſolides réfractent, briſent <pb o="95" file="0115" n="115" rhead="DE NEUTON."/> plus la lumiere abſolument, que les corps <lb/>fluides; </s> <s xml:id="echoid-s1286" xml:space="preserve">car quoiqu’en effet l’eau opére une <lb/>réfraction moins forte, abſolument parlant, <lb/>que le verre; </s> <s xml:id="echoid-s1287" xml:space="preserve">cependant par rapport à fa <lb/>denſité, elle opére une réfraction plus for-<lb/>te. </s> <s xml:id="echoid-s1288" xml:space="preserve">Il eſt bien vrai que la lumiere ſe briſe <lb/>environ un neuvième davantage dans le <lb/>verre, que dans l’eau; </s> <s xml:id="echoid-s1289" xml:space="preserve">mais ſi la réfraction <lb/>ſuivoit le rapport de la denſité, elle devroit, <lb/>dans le verre, aller fort au delà d’un neu-<lb/>vième. </s> <s xml:id="echoid-s1290" xml:space="preserve">Imaginez deux hommes, dont l’un <lb/>aura quatre fois plus de force, que l’autre. <lb/></s> <s xml:id="echoid-s1291" xml:space="preserve">Si le plus fort ne porte qu’un poids une fois <lb/>plus peſant, il ſera vrai de dire que par rap-<lb/>port à ſa force, il n’a pas, à beaucoup près, <lb/>tant porté que l’autre; </s> <s xml:id="echoid-s1292" xml:space="preserve">car il devroit por-<lb/> <anchor type="note" xlink:label="note-0115-01a" xlink:href="note-0115-01"/> ter quatre fois davantage.</s> <s xml:id="echoid-s1293" xml:space="preserve"/> </p> <div xml:id="echoid-div55" type="float" level="2" n="3"> <note position="left" xlink:label="note-0114-01" xlink:href="note-0114-01a" xml:space="preserve">Idée de <lb/>Deſcar-<lb/>tes in-<lb/>génieu-<lb/>ſe, mais <lb/>fauſſe.</note> <note position="left" xlink:label="note-0114-02" xlink:href="note-0114-02a" xml:space="preserve">Le <lb/>corps le <lb/>plus ſo-<lb/>lide <lb/>n’eſt pas <lb/>le plus <lb/>réfrac-<lb/>tant.</note> <note position="right" xlink:label="note-0115-01" xlink:href="note-0115-01a" xml:space="preserve">Preuve.</note> </div> <p> <s xml:id="echoid-s1294" xml:space="preserve">L’ambre opére une réfraction bien plus <lb/>forte que le criſtal, par rapport à ſa denſité. <lb/></s> <s xml:id="echoid-s1295" xml:space="preserve">Peut-on dire cependant que l’ambre ouvri-<lb/>ra un chemin plus facile à la lumiere, que <lb/>le criſtal? </s> <s xml:id="echoid-s1296" xml:space="preserve">C’eſt donc une ſuppoſition fauſ-<lb/>ſe: </s> <s xml:id="echoid-s1297" xml:space="preserve">que la lumiere ſe briſe vers la perpendicu-<lb/>laire, quand elie trouve un corps tranſparent <lb/>plus ſolide qui lui réſiſte moins, parce qu’il eſt <lb/>plus ſolide.</s> <s xml:id="echoid-s1298" xml:space="preserve"/> </p> <pb o="96" file="0116" n="116" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s1299" xml:space="preserve">Remarquez que toute expérience & </s> <s xml:id="echoid-s1300" xml:space="preserve">tout <lb/>calcul ruïne preſque toutes les idées de Deſ-<lb/>cartes, quand ce grand Philoſophe ne les <lb/>fonde que ſur des hypothèſes. </s> <s xml:id="echoid-s1301" xml:space="preserve">Ce ſont <lb/>des perſpectives brillantes & </s> <s xml:id="echoid-s1302" xml:space="preserve">trompeu-<lb/>ſes qui diminuent à meſure qu’on en <lb/>approche. </s> <s xml:id="echoid-s1303" xml:space="preserve">Tous les autres Philoſophes ont <lb/>cherché des ſolutions de ce Problême de la <lb/>Nature; </s> <s xml:id="echoid-s1304" xml:space="preserve">mais l’expérience a renverſé auſſi <lb/>leurs conjectures.</s> <s xml:id="echoid-s1305" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1306" xml:space="preserve">Barrow enſeignoit, après le Pere Deſ-<lb/> <anchor type="note" xlink:label="note-0116-01a" xlink:href="note-0116-01"/> challes, que la réfraction de la lumiere, <lb/>en approchant de la perpendicule, ſe fai-<lb/>ſoit par la réſiſtance du milieu; </s> <s xml:id="echoid-s1307" xml:space="preserve">que plus un <lb/>milieu réſiſtoit au cours de la lumiere, plus <lb/>cette réfraction devoit être forte.</s> <s xml:id="echoid-s1308" xml:space="preserve"/> </p> <div xml:id="echoid-div56" type="float" level="2" n="4"> <note position="left" xlink:label="note-0116-01" xlink:href="note-0116-01a" xml:space="preserve">Mépriſe <lb/>des au-<lb/>tres <lb/>grands <lb/>Géomé-<lb/>tres à ce <lb/>ſujet.</note> </div> <p> <s xml:id="echoid-s1309" xml:space="preserve">Cette idée étoit le contraire de celle de <lb/>Deſcartes; </s> <s xml:id="echoid-s1310" xml:space="preserve">elle prouvoit ſeulement qu’on <lb/>va à l’erreur par différens chemins. </s> <s xml:id="echoid-s1311" xml:space="preserve">Ils n’a-<lb/>voient qu’à voir les expériences; </s> <s xml:id="echoid-s1312" xml:space="preserve">ils n’a-<lb/>voient qu’à meſurer les réfractions qui ſe <lb/>font dans l’eſprit de vin, beaucoup plus <lb/>grandes que dans l’eau; </s> <s xml:id="echoid-s1313" xml:space="preserve">ils n’avoient qu’à <lb/>conſiderer qu’aſſûrément l’eſprit de vin ne <pb o="97" file="0117" n="117" rhead="DE NEUTON."/> réſiſte pas plus que l’eau, & </s> <s xml:id="echoid-s1314" xml:space="preserve">que cependant <lb/>il opére une réfraction une fois plus forte, <lb/>ils auroient corrigé cette petite erreur. <lb/></s> <s xml:id="echoid-s1315" xml:space="preserve">Auſſi le Pere Deſchalles avoue qu’il doute <lb/>fort de ſon explication.</s> <s xml:id="echoid-s1316" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1317" xml:space="preserve">Enfin Neuton ſeul a trouvé la véritable <lb/> <anchor type="note" xlink:label="note-0117-01a" xlink:href="note-0117-01"/> raiſon qu’on cherchoit. </s> <s xml:id="echoid-s1318" xml:space="preserve">Sa découverte mé-<lb/>rite aſſûrément l’attention de tous les Siè-<lb/>cles. </s> <s xml:id="echoid-s1319" xml:space="preserve">Car il ne s’agit pas ici ſeulement <lb/>d’une proprieté particuliere à la lumiere, <lb/>quoique ce fût déja beaucoup; </s> <s xml:id="echoid-s1320" xml:space="preserve">nous ver-<lb/>rons que cette proprieté appartient à tous <lb/>les corps de la Nature.</s> <s xml:id="echoid-s1321" xml:space="preserve"/> </p> <div xml:id="echoid-div57" type="float" level="2" n="5"> <note position="right" xlink:label="note-0117-01" xlink:href="note-0117-01a" xml:space="preserve">Grande <lb/>décou-<lb/>verte de <lb/>Neuton.</note> </div> <p> <s xml:id="echoid-s1322" xml:space="preserve">Conſiderez que les rayons de la lumiere <lb/>ſont en mouvement, que s’ils ſe détour-<lb/>nent en changeant leur courſe, ce doit être <lb/>par quelque loi primitive, & </s> <s xml:id="echoid-s1323" xml:space="preserve">qu’il ne doit <lb/>arriver à la lumiere, que ce qui arriveroit à <lb/>tous les corps de même petiteſſe que la lu-<lb/>miere, toutes choſes d’ailleurs égales.</s> <s xml:id="echoid-s1324" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1325" xml:space="preserve">Qu’une balle de plomb A. </s> <s xml:id="echoid-s1326" xml:space="preserve">ſoit pouſſée <lb/>obliquement de l’air dans l’eau, il lui arri-<lb/>vera d’abord le contraire de ce qui eſt arri-<lb/>vé à ce rayon de lumiere; </s> <s xml:id="echoid-s1327" xml:space="preserve">car ce rayon <pb o="98" file="0118" n="118" rhead="DE LA PHILOSOPHIE"/> délié paſſe dans des pores, & </s> <s xml:id="echoid-s1328" xml:space="preserve">cette balle, <lb/>dont la ſuperficie eſt large, rencontre la <lb/>ſuperficie de l’eau qui la ſoutient.</s> <s xml:id="echoid-s1329" xml:space="preserve"/> </p> <figure> <image file="0118-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0118-01"/> </figure> <p> <s xml:id="echoid-s1330" xml:space="preserve">Cette balle s’éloigne donc d’abord de la <lb/>perpendiculaire B.</s> <s xml:id="echoid-s1331" xml:space="preserve">; mais lorſqu’elle a perdu <lb/>tout ce mouvement oblique qu’on lui avoit <lb/>imprimé, elle eſt abandonnée à elle-même, <lb/>elle tombe alors, à peu près ſuivant une per-<lb/>pendiculaire, qu’on élèveroit du point où <lb/>elle commence à deſcendre. </s> <s xml:id="echoid-s1332" xml:space="preserve">Or Neuton a <lb/>découvert & </s> <s xml:id="echoid-s1333" xml:space="preserve">a prouvé qu’il y a dans la Na-<lb/>ture une force, qui fait tendre tous les <lb/>corps, en ligne perpendiculaire, les uns vers <lb/> <anchor type="note" xlink:label="note-0118-01a" xlink:href="note-0118-01"/> les autres en proportion directe de leur <lb/>maſſe. </s> <s xml:id="echoid-s1334" xml:space="preserve">Donc cette force (telle qu’elle ſoit) <pb o="99" file="0119" n="119" rhead="DE NEUTON."/> doit agir dans l’eau ſur ce rayon; </s> <s xml:id="echoid-s1335" xml:space="preserve">& </s> <s xml:id="echoid-s1336" xml:space="preserve">la <lb/>maſſe du rayon étant incomparablement <lb/>moindre que celle de l’eau, ce rayon doit <lb/>ſenſiblement être mu vers elle.</s> <s xml:id="echoid-s1337" xml:space="preserve"/> </p> <div xml:id="echoid-div58" type="float" level="2" n="6"> <note position="left" xlink:label="note-0118-01" xlink:href="note-0118-01a" xml:space="preserve">Attrac-<lb/>tion.</note> </div> <p> <s xml:id="echoid-s1338" xml:space="preserve">Regardez donc ce rayon de lumiere qui <lb/>deſcend perpendiculairement de l’air ſur la <lb/>ſurface de ce criſtal.</s> <s xml:id="echoid-s1339" xml:space="preserve"/> </p> <figure> <image file="0119-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0119-01"/> </figure> <p> <s xml:id="echoid-s1340" xml:space="preserve">Comme cette ligne deſcend perpendiculai-<lb/> <anchor type="note" xlink:label="note-0119-01a" xlink:href="note-0119-01"/> rement, le pouvoir de l’attraction, tel <lb/>qu’il ſoit, agiſſant en ligne droite, le rayon <lb/>ne ſe détourne point de ſon chemin; </s> <s xml:id="echoid-s1341" xml:space="preserve">mais <lb/>il arrive plus promptement, qu’il n’auroit <lb/>fait en B.</s> <s xml:id="echoid-s1342" xml:space="preserve">, & </s> <s xml:id="echoid-s1343" xml:space="preserve">c’eſt encore une vérité ap-<lb/>perçue par Neuton.</s> <s xml:id="echoid-s1344" xml:space="preserve"/> </p> <div xml:id="echoid-div59" type="float" level="2" n="7"> <note position="right" xlink:label="note-0119-01" xlink:href="note-0119-01a" xml:space="preserve">L’at-<lb/>traction <lb/>agit en <lb/>perpen-<lb/>dicule, <lb/>& accé-<lb/>lere la <lb/>chûte <lb/>des <lb/>rayons.</note> </div> <pb o="100" file="0120" n="120" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s1345" xml:space="preserve">Avant lui on croioit que ce rayon de lu-<lb/>miere étoit retardé dans ſon cours en en-<lb/>trant dans l’eau. </s> <s xml:id="echoid-s1346" xml:space="preserve">Au contraire, il y entre <lb/>avec accélération. </s> <s xml:id="echoid-s1347" xml:space="preserve">Pourquoi? </s> <s xml:id="echoid-s1348" xml:space="preserve">Parce qu’il <lb/>y eſt porté, & </s> <s xml:id="echoid-s1349" xml:space="preserve">par ſon propre mouvement, <lb/>& </s> <s xml:id="echoid-s1350" xml:space="preserve">par celui de l’attraction que l’eau, ou le <lb/>verre, lui imprime. </s> <s xml:id="echoid-s1351" xml:space="preserve">Ce rayon arrive donc <lb/>en B. </s> <s xml:id="echoid-s1352" xml:space="preserve">par cette force accélératrice plus <lb/>promptement qu’il n’eût franchi l’air.</s> <s xml:id="echoid-s1353" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1354" xml:space="preserve">Mais ſi nous conſiderons dans cè même <lb/>baſſin d’eau, ou dans cette même maſſe de <lb/>verre, ce rayon oblique qui tombe deſſus, <lb/>qu’arrive-t-il? </s> <s xml:id="echoid-s1355" xml:space="preserve">Il conſerve ſon mouvement <lb/>d’obliquité en ligne droite, & </s> <s xml:id="echoid-s1356" xml:space="preserve">il en ac-<lb/>quiert un nouveau en ligne perpendicu-<lb/>laire.</s> <s xml:id="echoid-s1357" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1358" xml:space="preserve">Que cette attraction, que cette ten-<lb/>dance, que cette eſpèce de gravitation <lb/>exiſte, nous n’en pouvons douter: </s> <s xml:id="echoid-s1359" xml:space="preserve">car nous <lb/>avons vu la lumiere attirée par le verre, y <lb/>rentrer ſans toucher à rien; </s> <s xml:id="echoid-s1360" xml:space="preserve">or cette force <lb/>agit néceſſairement en ligne perpendicu-<lb/>laire, la ligne perpendiculaire étant le plus <lb/>court chemin.</s> <s xml:id="echoid-s1361" xml:space="preserve"/> </p> <pb o="101" file="0121" n="121" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s1362" xml:space="preserve">Puiſque cette force exiſte, elle eſt dans <lb/>toutes les parties de la matiere. </s> <s xml:id="echoid-s1363" xml:space="preserve">Les parties <lb/>de la ſuperficie d’un corps quelconque, é-<lb/>prouvent donc ce pouvoir, avant qu’il pé-<lb/>nétre l’intérieur de la ſubſtance, avant qu’il <lb/>parvienne au centre où il eſt dirigé. </s> <s xml:id="echoid-s1364" xml:space="preserve">Ainſi <lb/>dès que ce rayon eſt arrivé près de la ſu-<lb/>perficie du criſtal, ou de l’eau, il prend <lb/>déja un peu en cette maniere le chemin de <lb/>la perpendicule.</s> <s xml:id="echoid-s1365" xml:space="preserve"/> </p> <figure> <image file="0121-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0121-01"/> </figure> <p> <s xml:id="echoid-s1366" xml:space="preserve">Il ſe briſe déja un peu en C. </s> <s xml:id="echoid-s1367" xml:space="preserve">avant d’en-<lb/> <anchor type="note" xlink:label="note-0121-01a" xlink:href="note-0121-01"/> trer: </s> <s xml:id="echoid-s1368" xml:space="preserve">plus il entre, plus il ſe briſe; </s> <s xml:id="echoid-s1369" xml:space="preserve">c’eſt <lb/>que plus les corps ſont proches, plus ils <lb/>s’attirent, & </s> <s xml:id="echoid-s1370" xml:space="preserve">que celui qui a le plus de <pb o="102" file="0122" n="122" rhead="DE LA PHILOSOPHIE"/> maſſe détermine vers lui, celui qui en a <lb/>moins. </s> <s xml:id="echoid-s1371" xml:space="preserve">Ainſi il arrive à ce rayon de lu-<lb/>miere la même choſe qu’à tout corps, qui <lb/>a un mouvement compoſé de deux direc-<lb/>tions différentes; </s> <s xml:id="echoid-s1372" xml:space="preserve">il n’obéït à aucune, & </s> <s xml:id="echoid-s1373" xml:space="preserve"><lb/>tient un chemin qui participe des deux. <lb/></s> <s xml:id="echoid-s1374" xml:space="preserve">Ainſi ce rayon netombe pas tout-à-fait per-<lb/>pendiculairement, & </s> <s xml:id="echoid-s1375" xml:space="preserve">ne ſuit pas ſa pre-<lb/>miere ligne droite oblique, en traverſant <lb/>cette eau, ou ce verre; </s> <s xml:id="echoid-s1376" xml:space="preserve">mais il ſuit une ligne <lb/>qui participe des deux côtés, & </s> <s xml:id="echoid-s1377" xml:space="preserve">qui deſ-<lb/>cend d’autant plus vîte, que l’attraction de <lb/>cette eau, ou de ce criſtal, eſt plus forte. </s> <s xml:id="echoid-s1378" xml:space="preserve"><lb/>Donc loin que l’eau rompe les rayons de <lb/>lumiere, en leur réſiſtant, comme on le <lb/>croioit, elle les rompt en effet, parce <lb/>qu’elle ne réſiſte pas, &</s> <s xml:id="echoid-s1379" xml:space="preserve">, au contraire, par-<lb/>ce qu’elle les attire. </s> <s xml:id="echoid-s1380" xml:space="preserve">Il faut donc dire que <lb/>les rayons ſe briſent vers la perpendiculai-<lb/>re, non pas quand ils paſſent d’un milieu <lb/>plus facile dans un milieu plus réſiſtant, <lb/>mais quand ils paſſent d’un milieu moins atti-<lb/>ant dans un milieu plus attirant. </s> <s xml:id="echoid-s1381" xml:space="preserve">Obſervez <lb/>qu’il ne faut jamais entendre par ce mot <lb/>attirant, que le point vers lequel ſe dirige <lb/>une force reconnue, une proprieté incon-<lb/>teſtable de la matiere.</s> <s xml:id="echoid-s1382" xml:space="preserve"/> </p> <div xml:id="echoid-div60" type="float" level="2" n="8"> <note position="right" xlink:label="note-0121-01" xlink:href="note-0121-01a" xml:space="preserve">Lumie-<lb/>re briſée <lb/>avant <lb/>d’entrer <lb/>dans les <lb/>corps.</note> </div> <pb o="103" file="0123" n="123" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s1383" xml:space="preserve">Vous ſavez que beaucoup de gens, au-<lb/>tant attachés à la Philoſophie, ou plutôt <lb/>au nom de Deſcartes, qu’ils l’étoient au-<lb/>paravant au nom d’Ariſtote, ſe ſont ſou-<lb/>levés contre l’attraction. </s> <s xml:id="echoid-s1384" xml:space="preserve">Les uns n’ont pas <lb/>voulu l’étudier, les autres l’ont mépriſee, & </s> <s xml:id="echoid-s1385" xml:space="preserve"><lb/>l’ont inſultée après l’avoir à peine exami-<lb/>née; </s> <s xml:id="echoid-s1386" xml:space="preserve">mais je prie le Lecteur de faire les trois <lb/>réflexions ſuivantes.</s> <s xml:id="echoid-s1387" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1388" xml:space="preserve">1<emph style="super">0</emph>. </s> <s xml:id="echoid-s1389" xml:space="preserve">Qu’entendons-nous par attraction? <lb/></s> <s xml:id="echoid-s1390" xml:space="preserve"> <anchor type="note" xlink:label="note-0123-01a" xlink:href="note-0123-01"/> Rien autre choſe qu’une force par laquelle <lb/>un corps s’approche d’un autre, ſans que l’on <lb/>voye, ſans que l’on connaiſſe, aucune autre <lb/>force qui le pouſſe.</s> <s xml:id="echoid-s1391" xml:space="preserve"/> </p> <div xml:id="echoid-div61" type="float" level="2" n="9"> <note position="right" xlink:label="note-0123-01" xlink:href="note-0123-01a" xml:space="preserve">Il faut <lb/>exami-<lb/>ner <lb/>l’attrac-<lb/>tion a-<lb/>vant de <lb/>ſe révol-<lb/>ter con-<lb/>tre ce <lb/>mot.</note> </div> <p> <s xml:id="echoid-s1392" xml:space="preserve">2<emph style="super">0</emph>. </s> <s xml:id="echoid-s1393" xml:space="preserve">Cette propriété de la matiere eſt é-<lb/>tablie par les meilleurs Philoſophes en An-<lb/>gleterre, en Allemagne, en Hollande, & </s> <s xml:id="echoid-s1394" xml:space="preserve"><lb/>même dans pluſieurs Univerſitez d’Italie, où <lb/>des Loix un peu rigoureuſes ferment quel-<lb/>quefois l’accez à la Vérité. </s> <s xml:id="echoid-s1395" xml:space="preserve">Le conſen-<lb/>tement de tant de ſavans hommes n’eſt pas <lb/>une preuve, ſans doute; </s> <s xml:id="echoid-s1396" xml:space="preserve">mais c’eſt une rai-<lb/>ſon puiſſante pour examiner au moins ſi <lb/>cette force exiſte ou non.</s> <s xml:id="echoid-s1397" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1398" xml:space="preserve">3<emph style="super">0</emph>. </s> <s xml:id="echoid-s1399" xml:space="preserve">L’on devroit ſonger que l’on ne con- <pb o="104" file="0124" n="124" rhead="DE LA PHILOSOPHIE"/> nait pas plus la cauſe de l’impulſion, que <lb/>de l’attraction. </s> <s xml:id="echoid-s1400" xml:space="preserve">On n’a pas même plus d’i-<lb/>dée de l’une de ces forces que de l’autre; <lb/></s> <s xml:id="echoid-s1401" xml:space="preserve">car il n’y a perſonne qui puiſſe concevoir <lb/>pourquoi un corps a le pouvoir d’en re-<lb/>muer un autre de ſa place. </s> <s xml:id="echoid-s1402" xml:space="preserve">Nous ne con-<lb/>cevons pas non plus, il eſt vrai, comment <lb/>un corps en attire un autre, comment les <lb/>parties de la matiere gravitent mutuelle-<lb/>ment. </s> <s xml:id="echoid-s1403" xml:space="preserve">Auſſi ne dit-on pas que Neuton ſe <lb/>ſoit vanté de connaitre la raiſon de cette <lb/>attraction. </s> <s xml:id="echoid-s1404" xml:space="preserve">Il a prouvé ſimplement qu’elle <lb/>exiſte: </s> <s xml:id="echoid-s1405" xml:space="preserve">il a vu dans la matiere un phénomê-<lb/>ne conſtant, une propriété univerſelle. </s> <s xml:id="echoid-s1406" xml:space="preserve">Si <lb/>un homme trouvoit un nouveau métal dans <lb/>la terre, ce métal exiſteroit-il moins, parce <lb/>que l’on ne connaitrait pas les premiers <lb/>Principes dont il ſeroit formé? </s> <s xml:id="echoid-s1407" xml:space="preserve">Que le Lec-<lb/>teur qui jettera les yeux ſur cet Ouvrage ait <lb/>recours à la diſcuſſion métaphyſique ſur l’at-<lb/>traction, faite par Mr. </s> <s xml:id="echoid-s1408" xml:space="preserve">de Maupertuis, dans <lb/>le plus petit & </s> <s xml:id="echoid-s1409" xml:space="preserve">dans le meilleur Livre qu’on <lb/>ait écrit peut-être en Français, en fait de <lb/>Philoſophie. </s> <s xml:id="echoid-s1410" xml:space="preserve">On y verra à travers la reſer-<lb/>ve avec laquelle l’Auteur s’eſt expliqué, <lb/>ce qu’il penſe, & </s> <s xml:id="echoid-s1411" xml:space="preserve">ce qu’on doit penſer de <lb/>cette attraction, dont le nom a tout effarou-<lb/>ché.</s> <s xml:id="echoid-s1412" xml:space="preserve"/> </p> <pb o="105" file="0125" n="125" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s1413" xml:space="preserve">Nous avons vu dans le ſecond chapitre, <lb/>que les rayons réflechis d’un Miroir ne ſau-<lb/>roient venir à nous de ſa ſurface. </s> <s xml:id="echoid-s1414" xml:space="preserve">Nous <lb/>avons expérimenté que les rayons transmis <lb/>dans du verre à un certain angle, revien-<lb/>nent au lieu de paſſer dans l’air; </s> <s xml:id="echoid-s1415" xml:space="preserve">que, s’il y <lb/>a du vuide derriere ce verre, les rayons <lb/>qui étoient transmis auparavant reviennent <lb/>de ce vuide à nous. </s> <s xml:id="echoid-s1416" xml:space="preserve">Certainement il n’y <lb/>a point-là d’impulſion connue. </s> <s xml:id="echoid-s1417" xml:space="preserve">Il faut de <lb/>toute néceſſité admettre un autre pouvoir; <lb/></s> <s xml:id="echoid-s1418" xml:space="preserve">il faut bien auſſi avouer, qu’il y a dans la <lb/>réfraction quelque choſe qu’on n’entendoit <lb/>pas juſqu’à préſent.</s> <s xml:id="echoid-s1419" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1420" xml:space="preserve">Or qu’elle ſera cette puiſſance qui rom-<lb/>pra ce rayon de lumiere dans ce baſſin d’eau? <lb/></s> <s xml:id="echoid-s1421" xml:space="preserve">Il eſt démontré (comme nous le dirons au <lb/>chapitre ſuivant) que, ce qu’on avoit cru <lb/>juſqu’à préſent un ſimple rayon de lumiere, <lb/>eſt un faiſceau de pluſieurs rayons, qui ſe ré-<lb/>fractent tous différemment. </s> <s xml:id="echoid-s1422" xml:space="preserve">Si de ces traits <lb/>de lumiere contenus dans ce rayon, l’un ſe <lb/>ré@racte, par exemple, à quatre meſures de <lb/>la perpendiculaire, l’autre ſe rompra à trois <lb/>meſures. </s> <s xml:id="echoid-s1423" xml:space="preserve">Il eſt démontré que les plus ré- <pb o="106" file="0126" n="126" rhead="DE LA PHILOSOPHIE"/> frangibles, c’eſt-à-dire, par exemple, ceux <lb/>qui en ſe briſant au ſortir d’un verre, & </s> <s xml:id="echoid-s1424" xml:space="preserve">en <lb/> <anchor type="note" xlink:label="note-0126-01a" xlink:href="note-0126-01"/> prenant dans l’air une nouvelle direction, <lb/>s’approchent moins de la perpendiculaire <lb/>de ce verre, ſont auſſi ceux qui ſe reflechiſ-<lb/>ſent le plus aiſément, le plus vîte. </s> <s xml:id="echoid-s1425" xml:space="preserve">Il y a <lb/>donc déja bien de l’apparence, que ce ſe-<lb/>ra la même loi qui fera réflechir la lumiere, <lb/>& </s> <s xml:id="echoid-s1426" xml:space="preserve">qui la fera réfracter.</s> <s xml:id="echoid-s1427" xml:space="preserve"/> </p> <div xml:id="echoid-div62" type="float" level="2" n="10"> <note position="left" xlink:label="note-0126-01" xlink:href="note-0126-01a" xml:space="preserve">Preuves <lb/>de l’at-<lb/>traction.</note> </div> <p> <s xml:id="echoid-s1428" xml:space="preserve">Enfin, ſi nous trouvons encore quelque <lb/>nouvelle propriété de la lumiere, qui paraiſ-<lb/>ſe devoir ſon origine à la force de l’attrac-<lb/>tion, ne devrons-nous pas conclure que tant <lb/>d’effets appartiennent à la même cauſe?</s> <s xml:id="echoid-s1429" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1430" xml:space="preserve">Voici cette nouvelle propriété qui fut dé-<lb/>couverte par le Pere Grimaldi Jéſuite vers <lb/>l’an 1660. </s> <s xml:id="echoid-s1431" xml:space="preserve">& </s> <s xml:id="echoid-s1432" xml:space="preserve">ſur laquelle Neuton a pouſſé <lb/>l’examen juſqu’au point de meſurer l’om-<lb/>bre d’un cheveu à des diſtances différen-<lb/>tes. </s> <s xml:id="echoid-s1433" xml:space="preserve">Cette propriété eſt l’inflexion de la lu-<lb/>miere. </s> <s xml:id="echoid-s1434" xml:space="preserve">Non-ſeulement les rayons ſe briſent <lb/>en paſſant dans le milieu dont la maſſe les <lb/>attire; </s> <s xml:id="echoid-s1435" xml:space="preserve">mais d’autres rayons, qui paſſ@nt <lb/>dans l’air auprès des bords de ce corps at-<lb/>tirant, s’approchent ſenſiblement de ce corps, <pb o="107" file="0127" n="127" rhead="DE NEUTON."/> & </s> <s xml:id="echoid-s1436" xml:space="preserve">ſe détournent viſiblement de leur che-<lb/> <anchor type="note" xlink:label="note-0127-01a" xlink:href="note-0127-01"/> min. </s> <s xml:id="echoid-s1437" xml:space="preserve">Mettez dans un endroit obſcur cette <lb/>lame d’acier, ou de verre aminci, qui finit en <lb/>pointe: </s> <s xml:id="echoid-s1438" xml:space="preserve">expoſez-la auprès d’un petit trou <lb/>par lequel la lumiere paſſe; </s> <s xml:id="echoid-s1439" xml:space="preserve">que cette lumie-<lb/>re vienne raſer la pointe de ce métal.</s> <s xml:id="echoid-s1440" xml:space="preserve"/> </p> <div xml:id="echoid-div63" type="float" level="2" n="11"> <note position="right" xlink:label="note-0127-01" xlink:href="note-0127-01a" xml:space="preserve">In-<lb/>flexion <lb/>de la lu-<lb/>miere <lb/>auprès <lb/>des <lb/>corps <lb/>qui l’at-<lb/>tirent.</note> </div> <figure> <image file="0127-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0127-01"/> </figure> <p> <s xml:id="echoid-s1441" xml:space="preserve">Vous verrez les rayons ſe courber auprès <lb/>en telle maniere, que le rayon qui s’appro-<lb/>chera le plus de cette pointe, ſe courbera <lb/>davantage, & </s> <s xml:id="echoid-s1442" xml:space="preserve">que celui qui en ſera plus é-<lb/>loigné, ſe courbera moins à proportion. </s> <s xml:id="echoid-s1443" xml:space="preserve">N’eſt-<lb/>il pas de la plus grande vraiſemblance, que <lb/>le même pouvoir qui briſe ces rayons, quand <lb/>ils ſont dans ce milieu, les force à ſe dé-<lb/>tourner, quand ils ſont près de ce milieu? <lb/></s> <s xml:id="echoid-s1444" xml:space="preserve">Voilà donc la réfraction, la tranſparence, <lb/>la réflexion, aſſujeties à de nouvelles loix.</s> <s xml:id="echoid-s1445" xml:space="preserve"> <pb o="108" file="0128" n="128" rhead="DE LA PHILOSOPHIE"/> Voilà une inflexion de la lumiere, qui dé-<lb/>pend évidemment de l’attraction. </s> <s xml:id="echoid-s1446" xml:space="preserve">C’eſt un <lb/>nouvel Univers qui ſe préſente aux yeux de <lb/>ceux qui veulent voir.</s> <s xml:id="echoid-s1447" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1448" xml:space="preserve">Nous montrerons bien-tôt qu’il y a une <lb/>attraction évidente entre le Soleil & </s> <s xml:id="echoid-s1449" xml:space="preserve">les Pla-<lb/>netes, une tendance mutuelle de tous les <lb/>corps les uns vers les autres. </s> <s xml:id="echoid-s1450" xml:space="preserve">Mais nous <lb/>avertiſſons ici d’avance, que cette attraction, <lb/>qui fait graviter les Planetes ſur notre So-<lb/>leil, n’agit point du tout dans les mêmes <lb/>rapports que l’attraction des petits corps <lb/>qui ſe touchent. </s> <s xml:id="echoid-s1451" xml:space="preserve">Il faudra que l’on ſonge <lb/>bien, que ces rapports changent au point <lb/>de contact. </s> <s xml:id="echoid-s1452" xml:space="preserve">Qu’on ne croye point que la <lb/>lumiere eſt infléchie vers le criſtal & </s> <s xml:id="echoid-s1453" xml:space="preserve">dans <lb/>le criſtal, ſuivant le même rapport, par <lb/>exemple, que Mars eſt attiré par le Soleil. <lb/></s> <s xml:id="echoid-s1454" xml:space="preserve">Tous les corps, comme nous le verrons, <lb/>ſont attirez en raiſon inverſe du quarré de <lb/>leurs diſtances; </s> <s xml:id="echoid-s1455" xml:space="preserve">mais au point de contact, <lb/>ils le ſont en raiſon inverſe des cubes de leurs <lb/>diſtances, & </s> <s xml:id="echoid-s1456" xml:space="preserve">beaucoup plus encore. </s> <s xml:id="echoid-s1457" xml:space="preserve">Ainſi <lb/>l’attraction eſt bien plus forte, & </s> <s xml:id="echoid-s1458" xml:space="preserve">la for-<lb/>ce s’en diſſipe bien plus vîte; </s> <s xml:id="echoid-s1459" xml:space="preserve">& </s> <s xml:id="echoid-s1460" xml:space="preserve">cette <lb/>attraction des corps qui ſe touchent, aug- <pb o="109" file="0129" n="129" rhead="DE NEUTON."/> mente encore à meſure que les corps ſont <lb/>petits. </s> <s xml:id="echoid-s1461" xml:space="preserve">Ainſi des particules de lumiere <lb/>attirées par les petites maſſes du verre, ſont <lb/>bien loin de ſuivre les loix du Syſtême pla-<lb/>nétaire. </s> <s xml:id="echoid-s1462" xml:space="preserve">Deux atomes, & </s> <s xml:id="echoid-s1463" xml:space="preserve">deux Planetes <lb/>telles que Jupiter & </s> <s xml:id="echoid-s1464" xml:space="preserve">Saturne, obéïſſent à l’at-<lb/>traction, mais à différentes loix de l’at-<lb/>traction. </s> <s xml:id="echoid-s1465" xml:space="preserve">C’eſt ce que nous nous reſervons <lb/>d’expliquer dans l’avant dernier Chapitre, <lb/>& </s> <s xml:id="echoid-s1466" xml:space="preserve">ce que nous avons cru néceſſaire d’indi-<lb/>quer ici pour lever toute équivoque.</s> <s xml:id="echoid-s1467" xml:space="preserve"/> </p> <figure> <image file="0129-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0129-01"/> </figure> <pb file="0130" n="130"/> <figure> <image file="0130-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0130-01"/> </figure> </div> <div xml:id="echoid-div65" type="section" level="1" n="16"> <head xml:id="echoid-head25" xml:space="preserve">CHAPITRE HUIT.</head> <head xml:id="echoid-head26" style="it" xml:space="preserve">Suites des merveilles de la réfraction de la lu-<lb/>miere. Qu’un ſeul rayon de la lumiere <lb/>contient en ſoi toutes les couleurs poſ-<lb/>ſibles; ce que c’eſt que la réfran-<lb/>gibilité. Découvertes nou-<lb/>velles.</head> <p> <s xml:id="echoid-s1468" xml:space="preserve">SI vous demandez aux Philoſophes ce qui <lb/> <anchor type="note" xlink:label="note-0130-01a" xlink:href="note-0130-01"/> produit les couleurs, Deſcartes vous <lb/>répondra que les globules de ſes Elémens ſont <lb/>déterminez à tournoyer ſur eux-mêmes outre <lb/>leur tendance au mouvement en ligne droite, & </s> <s xml:id="echoid-s1469" xml:space="preserve"><lb/>que ce ſont les différens tournoyemens qui font <pb o="111" file="0131" n="131" rhead="DE NEUTON."/> es différentes couleurs. </s> <s xml:id="echoid-s1470" xml:space="preserve">Mais, en vérité, ſes <lb/>Elémens, ſes globules, ſon tournoyement, <lb/>ont-ils même beſoin de la pierre de touche <lb/>de l’expérience pour que le faux s’en faſſe <lb/>ſentir? </s> <s xml:id="echoid-s1471" xml:space="preserve">Une foule de démonſtrations a-<lb/>néantit ces chiméres. </s> <s xml:id="echoid-s1472" xml:space="preserve">Voici les plus ſim-<lb/>ples & </s> <s xml:id="echoid-s1473" xml:space="preserve">les plus ſenſibles.</s> <s xml:id="echoid-s1474" xml:space="preserve"/> </p> <div xml:id="echoid-div65" type="float" level="2" n="1"> <note position="left" xlink:label="note-0130-01" xlink:href="note-0130-01a" xml:space="preserve">Imagi-<lb/>nation <lb/>de Def-<lb/>cartes <lb/>ſur les <lb/>cou-<lb/>leurs.</note> </div> <p> <s xml:id="echoid-s1475" xml:space="preserve">Rangez des boules les unes contre les au-<lb/>tres: </s> <s xml:id="echoid-s1476" xml:space="preserve">ſuppoſez les pouſſées en tout ſens, & </s> <s xml:id="echoid-s1477" xml:space="preserve"><lb/>tournant toutes ſur elles-mêmes en tout ſens; <lb/></s> <s xml:id="echoid-s1478" xml:space="preserve">par le ſeul enoncé, il eſt impoſſible, que ces <lb/>boules contigues puiſſent avancer en lignes <lb/>droites réguliérement. </s> <s xml:id="echoid-s1479" xml:space="preserve">De plus, comment <lb/>verriez-vous ſur une muraille ce point bleu, <lb/>& </s> <s xml:id="echoid-s1480" xml:space="preserve">ce point verd?</s> <s xml:id="echoid-s1481" xml:space="preserve"/> </p> <figure> <image file="0131-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0131-01"/> </figure> <pb o="112" file="0132" n="132" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s1482" xml:space="preserve">Les voilà marquez ſur cette muraille; </s> <s xml:id="echoid-s1483" xml:space="preserve">il <lb/>faut qu’ils ſe croiſent en l’air au point A. <lb/></s> <s xml:id="echoid-s1484" xml:space="preserve">avant d’arriver à vos yeux. </s> <s xml:id="echoid-s1485" xml:space="preserve">Puisqu’ils ſe <lb/>croiſent, leur prétendu tournoyement doit <lb/>changer au point d’interſection. </s> <s xml:id="echoid-s1486" xml:space="preserve">Les tour-<lb/>noyemens qui faiſoient le bleu & </s> <s xml:id="echoid-s1487" xml:space="preserve">le verd ne <lb/>ſubſiſtent donc plus les mêmes: </s> <s xml:id="echoid-s1488" xml:space="preserve">il n’y au-<lb/>roit donc plus alors de point verd, ni de <lb/>point bleu. </s> <s xml:id="echoid-s1489" xml:space="preserve">Un Jéſuite Flamand fit cette <lb/>objection à Deſcartes. </s> <s xml:id="echoid-s1490" xml:space="preserve">Celui-ci en ſentit <lb/>toute la force, mais que croiriez-vous qu’il <lb/>répondit? </s> <s xml:id="echoid-s1491" xml:space="preserve">Que ces boules ne tournoyent <lb/>pas à la vérité, mais qu’elles ont une tendan-<lb/>ce au tournoyement. </s> <s xml:id="echoid-s1492" xml:space="preserve">Voilà ce que Deſcartes <lb/>dit dans ſes Lettres. </s> <s xml:id="echoid-s1493" xml:space="preserve">L’acte du tranſparent en-<lb/>tant que tranſparent, eſt-il plus intelligi-<lb/>ble?</s> <s xml:id="echoid-s1494" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1495" xml:space="preserve">Vous me direz, ſans doute, que cette dif-<lb/>ficulté eſt égale dans tous les Syſtêmes. <lb/></s> <s xml:id="echoid-s1496" xml:space="preserve">Vous me direz que ces rayons, qui partent <lb/>de ce point bleu & </s> <s xml:id="echoid-s1497" xml:space="preserve">de ce point verd, ſe eroi-<lb/>ſent néceſſairement, quelque opinion qu’on <lb/>embraſſe touchant les couleurs; </s> <s xml:id="echoid-s1498" xml:space="preserve">que cette <lb/>interſection des rayons devroit toujours em-<lb/>pêcher la viſion, qu’en un mot, il eſt tou- <pb o="113" file="0133" n="133" rhead="DE NEUTON."/> jours incompréhenſible que des rayons qui <lb/>ſe croiſent, arrivent à nos yeux dans leur <lb/>ordre; </s> <s xml:id="echoid-s1499" xml:space="preserve">mais ce ſcrupule ſera bien-tôt levé, <lb/>ſi vous conſiderez que toute partie de ma-<lb/>tiere a plus de pores incomparablement que <lb/>de ſubſtance. </s> <s xml:id="echoid-s1500" xml:space="preserve">Un rayon du Soleil, qui a <lb/>plus de trente millions de lieues en longueur, <lb/>n’a pas probablement un pied de matiere <lb/>ſolide miſe bout à bout. </s> <s xml:id="echoid-s1501" xml:space="preserve">Il ſeroit donc <lb/>très - poſſible qu’un rayon paſſât à travers <lb/>d’un autre en cette maniere, ſans rien dé-<lb/>ranger.</s> <s xml:id="echoid-s1502" xml:space="preserve"/> </p> <figure> <image file="0133-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0133-01"/> </figure> <p> <s xml:id="echoid-s1503" xml:space="preserve">Mais ce n’eſt pas ſeulement ainſi qu’ils <lb/>paſſent, c’eſt l’un par-deſſus l’autre comme <lb/>deux bâtons. </s> <s xml:id="echoid-s1504" xml:space="preserve">Mais direz-vous, des rayons <lb/>émanez d’un centre n’aboutiroient pas pré-<lb/>ciſément, & </s> <s xml:id="echoid-s1505" xml:space="preserve">en rigueur Mathématique, <lb/>à la même ligne de circonférence. </s> <s xml:id="echoid-s1506" xml:space="preserve">Cela eſt <pb o="114" file="0134" n="134" rhead="DE LA PHILOSOPHIE"/> vrai. </s> <s xml:id="echoid-s1507" xml:space="preserve">Il s’en faudra toujours un infiniment <lb/>petit. </s> <s xml:id="echoid-s1508" xml:space="preserve">Mais deux hommes ne verroient pas <lb/>les mêmes points du même objet. </s> <s xml:id="echoid-s1509" xml:space="preserve">Cela eſt <lb/>encore vrai. </s> <s xml:id="echoid-s1510" xml:space="preserve">De mille millions de perſonnes <lb/>qui regarderont une ſuperficie, il n’y en <lb/>aura pas deux qui verront les mêmes <lb/>points.</s> <s xml:id="echoid-s1511" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1512" xml:space="preserve">Il faut avouer que dans le plein de Deſ-<lb/>cartes, cette interſection de rayons eſt im-<lb/>poſſible; </s> <s xml:id="echoid-s1513" xml:space="preserve">mais tout eſt également impoſſi-<lb/>ble dans le plein, & </s> <s xml:id="echoid-s1514" xml:space="preserve">il n’y a aucun mouve-<lb/>ment, tel qu’il ſoit, qui ne ſuppoſe & </s> <s xml:id="echoid-s1515" xml:space="preserve">ne <lb/>prouve le vuide.</s> <s xml:id="echoid-s1516" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1517" xml:space="preserve">Mallebranche vient à ſon tour & </s> <s xml:id="echoid-s1518" xml:space="preserve">vous <lb/>dit: </s> <s xml:id="echoid-s1519" xml:space="preserve">Il eſt vrai que Deſcartes s’eſt trompé. <lb/></s> <s xml:id="echoid-s1520" xml:space="preserve">Son tournoyement de globules, n’eſt pas ſou-<lb/>tenable; </s> <s xml:id="echoid-s1521" xml:space="preserve">mais ce ne ſont pas des globules de <lb/>lumiere, ce ſont des petits tourbillons tour-<lb/>noyans de matiere ſubtile, capables de com-<lb/> <anchor type="note" xlink:label="note-0134-01a" xlink:href="note-0134-01"/> preſſion, qui ſont la cauſe des couleurs; </s> <s xml:id="echoid-s1522" xml:space="preserve">& </s> <s xml:id="echoid-s1523" xml:space="preserve"><lb/>les couleurs conſiſtent comme les ſons dans des <lb/>vibrations de preſſion. </s> <s xml:id="echoid-s1524" xml:space="preserve">Et il ajoute: </s> <s xml:id="echoid-s1525" xml:space="preserve">Il me <lb/>parait impoſſible de découvrir par aucun moyen <lb/>les rapports exacts de ces vibrations, c’eſt-<lb/>à-dire, des couleurs. </s> <s xml:id="echoid-s1526" xml:space="preserve">Vous remarquerez <pb o="115" file="0135" n="135" rhead="DE NEUTON."/> qu’il parloit ainſi dans l’Académie des Scien-<lb/>ces en 1699. </s> <s xml:id="echoid-s1527" xml:space="preserve">& </s> <s xml:id="echoid-s1528" xml:space="preserve">que l’on avoit déja décou-<lb/>vert ces proportions en 1675; </s> <s xml:id="echoid-s1529" xml:space="preserve">non pas pro-<lb/>portions de vibration de petits tourbillons <lb/>qui n’exiſtent point, mais proportions de <lb/>la réfrangibilité des rayons qui font les cou-<lb/>leurs, comme nous le dirons bien-tôt. </s> <s xml:id="echoid-s1530" xml:space="preserve">Ce <lb/>qu’il croioit impoſſible étoit déja démon-<lb/>tré, &</s> <s xml:id="echoid-s1531" xml:space="preserve">, qui plus eſt, démontré aux yeux, <lb/>reconnu vrai par les ſens, ce qui auroit <lb/>bien déplu au Pere Mallebranche.</s> <s xml:id="echoid-s1532" xml:space="preserve"/> </p> <div xml:id="echoid-div66" type="float" level="2" n="2"> <note position="left" xlink:label="note-0134-01" xlink:href="note-0134-01a" xml:space="preserve">Erreur <lb/>de Mal-<lb/>lebran-<lb/>che.</note> </div> <p> <s xml:id="echoid-s1533" xml:space="preserve">D’autres Philoſophes ſentant le faible de <lb/>ces ſuppoſitions, vous diſent au moins <lb/>avec plus de vraiſemblance: </s> <s xml:id="echoid-s1534" xml:space="preserve">Les couleurs <lb/>viennent du plus ou du moins de rayons réflechis <lb/>des corps colorez. </s> <s xml:id="echoid-s1535" xml:space="preserve">Le blanc eſt celui qui en <lb/>réflechit davantage; </s> <s xml:id="echoid-s1536" xml:space="preserve">le noir eſt celui qui en <lb/>réflechit le moins. </s> <s xml:id="echoid-s1537" xml:space="preserve">Les couleurs les plus bril-<lb/>lantes ſeront donc celles qui vous apporteront <lb/>plus de rayons. </s> <s xml:id="echoid-s1538" xml:space="preserve">Le rouge, par exemple, qui <lb/>fatigue un peu la vûe, doit être compoſé de <lb/>plus de rayons, que le verd qui la repoſe da-<lb/>vantage. </s> <s xml:id="echoid-s1539" xml:space="preserve">Cette Hypothèſe parait d’abord <lb/>plus ſenſée; </s> <s xml:id="echoid-s1540" xml:space="preserve">mais elle n’eſt qu’une conjec-<lb/>ture (d’ailleurs très-incomplette & </s> <s xml:id="echoid-s1541" xml:space="preserve">erro-<lb/>née), & </s> <s xml:id="echoid-s1542" xml:space="preserve">une conjecture n’eſt qu’une raiſon <pb o="116" file="0136" n="136" rhead="DE LA PHILOSOPHIE"/> de plus pour chercher, & </s> <s xml:id="echoid-s1543" xml:space="preserve">non pas une rai-<lb/>ſon pour croire.</s> <s xml:id="echoid-s1544" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1545" xml:space="preserve">Addreſſez-vous enfin à Neuton. </s> <s xml:id="echoid-s1546" xml:space="preserve">Il vous <lb/> <anchor type="note" xlink:label="note-0136-01a" xlink:href="note-0136-01"/> dira ne m’en croyez pas: </s> <s xml:id="echoid-s1547" xml:space="preserve">n’en croyez que <lb/>vos yeux & </s> <s xml:id="echoid-s1548" xml:space="preserve">les Mathématiques: </s> <s xml:id="echoid-s1549" xml:space="preserve">mettez-<lb/>vous dans une chambre tout-à-fait obſcu-<lb/>re, où le jour n’entre que par un trou ex-<lb/>trêmement petit; </s> <s xml:id="echoid-s1550" xml:space="preserve">le rayon de la lumiere <lb/>viendra ſur du papier vous donner la cou-<lb/>leur de la blancheur.</s> <s xml:id="echoid-s1551" xml:space="preserve"/> </p> <div xml:id="echoid-div67" type="float" level="2" n="3"> <note position="left" xlink:label="note-0136-01" xlink:href="note-0136-01a" xml:space="preserve">Expé-<lb/>rience <lb/>& dé-<lb/>monſ-<lb/>tration <lb/>de Neu-<lb/>ton.</note> </div> <p> <s xml:id="echoid-s1552" xml:space="preserve">Expoſez transverſalement à un rayon de <lb/>lumiere ce priſme de verre; </s> <s xml:id="echoid-s1553" xml:space="preserve">enſuite met-<lb/>tez à une diſtance d’environ ſeize ou dix-<lb/>ſept pieds une feuille de papier P. </s> <s xml:id="echoid-s1554" xml:space="preserve">vis-à-vis <lb/>ce priſme.</s> <s xml:id="echoid-s1555" xml:space="preserve"/> </p> <figure> <image file="0136-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0136-01"/> </figure> <pb o="117" file="0137" n="137" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s1556" xml:space="preserve">Vous ſavez déja que la lumiere ſe briſe <lb/>en entrant de l’air dans ce priſme; </s> <s xml:id="echoid-s1557" xml:space="preserve">vous <lb/>ſavez qu’elle ſe briſe, en ſens contraire, en <lb/>ſortant de ce priſme dans l’air. </s> <s xml:id="echoid-s1558" xml:space="preserve">Si elle ne <lb/>ſe briſoit pas ainſi, elle iroit de ce trou <lb/>tomber ſur le plancher de la chambre Z. <lb/></s> <s xml:id="echoid-s1559" xml:space="preserve">Mais comme il faut que la lumiere, en s’é-<lb/>chappant, s’éloigne de la ligne Z. </s> <s xml:id="echoid-s1560" xml:space="preserve">cette lu-<lb/>miere ira donc frapper le papier. </s> <s xml:id="echoid-s1561" xml:space="preserve">C’eſt-là <lb/>que ſe voit tout le ſecret de la lumiere & </s> <s xml:id="echoid-s1562" xml:space="preserve"><lb/>des couleurs. </s> <s xml:id="echoid-s1563" xml:space="preserve">Ce rayon qui eſt tombé ſur <lb/>ce priſme n’eſt pas, comme on croioit, un <lb/>ſimple rayon; </s> <s xml:id="echoid-s1564" xml:space="preserve">c’eſt un faiſceau de ſept prin-<lb/>cipaux faiſceaux de rayons, dont chacun <lb/>porte en ſoi une couleur primitive, primor-<lb/>diale, qui lui eſt propre. </s> <s xml:id="echoid-s1565" xml:space="preserve">Des mêlanges de <lb/>ces ſept rayons naiſſent toutes les couleurs <lb/>de la Nature; </s> <s xml:id="echoid-s1566" xml:space="preserve">& </s> <s xml:id="echoid-s1567" xml:space="preserve">les ſept réunis enſemble, <lb/>réflechis enſemble de deſſus un objet, for-<lb/>ment la blancheur.</s> <s xml:id="echoid-s1568" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1569" xml:space="preserve">Approfondiſſez cet artifice admirable. <lb/></s> <s xml:id="echoid-s1570" xml:space="preserve">Nous avions déja inſinué que les rayons <lb/>de la lumiere ne ſe réfractent pas, ne ſe <lb/>briſent pas tous également; </s> <s xml:id="echoid-s1571" xml:space="preserve">ce qui ſe paſſe <lb/>ici en eſt aux yeux une démonſtration évi-<lb/>dente. </s> <s xml:id="echoid-s1572" xml:space="preserve">Ces ſept rayons de lumiere échap- <pb o="118" file="0138" n="138" rhead="DE LA PHILOSOPHIE"/> pez du corps de ce rayon, qui s’eſt anato-<lb/>miſé au ſortir du priſme, viennent ſe placer, <lb/>chacun dans leur ordre, ſur ce papier blanc, <lb/>chaque rayon occupant une ovale. </s> <s xml:id="echoid-s1573" xml:space="preserve">Le rayon <lb/>qui a le moins de force pour ſuivre ſon che <lb/>min, le moins de roideur, le moins de ma-<lb/>tiere, s’écarte plus dans l’air de la perpen-<lb/>diculaire du priſme. </s> <s xml:id="echoid-s1574" xml:space="preserve">Celui qui eſt le plus <lb/>fort, le plus denſe, le plus vigoureux, s’en <lb/>écarte le moins. </s> <s xml:id="echoid-s1575" xml:space="preserve">Voyez-vous ces ſept ra-<lb/>yons qui viennent ſe briſer les uns au-deſſus <lb/>des autres?</s> <s xml:id="echoid-s1576" xml:space="preserve"/> </p> <figure> <image file="0138-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0138-01"/> </figure> <pb o="119" file="0139" n="139" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s1577" xml:space="preserve">Chacun d’eux peint ſur ce papier la cou-<lb/>leur primitive qu’il porte en lui-même. </s> <s xml:id="echoid-s1578" xml:space="preserve">Le <lb/>premier rayon, qui s’ecarte le moins de cet-<lb/>te perpendicule du priſme, eſt couleur de <lb/>feu; </s> <s xml:id="echoid-s1579" xml:space="preserve">le ſecond orangé; </s> <s xml:id="echoid-s1580" xml:space="preserve">le troiſième jaune; <lb/></s> <s xml:id="echoid-s1581" xml:space="preserve">le quatrième verd; </s> <s xml:id="echoid-s1582" xml:space="preserve">le cinquième bleu; </s> <s xml:id="echoid-s1583" xml:space="preserve">le <lb/>ſixième indigo. </s> <s xml:id="echoid-s1584" xml:space="preserve">Enfin celui qui s’écarte <lb/>davantage de la perpendicule, & </s> <s xml:id="echoid-s1585" xml:space="preserve">qui s’éleve <lb/>le dernier au-deſſus des autres, eſt le vio-<lb/>let.</s> <s xml:id="echoid-s1586" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1587" xml:space="preserve">Un ſeul faiſceau de lumiere, qui aupara-<lb/> <anchor type="note" xlink:label="note-0139-01a" xlink:href="note-0139-01"/> vant faiſoit la couleur blanche, eſt donc un <lb/>compoſé de ſept faiſceaux qui ont chacun <lb/>leur couleur. </s> <s xml:id="echoid-s1588" xml:space="preserve">L’aſſemblage de ſept rayons <lb/>primordiaux fait donc le blanc.</s> <s xml:id="echoid-s1589" xml:space="preserve"/> </p> <div xml:id="echoid-div68" type="float" level="2" n="4"> <note position="right" xlink:label="note-0139-01" xlink:href="note-0139-01a" xml:space="preserve">Anato-<lb/>mie de <lb/>la lu-<lb/>miere.</note> </div> <p> <s xml:id="echoid-s1590" xml:space="preserve">Si vous en doutez encore, prenez un des <lb/>verres lenticulaires de lunette, qui raſſem-<lb/>blent tous les rayons à leur foyer: </s> <s xml:id="echoid-s1591" xml:space="preserve">expoſez <lb/>ce verre au trou par lequel entre la lumie-<lb/>re; </s> <s xml:id="echoid-s1592" xml:space="preserve">vous ne verrez jamais à ce foyer qu’un <lb/>rond de blancheur. </s> <s xml:id="echoid-s1593" xml:space="preserve">Expoſez ce même ver-<lb/>re au point, où il pourra raſſembler tous <lb/>les ſept rayons partis-du priſme:</s> <s xml:id="echoid-s1594" xml:space="preserve"/> </p> <pb o="120" file="0140" n="140" rhead="DE LA PHILOSOPHIE"/> <figure> <image file="0140-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0140-01"/> </figure> <p> <s xml:id="echoid-s1595" xml:space="preserve">Il réunit, comme vous le voyez, ces ſept <lb/>rayons dans ſon foyer. </s> <s xml:id="echoid-s1596" xml:space="preserve">La couleur de ces <lb/>ſept rayons réunis eſt blanche; </s> <s xml:id="echoid-s1597" xml:space="preserve">donc il eſt <lb/>démontré que la couleur de tous les rayons <lb/>réunis eſt la blancheur. </s> <s xml:id="echoid-s1598" xml:space="preserve">Le noir par con-<lb/>ſéquent ſera le corps, qui ne réflechira point <lb/>de rayons.</s> <s xml:id="echoid-s1599" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1600" xml:space="preserve">Car, lorſqu’à l’aide du priſme vous avez <lb/>ſéparé un de ces rayons primitifs, expoſez-<lb/>le à un miroir, à un verre ardent, à un <lb/>autre priſme, jamais il ne changera de cou-<lb/>leur, jamais il ne ſe ſéparera en d’autres <lb/> <anchor type="note" xlink:label="note-0140-01a" xlink:href="note-0140-01"/> rayons. </s> <s xml:id="echoid-s1601" xml:space="preserve">Porter en ſoi une telle couleur eſt <lb/>ſon eſſence, rien ne peut plus l’altérer; </s> <s xml:id="echoid-s1602" xml:space="preserve">& </s> <s xml:id="echoid-s1603" xml:space="preserve"><lb/>pour ſurabondance de preuve, prenez des <pb o="121" file="0141" n="141" rhead="DE NEUTON."/> fils de ſoye de différentes couleurs; </s> <s xml:id="echoid-s1604" xml:space="preserve">expo-<lb/>ſez un fil de ſoye bleue, par exemple, au <lb/>rayon rouge, cette ſoye deviendra rouge. <lb/></s> <s xml:id="echoid-s1605" xml:space="preserve">Mettez la au rayon jaune, elle deviendra <lb/>jaune: </s> <s xml:id="echoid-s1606" xml:space="preserve">ainſi du reſte. </s> <s xml:id="echoid-s1607" xml:space="preserve">Enfin ni réfraction, <lb/>ni réflexion, ni aucun moyen imaginable, <lb/>ne peut changer ce rayon primitif, ſemblable <lb/>à l’or que le creuſet a éprouvé, & </s> <s xml:id="echoid-s1608" xml:space="preserve">encore <lb/>plus inaltérable.</s> <s xml:id="echoid-s1609" xml:space="preserve"/> </p> <div xml:id="echoid-div69" type="float" level="2" n="5"> <note position="left" xlink:label="note-0140-01" xlink:href="note-0140-01a" xml:space="preserve">Cou-<lb/>leurs <lb/>dans les <lb/>ravons <lb/>primi-<lb/>tifs.</note> </div> <p> <s xml:id="echoid-s1610" xml:space="preserve">Cette propriété de la lumiere, cette iné-<lb/>galité dans les réfractions de ſes rayons, eſt <lb/>appellée par Neuton réfrangibilité. </s> <s xml:id="echoid-s1611" xml:space="preserve">On <lb/>s’eſt d’abord révolté contre le fait, & </s> <s xml:id="echoid-s1612" xml:space="preserve">on l’a <lb/>nié long-tems, parce que Mr. </s> <s xml:id="echoid-s1613" xml:space="preserve">Mariote avoit <lb/>manqué en France les expériences de Neu-<lb/>ton. </s> <s xml:id="echoid-s1614" xml:space="preserve">On aima mieux dire que Neuton s’é-<lb/> <anchor type="note" xlink:label="note-0141-01a" xlink:href="note-0141-01"/> toit vanté d’avoir vu ce qu’il n’avoit point <lb/>vu, que de penſer que Mariote ne s’y étoit <lb/>pas bien pris pour voir, & </s> <s xml:id="echoid-s1615" xml:space="preserve">qu’il n’avoit pas <lb/>été aſſez heureux dans le choix des priſmes <lb/>qu’il employa. </s> <s xml:id="echoid-s1616" xml:space="preserve">Enſuite méme, lorſque ces <lb/>expériences ont été bien faites, & </s> <s xml:id="echoid-s1617" xml:space="preserve">que la <lb/>vérité s’eſt montrée à nos yeux, le pré-<lb/>jugé a ſubſiſté encore au point, que dans <lb/>pluſieurs Journaux & </s> <s xml:id="echoid-s1618" xml:space="preserve">dans pluſieurs Livres <lb/>faits depuis l’année 1730. </s> <s xml:id="echoid-s1619" xml:space="preserve">on nie hardi- <pb o="122" file="0142" n="142" rhead="DE LA PHILOSOPHIE"/> ment ces mêmes expériences, que cepen-<lb/>dant on fait dans toute l’Europe. </s> <s xml:id="echoid-s1620" xml:space="preserve">C’eſt <lb/>ainſi qu’après la découverte de la circula-<lb/>tion du ſang, on ſoutenoit encore des <lb/>Thèſes contre cette vérité, & </s> <s xml:id="echoid-s1621" xml:space="preserve">qu’on vou-<lb/>loit même rendre ridicules ceux qui expli-<lb/>quoient la découverte nouvelle en les appe-<lb/>lant Circulateurs.</s> <s xml:id="echoid-s1622" xml:space="preserve"/> </p> <div xml:id="echoid-div70" type="float" level="2" n="6"> <note position="right" xlink:label="note-0141-01" xlink:href="note-0141-01a" xml:space="preserve">Vaines <lb/>objec-<lb/>tions <lb/>contre <lb/>ces dé-<lb/>couver-<lb/>tes.</note> </div> <p> <s xml:id="echoid-s1623" xml:space="preserve">Enfin, quand on a été obligé de céder à <lb/>l’évidence, on ne s’eſt pas rendu encore: </s> <s xml:id="echoid-s1624" xml:space="preserve">on <lb/>a vu le fait, & </s> <s xml:id="echoid-s1625" xml:space="preserve">on a chicané ſur l’expreſ-<lb/>ſion: </s> <s xml:id="echoid-s1626" xml:space="preserve">on s’eſt révolté contre le terme de <lb/>réſrangibilité, auſſi-bien que contre celui <lb/>d’attraction, de gravitation. </s> <s xml:id="echoid-s1627" xml:space="preserve">Eh qu’im-<lb/>porte le terme, pourvû qu’il indique une vé-<lb/>rité? </s> <s xml:id="echoid-s1628" xml:space="preserve">Quand Chriſtofle Colomb découvrit <lb/>l’iſle Hiſpaniola, ne pouvoit-il pas lui im-<lb/>poſer le nom qu’il vouloit? </s> <s xml:id="echoid-s1629" xml:space="preserve">Et n’appartient-<lb/>il pas aux Inventeurs de nommer ce qu’ils <lb/>créent, ou ce qu’ils découvrent? </s> <s xml:id="echoid-s1630" xml:space="preserve">On s’eſt <lb/>récrié, on a écrit, contre des mots que Neu-<lb/>ton employe avec la précaution la plus ſagc<unsure/> <lb/>pour prévenir des erreurs.</s> <s xml:id="echoid-s1631" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1632" xml:space="preserve">Il appelle ces rayons, rouges, jaunes, & </s> <s xml:id="echoid-s1633" xml:space="preserve">c. <lb/></s> <s xml:id="echoid-s1634" xml:space="preserve"> <anchor type="note" xlink:label="note-0142-01a" xlink:href="note-0142-01"/> des rayons rubrifiques, jaunifiques, c’eſt-à- <pb o="123" file="0143" n="143" rhead="DE NEUTON."/> dire, excitant la ſenſation de rouge, de <lb/>jaune. </s> <s xml:id="echoid-s1635" xml:space="preserve">Il vouloit par-là fermer la bouche <lb/>à quiconque auroit l’ignorance, ou la mau-<lb/>vaiſe foi, de lui imputer qu’il croioit comme <lb/>Ariſtote, que les couleurs ſont dans les <lb/>choſes mêmes, dans ces rayons jaunes & </s> <s xml:id="echoid-s1636" xml:space="preserve"><lb/>rouges, & </s> <s xml:id="echoid-s1637" xml:space="preserve">non dans notre ame. </s> <s xml:id="echoid-s1638" xml:space="preserve">Il avoit rai-<lb/>ſon de craindre cette accuſation. </s> <s xml:id="echoid-s1639" xml:space="preserve">J’ai trou-<lb/>vé des hommes, d’ailleurs reſpectables, qui <lb/>m’ont aſſûré que Neuton étoit Péripatéti-<lb/>cien, qu’il penſoit que les rayons ſont co-<lb/>lorez en effet eux-mêmes, comme on pen-<lb/>ſoit autreſois que le feu étoit chaud; </s> <s xml:id="echoid-s1640" xml:space="preserve">mais <lb/>ces mêmes Critiques m’ont aſſûré auſſi que <lb/>Neuton étoit Athée. </s> <s xml:id="echoid-s1641" xml:space="preserve">Il eſt vrai qu’ils n’a-<lb/>voient pas lu ſon Livre, mais ils en avoient <lb/>entendu parler à des gens qui avoient écrit <lb/>contre ſes expériences, ſans les avoir vues.</s> <s xml:id="echoid-s1642" xml:space="preserve"/> </p> <div xml:id="echoid-div71" type="float" level="2" n="7"> <note position="left" xlink:label="note-0142-01" xlink:href="note-0142-01a" xml:space="preserve">Criti-<lb/>ques en-<lb/>core plus <lb/>vaines.</note> </div> <p> <s xml:id="echoid-s1643" xml:space="preserve">Ce qu’on écrivit d’abord de plus doux <lb/>contre Neuton, c’eſt que ſon Syſtême eſt <lb/>une Hypothèſe; </s> <s xml:id="echoid-s1644" xml:space="preserve">mais qu’eſt-ce qu’une hypo-<lb/>thèſe? </s> <s xml:id="echoid-s1645" xml:space="preserve">Une ſuppoſition. </s> <s xml:id="echoid-s1646" xml:space="preserve">En vérité, peut-<lb/>on appeller du nom de ſuppoſition, des ſaits <lb/>tant de fois démontrez? </s> <s xml:id="echoid-s1647" xml:space="preserve">Eſt-ce par amour <lb/>propre qu’on veut abſolument avoir l’hon-<lb/>neur d’écrire contre un grand Homme?</s> <s xml:id="echoid-s1648" xml:space="preserve"/> </p> <pb o="124" file="0144" n="144" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s1649" xml:space="preserve">Mais ne devroit-on pas être plus flatté d’en <lb/>être le Diſciple, que l’Adverſaire? </s> <s xml:id="echoid-s1650" xml:space="preserve">Eſt-ce <lb/>parce qu’on eſt né en France qu’on rougit de <lb/>recevoir la vérité des mains d’un Anglais? <lb/></s> <s xml:id="echoid-s1651" xml:space="preserve">Ce ſentiment ſeroit bien indigne d’un Phi-<lb/>loſophe. </s> <s xml:id="echoid-s1652" xml:space="preserve">Il n’y a, pour quiconque penſe, <lb/>ni Français, ni Anglais: </s> <s xml:id="echoid-s1653" xml:space="preserve">celui qui nous inſ-<lb/>truit eſt notre compatriote.</s> <s xml:id="echoid-s1654" xml:space="preserve"/> </p> <figure> <image file="0144-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0144-01"/> </figure> <pb file="0145" n="145"/> <figure> <image file="0145-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0145-01"/> </figure> </div> <div xml:id="echoid-div73" type="section" level="1" n="17"> <head xml:id="echoid-head27" xml:space="preserve">CHAPITRE NEUV.</head> <head xml:id="echoid-head28" style="it" xml:space="preserve">Où l’on indique la cauſe de la réfrangibilité, & <lb/>où l’on trouve par cette cauſe, qu’il y a des <lb/>Corps indiviſibles en Phyſique.</head> <p> <s xml:id="echoid-s1655" xml:space="preserve">CETTE réfrangibilité, que nous ve-<lb/>nons de voir, étant attachée à la ré-<lb/>fraction, doit avoir ſa ſource dans le méme <lb/>principe. </s> <s xml:id="echoid-s1656" xml:space="preserve">La même cauſe doit préſider au <lb/>jeu de tous ces reſſorts: </s> <s xml:id="echoid-s1657" xml:space="preserve">c’eſt-là l’ordre de <lb/>la Nature. </s> <s xml:id="echoid-s1658" xml:space="preserve">Tous les Végétaux ſe nourriſ-<lb/>ſent par les mêmes loix; </s> <s xml:id="echoid-s1659" xml:space="preserve">tous les Animaux <lb/>ont les mêmes principes de vie. </s> <s xml:id="echoid-s1660" xml:space="preserve">Quelque <pb o="126" file="0146" n="146" rhead="DE LA PHILOSOPHIE"/> choſe qui arrive aux corps en mouvement, <lb/>les loix du mouvement ſont invariables. <lb/></s> <s xml:id="echoid-s1661" xml:space="preserve">Nous avons déja vu que la réflection, la <lb/>réfraction, l’inflexion de la lumiere, ſont <lb/>les effets d’un pouvoir qui n’eſt point l’im-<lb/>pulſion (au moins connue): </s> <s xml:id="echoid-s1662" xml:space="preserve">ce même pou-<lb/>voir ſe fait ſentir dans la réfrangibilité; </s> <s xml:id="echoid-s1663" xml:space="preserve">ces <lb/>rayons, qui s’écartent à des diſtances diffé-<lb/>rentes, nous avertiſſent que le milieu, dans <lb/>lequel ils paſſent, agit ſur eux inégalement. </s> <s xml:id="echoid-s1664" xml:space="preserve"><lb/>Un faiſceau de rayons eſt attiré dans le <lb/>verre, mais ce faiſceau de rayons eſt com-<lb/>poſé de maſſes inégales. </s> <s xml:id="echoid-s1665" xml:space="preserve">Ces maſſes obéïſ-<lb/>ſent donc inégalement à ce pouvoir par le-<lb/>quel le milieu agit ſur elles. </s> <s xml:id="echoid-s1666" xml:space="preserve">Le trait de <lb/>lumiere le plus ſolide, le plus compact, doit <lb/>réſiſter le plus à ce pouvoir, doit être moins <lb/> <anchor type="note" xlink:label="note-0146-01a" xlink:href="note-0146-01"/> détourné de ſa route, doit être le moins <lb/>réfrangible. </s> <s xml:id="echoid-s1667" xml:space="preserve">C’eſt ce que l’expérience con-<lb/>firme dans tous les milieux, & </s> <s xml:id="echoid-s1668" xml:space="preserve">dans tous les <lb/>cas. </s> <s xml:id="echoid-s1669" xml:space="preserve">Le rayon rouge eſt toujours celui qui <lb/>ſe détourne le moins de ſon chemin; </s> <s xml:id="echoid-s1670" xml:space="preserve">le <lb/>rayon violet eſt toujours celui qui s’en dé-<lb/>tourne le plus. </s> <s xml:id="echoid-s1671" xml:space="preserve">Auſſi le rayon rouge a-t-il <lb/>le plus de ſubſtance, eſt-il le plus dur, le plus <lb/>brillant, & </s> <s xml:id="echoid-s1672" xml:space="preserve">fatigue-t-il la vûe davantage. </s> <s xml:id="echoid-s1673" xml:space="preserve">Le <lb/>violet qui de tous les rayons colorez repoſe <pb o="127" file="0147" n="147" rhead="DE NEUTON."/> le plus la vûe eſt le plus réfrangible, & </s> <s xml:id="echoid-s1674" xml:space="preserve">par <lb/>conſequent eſt compoſé de parties plus fi-<lb/>nes & </s> <s xml:id="echoid-s1675" xml:space="preserve">moins gravitantes; </s> <s xml:id="echoid-s1676" xml:space="preserve">& </s> <s xml:id="echoid-s1677" xml:space="preserve">ne croyez pas <lb/>que ce ſoit ici une ſimple conjecture, & </s> <s xml:id="echoid-s1678" xml:space="preserve"><lb/>qu’on devine au hazard, que la lumiere a <lb/>de la peſanteur, & </s> <s xml:id="echoid-s1679" xml:space="preserve">qu’un rayon peſe plus <lb/>qu’un autre.</s> <s xml:id="echoid-s1680" xml:space="preserve"/> </p> <div xml:id="echoid-div73" type="float" level="2" n="1"> <note position="left" xlink:label="note-0146-01" xlink:href="note-0146-01a" xml:space="preserve">Diffé-<lb/>rences <lb/>entreles <lb/>rayons <lb/>de la lu-<lb/>miere.</note> </div> <p> <s xml:id="echoid-s1681" xml:space="preserve">Des expériences, faites par les mains les <lb/> <anchor type="note" xlink:label="note-0147-01a" xlink:href="note-0147-01"/> plus exercées & </s> <s xml:id="echoid-s1682" xml:space="preserve">les plus habiles, nous ap-<lb/>prennent que pluſieurs corps acquiérent du <lb/>poids après avoir été long-tems imbibez de <lb/>lumiere. </s> <s xml:id="echoid-s1683" xml:space="preserve">Les particules de feu qui ont <lb/>pénétré leur ſubſtance l’ont augmentée. <lb/></s> <s xml:id="echoid-s1684" xml:space="preserve">Mais quand on révoqueroit en doute ces ex-<lb/>périences, le feu eſt une matiere; </s> <s xml:id="echoid-s1685" xml:space="preserve">donc <lb/>il peſe, & </s> <s xml:id="echoid-s1686" xml:space="preserve">la lumiere n’eſt autre choſe que <lb/>du feu.</s> <s xml:id="echoid-s1687" xml:space="preserve"/> </p> <div xml:id="echoid-div74" type="float" level="2" n="2"> <note position="right" xlink:label="note-0147-01" xlink:href="note-0147-01a" xml:space="preserve">La lu-<lb/>miere <lb/>eſt pe-<lb/>ſante.</note> </div> <p> <s xml:id="echoid-s1688" xml:space="preserve">Il eſt évident qu’un rayon blanc peſe <lb/>tous les rayons qui le compoſent. </s> <s xml:id="echoid-s1689" xml:space="preserve">Or ſup-<lb/>poſez, un moment, que ces rayons s’écar-<lb/>tent tous également l’un de l’autre, alors il <lb/>eſt évident, en ce cas, que le rayon rouge, <lb/>étant ſept fois moins réfrangible que le <lb/>rayon violet, doit avoir ſept fois plus de <lb/>maſſe, & </s> <s xml:id="echoid-s1690" xml:space="preserve">ſept fois plus de poids, que le rayon <pb o="128" file="0148" n="148" rhead="DE LA PHILOSOPHIE"/> violet. </s> <s xml:id="echoid-s1691" xml:space="preserve">Ainſi le rayon rouge peſant com-<lb/>me ſept; </s> <s xml:id="echoid-s1692" xml:space="preserve">l’orangé ſuppoſé ici, comme ſix: </s> <s xml:id="echoid-s1693" xml:space="preserve">le <lb/>jaune ſuppoſé, comme cinq: </s> <s xml:id="echoid-s1694" xml:space="preserve">le verd, com-<lb/>me quatre: </s> <s xml:id="echoid-s1695" xml:space="preserve">le bleu, comme trois: </s> <s xml:id="echoid-s1696" xml:space="preserve">le pour-<lb/>pre indigo, comme deux, & </s> <s xml:id="echoid-s1697" xml:space="preserve">le violet, comme <lb/>un: </s> <s xml:id="echoid-s1698" xml:space="preserve">la ſomme de tous ces poids étant <lb/>vingt-huit, & </s> <s xml:id="echoid-s1699" xml:space="preserve">le blanc étant l’aſſemblage de <lb/>tous ces poids, il eſt démontré qu’un rayon <lb/>blanc, dans la ſuppoſition de ce calcul, peſe <lb/>vingt-huit fois autant qu’un rayon violet; </s> <s xml:id="echoid-s1700" xml:space="preserve">&</s> <s xml:id="echoid-s1701" xml:space="preserve">, <lb/>quel que ſoit le calcul, il eſt évident que le <lb/>rayon blanc peſe beaucoup plus qu’aucun <lb/>autre rayon, puiſqu’il les peſe tous enſem-<lb/>ble.</s> <s xml:id="echoid-s1702" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1703" xml:space="preserve">Nous avons déja vu quelle doit être la <lb/>petiteſſe prodigieuſe de ces rayons de lu-<lb/>miere, contenant en eux toutes les couleurs, <lb/>qui viennent du Soleil pénétrer un pore <lb/>de diamant. </s> <s xml:id="echoid-s1704" xml:space="preserve">Une foule de rayons paſſe <lb/>dans ce pore, & </s> <s xml:id="echoid-s1705" xml:space="preserve">vient ſe réunir près de la <lb/>ſurface intérieure d’une facette. </s> <s xml:id="echoid-s1706" xml:space="preserve">De cette <lb/>foule de traits de lumiere qui occupe un ſi <lb/>petit eſpace, il n’y en a aucun qui ne con-<lb/>tienne ſept traits primordiaux. </s> <s xml:id="echoid-s1707" xml:space="preserve">Chacun de <lb/>ces traits eſt encore lui-même un faiſceau <lb/>de traits teints de ſa couleur. </s> <s xml:id="echoid-s1708" xml:space="preserve">La rayon <pb o="129" file="0149" n="149" rhead="DE NEUTON."/> rouge eſt un aſſemblage d’un très-grand nom-<lb/>bre de rayons rouges. </s> <s xml:id="echoid-s1709" xml:space="preserve">Le violet eſt un aſ-<lb/>ſemblage de rayons violets. </s> <s xml:id="echoid-s1710" xml:space="preserve">Si donc ce <lb/>faiſceau violet peſe vingt-huit fois moins <lb/>qu’un faiſceau blanc, que ſera-ce qu’un ſeul <lb/>des traits de ce faiſceau?</s> <s xml:id="echoid-s1711" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1712" xml:space="preserve">Conſidérons un de ces traits ſimples, qui <lb/>différe d’un autre trait: </s> <s xml:id="echoid-s1713" xml:space="preserve">par exemple, le <lb/>plus mince trait rouge différe en tout <lb/>du plus mince trait violet. </s> <s xml:id="echoid-s1714" xml:space="preserve">Il faut que ſes <lb/> <anchor type="note" xlink:label="note-0149-01a" xlink:href="note-0149-01"/> parties ſolides ſoient autant d’atomes par-<lb/>faitement durs, leſquels compoſent ſon ê-<lb/>tre. </s> <s xml:id="echoid-s1715" xml:space="preserve">En effet, ſi les corps n’étoient pas com-<lb/>poſés de parties ſolides, dures, indiviſibles, <lb/>de véritables atomes: </s> <s xml:id="echoid-s1716" xml:space="preserve">comment les eſpèces <lb/>des corps pourroient-elles reſter éternelle-<lb/>ment les mêmes? </s> <s xml:id="echoid-s1717" xml:space="preserve">Qui mettroit entre elles <lb/>une différence ſi conſtante? </s> <s xml:id="echoid-s1718" xml:space="preserve">Ne faut-il pas <lb/>que les parties qui font leur eſſence, ſoient <lb/>aſſez dures, aſſez ſolides, aſſez unes, pour <lb/>être toujours ce qu’elles ſont? </s> <s xml:id="echoid-s1719" xml:space="preserve">Car com-<lb/>ment eſt-ce que dans le germe d’un grain <lb/> <anchor type="note" xlink:label="note-0149-02a" xlink:href="note-0149-02"/> de bled ſeroient contenus tant de grains de <lb/>bled, & </s> <s xml:id="echoid-s1720" xml:space="preserve">rien autre choſe, ſi la configuration <lb/>des petites parties n’étoit pas toujours la <lb/>même, ſi elle n’étoit pas toujours ſolide, <pb o="130" file="0150" n="150" rhead="DE LA PHILOSOPHIE"/> indiviſible: </s> <s xml:id="echoid-s1721" xml:space="preserve">ce qui ne veut dire autre choſe <lb/>que toujours indiviſée? </s> <s xml:id="echoid-s1722" xml:space="preserve">Dans l’œuf d’une <lb/>mouche ſe trouvent des mouches à l’infi-<lb/>ni; </s> <s xml:id="echoid-s1723" xml:space="preserve">mais ſi ces petites parties qui contien-<lb/>nent tant de mouches n’étoient pas parfai-<lb/>tement dures, elles ſe briſeroient certaine-<lb/>ment l’une contre l’autre, par le mouve-<lb/>ment rapide où tout eſt dans la Nature. <lb/></s> <s xml:id="echoid-s1724" xml:space="preserve">Elles ſe briſeroient d’autant plus, que les <lb/>petits corps ont plus de ſurface par rapport <lb/>à leur groſſeur. </s> <s xml:id="echoid-s1725" xml:space="preserve">Cependant cet inconvé-<lb/>nient n’arrive point: </s> <s xml:id="echoid-s1726" xml:space="preserve">l’œuf d’une mouche <lb/>produit toujours les mouches qu’il conte-<lb/>noit; </s> <s xml:id="echoid-s1727" xml:space="preserve">chaque ſemence, depuis l’Or juſ-<lb/>ques au grain de moutarde, reſte éternelle-<lb/>ment la même. </s> <s xml:id="echoid-s1728" xml:space="preserve">Donc il eſt à croire que <lb/>chaque ſemence des choſes eſt compoſée <lb/>d’atomes toujours indiviſés, qui font la <lb/>ſubſtance de chaque choſe: </s> <s xml:id="echoid-s1729" xml:space="preserve">mais ce n’eſt <lb/>pas aſſez d’indiquer cette grande Vérité à <lb/>laquelle l’obſervation des rayons de la lu-<lb/>miere nous a conduits: </s> <s xml:id="echoid-s1730" xml:space="preserve">il la faut démon-<lb/>trer: </s> <s xml:id="echoid-s1731" xml:space="preserve">il faut prouver en rigueur qu’il y a <lb/>néceſſairement des atomes phyſiquement <lb/>indiviſibles; </s> <s xml:id="echoid-s1732" xml:space="preserve">& </s> <s xml:id="echoid-s1733" xml:space="preserve">c’eſt ce que nous allons fai-<lb/>re voir dans le Chapitre ſuivant.</s> <s xml:id="echoid-s1734" xml:space="preserve"/> </p> <div xml:id="echoid-div75" type="float" level="2" n="3"> <note position="right" xlink:label="note-0149-01" xlink:href="note-0149-01a" xml:space="preserve">Atomes <lb/>dont la <lb/>lumiere <lb/>eſt com-<lb/>poſée.</note> <note position="right" xlink:label="note-0149-02" xlink:href="note-0149-02a" xml:space="preserve">Les <lb/>princi-<lb/>pes des <lb/>corps <lb/>ſont des <lb/>atomes.</note> </div> <pb file="0151" n="151"/> <figure> <image file="0151-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0151-01"/> </figure> </div> <div xml:id="echoid-div77" type="section" level="1" n="18"> <head xml:id="echoid-head29" xml:space="preserve">CHAPITRE DIXIE’ME.</head> <head xml:id="echoid-head30" style="it" xml:space="preserve">Preuves qu’il y a des atomes indiviſibles, & que <lb/>les parties ſimples de la lumiere ſont de ces <lb/>atomes. Suite des découvertes.</head> <p> <s xml:id="echoid-s1735" xml:space="preserve">VOUS avez déja compris quelle eſt l’ex-<lb/>treme poroſité de tous les corps. </s> <s xml:id="echoid-s1736" xml:space="preserve">L’eau <lb/>mème qui n’eſt que dix-neuf fois moins pe-<lb/>ſante que l’or, paſſe pourtant entre les po-<lb/>res de l’or même, le plus ſolide des Métaux. <lb/></s> <s xml:id="echoid-s1737" xml:space="preserve">Il n’y a aucun corps qui n’ait incompara-<lb/>blement plus de pores que de matiere: </s> <s xml:id="echoid-s1738" xml:space="preserve">mais <pb o="132" file="0152" n="152" rhead="DE LA PHILOSOPHIE"/> ſuppoſons un cube qui même, ſi l’on veut, <lb/>ait autant de matiere apparente que de po-<lb/>res: </s> <s xml:id="echoid-s1739" xml:space="preserve">par cette ſuppoſition il n’aura donc <lb/>réellement que la moitié de la matiere qu’il <lb/>parait avoir; </s> <s xml:id="echoid-s1740" xml:space="preserve">mais chaque partie de ce corps <lb/>étant dans le même cas, & </s> <s xml:id="echoid-s1741" xml:space="preserve">perdant ainſi la <lb/>moitié d’elle-même, ce cube ne ſera donc <lb/>par cette deuxième opération que le quart <lb/>de lui-même; </s> <s xml:id="echoid-s1742" xml:space="preserve">il n’y aura donc dans lui que <lb/>le quart de la matiere qui ſemble y être. <lb/></s> <s xml:id="echoid-s1743" xml:space="preserve">Diviſez ainſi chaque partie de chaque par-<lb/>tie; </s> <s xml:id="echoid-s1744" xml:space="preserve">reſtera le huitième de matiere. </s> <s xml:id="echoid-s1745" xml:space="preserve">Con-<lb/> <anchor type="note" xlink:label="note-0152-01a" xlink:href="note-0152-01"/> tinuez toujours cette progreſſion juſqu’à <lb/>l’infini, & </s> <s xml:id="echoid-s1746" xml:space="preserve">faites paſſer votre diviſion par <lb/>tous les ordres d’infini; </s> <s xml:id="echoid-s1747" xml:space="preserve">la fin de la progreſ-<lb/>ſion des pores ſera donc l’infini, & </s> <s xml:id="echoid-s1748" xml:space="preserve">la fin de <lb/>la diminution de la matiere ſera zero. </s> <s xml:id="echoid-s1749" xml:space="preserve">Donc <lb/>ſi l’on pouvoit phyſiquement diviſer la ma-<lb/>tiere à l’infini, il ſe trouveroit qu’il n’y au-<lb/>roit que des pores & </s> <s xml:id="echoid-s1750" xml:space="preserve">point de matiere. </s> <s xml:id="echoid-s1751" xml:space="preserve">Donc <lb/>la matiere, telle qu’elle eſt, n’eſt pas réelle-<lb/>ment phyſiquement diviſible à l’infini: <lb/></s> <s xml:id="echoid-s1752" xml:space="preserve">Donc il eſt démontré qu’il y a des atomes <lb/>indiviſibles, c’eſt-à-dire, des atomes qui <lb/>ne ſeront jamais diviſés, tant que durera la <lb/>conſtitution préſente du Monde.</s> <s xml:id="echoid-s1753" xml:space="preserve"/> </p> <div xml:id="echoid-div77" type="float" level="2" n="1"> <note position="left" xlink:label="note-0152-01" xlink:href="note-0152-01a" xml:space="preserve">Preuve <lb/>qu’il y <lb/>a des <lb/>atomes.</note> </div> <pb o="133" file="0153" n="153" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s1754" xml:space="preserve">Préſentons cette démonſtration d’une ma-<lb/>niere encore plus palpable. </s> <s xml:id="echoid-s1755" xml:space="preserve">Je ſuis arrivé <lb/>par ma diviſion aux deux derniers pores: </s> <s xml:id="echoid-s1756" xml:space="preserve">il <lb/>y a entre eux un corps, ou non: </s> <s xml:id="echoid-s1757" xml:space="preserve">s’il n’y <lb/>en a point, il n’y avoit donc point de ma-<lb/>tiere; </s> <s xml:id="echoid-s1758" xml:space="preserve">s’il y en a, ce corps eſt donc ſans <lb/>pores. </s> <s xml:id="echoid-s1759" xml:space="preserve">Je dis qu’il eſt ſans pores; </s> <s xml:id="echoid-s1760" xml:space="preserve">puiſque <lb/>je ſuis arrivé aux derniers pores, cette par-<lb/>ticule de matiere eſt donc réellement indi-<lb/>viſible.</s> <s xml:id="echoid-s1761" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1762" xml:space="preserve">Au reſte, que cette propoſition ne vous <lb/>paraiſſe point contradictoire à la démonſtra-<lb/>tion géométrique, qui vous prouve qu’une <lb/>ligne eſt diviſible à l’infini.</s> <s xml:id="echoid-s1763" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1764" xml:space="preserve">Ces deux propoſitions qui ſemblent ſe <lb/> <anchor type="note" xlink:label="note-0153-01a" xlink:href="note-0153-01"/> détruire l’une l’autre, s’accordent très-bien <lb/>enſemble. </s> <s xml:id="echoid-s1765" xml:space="preserve">La Géométrie a pour objet les <lb/>idées de notre eſprit. </s> <s xml:id="echoid-s1766" xml:space="preserve">Une ligne géométri-<lb/>que eſt une ligne en idée, toujours diviſi-<lb/>ble en idée, comme une unité numérique <lb/>eſt toujours réductible en autant d’unités <lb/>qu’il me plaira d’en concevoir. </s> <s xml:id="echoid-s1767" xml:space="preserve">Je puis <lb/>diviſer l’unité d’un pied, en cent milles <lb/>milliaſſes d’autres unités; </s> <s xml:id="echoid-s1768" xml:space="preserve">mais enſuite je <pb o="134" file="0154" n="154" rhead="DE LA PHILOSOPHIE"/> pourrai toujours conſiderer ce pied comme <lb/>une unité <anchor type="note" xlink:href="" symbol="(*)"/>.</s> <s xml:id="echoid-s1769" xml:space="preserve"/> </p> <div xml:id="echoid-div78" type="float" level="2" n="2"> <note position="right" xlink:label="note-0153-01" xlink:href="note-0153-01a" xml:space="preserve">La divi-<lb/>ſibilité <lb/>de la <lb/>matiere <lb/>n’empê-<lb/>che <lb/>point <lb/>qu’il n’y <lb/>alt des <lb/>atomes.</note> </div> <p> <s xml:id="echoid-s1770" xml:space="preserve">Les points ſans ligne, les lignes ſans ſur-<lb/>faces, les ſurfaces ſans ſolides, l’infini 1.</s> <s xml:id="echoid-s1771" xml:space="preserve">, <lb/>l’infini 2.</s> <s xml:id="echoid-s1772" xml:space="preserve">, l’infini 3.</s> <s xml:id="echoid-s1773" xml:space="preserve">, ſont en effet les ob-<lb/>jets de propoſitions certaines de la Géomé-<lb/>trie; </s> <s xml:id="echoid-s1774" xml:space="preserve">mais il eſt également certain que la <lb/>Nature ne peut produire des ſurfaces, des <lb/>lignes, des points ſans ſolides. </s> <s xml:id="echoid-s1775" xml:space="preserve">De mê-<lb/>me il eſt indubitable qu’une ligne en Géo-<lb/>métrie eſt diviſible à l’infini; </s> <s xml:id="echoid-s1776" xml:space="preserve">& </s> <s xml:id="echoid-s1777" xml:space="preserve">il eſt indu-<lb/>bitable qu’il y a dans la Nature des corps <lb/>indiviſibles, c’eſt-à-dire, des corps indivi-<lb/>ſés, des corps qui reſteront tels, tant que <lb/>la conſtitution préſente des choſes ſubſiſ-<lb/>tera.</s> <s xml:id="echoid-s1778" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1779" xml:space="preserve">Tenons</s> </p> <note symbol="(*)" position="foot" xml:space="preserve">Mr. de Maleſieu, dans la Géométrie de Mr. le <lb/>Duc de Bourgogne, n’a pas fait aſſez d’attention à <lb/>cette vérité, p. 117. Il trouve de la contradiction où <lb/>il n’y en a point. Il demande, comme une queſtion <lb/>inſoluble, ſi un pied de matiere eſt une ſubſtance ou <lb/>pluſieurs? C’eſt une ſubſtance certainement, quand on <lb/>le conſidére comme un pied cube. Ce ſont dix ſept <lb/>cens vingt-huit ſubſtances, quand on le diviſe en <lb/>pouces.</note> <pb o="135" file="0155" n="155" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s1780" xml:space="preserve">Tenons donc pour certain qu’il y a des <lb/>atomes. </s> <s xml:id="echoid-s1781" xml:space="preserve">Chaque partie conſtituante d’un <lb/>rayon ſimple coloré, peut être conſidérée <lb/>comme un atome; </s> <s xml:id="echoid-s1782" xml:space="preserve">chacun de ces atomes eſt <lb/>peſant, c’eſt ſa différente attraction qui fait <lb/>ſa différente réfrangibilité. </s> <s xml:id="echoid-s1783" xml:space="preserve">Songeons que <lb/>ces atomes les plus réfrangibles ſont auſſi <lb/>les plus réflexibles, & </s> <s xml:id="echoid-s1784" xml:space="preserve">qu’enfin puiſqu’ils <lb/>ſont réfrangibles à raiſon de leur attraction <lb/>vers le milieu le plus agiſſant, il faut bien <lb/>qu’ils réflechiſſent auſſi en raiſon de cette <lb/>attraction. </s> <s xml:id="echoid-s1785" xml:space="preserve">Maintenant il eſt aiſé de connai-<lb/>tre que le rayon violet, par exemple, qui <lb/>eſt le plus réfrangible, eſt toujours le premier <lb/>qui ſe réflechit en ſortant du priſme qui a <lb/>reçu tous les rayons. </s> <s xml:id="echoid-s1786" xml:space="preserve">Mr. </s> <s xml:id="echoid-s1787" xml:space="preserve">Neuton a fait <lb/>cette expérience à l’aide de quatre priſmes <lb/>avec une fagacité & </s> <s xml:id="echoid-s1788" xml:space="preserve">une induſtrie dignes de <lb/>l’inventeur de tant de vérités.</s> <s xml:id="echoid-s1789" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1790" xml:space="preserve">Je donnerai ici la plus ſimple de ces ex-<lb/>périences.</s> <s xml:id="echoid-s1791" xml:space="preserve"/> </p> <pb o="136" file="0156" n="156" rhead="DE LA PHILOSOPHIE"/> <figure> <image file="0156-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0156-01"/> </figure> <p> <s xml:id="echoid-s1792" xml:space="preserve">Ce priſme a envoyé ſur ce papier ces ſept <lb/> <anchor type="note" xlink:label="note-0156-01a" xlink:href="note-0156-01"/> couleurs: </s> <s xml:id="echoid-s1793" xml:space="preserve">tournez ce priſme ſur lui-même <lb/>dans le ſens A, B, C. </s> <s xml:id="echoid-s1794" xml:space="preserve">vous aurez bien-tôt <lb/>cet angle ſelon lequel toute lumiere ſe ré-<lb/>flechira de dedans ce priſme au dehors, au <lb/>lieu de paſſer ſur ce papier; </s> <s xml:id="echoid-s1795" xml:space="preserve">ſi tôt que vous <lb/>commencez à approcher de cet angle, voila <lb/>tout d’un coup le rayon violet qui ſe déta-<lb/>che de ce papier, & </s> <s xml:id="echoid-s1796" xml:space="preserve">que vous voyez ſe <lb/>porter au Plat-fond de la chambre. </s> <s xml:id="echoid-s1797" xml:space="preserve">Après <lb/>le violet, vient le pourpre; </s> <s xml:id="echoid-s1798" xml:space="preserve">après le pour- <pb o="137" file="0157" n="157" rhead="DE NEUTON."/> pre, le bleu; </s> <s xml:id="echoid-s1799" xml:space="preserve">enfin le rouge quitte le der-<lb/>nier ce papier où il eſt peint, pour venir à <lb/>ſon tour ſe réflechir ſur le Plat-fond. </s> <s xml:id="echoid-s1800" xml:space="preserve">Donc <lb/>tout rayon eſt plus réflexible à meſure qu’il <lb/>eſt plus réfrangible; </s> <s xml:id="echoid-s1801" xml:space="preserve">donc la même cauſe <lb/>opére la réflexion & </s> <s xml:id="echoid-s1802" xml:space="preserve">la réfrangibilité.</s> <s xml:id="echoid-s1803" xml:space="preserve"/> </p> <div xml:id="echoid-div79" type="float" level="2" n="3"> <note position="left" xlink:label="note-0156-01" xlink:href="note-0156-01a" xml:space="preserve">Expé-<lb/>rience <lb/>impor-<lb/>tante.</note> </div> <p> <s xml:id="echoid-s1804" xml:space="preserve">Or la partie ſolide du verre ne fait ni <lb/>cette réfrangibilité, ni cette réflexion; </s> <s xml:id="echoid-s1805" xml:space="preserve">donc <lb/>encore une fois ces proprietés ont leur naiſ-<lb/>ſance dans une autre cauſe que dans l’impul-<lb/>ſion connue ſur la Terre. </s> <s xml:id="echoid-s1806" xml:space="preserve">Il n’y a rien à dire <lb/>contre ces expériences, il faut s’y ſoumet-<lb/>tre, quelque rebelle que l’on ſoit à l’évi-<lb/>dence.</s> <s xml:id="echoid-s1807" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1808" xml:space="preserve">On pourroit tirer des expériences même <lb/>de Neuton de quoi faire quelques difficul-<lb/>tés contre les loix qu’il établit. </s> <s xml:id="echoid-s1809" xml:space="preserve">On pourroit <lb/>lui dire, par exemple: </s> <s xml:id="echoid-s1810" xml:space="preserve">Vous nous avez <lb/> <anchor type="note" xlink:label="note-0157-01a" xlink:href="note-0157-01"/> prouvé que l’impulſion d’aucun corps con-<lb/>nu ne peut opérer le briſement de la lumie-<lb/>re, ni ſa réflexion, puiſqu’elle ſe briſe dans <lb/>des pores & </s> <s xml:id="echoid-s1811" xml:space="preserve">ſe réflechit dans du vuide: </s> <s xml:id="echoid-s1812" xml:space="preserve">Vous <lb/>nous avez dit qu’il y a un pouvoir dans la <lb/>Nature qui fait tendre tous les corps les uns <lb/>vers les autres, & </s> <s xml:id="echoid-s1813" xml:space="preserve">en attendant que vous <pb o="138" file="0158" n="158" rhead="DE LA PHILOSOPHIE"/> nous montriez, comme vous nous l’avez <lb/>promis, les loix de ce pouvoir, nous con-<lb/>cevons qu’en effet ſa puiſſance doit agir ſur <lb/>toute la matiere, & </s> <s xml:id="echoid-s1814" xml:space="preserve">que le plus petit des <lb/>corps imaginables doit être ſoumis à cette <lb/>puiſſance de même que le plus grand de tous <lb/>les corps poſſibles: </s> <s xml:id="echoid-s1815" xml:space="preserve">Vous nous avez dit qu’u-<lb/>ne des loix de ce pouvoir eſt d’agir ſur tous <lb/>les corps, ſelon leurs maſſes, & </s> <s xml:id="echoid-s1816" xml:space="preserve">nous <lb/>avouons que cela eſt bien vraiſemblable; <lb/></s> <s xml:id="echoid-s1817" xml:space="preserve">mais par vos propres expériences ne démen-<lb/>tez-vous pas ce Syſtême? </s> <s xml:id="echoid-s1818" xml:space="preserve">L’eau a beaucoup <lb/>plus de maſſe que l’eſprit de vin, que l’eſprit <lb/>de térébenthine: </s> <s xml:id="echoid-s1819" xml:space="preserve">cependant elle attire moins <lb/>un rayon de lumiere, la réfraction ſe fait <lb/>moindre dans l’eau que dans l’eſprit de vin; </s> <s xml:id="echoid-s1820" xml:space="preserve"><lb/>donc ce pouvoir de gravitation, d’attrac-<lb/>tion, n’agit pas comme vous le dites, ſelon <lb/>la maſſe.</s> <s xml:id="echoid-s1821" xml:space="preserve"/> </p> <div xml:id="echoid-div80" type="float" level="2" n="4"> <note position="right" xlink:label="note-0157-01" xlink:href="note-0157-01a" xml:space="preserve">Objec-<lb/>tion.</note> </div> <p> <s xml:id="echoid-s1822" xml:space="preserve">Cette objection loin d’ébranler la vérité <lb/> <anchor type="note" xlink:label="note-0158-01a" xlink:href="note-0158-01"/> des découvertes nouvelles, la confirme en <lb/>effet. </s> <s xml:id="echoid-s1823" xml:space="preserve">Pour la réſoudre clairement, conſi-<lb/>dérons que tous les corps tendent vers le <lb/>centre de la Terre, que tous tombent dans l’air <lb/>avec une force proportionnée à leur maſſe; <lb/></s> <s xml:id="echoid-s1824" xml:space="preserve">mais queſi outre cette force on leur en ap- <pb o="139" file="0159" n="159" rhead="DE NEUTON."/> plique encore une autre, ils iront plus vîte <lb/>qu’ils n’auroient été par leur propre poids. <lb/></s> <s xml:id="echoid-s1825" xml:space="preserve">Tel eſt le cas des rayons de la lumiere en-<lb/>trant dans des corps déja remplis de parti-<lb/>cules inflammables, leſquelles ne ſont que <lb/>la lumiere elle-même retenue dans leurs po-<lb/>res.</s> <s xml:id="echoid-s1826" xml:space="preserve"/> </p> <div xml:id="echoid-div81" type="float" level="2" n="5"> <note position="left" xlink:label="note-0158-01" xlink:href="note-0158-01a" xml:space="preserve">Répon-<lb/>ſe. <lb/>Pour-<lb/>quoi les <lb/>fluides <lb/>moins <lb/>peſants <lb/>que <lb/>l’eau at-<lb/>tirent <lb/>plus la <lb/>lumiere.</note> </div> <p> <s xml:id="echoid-s1827" xml:space="preserve">Ces atomes de feu qui réſident en effet <lb/>dans certains corps ſulphureux & </s> <s xml:id="echoid-s1828" xml:space="preserve">tranſpa-<lb/>rens, augmentent la réfraction de la lumie-<lb/>re vers la ligne perpendiculaire, comme <lb/>une nouvelle force qui lui eſt appliquée: </s> <s xml:id="echoid-s1829" xml:space="preserve">il <lb/>arrive alors ce qui arrive à un flambeau <lb/>qui vient d’etre éteint, & </s> <s xml:id="echoid-s1830" xml:space="preserve">qui fume encore; <lb/></s> <s xml:id="echoid-s1831" xml:space="preserve">il ſe rallume dés qu’il eſt à une certaine diſ-<lb/>tance d’un autre flambeau allumé.</s> <s xml:id="echoid-s1832" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1833" xml:space="preserve">Il eſt tout naturel que les rayons de lu-<lb/>miere entrent aiſément dans l’eſprit ſulphu-<lb/>reux de térébenthine, comme la flamme dans <lb/>la méche fumante d’un flambeau éteint; </s> <s xml:id="echoid-s1834" xml:space="preserve">or <lb/>une nouvelle cauſe jointe à la réfraction <lb/>augmente néceſſairement la réfraction.</s> <s xml:id="echoid-s1835" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1836" xml:space="preserve">De plus, la réaction eſt toujours égale á <lb/>l’action: </s> <s xml:id="echoid-s1837" xml:space="preserve">les corps ſulphureux ſont ceux ſur <lb/>leſquels le feu, qui n’eſt que la lumiere, <pb o="140" file="0160" n="160" rhead="DE LA PHILOSOPHIE"/> agit davantage; </s> <s xml:id="echoid-s1838" xml:space="preserve">donc ils doivent agir auſſi <lb/>plus que les autres corps ſur la lumiere, la <lb/>briſer, la réfracter davantage.</s> <s xml:id="echoid-s1839" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1840" xml:space="preserve">Remarquons ſur-tout ici que cette attrac-<lb/> <anchor type="note" xlink:label="note-0160-01a" xlink:href="note-0160-01"/> tion inhérente dans la matiere ne s’étend <lb/>pas à tout, n’opére pas tous les effets. </s> <s xml:id="echoid-s1841" xml:space="preserve">Le <lb/>myſtère de la lumiere réflechie du milieu <lb/>des pores, & </s> <s xml:id="echoid-s1842" xml:space="preserve">de deſſus les ſurſaces, ſans tou-<lb/>cher aux ſurfaces, a des profondeurs que <lb/>les loix de l’attraction ne peuvent ſonder: <lb/></s> <s xml:id="echoid-s1843" xml:space="preserve">il n’y a qu’un Charlatan, qui ſe vante d’a-<lb/>voir un remede univerſel, & </s> <s xml:id="echoid-s1844" xml:space="preserve">ce ſeroit être <lb/>Charlatan en Philoſophie que de rapporter <lb/>tout, ſans preuve, à la même cauſe; </s> <s xml:id="echoid-s1845" xml:space="preserve">cette <lb/>même force d’eſprit qui a fait découvrir à <lb/>Neuton le pouvoir de l’attraction, lui a fait <lb/>avouer que ce pouvoir eſt bien loin d’être <lb/>l’unique Agent de la Nature.</s> <s xml:id="echoid-s1846" xml:space="preserve"/> </p> <div xml:id="echoid-div82" type="float" level="2" n="6"> <note position="left" xlink:label="note-0160-01" xlink:href="note-0160-01a" xml:space="preserve">L’at-<lb/>traction <lb/>n’entre <lb/>pas dans <lb/>tous les <lb/>effets de <lb/>la lumie-<lb/>re.</note> </div> <p> <s xml:id="echoid-s1847" xml:space="preserve">Il eſt bien vrai que le rayon le plus ré-<lb/>frangible étant le plus réflexible, c’eſt une <lb/>preuve évidente que la même puiſſance <lb/>opére la réflexion, la réſraction, & </s> <s xml:id="echoid-s1848" xml:space="preserve">l’accélé-<lb/>ration de la chûte des rayons dans ce verre, <lb/>&</s> <s xml:id="echoid-s1849" xml:space="preserve">c.</s> <s xml:id="echoid-s1850" xml:space="preserve">; mais enfin la force de l’attraction ſem-<lb/>ble n’avoir rien de commun avec d’autres <pb o="141" file="0161" n="161" rhead="DE NEUTON."/> phénomênes. </s> <s xml:id="echoid-s1851" xml:space="preserve">Il y a ſur-tout des vibrations <lb/>de rayons, des jets alternatifs de la lumie-<lb/>miere allant & </s> <s xml:id="echoid-s1852" xml:space="preserve">venant ſur les corps, que <lb/>la gravitation n’expliqueroit pas; </s> <s xml:id="echoid-s1853" xml:space="preserve">mais ces <lb/>nouvelles difficultés, c’eſt Neuton lui-<lb/>même qui les a créées. </s> <s xml:id="echoid-s1854" xml:space="preserve">Non - ſeulement il <lb/>a découvert des myſtères que la gravitation <lb/>développe; </s> <s xml:id="echoid-s1855" xml:space="preserve">mais il en a trouvé qu’elle ne <lb/>développe pas. </s> <s xml:id="echoid-s1856" xml:space="preserve">Ces jets alternatifs de la <lb/>réflexion de la lumiere ſont un de ces Se-<lb/>crets de la Nature, dont il eſt bien étonnant <lb/>que les yeux humains ayent pu s’apperce-<lb/>voir.</s> <s xml:id="echoid-s1857" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1858" xml:space="preserve">Nous parlerons de cette ſingularité en ſon <lb/>lieu dans le Chapitre treizième; </s> <s xml:id="echoid-s1859" xml:space="preserve">continuons <lb/>à voir les effets de la réſrangibilité. </s> <s xml:id="echoid-s1860" xml:space="preserve">L’Arc-<lb/>en-Ciel eſt un de ces effets, & </s> <s xml:id="echoid-s1861" xml:space="preserve">le plus <lb/>conſidérable, nous allons l’expliquer dans le <lb/>Chapitre qui ſuit.</s> <s xml:id="echoid-s1862" xml:space="preserve"/> </p> <figure> <image file="0161-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0161-01"/> </figure> <pb file="0162" n="162"/> <figure> <image file="0162-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0162-01"/> </figure> </div> <div xml:id="echoid-div84" type="section" level="1" n="19"> <head xml:id="echoid-head31" xml:space="preserve">CHAPITRE ONZIE’ME.</head> <head xml:id="echoid-head32" style="it" xml:space="preserve">De l’ Arc-en-Ciel; que ce Météore eſt une ſuite <lb/>néceſſaire des loix de la réfrangibilité.</head> <p> <s xml:id="echoid-s1863" xml:space="preserve">L’Arc-en-Ciel, ou l’Iris, eſt une ſuite <lb/> <anchor type="note" xlink:label="note-0162-01a" xlink:href="note-0162-01"/> néceſſaire des proprietés de la lumiere <lb/>que nous venons d’obſerver. </s> <s xml:id="echoid-s1864" xml:space="preserve">Nous n’avons <lb/>rien, dans les Ecrits des Grecs, ni des Ro-<lb/>mains, ni des Arabes, qui puiſſe faire penſer <lb/>qu’ils connuſſent les raiſons de ce phénomê-<lb/>ne. </s> <s xml:id="echoid-s1865" xml:space="preserve">Lucrèce n’en dit rien, & </s> <s xml:id="echoid-s1866" xml:space="preserve">par tou@es <lb/>les abſurdités qu’il débite au nom d’Epicure <pb o="143" file="0163" n="163" rhead="DE NEUTON."/> ſur la lumiere & </s> <s xml:id="echoid-s1867" xml:space="preserve">ſur la viſion, il parait que <lb/>ſon Siècle, ſi poli d’ailleurs, étoit plongé <lb/>dans une profonde ignorance en fait de <lb/>Phyſique. </s> <s xml:id="echoid-s1868" xml:space="preserve">On ſavoit qu’il faut qu’une nuée <lb/>épaiſſe ſe réſolvant en pluye, ſoit expoſée <lb/>aux rayons du Soleil, & </s> <s xml:id="echoid-s1869" xml:space="preserve">que nos yeux ſe <lb/>trouvent entre l’Aſtre & </s> <s xml:id="echoid-s1870" xml:space="preserve">la nuée pour voir <lb/>ce qu’on appelloit l’Iris, mille trahit varios <lb/>adverſo ſole colores, mais voilà tout ce qu’on <lb/>ſavoit; </s> <s xml:id="echoid-s1871" xml:space="preserve">perſonne n’imaginoit ni pourquoi <lb/>une nuée donne des couleurs, ni comment <lb/>la nature & </s> <s xml:id="echoid-s1872" xml:space="preserve">l’ordre de ces couleurs ſont dé-<lb/>terminés, ni pourquoi il y a deux Arcs-en <lb/>Ciel l’un ſur l’autre, ni pourquoi on voit <lb/>toujours ce phénomêne ſous la figure d’un <lb/>demi-cercle.</s> <s xml:id="echoid-s1873" xml:space="preserve"/> </p> <div xml:id="echoid-div84" type="float" level="2" n="1"> <note position="left" xlink:label="note-0162-01" xlink:href="note-0162-01a" xml:space="preserve">Méca-<lb/>niſme <lb/>de <lb/>l’Arc-<lb/>en Ciel <lb/>inconnu <lb/>à toute <lb/>l’Anti-<lb/>quité.</note> </div> <p> <s xml:id="echoid-s1874" xml:space="preserve">Albert qu’on a ſurnommé le Grand, parce <lb/> <anchor type="note" xlink:label="note-0163-01a" xlink:href="note-0163-01"/> qu’il vivoit dans un Siècle où les hommes <lb/>étoient bien petits, imagina que les cou-<lb/>leurs de l’Arc-en-Ciel venoient d’une roſée <lb/>qui eſt entre nous & </s> <s xml:id="echoid-s1875" xml:space="preserve">la nuée, & </s> <s xml:id="echoid-s1876" xml:space="preserve">que ces <lb/>couleurs reçues ſur la nuée, nous étoient <lb/>envoyées par elle. </s> <s xml:id="echoid-s1877" xml:space="preserve">Vous remarquerez en-<lb/>core que cet Albert le Grand, croioit avec <lb/>toute l’Ecole que la lumiere étoit un ac-<lb/>cident.</s> <s xml:id="echoid-s1878" xml:space="preserve"/> </p> <div xml:id="echoid-div85" type="float" level="2" n="2"> <note position="right" xlink:label="note-0163-01" xlink:href="note-0163-01a" xml:space="preserve">Igno-<lb/>rance <lb/>d’Al-<lb/>bert le <lb/>Grand.</note> </div> <pb o="144" file="0164" n="164" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s1879" xml:space="preserve">Enfin le célèbre Antonio de Dominis Ar-<lb/> <anchor type="note" xlink:label="note-0164-01a" xlink:href="note-0164-01"/> cheveque de Spalatro en Dalmatie, chaſſé <lb/>de ſon Evêché par l’Inquiſition, écrivit <lb/>vers l’an 1590. </s> <s xml:id="echoid-s1880" xml:space="preserve">ſon petit Traité De radiis <lb/>Lucis & </s> <s xml:id="echoid-s1881" xml:space="preserve">de Iride, qui ne fut imprimé à Ve-<lb/>niſe que vingt ans après. </s> <s xml:id="echoid-s1882" xml:space="preserve">Il fut le premier <lb/>qui fit voir que les rayons du Soleil réflechis <lb/>de l’intérieur même des goûtes de pluye, <lb/>formoient cette peinture qui parait en Arc, <lb/>& </s> <s xml:id="echoid-s1883" xml:space="preserve">qui ſembloit un miracle inexplicable; </s> <s xml:id="echoid-s1884" xml:space="preserve">il <lb/>rendit le miracle naturel, ou plutôt il l’ex-<lb/>pliqua par de nouveaux prodiges de la Na-<lb/>ture.</s> <s xml:id="echoid-s1885" xml:space="preserve"/> </p> <div xml:id="echoid-div86" type="float" level="2" n="3"> <note position="left" xlink:label="note-0164-01" xlink:href="note-0164-01a" xml:space="preserve">L’Ar-<lb/>chevê-<lb/>que An-<lb/>tonio de <lb/>Domi-<lb/>nis eſt <lb/>le pre-<lb/>mier qui <lb/>ait ex-<lb/>pliqué <lb/>l’Arc-<lb/>en-Ciel.</note> </div> <p> <s xml:id="echoid-s1886" xml:space="preserve">Sa découverte étoit d’autant plus ſingu-<lb/>liére, qu’il n’avoit d’ailleurs que des no-<lb/>tions très-fauſſes de la maniere dont ſe fait <lb/>la viſion. </s> <s xml:id="echoid-s1887" xml:space="preserve">Il aſſûre dans ſon Livre que les <lb/>images des objets ſont dans la prunelle, & </s> <s xml:id="echoid-s1888" xml:space="preserve"><lb/>qu’il ne ſe fait point de réfraction dans nos <lb/>yeux: </s> <s xml:id="echoid-s1889" xml:space="preserve">choſe aſſez ſinguliére pour un bon <lb/>Philoſophe! Il avoit découvert les réſrac-<lb/>tions alors inconnues dans les goûtes de <lb/>l’Arc-en-Ciel, & </s> <s xml:id="echoid-s1890" xml:space="preserve">il nioit celles qui ſe font <lb/>dans les humeurs de l’œil, qui commen-<lb/>çoient à être démontrées; </s> <s xml:id="echoid-s1891" xml:space="preserve">mais laiſſons ſes <pb o="145" file="0165" n="165" rhead="DE NEUTON."/> erreurs pour examiner la vérité qu’il a trou-<lb/>vée.</s> <s xml:id="echoid-s1892" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1893" xml:space="preserve">Il vit avec une ſagacité alors bien peu <lb/>commune, que chaque rangée, chaque ban-<lb/>de de goûtes de pluye qui forme l’Arc-en-<lb/>Ciel, devoit renvoyer des rayons de lumie-<lb/>re ſous différens angles: </s> <s xml:id="echoid-s1894" xml:space="preserve">il vit que la diffé-<lb/>rence de ces angles devoit faire celle des <lb/>couleurs: </s> <s xml:id="echoid-s1895" xml:space="preserve">il ſut meſurer la grandeur de ces <lb/> <anchor type="note" xlink:label="note-0165-01a" xlink:href="note-0165-01"/> angles: </s> <s xml:id="echoid-s1896" xml:space="preserve">il prit une boule d’un cryſtal bien <lb/>tranſparent qu’il remplit d’eau; </s> <s xml:id="echoid-s1897" xml:space="preserve">il la ſuſpen-<lb/>dit à une certaine hauteur expoſée aux <lb/>rayons du Soleil.</s> <s xml:id="echoid-s1898" xml:space="preserve"/> </p> <div xml:id="echoid-div87" type="float" level="2" n="4"> <note position="right" xlink:label="note-0165-01" xlink:href="note-0165-01a" xml:space="preserve">Son ex-<lb/>périen-<lb/>ce.</note> </div> <p> <s xml:id="echoid-s1899" xml:space="preserve">Deſcartes qui a ſuivi Antonio de Dominis, <lb/> <anchor type="note" xlink:label="note-0165-02a" xlink:href="note-0165-02"/> qui l’a rectifié & </s> <s xml:id="echoid-s1900" xml:space="preserve">ſurpaſſé en quelque choſe, <lb/>& </s> <s xml:id="echoid-s1901" xml:space="preserve">qui peut-être auroit du le citer, fit auſſi la <lb/>même expérience. </s> <s xml:id="echoid-s1902" xml:space="preserve">Quand cette boule eſt <lb/>ſuſpendue à telle hauteur que le rayon de <lb/>lumiere, qui donne du Soleil ſur la boule, <lb/>fait ainſi avec le rayon allant de la boule à <lb/>l’œil un angle de quarante-deux degrez <lb/>deux ou trois minutes, cette boule donne <lb/>toujours une couleur rouge.</s> <s xml:id="echoid-s1903" xml:space="preserve"/> </p> <div xml:id="echoid-div88" type="float" level="2" n="5"> <note position="right" xlink:label="note-0165-02" xlink:href="note-0165-02a" xml:space="preserve">Imitée <lb/>par Deſ-<lb/>cartes.</note> </div> <pb o="146" file="0166" n="166" rhead="DE LA PHILOSOPHIE"/> <figure> <image file="0166-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0166-01"/> </figure> <p> <s xml:id="echoid-s1904" xml:space="preserve">Quand cette boule eſt ſuſpendue un peu <lb/>plus bas, & </s> <s xml:id="echoid-s1905" xml:space="preserve">que ces angles ſont plus petits, <lb/>les autres couleurs de l’Arc-en-Ciel paraiſ-<lb/>ſent ſucceſſivement de façon, que le plus <lb/>grand angle, en ce cas, fait le rouge, & </s> <s xml:id="echoid-s1906" xml:space="preserve">que <lb/>le plus petit angle de 40 degrez 17 minu-<lb/>tes forme le violet. </s> <s xml:id="echoid-s1907" xml:space="preserve">C’eſt-là le fondement <lb/>de la connaiſſance de l’Arc-en-Ciel; </s> <s xml:id="echoid-s1908" xml:space="preserve">mais <lb/>ce n’en eſt encore que le fondement.</s> <s xml:id="echoid-s1909" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1910" xml:space="preserve">La réfrangibilité ſeule rend raiſon de ce <lb/> <anchor type="note" xlink:label="note-0166-01a" xlink:href="note-0166-01"/> phénomêne ſi ordinaire, ſi peu connu, & </s> <s xml:id="echoid-s1911" xml:space="preserve"><lb/>dont très-peu de Commençans ont une idée <lb/>nette; </s> <s xml:id="echoid-s1912" xml:space="preserve">tâchons de rendre la choſe ſenſible <lb/>à tout le monde. </s> <s xml:id="echoid-s1913" xml:space="preserve">Suſpendons une boule <lb/>de cryſtal pleine d’eau, expoſée au Soleil: <lb/></s> <s xml:id="echoid-s1914" xml:space="preserve">plaçons-nous entre le Soleil & </s> <s xml:id="echoid-s1915" xml:space="preserve">elle; </s> <s xml:id="echoid-s1916" xml:space="preserve">pour- <pb o="147" file="0167" n="167" rhead="DE NEUTON."/> quoi cette boule m’envoye-t-elle des cou-<lb/>leurs? </s> <s xml:id="echoid-s1917" xml:space="preserve">& </s> <s xml:id="echoid-s1918" xml:space="preserve">pourquoi certaines couleurs? </s> <s xml:id="echoid-s1919" xml:space="preserve">Des <lb/>maſſes de lumiere, des millions de faiſ-<lb/>ceaux, tombent du Soleil ſur cette boule: <lb/></s> <s xml:id="echoid-s1920" xml:space="preserve">dans chacun de ces faiſceaux il y a des traits <lb/>primitifs, des rayons homogênes, pluſieurs <lb/>rouges, pluſieurs jaunes, pluſieurs verds, <lb/>& </s> <s xml:id="echoid-s1921" xml:space="preserve">c. </s> <s xml:id="echoid-s1922" xml:space="preserve">tous ſe briſent à leur incidence dans la <lb/>boule, chacun d’eux ſe briſe différemment <lb/>& </s> <s xml:id="echoid-s1923" xml:space="preserve">ſelon l’eſpèce dont il eſt, & </s> <s xml:id="echoid-s1924" xml:space="preserve">ſelon l’en-<lb/>droit dans lequel il entre.</s> <s xml:id="echoid-s1925" xml:space="preserve"/> </p> <div xml:id="echoid-div89" type="float" level="2" n="6"> <note position="left" xlink:label="note-0166-01" xlink:href="note-0166-01a" xml:space="preserve">La ré-<lb/>frangi-<lb/>bilité <lb/>unique <lb/>raiſon <lb/>de <lb/>l’Arc-<lb/>en- Ciel.</note> </div> <p> <s xml:id="echoid-s1926" xml:space="preserve">Vous ſavez déja que les rayons rouges ſont <lb/>les moins réfrangibles; </s> <s xml:id="echoid-s1927" xml:space="preserve">les rayons rouges d’un <lb/>certain faiſceau déterminé iront done ſe <lb/>réunir dans un certain point déterminé au <lb/>fond de la boule, tandis que les rayons bleus <lb/>& </s> <s xml:id="echoid-s1928" xml:space="preserve">pourpres du même faiſceau iront ailleurs. <lb/></s> <s xml:id="echoid-s1929" xml:space="preserve">Ces rayons rouges ſortiront auſſi de la boule <lb/>en un endroit, & </s> <s xml:id="echoid-s1930" xml:space="preserve">les verds, les bleus, les pour-<lb/>pres en un autre endroit. </s> <s xml:id="echoid-s1931" xml:space="preserve">Ce n’eſt pas aſſez. </s> <s xml:id="echoid-s1932" xml:space="preserve"><lb/>Il faut examiner les points, où tombent ces <lb/>rayons rouges en entrant dans cette boule <lb/>& </s> <s xml:id="echoid-s1933" xml:space="preserve">en ſortant pour venir à votre œil.</s> <s xml:id="echoid-s1934" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1935" xml:space="preserve">Pour donner à ceci tout le degré de clarté <lb/>néceſſaire, concevons cette boule telle <pb o="148" file="0168" n="168" rhead="DE LA PHILOSOPHIE"/> qu’elle eſt en effet, un aſſemblage d’une in-<lb/>finité de ſurfaces planes; </s> <s xml:id="echoid-s1936" xml:space="preserve">car le cercle étant <lb/>compoſé d’une infinité de courbes, la boule <lb/>n’eſt qu’une infinité de ſurfaces.</s> <s xml:id="echoid-s1937" xml:space="preserve"/> </p> <figure> <image file="0168-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0168-01"/> </figure> <p> <s xml:id="echoid-s1938" xml:space="preserve">Des rayons rouges A, B, C. </s> <s xml:id="echoid-s1939" xml:space="preserve">viennent <lb/>parallèles du Soleil ſur ces trois petites ſur-<lb/>faces. </s> <s xml:id="echoid-s1940" xml:space="preserve">N’eſt-il pas vrai que chacun ſe bri-<lb/>ſe ſelon ſon degré d’incidence? </s> <s xml:id="echoid-s1941" xml:space="preserve">N’eſt-il pas <lb/>manifeſte que le rayon rouge A. </s> <s xml:id="echoid-s1942" xml:space="preserve">tombe plus <pb o="149" file="0169" n="169" rhead="DE NEUTON."/> obliquement ſur ſa petite ſurface, que le <lb/>rayon rouge B. </s> <s xml:id="echoid-s1943" xml:space="preserve">ne tombe ſur la ſienne? </s> <s xml:id="echoid-s1944" xml:space="preserve">Ainſi <lb/>tous deux viennent au point R. </s> <s xml:id="echoid-s1945" xml:space="preserve">par diffé-<lb/>rens chemins.</s> <s xml:id="echoid-s1946" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1947" xml:space="preserve">Le rayon rouge C. </s> <s xml:id="echoid-s1948" xml:space="preserve">tombant ſur ſa petite <lb/>ſurface encore moins obliquement ſe rompt <lb/>bien moins, & </s> <s xml:id="echoid-s1949" xml:space="preserve">arrive auſſi au point R. </s> <s xml:id="echoid-s1950" xml:space="preserve">en <lb/>ne ſe briſant que très-peu.</s> <s xml:id="echoid-s1951" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1952" xml:space="preserve">J’ai donc déja trois rayons rouges, c’eſt-<lb/> <anchor type="note" xlink:label="note-0169-01a" xlink:href="note-0169-01"/> à-dire, trois faiſceaux de rayons rouges, <lb/>qui aboutiſſent au même point R.</s> <s xml:id="echoid-s1953" xml:space="preserve"/> </p> <div xml:id="echoid-div90" type="float" level="2" n="7"> <note position="right" xlink:label="note-0169-01" xlink:href="note-0169-01a" xml:space="preserve">Explica-<lb/>tion de <lb/>ce phé-<lb/>nomê-<lb/>ne.</note> </div> <p> <s xml:id="echoid-s1954" xml:space="preserve">A ce point R. </s> <s xml:id="echoid-s1955" xml:space="preserve">chacun fait un angle de <lb/>réflexion égal à ſon angle d’incidence, cha-<lb/>cun ſe briſe à ſon émergence de la boule, <lb/>en s’éloignant de la perpendiculaire de la <lb/>nouvelle petite ſurface qu’il rencontre, de <lb/>même que chacun s’eſt rompu à ſon inci-<lb/>dence en s’approchant de ſa perpendicule; <lb/></s> <s xml:id="echoid-s1956" xml:space="preserve">donc tous reviennent parallèles, donctous <lb/>entrent dans l’œil, ſelon l’ouverture de l’an-<lb/>gle propre aux rayons rouges.</s> <s xml:id="echoid-s1957" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1958" xml:space="preserve">S’il y a une quantité ſuffiſante de ces traits <lb/>homogênes rouges pour ébranler le nerf op- <pb o="150" file="0170" n="170" rhead="DE LA PHILOSOPHIE"/> tique, il eſt inconteſtable que vous ne de-<lb/>vez avoir que la ſenſation de rouge.</s> <s xml:id="echoid-s1959" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1960" xml:space="preserve">Ce ſont ces rayons A, B, C. </s> <s xml:id="echoid-s1961" xml:space="preserve">qu’on nom-<lb/>me rayons viſibles, rayons efficaces de cette <lb/>goûte; </s> <s xml:id="echoid-s1962" xml:space="preserve">car chaque goûte a ſes rayons viſi-<lb/>bles.</s> <s xml:id="echoid-s1963" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1964" xml:space="preserve">Il y a des milliers d’autres rayons rouges, <lb/>qui, venant ſur d’autres petites ſurfaces de <lb/>la boule, plus haut & </s> <s xml:id="echoid-s1965" xml:space="preserve">plus bas, n’aboutiſſent <lb/>point en R, ou qui, tombés en ces mêmes <lb/>ſurfaces à une autre obliquité, n’aboutiſſent <lb/>point non plus en R.</s> <s xml:id="echoid-s1966" xml:space="preserve">; ceux-là ſont perdus <lb/>pour vous, ils viendront à un autre œil <lb/>placé plus haut, ou plus bas.</s> <s xml:id="echoid-s1967" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1968" xml:space="preserve">Des milliers de rayons orangés, verds, <lb/>bleus, violets, ſont venus à la vérité avec <lb/>les rouges viſibles ſur ces ſurfaces A, B, <lb/>C.</s> <s xml:id="echoid-s1969" xml:space="preserve">; mais vous ne pourrez les recevoir. <lb/></s> <s xml:id="echoid-s1970" xml:space="preserve">Vous en ſavez la raiſon, c’eſt qu’ils ſont <lb/>tous plus réfrangibles que les rouges: </s> <s xml:id="echoid-s1971" xml:space="preserve">c’eſt <lb/>qu’en entrant tous au même point, chacun <lb/>prend dans la boule un chemin différent; </s> <s xml:id="echoid-s1972" xml:space="preserve"><lb/>tous rompus davantage, ils viennent au-<lb/>deſſous du point R.</s> <s xml:id="echoid-s1973" xml:space="preserve">, ils ſe rompent auſſi <pb o="151" file="0171" n="171" rhead="DE NEUTON."/> plus que les rouges en ſortant de la boule. <lb/></s> <s xml:id="echoid-s1974" xml:space="preserve">Ce même pouvoir qui les approchoit plus <lb/>du perpendicule de chaque ſurface dans <lb/>l’intérieur de la boule, les en écarte donc <lb/>davantage à leur retour dans l’air: </s> <s xml:id="echoid-s1975" xml:space="preserve">ils re-<lb/>viennent donc tous au-deſſous de votre œil; </s> <s xml:id="echoid-s1976" xml:space="preserve"><lb/>mais baiſſez la boule, vous rendez l’angle <lb/>plus petit. </s> <s xml:id="echoid-s1977" xml:space="preserve">Que cet angle ſoit de quaran-<lb/>te degrez environ dix - ſept minutes, vous <lb/>ne recevez que les objets violets.</s> <s xml:id="echoid-s1978" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1979" xml:space="preserve">Il n’y a perſonne qui ſur ce principe ne <lb/>conçoive très - aiſément l’artifice de l’Arc-<lb/>en-Ciel; </s> <s xml:id="echoid-s1980" xml:space="preserve">imaginez pluſieurs rangées, plu-<lb/>ſieurs bandes de goûtes de pluye, chaque <lb/>goûte fait préciſément le même effet que <lb/>cette boule.</s> <s xml:id="echoid-s1981" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1982" xml:space="preserve">Jettez les yeux ſur cet Arc, &</s> <s xml:id="echoid-s1983" xml:space="preserve">, pour évi-<lb/>ter la confuſion, ne conſiderez que trois <lb/>rangées de goûtes de pluye, trois bandes <lb/>colorées.</s> <s xml:id="echoid-s1984" xml:space="preserve"/> </p> <pb o="152" file="0172" n="172" rhead="DE LA PHILOSOPHIE"/> <figure> <image file="0172-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0172-01"/> </figure> <p> <s xml:id="echoid-s1985" xml:space="preserve">Il eſt viſible que l’angle P, O, L. </s> <s xml:id="echoid-s1986" xml:space="preserve">eſt <lb/>plus petit que l’angle V, O, L.</s> <s xml:id="echoid-s1987" xml:space="preserve">, & </s> <s xml:id="echoid-s1988" xml:space="preserve">que <lb/>l’angle R, O, L. </s> <s xml:id="echoid-s1989" xml:space="preserve">eſt le plus grand des trois. <lb/></s> <s xml:id="echoid-s1990" xml:space="preserve">Ce plus grand angle des trois eſt donc celui <lb/>des rayons primitifs rouges: </s> <s xml:id="echoid-s1991" xml:space="preserve">cet autre mi-<lb/>toyen eſt celui des primitifs verds; </s> <s xml:id="echoid-s1992" xml:space="preserve">ce plus <lb/>petit P, O, L. </s> <s xml:id="echoid-s1993" xml:space="preserve">eſt celui des primitifs pour-<lb/>pres. </s> <s xml:id="echoid-s1994" xml:space="preserve">Donc vous devez voir l’Iris rouge <lb/>dans ſon bord extérieur, verte dans ſon mi-<lb/>lieu, pourpre & </s> <s xml:id="echoid-s1995" xml:space="preserve">violette dans ſa bande in-<lb/>térieure. </s> <s xml:id="echoid-s1996" xml:space="preserve">Remarquez ſeulement que la der- <pb o="153" file="0173" n="173" rhead="DE NEUTON."/> niére couche violette eſt toujours teinte de <lb/>la couleur blanchâtre de la nuée dans la-<lb/>quelle elle ſe perd.</s> <s xml:id="echoid-s1997" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s1998" xml:space="preserve">Vous concevez donc aiſément que vous <lb/>ne voyez ces goûtes que ſous les rayons <lb/>efficaces parvenus à vos yeux après une <lb/>reflexion & </s> <s xml:id="echoid-s1999" xml:space="preserve">deux réfractions, & </s> <s xml:id="echoid-s2000" xml:space="preserve">parvenus <lb/>ſous des angles déterminés. </s> <s xml:id="echoid-s2001" xml:space="preserve">Que votre œil <lb/>change de place, qu’au lieu d’être en O. </s> <s xml:id="echoid-s2002" xml:space="preserve">il <lb/>ſoit en T. </s> <s xml:id="echoid-s2003" xml:space="preserve">ce ne ſont plus les mêmes rayons <lb/>que vous voyez: </s> <s xml:id="echoid-s2004" xml:space="preserve">la bande qui vous donnoit <lb/>du rouge vous donne alors de l’orangé, ou <lb/>du verd, ainſi du reſte; </s> <s xml:id="echoid-s2005" xml:space="preserve">& </s> <s xml:id="echoid-s2006" xml:space="preserve">à chaque mouve-<lb/>ment de tête vous voyez une Iris nouvelle.</s> <s xml:id="echoid-s2007" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2008" xml:space="preserve">Ce premier Arc-en-Ciel bien conçu, vous <lb/>aurez aiſément l’intelligence du ſecond que <lb/>l’on voit d’ordinaire qui embraſſe ce pre-<lb/>mier, & </s> <s xml:id="echoid-s2009" xml:space="preserve">qu’on appelle le faux Arc-en-Ciel, <lb/>parce que ſes couleurs ſont moins vives, & </s> <s xml:id="echoid-s2010" xml:space="preserve"><lb/>qu’elles ſont dans un ordre renverſé.</s> <s xml:id="echoid-s2011" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2012" xml:space="preserve">Pour que vous puiſſiez voir deux Arcs-en-<lb/> <anchor type="note" xlink:label="note-0173-01a" xlink:href="note-0173-01"/> Ciel, il ſuffit que la nuée ſoit aſſez étendue <lb/>& </s> <s xml:id="echoid-s2013" xml:space="preserve">aſſez épaiſſe. </s> <s xml:id="echoid-s2014" xml:space="preserve">Cet Arc, qui ſe peint ſur <lb/>le premier & </s> <s xml:id="echoid-s2015" xml:space="preserve">qui l’embraſſe, eſt formé de <pb o="154" file="0174" n="174" rhead="DE LA PHILOSOPHIE"/> même par des rayons que le Soleil darde <lb/>dans ces goûtes de pluye, qui s’y rompent, <lb/>qui s’y réflechiſſent de façon, que chaque <lb/>rangée des goûtes vous envoye auſſi des <lb/>rayons primitifs; </s> <s xml:id="echoid-s2016" xml:space="preserve">cette goûte un rayon <lb/>rouge, cette autre goûte un rayon violet.</s> <s xml:id="echoid-s2017" xml:space="preserve"/> </p> <div xml:id="echoid-div91" type="float" level="2" n="8"> <note position="right" xlink:label="note-0173-01" xlink:href="note-0173-01a" xml:space="preserve">Les <lb/>deux <lb/>Arcs-<lb/>en-Ciel.</note> </div> <p> <s xml:id="echoid-s2018" xml:space="preserve">Mais tout ſe fait dans ce grand Arc d’une <lb/>maniere oppoſée à ce qui ſe paſſe dans le <lb/>petit; </s> <s xml:id="echoid-s2019" xml:space="preserve">pourquoi cela? </s> <s xml:id="echoid-s2020" xml:space="preserve">C’eſt que votre œil <lb/>qui reçoit les rayons efficaces du petit Arc <lb/>venus du Soleil dans la partie ſupérieure des <lb/>goûtes, reçoit au contraire les rayons du <lb/>grandArc venus par la partie baſſe des goûtes.</s> <s xml:id="echoid-s2021" xml:space="preserve"/> </p> <figure> <image file="0174-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0174-01"/> </figure> <pb o="155" file="0175" n="175" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s2022" xml:space="preserve">Vous appercevez que les goûtes d’eau du <lb/>petit Arc reçoivent les rayons du Soleil par <lb/>la partie ſupérieure, par le haut de chaque <lb/>goûte; </s> <s xml:id="echoid-s2023" xml:space="preserve">les goûtes du grand Arc - en - Ciel <lb/>au contraire reçoivent les rayons qui par-<lb/>viennent par leur partie baſſe. </s> <s xml:id="echoid-s2024" xml:space="preserve">Rien ne <lb/>vous ſera, je crois, plus facile que de con-<lb/>cevoir comment les rayons ſe réflechiſſent <lb/>deux fois dans les goûtes de ce grand Arc-<lb/>en - Ciel, & </s> <s xml:id="echoid-s2025" xml:space="preserve">comment ces rayons deux fois <lb/>réfractés, & </s> <s xml:id="echoid-s2026" xml:space="preserve">deux fois réflechis, vous don-<lb/>nent une Iris dans un ordre oppoſé à la pre-<lb/>miere, & </s> <s xml:id="echoid-s2027" xml:space="preserve">plus affaiblie de couleur. </s> <s xml:id="echoid-s2028" xml:space="preserve">Vous <lb/>venez de voir que les rayons entrent ainſi <lb/>dans la petite partie baſſe des goûtes d’eau <lb/>de cette Iris extérieure.</s> <s xml:id="echoid-s2029" xml:space="preserve"/> </p> <figure> <image file="0175-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0175-01"/> </figure> <pb o="156" file="0176" n="176" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s2030" xml:space="preserve">Une maſſe de rayons ſe préſente à la <lb/>ſurface de la goûte en G. </s> <s xml:id="echoid-s2031" xml:space="preserve">là une partie de <lb/>ces rayons ſe réfracte en dedans, & </s> <s xml:id="echoid-s2032" xml:space="preserve">une <lb/>autre s’éparpille en dehors; </s> <s xml:id="echoid-s2033" xml:space="preserve">voilà déja une <lb/>perte de rayons pour l’œil. </s> <s xml:id="echoid-s2034" xml:space="preserve">La partie réfrac-<lb/>tée parvient en H. </s> <s xml:id="echoid-s2035" xml:space="preserve">une moitie de cette par-<lb/>tie s’échappe dans l’air en ſortant de la goû-<lb/>te, & </s> <s xml:id="echoid-s2036" xml:space="preserve">eſt encore perdue pour vous. </s> <s xml:id="echoid-s2037" xml:space="preserve">Le peu <lb/>qui s’eſt conſervé dans la goûte, s’en va en <lb/>K. </s> <s xml:id="echoid-s2038" xml:space="preserve">là une partie s’échappe encore: </s> <s xml:id="echoid-s2039" xml:space="preserve">troiſiè-<lb/>me diminution. </s> <s xml:id="echoid-s2040" xml:space="preserve">Ce qui en eſt reſté en K. </s> <s xml:id="echoid-s2041" xml:space="preserve">s’en <lb/>va en M. </s> <s xml:id="echoid-s2042" xml:space="preserve">& </s> <s xml:id="echoid-s2043" xml:space="preserve">à cette émergence en M.</s> <s xml:id="echoid-s2044" xml:space="preserve">, une <lb/>partie s’éparpille encore: </s> <s xml:id="echoid-s2045" xml:space="preserve">quatrième dimi-<lb/>nution; </s> <s xml:id="echoid-s2046" xml:space="preserve">& </s> <s xml:id="echoid-s2047" xml:space="preserve">ce qui en reſte parvient enfin <lb/>dans la ligne M, N. </s> <s xml:id="echoid-s2048" xml:space="preserve">Voilà donc dans cette <lb/>goûte autant de réfractions que dans les <lb/>goûtes du petit Arc; </s> <s xml:id="echoid-s2049" xml:space="preserve">mais il y a comme <lb/>vous voyez deux réflexions au lieu d’une <lb/>dans ce grand Arc. </s> <s xml:id="echoid-s2050" xml:space="preserve">Il ſe perd donc le dou-<lb/>ble de la lumiere dans ce grand Arc où la <lb/>lumiere ſe réflechit deux fois, & </s> <s xml:id="echoid-s2051" xml:space="preserve">il s’en <lb/>perd la moitié moins dans le petit Arc in-<lb/>térieur, où les goûtes n’éprouvent qu’une <lb/>réflexion. </s> <s xml:id="echoid-s2052" xml:space="preserve">Il eſt donc démontré que l’Arc-<lb/>en-Ciel extérieur doit toujours être de moi-<lb/>tié plus faible en couleur que le petit Arc <pb o="157" file="0177" n="177" rhead="DE NEUTON."/> intérieur. </s> <s xml:id="echoid-s2053" xml:space="preserve">Il eſt auſſi démontré par ce dou-<lb/>ble chemin que font les rayons, qu’ils doi-<lb/>vent parvenir à vos yeux dans un ſens op-<lb/>poſé à celui du premier Arc, car votre œil <lb/>eſt placé en O.</s> <s xml:id="echoid-s2054" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2055" xml:space="preserve">Dans cette place O. </s> <s xml:id="echoid-s2056" xml:space="preserve">il reçoit les rayons <lb/>les moins réfrangibles de la premiere bande <lb/>extérieure du petit Arc, & </s> <s xml:id="echoid-s2057" xml:space="preserve">il doit recevoir <lb/>les plus réfrangibles de la premiere bande <lb/>extérieure de ce ſecond Arc; </s> <s xml:id="echoid-s2058" xml:space="preserve">ces plus ré-<lb/>frangibles ſont les violets. </s> <s xml:id="echoid-s2059" xml:space="preserve">Voici done les deux <lb/>Arcs-en-Ciel ici dans leur ordre, en ne met-<lb/>tant que trois couleurs pour éviter la con-<lb/>fuſion.</s> <s xml:id="echoid-s2060" xml:space="preserve"/> </p> <figure> <image file="0177-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0177-01"/> </figure> <pb o="158" file="0178" n="178" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s2061" xml:space="preserve">Il ne reſte plus qu’à voir pourquoi ces cou-<lb/> <anchor type="note" xlink:label="note-0178-01a" xlink:href="note-0178-01"/> leurs ſont toujours apperçues ſous une figure <lb/>circulaire. </s> <s xml:id="echoid-s2062" xml:space="preserve">Conſidérez cette ligne O, Z. </s> <s xml:id="echoid-s2063" xml:space="preserve">qui <lb/>paſſe par votre œil. </s> <s xml:id="echoid-s2064" xml:space="preserve">Soient conçues ſe <lb/>mouvoir ces deux boules toujours à égale <lb/>diſtance de votre œil, elles décriront des <lb/>baſes de cones, dont la pointe ſera tou-<lb/>jours dans votre œil.</s> <s xml:id="echoid-s2065" xml:space="preserve"/> </p> <div xml:id="echoid-div92" type="float" level="2" n="9"> <note position="left" xlink:label="note-0178-01" xlink:href="note-0178-01a" xml:space="preserve">Cephé-<lb/>nomêne <lb/>vu tou-<lb/>jours en <lb/>demi-<lb/>cercle.</note> </div> <figure> <image file="0178-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0178-01"/> </figure> <p> <s xml:id="echoid-s2066" xml:space="preserve">Concevez que le rayon de cette goûte <lb/>d’eau R. </s> <s xml:id="echoid-s2067" xml:space="preserve">venant à votre œil O. </s> <s xml:id="echoid-s2068" xml:space="preserve">tourne au-<lb/>tour de cette ligne O, Z. </s> <s xml:id="echoid-s2069" xml:space="preserve">comme autour <lb/>d’unaxe, faiſant toujours, par exemple, un <lb/>angle avec votre œil de 42 degrez deux <lb/>minutes; </s> <s xml:id="echoid-s2070" xml:space="preserve">il eſt clair que cette goûte décrira <lb/>un cercle qui vous paraitra rouge. </s> <s xml:id="echoid-s2071" xml:space="preserve">Que <pb o="159" file="0179" n="179" rhead="DE NEUTON."/> cette autre goûte V. </s> <s xml:id="echoid-s2072" xml:space="preserve">ſoit conçue tourner de <lb/>même, faiſant toujours un autre angle de <lb/>quarante degrez dix-ſept minutes, elle for-<lb/>mera un cercle violet; </s> <s xml:id="echoid-s2073" xml:space="preserve">toutes les goûtes qui <lb/>ſeront dans ce plan formeront donc un cer-<lb/>cle violet, & </s> <s xml:id="echoid-s2074" xml:space="preserve">les goûtes qui ſont dans le <lb/>plan de la goûte R. </s> <s xml:id="echoid-s2075" xml:space="preserve">feront un cercle rouge. <lb/></s> <s xml:id="echoid-s2076" xml:space="preserve">Vous verrez donc cette Iris comme un cer-<lb/>cle, mais vous ne voyez pas tout un cer-<lb/>cle; </s> <s xml:id="echoid-s2077" xml:space="preserve">parce que la Terre le coupe, vous ne <lb/>voyez qu’un Arc, une portion de cercle.</s> <s xml:id="echoid-s2078" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2079" xml:space="preserve">La plûpart de ces vérités ne purent encore <lb/>être apperçues ni par Antonio de Dominis, <lb/>ni par Deſcartes: </s> <s xml:id="echoid-s2080" xml:space="preserve">ils ne pouvoient ſavoir <lb/>pourquoi ces différens angles donnoient dif-<lb/>férentes couleurs; </s> <s xml:id="echoid-s2081" xml:space="preserve">mais c’étoit beaucoup <lb/>d’avoir trouvél’Art. </s> <s xml:id="echoid-s2082" xml:space="preserve">Les fineſſes de l’Art ſont <lb/>rarement dues aux premiers inventeurs. </s> <s xml:id="echoid-s2083" xml:space="preserve">Ne <lb/>pouvant donc deviner que les couleurs dé-<lb/>pendoient de la réfrangibilité des rayons, <lb/>que chaque rayon contenoit en ſoi une cou-<lb/>leur primitive, que la différente attraction de <lb/>ces rayons faiſoit leur réfrangibilité, & </s> <s xml:id="echoid-s2084" xml:space="preserve">opé-<lb/>roit ces écartemens qui font les différens <lb/>angles, Deſcartes s’abandonna à ſon eſprit <lb/>d’invention pour expliquer les couleurs de <pb o="160" file="0180" n="180" rhead="DE LA PHILOSOPHIE"/> l’Arc-en-Ciel. </s> <s xml:id="echoid-s2085" xml:space="preserve">Il y employa le tournoye-<lb/>ment imaginaire de ces globules & </s> <s xml:id="echoid-s2086" xml:space="preserve">cette <lb/>tendance au tournoyement; </s> <s xml:id="echoid-s2087" xml:space="preserve">preuve de génie, <lb/>mais preuve d’erreur. </s> <s xml:id="echoid-s2088" xml:space="preserve">C’eſt ainſi que pour <lb/>expliquer la ſyſtole & </s> <s xml:id="echoid-s2089" xml:space="preserve">la diaſtole du cœur, il <lb/>imagina un mouvement & </s> <s xml:id="echoid-s2090" xml:space="preserve">une conforma-<lb/>tion dans ce viſcère, dont tous les Anato-<lb/>miſtes ont reconnu la fauſſeté. </s> <s xml:id="echoid-s2091" xml:space="preserve">Deſcartes <lb/>auroit été le plus grand Philoſophe de la <lb/>Terre, s’il eût moins inventé.</s> <s xml:id="echoid-s2092" xml:space="preserve"/> </p> <figure> <image file="0180-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0180-01"/> </figure> <pb file="0181" n="181"/> <figure> <image file="0181-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0181-01"/> </figure> </div> <div xml:id="echoid-div94" type="section" level="1" n="20"> <head xml:id="echoid-head33" xml:space="preserve">CHAPITRE DOUZE.</head> <head xml:id="echoid-head34" style="it" xml:space="preserve">Nouvelles découvertes ſur la cauſe des couleurs <lb/>qui confirment la doctrine précédente. Dé-<lb/>monſtration que les couleurs ſont occa-<lb/>ſionnées par l’épaiſſeur des parties <lb/>qui compoſent les corps.</head> <p> <s xml:id="echoid-s2093" xml:space="preserve">PAr tout ce qui a été dit juſqu’à préſent <lb/>il réſulte donc, que toutes les couleurs <lb/>nous viennent du mêlange des ſept couleurs <lb/>primordiales que l’Arc-en-Ciel & </s> <s xml:id="echoid-s2094" xml:space="preserve">le priſme <lb/>nous font voir diſtinctement.</s> <s xml:id="echoid-s2095" xml:space="preserve"/> </p> <pb o="162" file="0182" n="182" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s2096" xml:space="preserve">Les corps les plus propres à réflechir des <lb/>rayons rouges, & </s> <s xml:id="echoid-s2097" xml:space="preserve">dont les parties abſor-<lb/>bent ou laiſſent paſſer les autres rayons, ſe-<lb/>ront rouges, & </s> <s xml:id="echoid-s2098" xml:space="preserve">ainſi du reſte. </s> <s xml:id="echoid-s2099" xml:space="preserve">Cela ne <lb/>veut pas dire que les parties de ces corps <lb/>réflechiſſent en effet les rayons rouges; </s> <s xml:id="echoid-s2100" xml:space="preserve">mais <lb/>qu’il y a un pouvoir, une force juſqu’ici in-<lb/>connue, qui réflechit ces rayons d’auprès <lb/>des ſurfaces & </s> <s xml:id="echoid-s2101" xml:space="preserve">du ſein des pores des corps.</s> <s xml:id="echoid-s2102" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2103" xml:space="preserve">Les couleurs ſont donc dans les rayons <lb/>du Soleil, & </s> <s xml:id="echoid-s2104" xml:space="preserve">rejailliſſent à nous d’auprès <lb/>des ſurfaces, & </s> <s xml:id="echoid-s2105" xml:space="preserve">des pores & </s> <s xml:id="echoid-s2106" xml:space="preserve">du vuide. <lb/></s> <s xml:id="echoid-s2107" xml:space="preserve">Cherchons à préfent en quoi conſiſte le pou-<lb/> <anchor type="note" xlink:label="note-0182-01a" xlink:href="note-0182-01"/> voir apparent des corps de nous réflechir <lb/>ces couleurs, ce qui fait que l’écarlate pa-<lb/>rait rouge, que les Prés ſont verds, qu’un <lb/>Ciel pur eſt bleu; </s> <s xml:id="echoid-s2108" xml:space="preserve">car dire que cela vient de <lb/>la différence de leurs parties, c’eſt dire une <lb/>choſe vague qui n’apprend rien du tout.</s> <s xml:id="echoid-s2109" xml:space="preserve"/> </p> <div xml:id="echoid-div94" type="float" level="2" n="1"> <note position="left" xlink:label="note-0182-01" xlink:href="note-0182-01a" xml:space="preserve">Con-<lb/>naiſſan-<lb/>ce plus <lb/>appro-<lb/>fondie <lb/>de la <lb/>forma-<lb/>tion des <lb/>cou-<lb/>leurs.</note> </div> <p> <s xml:id="echoid-s2110" xml:space="preserve">Un divertiſſement d’enfant, qui ſemble <lb/>n’avoir rien en ſoi que de mépriſable, don-<lb/>na à Mr. </s> <s xml:id="echoid-s2111" xml:space="preserve">Neuton la premiere idée de ces <lb/>nouvelles vérités que nous allons expliquer.</s> <s xml:id="echoid-s2112" xml:space="preserve"> <pb o="163" file="0183" n="183" rhead="DE NEUTON."/> Tout doit être pour un Philoſophe un ſujet <lb/> <anchor type="note" xlink:label="note-0183-01a" xlink:href="note-0183-01"/> de méditation, & </s> <s xml:id="echoid-s2113" xml:space="preserve">rien n’eſt petit à ſes yeux. <lb/></s> <s xml:id="echoid-s2114" xml:space="preserve">Il s’apperçut que dans ces bouteilles dè Sa <lb/>von que font les Enfants, les couleurs chan-<lb/>gent de moment en moment, en comptant <lb/>du haut de la boule à meſure que l’épaiſſeur <lb/>de cette boule diminue, juſqu’à ce qu’en-<lb/>fin la peſanteur de l’eau & </s> <s xml:id="echoid-s2115" xml:space="preserve">du ſavon qui <lb/>tombe toujours au fond, rompe l’équilibre <lb/>de cette ſphére legére, & </s> <s xml:id="echoid-s2116" xml:space="preserve">la faſſe évanouïr. </s> <s xml:id="echoid-s2117" xml:space="preserve"><lb/>Il en préſuma que les couleurs pourroient <lb/>bien dépendre de l’épaiſſeur des parties qui <lb/>compoſent les ſurfaces des corps, & </s> <s xml:id="echoid-s2118" xml:space="preserve">pour <lb/>s’en aſſûrer il fit les expériences ſuivantes.</s> <s xml:id="echoid-s2119" xml:space="preserve"/> </p> <div xml:id="echoid-div95" type="float" level="2" n="2"> <note position="right" xlink:label="note-0183-01" xlink:href="note-0183-01a" xml:space="preserve">Gran-<lb/>des vé-<lb/>rités ti-<lb/>rées <lb/>d’une <lb/>expé-<lb/>rience <lb/>commu-<lb/>ne.</note> </div> <p> <s xml:id="echoid-s2120" xml:space="preserve">Que deux cryſtaux ſe touchent en un <lb/> <anchor type="note" xlink:label="note-0183-02a" xlink:href="note-0183-02"/> point: </s> <s xml:id="echoid-s2121" xml:space="preserve">il n’importe qu’ils ſoient tous deux <lb/>convexes; </s> <s xml:id="echoid-s2122" xml:space="preserve">il ſuffit que le premier le ſoit, & </s> <s xml:id="echoid-s2123" xml:space="preserve"><lb/>qu’il ſoit poſé ſur l’autre en cette façon.</s> <s xml:id="echoid-s2124" xml:space="preserve"/> </p> <div xml:id="echoid-div96" type="float" level="2" n="3"> <note position="right" xlink:label="note-0183-02" xlink:href="note-0183-02a" xml:space="preserve">Expé-<lb/>rience <lb/>de Neu-<lb/>ton.</note> </div> <figure> <image file="0183-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0183-01"/> </figure> <p> <s xml:id="echoid-s2125" xml:space="preserve">Qu’on mette de l’eau entre ces deux ver-<lb/>res pour rendre plus ſenſible l’expérience <lb/>qui ſe fait auſſi dans l’air: </s> <s xml:id="echoid-s2126" xml:space="preserve">qu’on preſſe un <pb o="164" file="0184" n="184" rhead="DE LA PHILOSOPHIE"/> peu ces verres l’un contre l’autre, une <lb/>petite tache noire tranſparente parait au <lb/>point du contact des deux verres: </s> <s xml:id="echoid-s2127" xml:space="preserve">de ce <lb/>point entouré d’un peu d’eau ſe forment <lb/>des anneaux colorés dans le même ordre & </s> <s xml:id="echoid-s2128" xml:space="preserve"><lb/>de la même maniere que dans la bouteille <lb/>de ſavon: </s> <s xml:id="echoid-s2129" xml:space="preserve">enfin en meſurant le diamétre <lb/>de ces anneaux & </s> <s xml:id="echoid-s2130" xml:space="preserve">la convéxité du verre, <lb/> <anchor type="note" xlink:label="note-0184-01a" xlink:href="note-0184-01"/> Neuton détermina les différentes épaiſſeurs <lb/>des parties d’eau qui donnoient ces diffé-<lb/>rentes couleurs; </s> <s xml:id="echoid-s2131" xml:space="preserve">il calcula l’épaiſſeur néceſ-<lb/>ſaire à l’eau pour réflechir les rayons blancs: <lb/></s> <s xml:id="echoid-s2132" xml:space="preserve">Cette épaiſſeur eſt d’environ quatre parties <lb/>d’un pouce diviſé en un million, c’eſt-à-<lb/>dire, quatre millionêmes d’un pouce; </s> <s xml:id="echoid-s2133" xml:space="preserve">le <lb/>bleu azur & </s> <s xml:id="echoid-s2134" xml:space="preserve">les couleurs tirant ſur le violet <lb/>dépendent d’une épaiſſeur beaucoup moin-<lb/>dre. </s> <s xml:id="echoid-s2135" xml:space="preserve">Ainſi les vapeurs les plus petites qui <lb/>s’élevent de la Terre, & </s> <s xml:id="echoid-s2136" xml:space="preserve">qui colorent l’air <lb/>ſans nuages, étant d’une très-mince ſurface, <lb/>produiſent ce bleu céleſte qui charme la <lb/>vûe.</s> <s xml:id="echoid-s2137" xml:space="preserve"/> </p> <div xml:id="echoid-div97" type="float" level="2" n="4"> <note position="left" xlink:label="note-0184-01" xlink:href="note-0184-01a" xml:space="preserve">Les <lb/>cou-<lb/>leurs <lb/>dépen-<lb/>dent de <lb/>l’épaiſ-<lb/>ſeur des <lb/>parties <lb/>des <lb/>corps, <lb/>ſans que <lb/>ces par-<lb/>ties ré-<lb/>fléchiſ-<lb/>ſent el-<lb/>les-mê-<lb/>mes la <lb/>lumiere.</note> </div> <p> <s xml:id="echoid-s2138" xml:space="preserve">D’autres expériences auſſi fines ont en-<lb/>core appuyé cette découverte, que c’eſt <lb/>à l’épaiſſeur des ſurfaces que ſont attachées <lb/>les couleurs.</s> <s xml:id="echoid-s2139" xml:space="preserve"/> </p> <pb o="165" file="0185" n="185" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s2140" xml:space="preserve">Le même corps qui étoit verd, quand il <lb/>étoit un peu épais, eſt devenu bleu, quand <lb/>il a été rendu aſſez mince pour ne réflechir <lb/>que les rayons bleus, & </s> <s xml:id="echoid-s2141" xml:space="preserve">pour laiſſer paſſer <lb/>les autres. </s> <s xml:id="echoid-s2142" xml:space="preserve">Ces vérités d’une recherche ſi <lb/>délicate, & </s> <s xml:id="echoid-s2143" xml:space="preserve">qui ſembloient ſe dérober à la <lb/>vûe humaine, méritent bien d’être ſuivies <lb/>de près; </s> <s xml:id="echoid-s2144" xml:space="preserve">cette partie de la Philoſophie eſt <lb/>un Microſcope avec lequel notre eſprit dé-<lb/>couvre des grandeurs infiniment petites.</s> <s xml:id="echoid-s2145" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2146" xml:space="preserve">Tous les corps ſont tranſparens, il n’y a <lb/> <anchor type="note" xlink:label="note-0185-01a" xlink:href="note-0185-01"/> qu’à les rendre aſſez minces, pour que les <lb/>rayons ne trouvant qu’une lame, qu’une <lb/>feuille à traverſer, paſſent à travers cette <lb/>lame. </s> <s xml:id="echoid-s2147" xml:space="preserve">Ainſi quand l’Or en feuilles eſt ex-<lb/>poſé à un trou dans une chambre obſcure, <lb/>il renvoye par ſa ſurface des rayons jaunes <lb/>qui ne peuvent ſe tranſmettre à travers ſa <lb/>ſubſtance, & </s> <s xml:id="echoid-s2148" xml:space="preserve">il tranſmet dans la chambre <lb/>obſcure des rayons verds, de ſorte que l’Or <lb/>produit alors une couleur verte; </s> <s xml:id="echoid-s2149" xml:space="preserve">nouvelle <lb/>confirmation que les couleurs dépendent <lb/>des différentes épaiſſeurs.</s> <s xml:id="echoid-s2150" xml:space="preserve"/> </p> <div xml:id="echoid-div98" type="float" level="2" n="5"> <note position="right" xlink:label="note-0185-01" xlink:href="note-0185-01a" xml:space="preserve">Tous <lb/>les <lb/>corps <lb/>ſont <lb/>trans-<lb/>parens.</note> </div> <p> <s xml:id="echoid-s2151" xml:space="preserve">Une preuve encore plus forte, c’eſt que <pb o="166" file="0186" n="186" rhead="DE LA PHILOSOPHIE"/> dans l’expérience de ce verre convexe-plan, <lb/> <anchor type="note" xlink:label="note-0186-01a" xlink:href="note-0186-01"/> touchant en un point ce verre convexe, l’eau <lb/>n’eſt pas le ſeul élément qui dans des épaiſ-<lb/>ſeurs diverſes donne diverſes couleurs: </s> <s xml:id="echoid-s2152" xml:space="preserve">l’air <lb/>fait le méme effet, ſeulement les anneaux <lb/>colorés qu’il produit entre les deux verres, <lb/>ont plus de diamétre que ceux de l’eau.</s> <s xml:id="echoid-s2153" xml:space="preserve"/> </p> <div xml:id="echoid-div99" type="float" level="2" n="6"> <note position="left" xlink:label="note-0186-01" xlink:href="note-0186-01a" xml:space="preserve">Preuve <lb/>que les <lb/>cou-<lb/>leurs <lb/>dépen-<lb/>dent <lb/>des é-<lb/>paiſ-<lb/>ſeurs.</note> </div> <p> <s xml:id="echoid-s2154" xml:space="preserve">Il y a donc une proportion ſecrete éta-<lb/>blie par la Nature entre la force des parties <lb/>conſtituantes de tous les corps & </s> <s xml:id="echoid-s2155" xml:space="preserve">les rayons <lb/>primitifs qui colorent les corps; </s> <s xml:id="echoid-s2156" xml:space="preserve">les lames <lb/>les plus minces donneront les couleurs les <lb/>plus faibles, & </s> <s xml:id="echoid-s2157" xml:space="preserve">pour donner le noir il fau-<lb/>dra juſtement la même épaiſſeur, ou plutôt <lb/>la même ténuité, la même mincité, qu’en a <lb/>la petite partie ſupérieure de la boule de <lb/>ſavon, dans laquelle on appercevoit un pe-<lb/>tit point noir, ou bien la même ténuité qu’en <lb/>a le point de contact du verre convexe & </s> <s xml:id="echoid-s2158" xml:space="preserve"><lb/>du verre plat, lequel contact produit auſſi <lb/>une tache noire.</s> <s xml:id="echoid-s2159" xml:space="preserve"/> </p> <note position="left" xml:space="preserve">Sans <lb/>que les <lb/>parties <lb/>ſolides <lb/>ren-<lb/>voyent <lb/>en effet <lb/>la lu-<lb/>miere.</note> <p> <s xml:id="echoid-s2160" xml:space="preserve">Mais encore une fois qu’on ne croye pas <lb/>que les corps renvoyent la lumiere par leurs <lb/>parties ſolides, ſur ce que les couleurs dé-<lb/>pendent de l’épaiſſeur des parties: </s> <s xml:id="echoid-s2161" xml:space="preserve">il y a <pb o="167" file="0187" n="187" rhead="DE NEUTON."/> un pouvoir attaché à cette épaiſſeur, un <lb/>pouvoir qui agit auprès de la ſurface; </s> <s xml:id="echoid-s2162" xml:space="preserve">mais <lb/>ce n’eſt point du tout la ſurface ſolide qui <lb/>repouſſe, qui réflechit. </s> <s xml:id="echoid-s2163" xml:space="preserve">Cette vérité ſera <lb/>encore plus viſiblement démontrée dans le <lb/>chapitre ſuivant qu’elle n’a été prouvée juſ-<lb/>qu’ici. </s> <s xml:id="echoid-s2164" xml:space="preserve">Il me ſemble que le Lecteur doit <lb/>être venu au point où rien ne doit plus le <lb/>ſurprendre; </s> <s xml:id="echoid-s2165" xml:space="preserve">mais ce qu’il vient de voir me-<lb/>ne encore plus loin qu’on ne penſe, & </s> <s xml:id="echoid-s2166" xml:space="preserve">tant <lb/>de ſingularités ne ſont, pour ainſi dire, que <lb/>les frontiéres d’un Nouveau Monde.</s> <s xml:id="echoid-s2167" xml:space="preserve"/> </p> <figure> <image file="0187-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0187-01"/> </figure> <pb file="0188" n="188"/> <figure> <image file="0188-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0188-01"/> </figure> </div> <div xml:id="echoid-div101" type="section" level="1" n="21"> <head xml:id="echoid-head35" xml:space="preserve">CHAPITRE TREIZE.</head> <head xml:id="echoid-head36" style="it" xml:space="preserve">Suites de ces découvertes; Action mutuelle des <lb/>Corps ſur la lumiere.</head> <p> <s xml:id="echoid-s2168" xml:space="preserve">LA réfléxion de la lumiere, ſon infléxion, <lb/>ſa réfraction, ſa réfrangibilité, étant <lb/>connues, l’origine des couleurs étant dé-<lb/>couverte, & </s> <s xml:id="echoid-s2169" xml:space="preserve">l’épaiſſeur même des corps <lb/>néceſſaire pour occaſionner certaines cou-<lb/>leurs étant déterminée: </s> <s xml:id="echoid-s2170" xml:space="preserve">il nous reſte enco-<lb/>re à examiner deux propriétés de la lumie-<lb/>re non moins étonnantes & </s> <s xml:id="echoid-s2171" xml:space="preserve">non moins nou-<lb/>velles. </s> <s xml:id="echoid-s2172" xml:space="preserve">La premiere de ces propriétés eſt <pb o="169" file="0189" n="189" rhead="DE NEUTON."/> ce pouvoir même qui agit près des ſurfaces, <lb/>c’eſt une action mutuelle de la lumiere ſur <lb/>les corps, & </s> <s xml:id="echoid-s2173" xml:space="preserve">des corps ſur la lumiere.</s> <s xml:id="echoid-s2174" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2175" xml:space="preserve">La ſeconde eſt un rapport qui ſe trouve <lb/>entre les couleurs & </s> <s xml:id="echoid-s2176" xml:space="preserve">les tons de la Muſique, <lb/>entre les Objets de la vûe & </s> <s xml:id="echoid-s2177" xml:space="preserve">ceux de l’ouïe; <lb/></s> <s xml:id="echoid-s2178" xml:space="preserve">nous allons rendre compte de ces deux eſpè-<lb/>ces de miracles, & </s> <s xml:id="echoid-s2179" xml:space="preserve">c’eſt par-là que nous fi-<lb/>nirons cette petite introduction à l’Optique <lb/>de Neuton.</s> <s xml:id="echoid-s2180" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2181" xml:space="preserve">Vous avez vu que ces deux cryſtaux ſe <lb/>touchant en un point, produiſent des an-<lb/>neaux de couleurs différentes, rouges, <lb/>bleus, verds, blancs, &</s> <s xml:id="echoid-s2182" xml:space="preserve">c. </s> <s xml:id="echoid-s2183" xml:space="preserve">Faites cette même <lb/>épreuve dans une chambre obſcure, où vous <lb/>avez fait l’expérience du priſme expoſé à la <lb/>lumiere qui lui vient par un trou. </s> <s xml:id="echoid-s2184" xml:space="preserve">Vous <lb/>vous ſouvenez que dans cette expérience <lb/>du priſme vous avez vu la décompoſition <lb/>de la lumiere & </s> <s xml:id="echoid-s2185" xml:space="preserve">l’anatomie de ſes rayons: <lb/></s> <s xml:id="echoid-s2186" xml:space="preserve">vous placiez une feuille de papier blanc vis-<lb/>à-vis ce priſme: </s> <s xml:id="echoid-s2187" xml:space="preserve">ce papier recevoit les ſept <lb/>couleurs primitives, chacune dans leur or-<lb/> <anchor type="note" xlink:label="note-0189-01a" xlink:href="note-0189-01"/> dre: </s> <s xml:id="echoid-s2188" xml:space="preserve">maintenant expoſez vos deux verres à <lb/>tel rayon coloré qu’il vous plaira, réflechi <pb o="170" file="0190" n="190" rhead="DE LA PHILOSOPHIE"/> de ce papier, vous y verrez toujours entre <lb/>ces verres ſe former des anneaux colorés; <lb/></s> <s xml:id="echoid-s2189" xml:space="preserve">mais tous ces anneaux alors ſont de la cou-<lb/>leur des rayons qui vous viennent du pa-<lb/>pier. </s> <s xml:id="echoid-s2190" xml:space="preserve">Expoſez vos verres à la lumiere des <lb/>rayons rouges, vous n’aurez entre vos ver-<lb/>res que des anneaux rouges; </s> <s xml:id="echoid-s2191" xml:space="preserve"><lb/> <anchor type="figure" xlink:label="fig-0190-01a" xlink:href="fig-0190-01"/> Mais ce qui doit ſurprendre, c’eſt qu’entre <lb/>chacun de ces anneaux rouges il y a un an-<lb/>neau tout noir. </s> <s xml:id="echoid-s2192" xml:space="preserve">Pour conſtater encore plus <lb/>ce fait & </s> <s xml:id="echoid-s2193" xml:space="preserve">les ſingularités qui y ſont atta-<lb/>tachées, préſentez vos deux verres, non <lb/>plus au papier, mais au priſme, de façon <lb/>que l’un des rayons qui s’échappent de ce <pb o="171" file="0191" n="191" rhead="DE NEUTON."/> priſme, un rouge, par exemple, vienne à <lb/>tomber ſur ces verres, il ne ſe forme en-<lb/>core que des anneaux rouges entre les an-<lb/>neaux noirs; </s> <s xml:id="echoid-s2194" xml:space="preserve">mettez derriére vos verres la <lb/>feuille de papier blanc, chaque anneau noir <lb/>produit ſur cette feuille de papier un an-<lb/>neau rouge, & </s> <s xml:id="echoid-s2195" xml:space="preserve">chaque anneau rouge, étant <lb/>réflechi vers vous, produit du noir ſur le <lb/>papier.</s> <s xml:id="echoid-s2196" xml:space="preserve"/> </p> <div xml:id="echoid-div101" type="float" level="2" n="1"> <note position="right" xlink:label="note-0189-01" xlink:href="note-0189-01a" xml:space="preserve">Expé-<lb/>rience <lb/>très-fin-<lb/>guliére.</note> <figure xlink:label="fig-0190-01" xlink:href="fig-0190-01a"> <image file="0190-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0190-01"/> </figure> </div> <figure> <image file="0191-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0191-01"/> </figure> <p> <s xml:id="echoid-s2197" xml:space="preserve">Il réſulte de cette expérience que l’air <lb/>ou l’eau qui eſt entre vos verres, réflechit <lb/>en un endroit la lumiere & </s> <s xml:id="echoid-s2198" xml:space="preserve">en un autre en-<lb/>droit la laiſſe paſſer, la tranſmet. </s> <s xml:id="echoid-s2199" xml:space="preserve">J’avoue <lb/>que je ne peux aſſez admirer ici cette pro-<lb/>fondeur de recherche, cette ſagacité plus <lb/>qu’humaine, avec laquelle Neuton à pour- <pb o="172" file="0192" n="192" rhead="DE LA PHILOSOPHIE"/> ſuivi ces vérités ſi imperceptibles; </s> <s xml:id="echoid-s2200" xml:space="preserve">il a re-<lb/>connu par les meſures & </s> <s xml:id="echoid-s2201" xml:space="preserve">par le calcul ces <lb/>étranges proportions-ci.</s> <s xml:id="echoid-s2202" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2203" xml:space="preserve">Au point de contact des deux verres, il <lb/>ne ſe réflechit à vos yeux aucune lumiere: <lb/></s> <s xml:id="echoid-s2204" xml:space="preserve">immédiatement après ce contact, la pre-<lb/>miere petite lame d’air ou d’eau, qui touche <lb/>à ce point noir, vous réflechit des rayons: </s> <s xml:id="echoid-s2205" xml:space="preserve"><lb/>la ſeconde lame eſt deux fois épaiſſe comme <lb/>la premiere, & </s> <s xml:id="echoid-s2206" xml:space="preserve">ne réflechit rien: </s> <s xml:id="echoid-s2207" xml:space="preserve">la troiſiè-<lb/>me lame eſt triple en épaiſſeur de la pre-<lb/>miere, & </s> <s xml:id="echoid-s2208" xml:space="preserve">réflechit: </s> <s xml:id="echoid-s2209" xml:space="preserve">la quatrième lame eſt <lb/>quatre fois plus épaiſſe, & </s> <s xml:id="echoid-s2210" xml:space="preserve">ne réflechit point: </s> <s xml:id="echoid-s2211" xml:space="preserve"><lb/>la cinquième eſt cinq fois plus épaiſſe, & </s> <s xml:id="echoid-s2212" xml:space="preserve"><lb/>tranſmet; </s> <s xml:id="echoid-s2213" xml:space="preserve">& </s> <s xml:id="echoid-s2214" xml:space="preserve">la ſixième ſix fois plus épaiſſe, <lb/>ne tranſmet rien.</s> <s xml:id="echoid-s2215" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2216" xml:space="preserve">De ſorte que les anneaux noirs vont en <lb/>cette progreſſion 0, 2, 4, 6, 8. </s> <s xml:id="echoid-s2217" xml:space="preserve">& </s> <s xml:id="echoid-s2218" xml:space="preserve">les anneaux <lb/>lumineux & </s> <s xml:id="echoid-s2219" xml:space="preserve">colorés en cette progreſ-<lb/>ſion, 1, 3, 5, 7, 9.</s> <s xml:id="echoid-s2220" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2221" xml:space="preserve">Ce qui ſe paſſe dans cette expérience ar-<lb/> <anchor type="note" xlink:label="note-0192-01a" xlink:href="note-0192-01"/> rive de même dans tous les corps, qui tous <lb/>réflechiſſent une partie de la lumiere & </s> <s xml:id="echoid-s2222" xml:space="preserve">en <lb/>reçoivent dans leurs ſubſtances une autre <pb o="173" file="0193" n="193" rhead="DE NEUTON."/> partie. </s> <s xml:id="echoid-s2223" xml:space="preserve">C’eſt donc encore une proprieté <lb/>démontrée à l’eſprit & </s> <s xml:id="echoid-s2224" xml:space="preserve">aux yeux, que les <lb/>ſurſaces ſolides ne ſont point ce qui réfle-<lb/>chit les rayons. </s> <s xml:id="echoid-s2225" xml:space="preserve">Car ſi les ſurfaces ſolides <lb/>réflechiſſoient en effet; </s> <s xml:id="echoid-s2226" xml:space="preserve">1<emph style="super">0</emph>. </s> <s xml:id="echoid-s2227" xml:space="preserve">le point où les <lb/>deux verres ſe touchent réflechiroit & </s> <s xml:id="echoid-s2228" xml:space="preserve">ne <lb/>ſeroit point obſcur. </s> <s xml:id="echoid-s2229" xml:space="preserve">2<emph style="super">0</emph>. </s> <s xml:id="echoid-s2230" xml:space="preserve">Chaque partie ſo-<lb/>lide qui vous donneroit une ſeule eſpèce de <lb/>rayons devroit auſſi vous renvoyer toutes <lb/>les eſpèces de rayons. </s> <s xml:id="echoid-s2231" xml:space="preserve">3<emph style="super">0</emph>. </s> <s xml:id="echoid-s2232" xml:space="preserve">Les parties ſo-<lb/>lides ne tranſmettroient point la lumiere en <lb/>un endroit & </s> <s xml:id="echoid-s2233" xml:space="preserve">ne la réflechiroient pas en <lb/>un autre endroit, car étant toutes ſolides <lb/>toutes réflechiroient. </s> <s xml:id="echoid-s2234" xml:space="preserve">4<emph style="super">0</emph>. </s> <s xml:id="echoid-s2235" xml:space="preserve">Si les parties ſo-<lb/>lides réflechiſſoient la lumiere, il ſeroit im-<lb/>poſſible de ſe voir dans un miroir, comme <lb/>nous l’avons dit, puiſque le miroir étant <lb/>ſillonné & </s> <s xml:id="echoid-s2236" xml:space="preserve">raboteux, il ne pourroit ren-<lb/>voyer la lumiere d’une maniere réguliére. <lb/></s> <s xml:id="echoid-s2237" xml:space="preserve">Il eſt donc indubitable qu’il y a un pouvoir <lb/>agiſſant ſur les corps ſans toucher aux corps, <lb/>& </s> <s xml:id="echoid-s2238" xml:space="preserve">que ce pouvoir agit entre les corps & </s> <s xml:id="echoid-s2239" xml:space="preserve"><lb/>la lumiere. </s> <s xml:id="echoid-s2240" xml:space="preserve">Enfin loin que la lumiere rebon-<lb/>diſſe ſur les corps mêmes & </s> <s xml:id="echoid-s2241" xml:space="preserve">revienne à <lb/>nous, il faut croire que la plus grande par-<lb/>tie des rayons qui va choquer des parties <lb/>ſolides y reſte, s’y perd, s’y éteint.</s> <s xml:id="echoid-s2242" xml:space="preserve"/> </p> <div xml:id="echoid-div102" type="float" level="2" n="2"> <note position="left" xlink:label="note-0192-01" xlink:href="note-0192-01a" xml:space="preserve">Conſé-<lb/>quences <lb/>de ces <lb/>expé-<lb/>riences.</note> </div> <pb o="174" file="0194" n="194" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s2243" xml:space="preserve">Ce pouvoir qui agit aux ſurfaces, agit d’u-<lb/>ne ſurface à l’autre: </s> <s xml:id="echoid-s2244" xml:space="preserve">c’eſt principalement <lb/>de la derniere ſurface ultérieure du corps <lb/>tranſparent que les rayons rejailliſſent; </s> <s xml:id="echoid-s2245" xml:space="preserve">nous <lb/>l’avons déja prouvé. </s> <s xml:id="echoid-s2246" xml:space="preserve">C’eſt, par exemple, <lb/>de ce point B. </s> <s xml:id="echoid-s2247" xml:space="preserve">plus que de ce point A. </s> <s xml:id="echoid-s2248" xml:space="preserve">que <lb/>la lumiere eſt réflechie.</s> <s xml:id="echoid-s2249" xml:space="preserve"/> </p> <figure> <image file="0194-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0194-01"/> </figure> <p> <s xml:id="echoid-s2250" xml:space="preserve">Il faut donc admettre un pouvoir lequel <lb/>agit ſur les rayons de lumiere de-deſſus l’u-<lb/>ne de ces ſurfaces à l’autre, un pouvoir qui <lb/>tranſmet & </s> <s xml:id="echoid-s2251" xml:space="preserve">qui réflechit alternativement les <lb/> <anchor type="note" xlink:label="note-0194-01a" xlink:href="note-0194-01"/> rayons. </s> <s xml:id="echoid-s2252" xml:space="preserve">Ce jeu de la lumiere & </s> <s xml:id="echoid-s2253" xml:space="preserve">des corps n’é-<lb/>toit pas ſeulement ſoupçonné avant Neu-<lb/>ton, il a compté pluſieurs milliers de ces <lb/>vibrations alternatives, de ces jets tranſ-<lb/>mis & </s> <s xml:id="echoid-s2254" xml:space="preserve">réflechis. </s> <s xml:id="echoid-s2255" xml:space="preserve">Cette action des corps ſur <lb/>la lumiere, & </s> <s xml:id="echoid-s2256" xml:space="preserve">de la lumiere ſur les corps, <pb o="175" file="0195" n="195" rhead="DE NEUTON."/> laiſſe encore bien des incertitudes dans la <lb/>maniere de l’expliquer.</s> <s xml:id="echoid-s2257" xml:space="preserve"/> </p> <div xml:id="echoid-div103" type="float" level="2" n="3"> <note position="left" xlink:label="note-0194-01" xlink:href="note-0194-01a" xml:space="preserve">Action <lb/>mutuel-<lb/>le des <lb/>corps <lb/>ſur la <lb/>lumiere.</note> </div> <p> <s xml:id="echoid-s2258" xml:space="preserve">Celui qui a découvert ce myſtère n’a pu, <lb/>dans le cours de ſa longue vie, faire aſſez <lb/>d’expériences pour aſſigner la cauſe certai-<lb/>ne de ces effets. </s> <s xml:id="echoid-s2259" xml:space="preserve">Mais quand par ſes dé-<lb/>couvertes il ne nous auroit appris que des <lb/>nouvelles proprietés de la matiere, ne ſe-<lb/>roit-ce pas déja un aſſez grand ſervice ren-<lb/>du à la Philoſophie? </s> <s xml:id="echoid-s2260" xml:space="preserve">Il a conjecturé que <lb/> <anchor type="note" xlink:label="note-0195-01a" xlink:href="note-0195-01"/> la lumiere émane du Soleil & </s> <s xml:id="echoid-s2261" xml:space="preserve">des Corps lu-<lb/>mineux par accès, par vibrations; </s> <s xml:id="echoid-s2262" xml:space="preserve">que de <lb/>ces vibrations du Corps lumineux, la pre-<lb/>miere opére une réflexion, la ſeconde une <lb/>tranſmiſſion, & </s> <s xml:id="echoid-s2263" xml:space="preserve">ainſi de ſuite à l’infini. </s> <s xml:id="echoid-s2264" xml:space="preserve">Il <lb/>avoit auſſi préparé des expériences, qui <lb/>conduiſoient à faire voir en quoi ce jeu de <lb/>la Nature tient au grand principe de l’at-<lb/>traction; </s> <s xml:id="echoid-s2265" xml:space="preserve">mais il n’a pas eu le tems d’ache-<lb/>ver ſes expériences. </s> <s xml:id="echoid-s2266" xml:space="preserve">Il avoit conjecturé <lb/> <anchor type="note" xlink:label="note-0195-02a" xlink:href="note-0195-02"/> encore qu’il y a dans la Nature une ma-<lb/>tiere très-élaſtique & </s> <s xml:id="echoid-s2267" xml:space="preserve">très-rare, qui devient <lb/>d’autant moins rare qu’elle eſt plus éloi-<lb/>gnée des corps opaques: </s> <s xml:id="echoid-s2268" xml:space="preserve">que les traits de <lb/>lumiere excitent des vibrations dans cette <lb/>matiere élaſtique: </s> <s xml:id="echoid-s2269" xml:space="preserve">& </s> <s xml:id="echoid-s2270" xml:space="preserve">il faut avouer, que <pb o="176" file="0196" n="196" rhead="DE LA PHIL OSOPHIE"/> cette hypothèſe rendroit raiſon de preſque <lb/>tous les myſtères de la lumiere, & </s> <s xml:id="echoid-s2271" xml:space="preserve">ſur-tout <lb/>de l’attraction & </s> <s xml:id="echoid-s2272" xml:space="preserve">de la gravitation des <lb/>corps; </s> <s xml:id="echoid-s2273" xml:space="preserve">mais une hypothèſe, quand même <lb/>elle rendroit raiſon preſque de tout, ne <lb/>doit point être admiſe. </s> <s xml:id="echoid-s2274" xml:space="preserve">Il ne ſuffit pas qu’un <lb/>Syſtême ſoit poſſible pour mériter d’être <lb/>cru, il faut qu’il ſoit prouvé: </s> <s xml:id="echoid-s2275" xml:space="preserve">ſi les Tour-<lb/>billons de Deſcartes pouvoient ſe ſoutenir <lb/>contre toutes les difficultés dont on les ac-<lb/>cable, il faudroit encore les rejetter, parce <lb/>qu’ils ne ſeroient que poſſibles; </s> <s xml:id="echoid-s2276" xml:space="preserve">ainſi nous <lb/>ne ferons aucun fondement réel ſur les con-<lb/>jectures de Neuton même.</s> <s xml:id="echoid-s2277" xml:space="preserve"/> </p> <div xml:id="echoid-div104" type="float" level="2" n="4"> <note position="right" xlink:label="note-0195-01" xlink:href="note-0195-01a" xml:space="preserve">Conjec-<lb/>tures de <lb/>Neuton.</note> <note position="right" xlink:label="note-0195-02" xlink:href="note-0195-02a" xml:space="preserve">Mais il <lb/>faut ſe <lb/>défier <lb/>de toute <lb/>conjec-<lb/>ture.</note> </div> <p> <s xml:id="echoid-s2278" xml:space="preserve">Si j’en parle, c’eſt plutôt pour faire con-<lb/>naitre l’hiſtoire de ſes penſées, que pour <lb/>tirer la moindre induction de ſes idées que <lb/>je regarde comme les rêves d’un grand <lb/>Homme; </s> <s xml:id="echoid-s2279" xml:space="preserve">il ne s’y arrête en aucune manie-<lb/>re, il s’eſt contenté des faits, ſans rien oſer <lb/>déterminer ſur les cauſes. </s> <s xml:id="echoid-s2280" xml:space="preserve">Paſſons à l’autre <lb/>découverte, ſur le rapport qui exiſte entre <lb/>les raïons de la lumiere & </s> <s xml:id="echoid-s2281" xml:space="preserve">les tons de la <lb/>Muſique.</s> <s xml:id="echoid-s2282" xml:space="preserve"/> </p> <pb file="0197" n="197"/> <figure> <image file="0197-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0197-01"/> </figure> </div> <div xml:id="echoid-div106" type="section" level="1" n="22"> <head xml:id="echoid-head37" xml:space="preserve">CHAPITRE QUATORZE.</head> <head xml:id="echoid-head38" style="it" xml:space="preserve">Du rapport des ſept couleurs primitives avec <lb/>les ſept tons de la Muſique.</head> <p> <s xml:id="echoid-s2283" xml:space="preserve">VOus ſavez que très - long - tems avant <lb/>Deſcartes on s’étoit apperçu, qu’un <lb/>priſme expoſé au Soleil donne les cou-<lb/>leurs de l’Arc-en-Ciel: </s> <s xml:id="echoid-s2284" xml:space="preserve">on avoit vu ſouvent <lb/>ces couleurs ſe peindre ſur un linge, ou ſur <lb/>un papier blanc, dans un ordre qui eſt tou-<lb/>jours le même: </s> <s xml:id="echoid-s2285" xml:space="preserve">bien-tôt on alla, d’expé- <pb o="178" file="0198" n="198" rhead="DE LA PHILOSOPHIE"/> rience en expérience, juſqu’à meſurer l’eſpa-<lb/>ce qu’occupe chacune de ces couleurs; </s> <s xml:id="echoid-s2286" xml:space="preserve">enfin <lb/>on s’eſt apperçu que ces eſpaces ſont entre <lb/>eux les mêmes que ceux des longueurs d’u-<lb/>ne corde, qui donne les ſept tons de la Mu-<lb/>ſique.</s> <s xml:id="echoid-s2287" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2288" xml:space="preserve">J’avois toujours entendu dire, que c’é-<lb/>toit dans Kirker, que Neuton avoit puiſé <lb/>cette découverte de l’analogie de la lumie-<lb/>re & </s> <s xml:id="echoid-s2289" xml:space="preserve">du ſon. </s> <s xml:id="echoid-s2290" xml:space="preserve">Kirker en effet dans ſon Ars <lb/> <anchor type="note" xlink:label="note-0198-01a" xlink:href="note-0198-01"/> Magna Lucis & </s> <s xml:id="echoid-s2291" xml:space="preserve">Umbræ, & </s> <s xml:id="echoid-s2292" xml:space="preserve">dans d’autres Li-<lb/>vres encore, appelle le Son le Singe de la <lb/>lumiere. </s> <s xml:id="echoid-s2293" xml:space="preserve">Quelques perſonnes en inſé-<lb/>roient, que Kirker avoit connu ces rap-<lb/>ports; </s> <s xml:id="echoid-s2294" xml:space="preserve">mais il eſt bon, de peur de mépri-<lb/>ſe, de mettre ici ſous les yeux ce que dit <lb/>Kirker, page 146. </s> <s xml:id="echoid-s2295" xml:space="preserve">& </s> <s xml:id="echoid-s2296" xml:space="preserve">ſuivantes. </s> <s xml:id="echoid-s2297" xml:space="preserve">„ Ceux, <lb/>dit-il, qui ont une voix haute & </s> <s xml:id="echoid-s2298" xml:space="preserve">forte <lb/>tiennent de la nature de l’Ane: </s> <s xml:id="echoid-s2299" xml:space="preserve">ils ſont <lb/>indiſcrets & </s> <s xml:id="echoid-s2300" xml:space="preserve">pétulans, comme on ſait <lb/>que ſont les Anes; </s> <s xml:id="echoid-s2301" xml:space="preserve">& </s> <s xml:id="echoid-s2302" xml:space="preserve">cette voix reſſem-<lb/>ble à la couleur noire. </s> <s xml:id="echoid-s2303" xml:space="preserve">Ceux dont la <lb/>voix eſt grave d’abord, & </s> <s xml:id="echoid-s2304" xml:space="preserve">enſuite aigue, <lb/>tiennent du Bœuf; </s> <s xml:id="echoid-s2305" xml:space="preserve">ils ſont, comme lui, <lb/>triſtes & </s> <s xml:id="echoid-s2306" xml:space="preserve">coléres, & </s> <s xml:id="echoid-s2307" xml:space="preserve">leur voix répond <lb/>au bleu céleſte”.</s> <s xml:id="echoid-s2308" xml:space="preserve"/> </p> <div xml:id="echoid-div106" type="float" level="2" n="1"> <note position="left" xlink:label="note-0198-01" xlink:href="note-0198-01a" xml:space="preserve">Choſe <lb/>très-re-<lb/>marqua-<lb/>ble dans <lb/>Kirker.</note> </div> <pb o="179" file="0199" n="199" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s2309" xml:space="preserve">Il a grand ſoin de fortifier ces belles dé-<lb/>couvertes du témoignage d’Ariſtote. </s> <s xml:id="echoid-s2310" xml:space="preserve">C’eſt-<lb/>là tout ce que nous apprend le Pere Kir-<lb/>ker, d’ailleurs l’un des plus grands Mathé-<lb/>maticiens & </s> <s xml:id="echoid-s2311" xml:space="preserve">des plus ſavans hommes de <lb/>ſon tems; </s> <s xml:id="echoid-s2312" xml:space="preserve">& </s> <s xml:id="echoid-s2313" xml:space="preserve">c’eſt ainſi, à-peu-près, que <lb/>tous ceux qui n’étoient que Savans, rai-<lb/>ſonnoient alors. </s> <s xml:id="echoid-s2314" xml:space="preserve">Voyons comment Neuton <lb/>a raiſonné.</s> <s xml:id="echoid-s2315" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2316" xml:space="preserve">Il y a, comme vous ſavez, dans un <lb/> <anchor type="note" xlink:label="note-0199-01a" xlink:href="note-0199-01"/> ſeul rayon de lumiere ſept principaux <lb/>rayons, qui ont chacun leur réfrangibili-<lb/>té: </s> <s xml:id="echoid-s2317" xml:space="preserve">chacun de ces rayons a ſon ſinus, <lb/>chacun de ces ſinus a ſa proportion avec <lb/>le ſinus commun d’incidence; </s> <s xml:id="echoid-s2318" xml:space="preserve">obſervez <lb/>ce qui ſe paſſe dans ces ſept traits pri-<lb/>mordiaux, qui s’échappent en s’écartant <lb/>dans l’air.</s> <s xml:id="echoid-s2319" xml:space="preserve"/> </p> <div xml:id="echoid-div107" type="float" level="2" n="2"> <note position="right" xlink:label="note-0199-01" xlink:href="note-0199-01a" xml:space="preserve">Manie-<lb/>re de <lb/>connai-<lb/>tre les <lb/>propor-<lb/>tions <lb/>des cou-<lb/>leurs <lb/>primiti-<lb/>ves de la <lb/>lumiere.</note> </div> <p> <s xml:id="echoid-s2320" xml:space="preserve">Il ne s’agit pas ici de conſidérer que <lb/>dans ce verre même tous ces traits ſont <lb/>écartés, & </s> <s xml:id="echoid-s2321" xml:space="preserve">que chacun de ces traits y <lb/>prend un ſinus différent: </s> <s xml:id="echoid-s2322" xml:space="preserve">il faut regarder <lb/>cet aſſemblage de rayons dans le verre <lb/>comme un ſeul rayon, qui n’a que ce ſi- <pb o="180" file="0200" n="200" rhead="DE LA PHILOSOPHIE"/> nus commun A, B.</s> <s xml:id="echoid-s2323" xml:space="preserve">: mais à l’émergence <lb/>de ce cryſtal chacun de ces traits s’écar-<lb/>tant ſenſiblement prend chacun ſon ſinus <lb/>différent; </s> <s xml:id="echoid-s2324" xml:space="preserve">celui du rouge, (rayon le moins <lb/>réfrangible,) eſt cette ligne C, B. </s> <s xml:id="echoid-s2325" xml:space="preserve">celui <lb/>du violet, (rayon le plus réfrangible,) eſt <lb/>cette ligne C, B, D.</s> <s xml:id="echoid-s2326" xml:space="preserve"/> </p> <figure> <image file="0200-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0200-01"/> </figure> <p> <s xml:id="echoid-s2327" xml:space="preserve">Ces proportions poſées, voions quel eſt <lb/>ce rapport, auſſi exact que ſingulier, entre <lb/>les couleurs & </s> <s xml:id="echoid-s2328" xml:space="preserve">la Muſique. </s> <s xml:id="echoid-s2329" xml:space="preserve">Que le ſinus <lb/>d’incidence du faiſceau blanc de rayons, <lb/>ſoit au ſinus d’émergence du rayon rouge, <lb/>comme cette ligne A, B, eſt à la ligne <lb/>A, B, C.</s> <s xml:id="echoid-s2330" xml:space="preserve"/> </p> <pb file="0201" n="201"/> <pb file="0201a" n="202"/> </div> <div xml:id="echoid-div109" type="section" level="1" n="23"> <head xml:id="echoid-head39" style="it" xml:space="preserve">Table des couleurs & des tons de la Muſique. Pag. 182.</head> <note style="it" position="right" xml:space="preserve"> <lb/>A # C # H # G # F # E # B # D <lb/># Rouge # Oran \\ ge # J<unsure/>aune # Verd # Bleu # Pourpre # Violet <lb/># se jouë \\ de ce de: \\ mi-cercle \\ en C # de C \\ en H # de H \\ en G # de G \\ en F # de F \\ en E # de E \\ en B # de B \\ en D <lb/># 45 # 27 # 48 # 60 # 60 # 40 # 80 <lb/>{1/2} # {9/16} # {3/4} # {1/3} # {3/4} # {5/6} # {8/9} # 1 <lb/>re # ut # si # la # sol # fa # mi # re <lb/># la plus \\ grande \\ refran: \\ gibilité \\ durouge \\ répond \\ à # celle \\ de ló \\ range \\ à # celle \\ dujaune \\ à # celle du \\ verd \\ à # celle du \\ bleu \\ à # celle \\ du \\ pourpre \\ à # celle du \\ violet \\ à <lb/># ut # si # la # sol # fa # mi # re <lb/></note> <pb file="0202" n="203"/> <pb o="181" file="0203" n="204" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s2331" xml:space="preserve">Sinus donné dans le verre</s> </p> <figure> <image file="0203-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0203-01"/> </figure> <p> <s xml:id="echoid-s2332" xml:space="preserve">Sinus donné dans l’air</s> </p> <figure> <image file="0203-02" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0203-02"/> </figure> <p> <s xml:id="echoid-s2333" xml:space="preserve">Que ce même ſinus A, B, d’incidence <lb/>commune ſoit au ſinus de réfraction du <lb/>rayon violet, comme la ligne A, B, eſt <lb/>à la ligne A, B, C, D.</s> <s xml:id="echoid-s2334" xml:space="preserve"/> </p> <figure> <image file="0203-03" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0203-03"/> </figure> <figure> <image file="0203-04" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0203-04"/> </figure> <p> <s xml:id="echoid-s2335" xml:space="preserve">Vous voyez que le point C eſt le terme <lb/>de la plus petite refrangibilitè, & </s> <s xml:id="echoid-s2336" xml:space="preserve">D le ter-<lb/>me de la plus grande; </s> <s xml:id="echoid-s2337" xml:space="preserve">la petite ligne C, <lb/>D, contient donc tous les degrés de ré-<lb/>frangibilité des ſept rayons. </s> <s xml:id="echoid-s2338" xml:space="preserve">Doublez main-<lb/>tenant C, D, ci-deſſus, en ſorte que I, en <lb/>devienne le milieu, comme ci-deſſous.</s> <s xml:id="echoid-s2339" xml:space="preserve"/> </p> <figure> <image file="0203-05" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0203-05"/> </figure> <p> <s xml:id="echoid-s2340" xml:space="preserve">Alors la longueur depuis A en C fait le <pb o="182" file="0204" n="205" rhead="DE LA PHILOSOPHIE"/> rouge: </s> <s xml:id="echoid-s2341" xml:space="preserve">la longúeur de A en H, fait l’oran-<lb/>gé: </s> <s xml:id="echoid-s2342" xml:space="preserve">de A en G, le jaune: </s> <s xml:id="echoid-s2343" xml:space="preserve">de A en F, le <lb/>verd: </s> <s xml:id="echoid-s2344" xml:space="preserve">de A en E, le bleu: </s> <s xml:id="echoid-s2345" xml:space="preserve">de A en B, le <lb/>pourpre; </s> <s xml:id="echoid-s2346" xml:space="preserve">de A en D, le violet. </s> <s xml:id="echoid-s2347" xml:space="preserve">Or ces <lb/>eſpaces ſont tels que chaque rayon peut <lb/>bien être réfracté, un peu plus ou moins, <lb/>dans chacun de ces eſpaces, mais jamais il <lb/>ne ſortira de cet eſpace qui lui eſt preſcrit: <lb/></s> <s xml:id="echoid-s2348" xml:space="preserve">le rayon violet ſe jouera toujours entre B & </s> <s xml:id="echoid-s2349" xml:space="preserve"><lb/>D: </s> <s xml:id="echoid-s2350" xml:space="preserve">le rayon rouge entre C & </s> <s xml:id="echoid-s2351" xml:space="preserve">I, ainſi du <lb/>reſte; </s> <s xml:id="echoid-s2352" xml:space="preserve">le tout en telle proportion que ſi <lb/>vous diviſez cette longueur depuis I juſqu’a <lb/>D, en trois cens ſoixante parties, chaque <lb/>rayon aura pour ſoi les dimenſions que vous <lb/>voyez dans la grande figure ci-jointe.</s> <s xml:id="echoid-s2353" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2354" xml:space="preserve">Ces proportions ſont préciſément les mê-<lb/> <anchor type="note" xlink:label="note-0204-01a" xlink:href="note-0204-01"/> mes que celles des tons de la Muſique: </s> <s xml:id="echoid-s2355" xml:space="preserve">la <lb/>longueur de la corde qui étant pincée ſera <lb/>Re, eſt à la corde, qui donnera l’octave de <lb/>Re, comme la ligne A, I, qui donne le rouge <lb/>en I, eſt à la ligne A, D, qui donne le <lb/>violet en D; </s> <s xml:id="echoid-s2356" xml:space="preserve">ainſi les eſpaces qui marquent <lb/>les couleurs, dans cette figure, marquent <lb/>auſſi les tons de la Muſique.</s> <s xml:id="echoid-s2357" xml:space="preserve"/> </p> <div xml:id="echoid-div109" type="float" level="2" n="1"> <note position="left" xlink:label="note-0204-01" xlink:href="note-0204-01a" xml:space="preserve">Analo-<lb/>gie des <lb/>tons de <lb/>la Muſi-<lb/>que & <lb/>des cou-<lb/>leurs.</note> </div> <p> <s xml:id="echoid-s2358" xml:space="preserve">La plus grande réfrangibilité du violet ré-<lb/>pond à Re: </s> <s xml:id="echoid-s2359" xml:space="preserve">la plus grande réfrangibilité du <pb o="183" file="0205" n="206" rhead="DE NEUTON."/> pourpre répond à Mi: </s> <s xml:id="echoid-s2360" xml:space="preserve">celle du bleu répond <lb/>à Fa: </s> <s xml:id="echoid-s2361" xml:space="preserve">celle du verd à Sol: </s> <s xml:id="echoid-s2362" xml:space="preserve">celle du jaune <lb/>à La: </s> <s xml:id="echoid-s2363" xml:space="preserve">celle de l’orangé à Si: </s> <s xml:id="echoid-s2364" xml:space="preserve">celle du rou-<lb/>ge à l’Ut; </s> <s xml:id="echoid-s2365" xml:space="preserve">& </s> <s xml:id="echoid-s2366" xml:space="preserve">enfin la plus petite réfrangibi-<lb/>lité du rouge ſe rapporte à Re, qui eſt l’oc-<lb/>tave ſupérieure. </s> <s xml:id="echoid-s2367" xml:space="preserve">Le ton le plus grave ré-<lb/>pond ainſi au violet, & </s> <s xml:id="echoid-s2368" xml:space="preserve">le ton le plus aigu <lb/>répond au rouge. </s> <s xml:id="echoid-s2369" xml:space="preserve">On peut ſe former une <lb/>idée complette de toutes ces proprietés, en <lb/>jettant les yeux ſur la Table que j’ai dreſ-<lb/>ſée, & </s> <s xml:id="echoid-s2370" xml:space="preserve">que vous devez trouver à côté.</s> <s xml:id="echoid-s2371" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2372" xml:space="preserve">Il y a encore un autre rapport entre les <lb/>ſons & </s> <s xml:id="echoid-s2373" xml:space="preserve">les couleurs, c’eſt que les rayons <lb/>les plus diſtants (les violets & </s> <s xml:id="echoid-s2374" xml:space="preserve">les rouges) <lb/>viennent à nos yeux en même-tems, & </s> <s xml:id="echoid-s2375" xml:space="preserve">que <lb/>les ſons les plus diſtants (les plus graves & </s> <s xml:id="echoid-s2376" xml:space="preserve">les <lb/>plus aigus) viennent auſſi à nos oreilles en <lb/>même-tems. </s> <s xml:id="echoid-s2377" xml:space="preserve">Cela ne veut pas dire, que <lb/>nous voyons & </s> <s xml:id="echoid-s2378" xml:space="preserve">que nous entendons en mê-<lb/>me-tems à la même diſtance; </s> <s xml:id="echoid-s2379" xml:space="preserve">car la lumie-<lb/>re ſe fait ſentir ſix cens mille fois plus vîte, <lb/>au moins, que le ſon; </s> <s xml:id="echoid-s2380" xml:space="preserve">mais cela veut dire, <lb/>que les rayons bleus, par exemple, ne vien-<lb/>nent pas du Soleil à nos yeux, plutôt que <lb/>les rayons rouges, de même que le ſon de <pb o="184" file="0206" n="207" rhead="DE LA PHILOSOPHIE"/> la note Si, ne vient pas à nos oreilles, plu-<lb/>tôt que le ſon de la note Re.</s> <s xml:id="echoid-s2381" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2382" xml:space="preserve">Cette analogie ſecrete entre la lumiere <lb/>& </s> <s xml:id="echoid-s2383" xml:space="preserve">le ſon, donne lieu de ſoupçonner, que <lb/>toutes les choſes de la Nature ont des <lb/>rapports cachés, que peut-être on décou-<lb/>vrira quelque jour. </s> <s xml:id="echoid-s2384" xml:space="preserve">Il eſt déja certain qu’il <lb/>y a un rapport entre le Toucher & </s> <s xml:id="echoid-s2385" xml:space="preserve">la Vûe, <lb/>puiſque les couleurs dépendent de la confi-<lb/>guration des parties; </s> <s xml:id="echoid-s2386" xml:space="preserve">on prétend méme qu’il <lb/>y a eu des Aveugles nés, qui diſtinguoient <lb/>au toucher la différence du noir, du blanc, <lb/>& </s> <s xml:id="echoid-s2387" xml:space="preserve">de quelques autres couleurs.</s> <s xml:id="echoid-s2388" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2389" xml:space="preserve">Un Philoſophe ingénieux a voulu pouſſer <lb/>ce rapport des Sens & </s> <s xml:id="echoid-s2390" xml:space="preserve">de la lumiere peut-<lb/>être plus loin qu’il ne ſemble permis aux hom-<lb/>mes d’aller. </s> <s xml:id="echoid-s2391" xml:space="preserve">Il a imaginé un Claveſſin ocu-<lb/> <anchor type="note" xlink:label="note-0206-01a" xlink:href="note-0206-01"/> laire, qui doit faire paraitre ſucceſſivement <lb/>des couleurs harmoniques, comme nos Cla-<lb/>veſſins nous font entendre des ſons: </s> <s xml:id="echoid-s2392" xml:space="preserve">il y a <lb/>travaillé de ſes mains, il prétend enfin qu’on <lb/>joueroit des airs aux yeux. </s> <s xml:id="echoid-s2393" xml:space="preserve">On ne peut <lb/>que remercier un homme qui cherche à <lb/>donner aux autres de nouveaux Arts & </s> <s xml:id="echoid-s2394" xml:space="preserve"><lb/>de nouveaux plaiſirs. </s> <s xml:id="echoid-s2395" xml:space="preserve">Il y a eu des Pays, <pb o="185" file="0207" n="208" rhead="DE NEUTON."/> où le Public l’auroit récompenſé. </s> <s xml:id="echoid-s2396" xml:space="preserve">Il eſt à <lb/>ſouhaiter ſans doute, que cette invention <lb/>ne ſoit pas, comme tant d’autres, un ef-<lb/>fort ingénieux & </s> <s xml:id="echoid-s2397" xml:space="preserve">inutile: </s> <s xml:id="echoid-s2398" xml:space="preserve">ce paſſage rapide <lb/>de pluſieurs couleurs devant les yeux ſem-<lb/>ble peut-être devoir étonner, éblouïr, & </s> <s xml:id="echoid-s2399" xml:space="preserve"><lb/>fatiguer la vûe; </s> <s xml:id="echoid-s2400" xml:space="preserve">nos yeux veulent peut-être <lb/>du repos, pour jouïr de l’agrément des <lb/>couleurs. </s> <s xml:id="echoid-s2401" xml:space="preserve">Ce n’eſt pas aſſez de nous pro-<lb/>poſer un plaiſir, il faut que la Nature nous <lb/>ait rendus capables de recevoir ce plaiſir: <lb/></s> <s xml:id="echoid-s2402" xml:space="preserve">c’eſt à l’expérience ſeule à juſtiſier cette <lb/>invention. </s> <s xml:id="echoid-s2403" xml:space="preserve">En attendant il me parait que <lb/>tout eſprit équitable ne peut que louer l’ef-<lb/>fort & </s> <s xml:id="echoid-s2404" xml:space="preserve">le génie de celui qui cherche à agran-<lb/>dir la carriére des Arts & </s> <s xml:id="echoid-s2405" xml:space="preserve">de la Nature.</s> <s xml:id="echoid-s2406" xml:space="preserve"/> </p> <div xml:id="echoid-div110" type="float" level="2" n="2"> <note position="left" xlink:label="note-0206-01" xlink:href="note-0206-01a" xml:space="preserve">Idée <lb/>d’un <lb/>Claveſ-<lb/>ſin ocu-<lb/>laire.</note> </div> <p> <s xml:id="echoid-s2407" xml:space="preserve">Nous ne pouſſerons pas plus loin cette <lb/>Introduction ſur la lumiere, peut-être en <lb/>avons nous trop dit dans de ſimples Elé-<lb/> <anchor type="note" xlink:label="note-0207-01a" xlink:href="note-0207-01"/> mens; </s> <s xml:id="echoid-s2408" xml:space="preserve">mais la plûpart de ces vérités ſont <lb/>nouvelles pour bien des Lecteurs. </s> <s xml:id="echoid-s2409" xml:space="preserve">Avant que <lb/>de paſſer à l’autre partie de la Philoſophie, <lb/>ſouvenons-nous, que la Théorie de la lu-<lb/>miere a quelque choſe de commun avec <lb/>la Théorie de l’Univers dans laquelle nous <lb/>allons entrer. </s> <s xml:id="echoid-s2410" xml:space="preserve">Cette Théorie eſt, qu’il y <pb o="186" file="0208" n="209" rhead="DE LA PHILOSOPHIE"/> a une eſpèce d’attraction marquée entre les <lb/>corps & </s> <s xml:id="echoid-s2411" xml:space="preserve">la lumiere, comme nous en allons <lb/>obſerver une entre tous les Globes de no-<lb/>tre Univers: </s> <s xml:id="echoid-s2412" xml:space="preserve">ces attractions ſe manifeſtent <lb/>par différens effets; </s> <s xml:id="echoid-s2413" xml:space="preserve">mais enfin c’eſt tou-<lb/>jours une tendance des corps, ſans qu’il pa-<lb/>raiſſe aucune impulſion.</s> <s xml:id="echoid-s2414" xml:space="preserve"/> </p> <div xml:id="echoid-div111" type="float" level="2" n="3"> <note position="right" xlink:label="note-0207-01" xlink:href="note-0207-01a" xml:space="preserve">Toute <lb/>cette <lb/>Théorie <lb/>de la lu-<lb/>miere a <lb/>rapport <lb/>avec la <lb/>Théorie <lb/>de l’U-<lb/>nivers.</note> </div> <p> <s xml:id="echoid-s2415" xml:space="preserve">Parmi tant de proprietés de la matiere <lb/>telle que ces accès de tranſmiffion & </s> <s xml:id="echoid-s2416" xml:space="preserve">de ré-<lb/>flexion des traits de lumiere, cette répul-<lb/>fion que la lumiere éprouve dans le vuide, <lb/>dans les pores des corps, & </s> <s xml:id="echoid-s2417" xml:space="preserve">fur les ſurfa-<lb/>ces des corps; </s> <s xml:id="echoid-s2418" xml:space="preserve">parmi ces proprietés, dis-je, <lb/>il faut ſur-tout faire attention à ce pouvoir <lb/>par lequel les rayons ſont réflechis & </s> <s xml:id="echoid-s2419" xml:space="preserve">rom-<lb/>pus, à cette force par laquelle les corps <lb/>agiſſent ſur la lumiere & </s> <s xml:id="echoid-s2420" xml:space="preserve">la lumiere ſur <lb/>eux, ſans même les toucher. </s> <s xml:id="echoid-s2421" xml:space="preserve">Ces décou-<lb/>vertes doivent au moins ſervir à nous ren-<lb/>dre extrêmement circonſpects dans nos dé-<lb/> <anchor type="note" xlink:label="note-0208-01a" xlink:href="note-0208-01"/> ciſions ſur la nature & </s> <s xml:id="echoid-s2422" xml:space="preserve">l’eſſence des cho-<lb/>ſes. </s> <s xml:id="echoid-s2423" xml:space="preserve">Songeons que nous ne connaiſſons rien <lb/>du tout que par l’expérience. </s> <s xml:id="echoid-s2424" xml:space="preserve">Sans le tou-<lb/>cher nous n’aurions point d’idée de l’éten-<lb/>due des corps: </s> <s xml:id="echoid-s2425" xml:space="preserve">ſans les yeux, nous n’au-<lb/>rions pu deviner la lumiere: </s> <s xml:id="echoid-s2426" xml:space="preserve">ſi nous n’a- <pb o="187" file="0209" n="210" rhead="DE NEUTON."/> vions jamais éprouvé de mouvement, nous <lb/>n’aurions jamais cru la matiere mobile; </s> <s xml:id="echoid-s2427" xml:space="preserve">un <lb/>très-petit nombre de ſens que Dieu nous a <lb/>donnés, ſert à nous découvrir un très-petit <lb/>nombre de proprietés de la matiere. </s> <s xml:id="echoid-s2428" xml:space="preserve">Le <lb/>raiſonnement ſupplée aux ſens qui nous man-<lb/>quent, & </s> <s xml:id="echoid-s2429" xml:space="preserve">nous apprend encore que la ma-<lb/>tiere a d’autres attributs, comme l’attrac-<lb/>tion, la gravitation; </s> <s xml:id="echoid-s2430" xml:space="preserve">elle en a probable-<lb/>ment beaucoup d’autres qui tiennent à ſa <lb/>nature, & </s> <s xml:id="echoid-s2431" xml:space="preserve">dont peut-être un jour la Philo-<lb/>ſophie donnera quelques idées aux hom-<lb/>mes.</s> <s xml:id="echoid-s2432" xml:space="preserve"/> </p> <div xml:id="echoid-div112" type="float" level="2" n="4"> <note position="left" xlink:label="note-0208-01" xlink:href="note-0208-01a" xml:space="preserve">La ma-<lb/>tiere a <lb/>plus de <lb/>proprie-<lb/>tés <lb/>qu’on <lb/>ne pen-<lb/>fe.</note> </div> <figure> <image file="0209-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0209-01"/> </figure> <pb file="0210" n="211"/> <figure> <image file="0210-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0210-01"/> </figure> </div> <div xml:id="echoid-div114" type="section" level="1" n="24"> <head xml:id="echoid-head40" xml:space="preserve">CHAPITRE QUINZE.</head> <head xml:id="echoid-head41" style="it" xml:space="preserve">Premieres idées touchant la peſanteur & les <lb/>loix de la gravitation: Que la matiere <lb/>ſubtile, les tourbillons & le plein <lb/>doivent étre rejettés.</head> <p> <s xml:id="echoid-s2433" xml:space="preserve">UN Lecteur ſage qui aura vu avec at-<lb/>tention ces merveilles de la lumiere, <lb/>convaincu par l’expérience qu’aucune im-<lb/>pulſion connue ne les opére, ſera ſans dou-<lb/>te impatient d’obſerver cette puiſſance nou-<lb/>velle dont nous avons parlé ſous le nom <lb/>d’attraction, qui doit agir ſur tous les au- <pb o="189" file="0211" n="212" rhead="DE NEUTON."/> tres corps plus’ ſenſiblement que ſur celui de <lb/>la lumiere. </s> <s xml:id="echoid-s2434" xml:space="preserve">Que les noms encore une fois <lb/>ne nous effarouchent point; </s> <s xml:id="echoid-s2435" xml:space="preserve">examinons ſim-<lb/>plement les faits.</s> <s xml:id="echoid-s2436" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2437" xml:space="preserve">Je me ſervirai toujours indifféremment <lb/>des termes d’attraction & </s> <s xml:id="echoid-s2438" xml:space="preserve">de gravitation en <lb/> <anchor type="note" xlink:label="note-0211-01a" xlink:href="note-0211-01"/> parlant des corps, ſoit qu’il tendent ſenſi-<lb/>blement les uns vers les autres, ſoit qu’ils <lb/>tournent dans des orbes immenſes, autour <lb/>d’un contre commun, ſoit qu’ils tombent <lb/>ſur la Terre, ſoit qu’ils s’uniſſent pour com-<lb/>poſer des corps ſolides, ſoit qu’ils s’aron-<lb/>diſſent en goutes pour former des liquides. <lb/></s> <s xml:id="echoid-s2439" xml:space="preserve">Entrons en matiere.</s> <s xml:id="echoid-s2440" xml:space="preserve"/> </p> <div xml:id="echoid-div114" type="float" level="2" n="1"> <note position="right" xlink:label="note-0211-01" xlink:href="note-0211-01a" xml:space="preserve">Attrac-<lb/>tion.</note> </div> <p> <s xml:id="echoid-s2441" xml:space="preserve">Tous les corps connus peſent, & </s> <s xml:id="echoid-s2442" xml:space="preserve">il y a <lb/>long-tems que la legéreté ſpécifique a été <lb/>comptée parmi les erreurs reconnues d’A-<lb/>riſtote & </s> <s xml:id="echoid-s2443" xml:space="preserve">de ſes Sectateurs.</s> <s xml:id="echoid-s2444" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2445" xml:space="preserve">Depuis que la fameuſe Machine pneu-<lb/>matique fut inventée, on a été plus à por-<lb/>tée de connoître la peſanteur des corps, car <lb/>lorſqu’ils tombent dans l’air, les parties de <lb/>l’air retardent ſenſiblement la chûte de ceux <lb/>qui ont beaucoup de ſurface & </s> <s xml:id="echoid-s2446" xml:space="preserve">peu de vo-<lb/>lume; </s> <s xml:id="echoid-s2447" xml:space="preserve">mais dans cette Machine privée <pb o="190" file="0212" n="213" rhead="DE LA PHILOSOPHIE"/> d’air, les corps abandonnés à la force, tel-<lb/>le qu’elle ſoit, qui les précipite ſans obſta-<lb/>cle, tombent ſelon tout leur poids.</s> <s xml:id="echoid-s2448" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2449" xml:space="preserve">La Machine pneumatique inventée par <lb/>Ottoguerike, fut bien - tôt perfectionnée <lb/>par Boyle; </s> <s xml:id="echoid-s2450" xml:space="preserve">on fit enſuite des récipiens de <lb/>verre beaucoup plus longs, qui furent-<lb/>entiérement purgés d’air. </s> <s xml:id="echoid-s2451" xml:space="preserve">Dans un de ces <lb/> <anchor type="note" xlink:label="note-0212-01a" xlink:href="note-0212-01"/> longs récipiens compoſé de quatre tubes, <lb/>le tout enſemble aïant huit pieds de hauteur, <lb/>on ſuſpendit en haut, par un reſſort, des piè-<lb/>ces d’or, des morceaux de papier, des plu-<lb/>mes; </s> <s xml:id="echoid-s2452" xml:space="preserve">il s’agiſſoit de ſavoir ce qui arrive-<lb/>roit, quand on détendroit le reſſort. </s> <s xml:id="echoid-s2453" xml:space="preserve">Les bons <lb/>Philoſophes prévoioient, que tout cela tom-<lb/>beroit en même-tems: </s> <s xml:id="echoid-s2454" xml:space="preserve">le plus grand nom-<lb/>bre aſſûroit que les corps les plus maſſifs <lb/>tomberoient bien plus vîte que les autres; <lb/></s> <s xml:id="echoid-s2455" xml:space="preserve">ce grand nombre, qui ſe trompe preſque <lb/>toujours, fut bien étonné, quand il vit dans <lb/>toutes les expériences, l’or, le plomb, le <lb/>papier & </s> <s xml:id="echoid-s2456" xml:space="preserve">la plume tomber également vîte, <lb/>& </s> <s xml:id="echoid-s2457" xml:space="preserve">arriver au fond du récipient en même-<lb/>tems.</s> <s xml:id="echoid-s2458" xml:space="preserve"/> </p> <div xml:id="echoid-div115" type="float" level="2" n="2"> <note position="left" xlink:label="note-0212-01" xlink:href="note-0212-01a" xml:space="preserve">Expé-<lb/>rience <lb/>qui dé-<lb/>montre <lb/>le vuide <lb/>& les <lb/>effets de <lb/>la gravi-<lb/>tation.</note> </div> <p> <s xml:id="echoid-s2459" xml:space="preserve">Ceux qui tenoient encore pour le Plein <pb o="191" file="0213" n="214" rhead="DE NEUTON."/> de Deſcartes, & </s> <s xml:id="echoid-s2460" xml:space="preserve">pour les prétendus effets <lb/>de la matiere ſubtile, ne pouvoient rendre <lb/>aucune bonne raiſon de ce fait; </s> <s xml:id="echoid-s2461" xml:space="preserve">car les faits <lb/>étoient leurs écuëils. </s> <s xml:id="echoid-s2462" xml:space="preserve">Si tout étoit plein, <lb/>quand on leur accorderoit qu’il pût y avoir <lb/>alors du mouvement, (ce qui eſt abſolu-<lb/>ment impoſſible) au moins cette préten-<lb/>due matiere ſubtile rempliroit éxactement <lb/>tout le récipient: </s> <s xml:id="echoid-s2463" xml:space="preserve">elle y ſeroit en auſſi grande <lb/>quantité que de l’eau, ou du mercure, qu’on <lb/>y auroit mis: </s> <s xml:id="echoid-s2464" xml:space="preserve">elle s’oppoſeroit au moins à <lb/>cette deſcente ſi rapide des corps: </s> <s xml:id="echoid-s2465" xml:space="preserve">elle ré-<lb/>ſiſteroit à ce large morceau de papier, ſe-<lb/>lon la ſurface de ce papier, & </s> <s xml:id="echoid-s2466" xml:space="preserve">laiſſeroit tom-<lb/>ber la balle d’or ou de plomb beaucoup plus <lb/>vîte, mais cette chûte ſe fait au même <lb/>inſtant; </s> <s xml:id="echoid-s2467" xml:space="preserve">donc il n’y a rien dans le réci-<lb/>pient qui réſiſte; </s> <s xml:id="echoid-s2468" xml:space="preserve">donc cette prétendue ma-<lb/>tiere ſubtile ne peut faire aucun effet <lb/>ſenſible dans ce récipient; </s> <s xml:id="echoid-s2469" xml:space="preserve">donc il y a <lb/>une autre force qui fait la peſanteur.</s> <s xml:id="echoid-s2470" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2471" xml:space="preserve">En vain diroit-on qu’il eſt poſſible qu’il <lb/>reſte une matiere ſubtile dans ce réci-<lb/>pient, puiſque la lumiere le pénétre; </s> <s xml:id="echoid-s2472" xml:space="preserve">il y <lb/>a bien de la différence. </s> <s xml:id="echoid-s2473" xml:space="preserve">La lumiere qui <lb/>eſt dans ce Vaſe de verre, n’en occupe <pb o="192" file="0214" n="215" rhead="DE LA PHILOSOPHIE"/> certainement pas la cent-millième partie; <lb/></s> <s xml:id="echoid-s2474" xml:space="preserve">mais ſelon les Cartéſiens, il faut que leur <lb/>matiere imaginaire rempliſſe bien plus éxac-<lb/>tement le récipent, que ſi je le ſuppoſois <lb/>rempli d’or, car il y a beaucoup de vuide <lb/>dans l’or, & </s> <s xml:id="echoid-s2475" xml:space="preserve">ils n’en admettent point dans <lb/>leur matiere ſubtile.</s> <s xml:id="echoid-s2476" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2477" xml:space="preserve">Or par cette expérience la pièce d’or, <lb/> <anchor type="note" xlink:label="note-0214-01a" xlink:href="note-0214-01"/> qui peſe cent-mille fois plus que le morceau <lb/>de papier, eſt deſcendue auſſi vîte que le <lb/>papier; </s> <s xml:id="echoid-s2478" xml:space="preserve">donc la force, qui l’a fait deſcen-<lb/>dre, a agi cent mille fois plus ſur lui que <lb/>ſur le papier; </s> <s xml:id="echoid-s2479" xml:space="preserve">de même qu’il faudra cent <lb/>fois plus de force à mon bras pour remuer <lb/>cent livres, que pour remuer une livre; <lb/></s> <s xml:id="echoid-s2480" xml:space="preserve">donc cette puiſſance qui opére la gravita-<lb/>tion, agit en raiſon directe de la maſſe des <lb/>corps. </s> <s xml:id="echoid-s2481" xml:space="preserve">Elle agit en effet tellement ſelon la <lb/>maſſe des corps, non ſelon les ſurfaces, qu’u-<lb/>ne livre d’or réduite en poudre peſera pré-<lb/>ciſément comme cette mê<unsure/>me livre en feuil-<lb/>le. </s> <s xml:id="echoid-s2482" xml:space="preserve">La figure des corps ne change ici en <lb/>rien leur gravité; </s> <s xml:id="echoid-s2483" xml:space="preserve">ce pouvoir de gravita-<lb/>tion agit donc ſur la nature interne des <lb/>corps, & </s> <s xml:id="echoid-s2484" xml:space="preserve">non en raiſon des ſuperficies.</s> <s xml:id="echoid-s2485" xml:space="preserve"/> </p> <div xml:id="echoid-div116" type="float" level="2" n="3"> <note position="left" xlink:label="note-0214-01" xlink:href="note-0214-01a" xml:space="preserve">La pe-<lb/>ſanteur <lb/>agit en <lb/>raiſon <lb/>des maſ-<lb/>ſes.</note> </div> <pb o="193" file="0215" n="216" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s2486" xml:space="preserve">Ce pouvoir ne réſide point dans la pré-<lb/> <anchor type="note" xlink:label="note-0215-01a" xlink:href="note-0215-01"/> tendue matiere ſubtile, dont nous parle-<lb/>rons au Chapitre 16.</s> <s xml:id="echoid-s2487" xml:space="preserve">, cette matiere ſeroit <lb/>un fluide. </s> <s xml:id="echoid-s2488" xml:space="preserve">Tout fluide agit ſur les ſolides <lb/>en raiſon de leurs ſuperficies; </s> <s xml:id="echoid-s2489" xml:space="preserve">ainſi le Vaiſ-<lb/>ſeau préſentant moins de ſurface par ſa <lb/>proue, fend la Mer qui réſiſteroit à ſes <lb/>flancs. </s> <s xml:id="echoid-s2490" xml:space="preserve">Or quand la ſuperficie d’un corps <lb/>eſt le quarré de ſon diametre, la ſolidité <lb/>de ce corps eſt le cube de ce même dia-<lb/>metre: </s> <s xml:id="echoid-s2491" xml:space="preserve">le même pouvoir ne peut agir à <lb/>la fois en raiſon du cube & </s> <s xml:id="echoid-s2492" xml:space="preserve">du quarré; <lb/></s> <s xml:id="echoid-s2493" xml:space="preserve">donc la peſanteur, la gravitation n’eſt <lb/>point l’effet de ce fluide. </s> <s xml:id="echoid-s2494" xml:space="preserve">De plus, il <lb/>eſt impoſſible que cette prétendue matie-<lb/>re ſubtile ait d’un côté aſſez de force, <lb/>pour précipiter un corps de 54000 pieds <lb/>de haut en une minute, (car telle eſt la <lb/>chûte des corps) & </s> <s xml:id="echoid-s2495" xml:space="preserve">que de l’autre elle ſoit <lb/>aſſez impuiſſante, pour ne pouvoir empê-<lb/>cher le pendule du bois le plus leger de <lb/>remonter de vibration en vibration dans <lb/>la Machine pneumatique, dont cette ma-<lb/>tiere imaginaire eſt ſuppoſée remplir exac-<lb/>tement tout l’eſpace.</s> <s xml:id="echoid-s2496" xml:space="preserve"/> </p> <div xml:id="echoid-div117" type="float" level="2" n="4"> <note position="right" xlink:label="note-0215-01" xlink:href="note-0215-01a" xml:space="preserve">D’où <lb/>vient ce <lb/>pouvoir <lb/>de pe-<lb/>ſanteur.</note> </div> <pb o="194" file="0216" n="217" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s2497" xml:space="preserve">Je ne craindrai donc point d’affirmer <lb/>que, ſi l’on découvroit jamais une im-<lb/>pulſion, qui fût la cauſe de la peſanteur <lb/>des corps vers un centre, en un mot la <lb/>cauſe de la gravitation, de l’attraction, <lb/>cette impulſion ſeroit d’une toute autre <lb/>nature qu’eſt celle que nous connoiſſons.</s> <s xml:id="echoid-s2498" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2499" xml:space="preserve">Voilà donc une premiere vérité déja <lb/>indiquée ailleurs, & </s> <s xml:id="echoid-s2500" xml:space="preserve">prouvée ici: </s> <s xml:id="echoid-s2501" xml:space="preserve">il y a <lb/>un pouvoir qui fait graviter tous les corps <lb/>en raiſon directe de leur maſſe.</s> <s xml:id="echoid-s2502" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2503" xml:space="preserve">Si l’on cherche actuellement pourquoi <lb/> <anchor type="note" xlink:label="note-0216-01a" xlink:href="note-0216-01"/> un corps eſt plus peſant qu’un autre, on <lb/>en trouvera aiſément l’unique raiſon: </s> <s xml:id="echoid-s2504" xml:space="preserve">on <lb/>jugera que ce corps doit avoir plus de <lb/>maſſe, plus de matiere ſous une même <lb/>étendue; </s> <s xml:id="echoid-s2505" xml:space="preserve">ainſi l’or peſe plus que le bois, <lb/>parce qu’il y a dans l’or bien plus de ma-<lb/>tiere & </s> <s xml:id="echoid-s2506" xml:space="preserve">moins de vuide que dans le bois.</s> <s xml:id="echoid-s2507" xml:space="preserve"/> </p> <div xml:id="echoid-div118" type="float" level="2" n="5"> <note position="left" xlink:label="note-0216-01" xlink:href="note-0216-01a" xml:space="preserve">Pour-<lb/>quoi un <lb/>corps <lb/>peſe <lb/>plus <lb/>qu’un <lb/>autre.</note> </div> <p> <s xml:id="echoid-s2508" xml:space="preserve">Deſcartes & </s> <s xml:id="echoid-s2509" xml:space="preserve">ſes Sectateurs ſoutiennent <lb/> <anchor type="note" xlink:label="note-0216-02a" xlink:href="note-0216-02"/> qu’un corps eſt plus peſant qu’un autre <lb/>ſans avoir plus de matiere: </s> <s xml:id="echoid-s2510" xml:space="preserve">non contents <lb/>de cette idée, ils la ſoutiennent par une <pb o="195" file="0217" n="218" rhead="DE NEUTON."/> autre auſſi peu vraie: </s> <s xml:id="echoid-s2511" xml:space="preserve">ils admettent un grand <lb/>tourbillon de matiere ſubtile autour de notre <lb/>Globe; </s> <s xml:id="echoid-s2512" xml:space="preserve">& </s> <s xml:id="echoid-s2513" xml:space="preserve">c’eſt ce grand tourbillon, diſent-<lb/>ils, qui en circulant chaſſe tous les corps vers <lb/>le centre de la Terre, & </s> <s xml:id="echoid-s2514" xml:space="preserve">leur fait éprouver <lb/>ce que nous appellons peſanteur.</s> <s xml:id="echoid-s2515" xml:space="preserve"/> </p> <div xml:id="echoid-div119" type="float" level="2" n="6"> <note position="left" xlink:label="note-0216-02" xlink:href="note-0216-02a" xml:space="preserve">Le Syſ-<lb/>tême de <lb/>Deſcar-<lb/>tes ne <lb/>peut en <lb/>rendre <lb/>raiſon</note> </div> <p> <s xml:id="echoid-s2516" xml:space="preserve">Il eſt vrai qu’ils n’ont donné aucune preu-<lb/>ve de cette aſſertion: </s> <s xml:id="echoid-s2517" xml:space="preserve">il n’y a pas la moin-<lb/>dre expérience, pas la moindre analogie <lb/>dans les choſes que nous connoiſſons un peu, <lb/>qui puiſſe fonder une préſomption legére <lb/>en faveur de ce tourbillon de matiere ſub-<lb/>tile; </s> <s xml:id="echoid-s2518" xml:space="preserve">ainſi de cela ſeul que ce Syſtême eſt <lb/>une pure hipothèſe, il doit être rejetté. </s> <s xml:id="echoid-s2519" xml:space="preserve">C’eſt <lb/>cependant par cela ſeul qu’il a été accrédi-<lb/>té. </s> <s xml:id="echoid-s2520" xml:space="preserve">On concevoit ce tourbillon ſans effort, <lb/>on donnoit une explication vague des cho-<lb/>ſes en prononçant ce mot de matiere ſub-<lb/>tile; </s> <s xml:id="echoid-s2521" xml:space="preserve">& </s> <s xml:id="echoid-s2522" xml:space="preserve">quand les Philoſophes ſentoient les <lb/>contradictions & </s> <s xml:id="echoid-s2523" xml:space="preserve">les abſurdités attachées à <lb/>ce Roman Philoſophique, ils ſongeoient à <lb/>le corriger plutôt qu’à l’abandonner.</s> <s xml:id="echoid-s2524" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2525" xml:space="preserve">Hugens & </s> <s xml:id="echoid-s2526" xml:space="preserve">tant d’autres y ont fait mille <lb/>corrections, dont ils avouoient eux-mêmes <lb/>l’inſuffiſance; </s> <s xml:id="echoid-s2527" xml:space="preserve">mais que mettrons-nous à la <pb o="196" file="0218" n="219" rhead="DE LA PHILOSOPHIE"/> place des tourbillons & </s> <s xml:id="echoid-s2528" xml:space="preserve">de la matiere ſubti-<lb/>le? </s> <s xml:id="echoid-s2529" xml:space="preserve">Ce raiſonnement trop ordinaire eſt ce-<lb/>lui qui affermit le plus les hommes dans l’er-<lb/>reur & </s> <s xml:id="echoid-s2530" xml:space="preserve">dans le mauvais parti. </s> <s xml:id="echoid-s2531" xml:space="preserve">Il faut aban-<lb/>donner ce que l’on voit faux & </s> <s xml:id="echoid-s2532" xml:space="preserve">inſoutena-<lb/>ble, auſſi-bien quand on n’a rien à lui ſub-<lb/>ſtituer, que quand on auroit les démonſtra-<lb/>tions d’Euclide à mettre à la place. </s> <s xml:id="echoid-s2533" xml:space="preserve">Une <lb/>erreur n’eſt ni plus ni moins erreur, ſoit <lb/>qu’on la remplace ou non par des vérités; <lb/></s> <s xml:id="echoid-s2534" xml:space="preserve">devrois-je admettre l’horreur du vuide dans <lb/>une pompe, parce que je ne ſaurois pas <lb/>encore par quel méchaniſme l’eau monte <lb/>dans cette pompe?</s> <s xml:id="echoid-s2535" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2536" xml:space="preserve">Commençons donc, avant que d’aller <lb/>plus loin, par prouver que les tourbillons <lb/>de matiere ſubtile n’exiſtent pas: </s> <s xml:id="echoid-s2537" xml:space="preserve">que le Plein <lb/>n’eſt pas moins chimérique; </s> <s xml:id="echoid-s2538" xml:space="preserve">qu’ainſi tout <lb/>ce Syſtê<unsure/>me, fondé ſur ces imaginations, n’eſt <lb/>qu’un Roman ingénieux ſans vraiſemblan-<lb/>ce. </s> <s xml:id="echoid-s2539" xml:space="preserve">Voyons ce que c’eſt que ces tourbil-<lb/>lons imaginaires, & </s> <s xml:id="echoid-s2540" xml:space="preserve">examinons enſuite ſi <lb/>le Plein eſt poſſible.</s> <s xml:id="echoid-s2541" xml:space="preserve"/> </p> <pb file="0219" n="220"/> <figure> <image file="0219-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0219-01"/> </figure> </div> <div xml:id="echoid-div121" type="section" level="1" n="25"> <head xml:id="echoid-head42" xml:space="preserve">CHAPITRE SEIZE.</head> <head xml:id="echoid-head43" style="it" xml:space="preserve">Que les tourbillons de Deſcartes & le Plein ſont <lb/>impoſſibles, & que par conſéquent il y a <lb/>une autre cauſe de la peſanteur.</head> <p> <s xml:id="echoid-s2542" xml:space="preserve">DESCARTES ſuppoſe un amas im-<lb/>menſe de particules inſenſibles, qui <lb/>emporte la Terre d’un mouvement rapide <lb/>d’Occident en Orient, & </s> <s xml:id="echoid-s2543" xml:space="preserve">qui d’un Pole à <lb/>l’autre ſe meut parallèlement à l’Equateur; <lb/></s> <s xml:id="echoid-s2544" xml:space="preserve">ce tourbillon qui s’étend au-delà de la Lu- <pb o="198" file="0220" n="221" rhead="DE LA PHILOSOPHIE"/> ne, & </s> <s xml:id="echoid-s2545" xml:space="preserve">qui entraîne la Lune dans ſon cours, <lb/>eſt lui-même enchaſſé dans un autre tour-<lb/>billon plus vaſte encore, qui touche à un <lb/>autre tourbillon ſans ſe confondre avec lui, <lb/>&</s> <s xml:id="echoid-s2546" xml:space="preserve">c.</s> <s xml:id="echoid-s2547" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2548" xml:space="preserve">1<emph style="super">0</emph>. </s> <s xml:id="echoid-s2549" xml:space="preserve">Si cela étoit, le tourbillon qui eſt <lb/> <anchor type="note" xlink:label="note-0220-01a" xlink:href="note-0220-01"/> ſuppoſé ſe mouvoir autour de la Terre d’Oc-<lb/>cident en Orient, devroit chaſſer les corps <lb/>ſur la Terre d’Occident en Orient: </s> <s xml:id="echoid-s2550" xml:space="preserve">or les <lb/>corps en tombant décrivent tous une ligne, <lb/>qui étant prolongée paſſeroit, à-peu-près, <lb/>par le centre de la Terre; </s> <s xml:id="echoid-s2551" xml:space="preserve">donc ce tour-<lb/>billon n’exiſte pas.</s> <s xml:id="echoid-s2552" xml:space="preserve"/> </p> <div xml:id="echoid-div121" type="float" level="2" n="1"> <note position="left" xlink:label="note-0220-01" xlink:href="note-0220-01a" xml:space="preserve">Preuve <lb/>de l’im-<lb/>poſſibi-<lb/>lité des <lb/>tourbil-<lb/>lons.</note> </div> <p> <s xml:id="echoid-s2553" xml:space="preserve">2<emph style="super">0</emph>. </s> <s xml:id="echoid-s2554" xml:space="preserve">Si les cercles de ce prétendu tour-<lb/>billon ſe meuvent & </s> <s xml:id="echoid-s2555" xml:space="preserve">agiſſent parallèlement <lb/>à l’Equateur, tous les corps devroient tom-<lb/>ber chacun perpendiculairement ſous le cer-<lb/>cle de cette matiere ſubtile auquel il ré-<lb/>pond: </s> <s xml:id="echoid-s2556" xml:space="preserve">un corps en A. </s> <s xml:id="echoid-s2557" xml:space="preserve">près du Pole P. </s> <s xml:id="echoid-s2558" xml:space="preserve">de-<lb/>vroit, ſelon Deſcartes, tomber en R.</s> <s xml:id="echoid-s2559" xml:space="preserve"/> </p> <pb o="199" file="0221" n="222" rhead="DE NEUTON."/> <figure> <image file="0221-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0221-01"/> </figure> <p> <s xml:id="echoid-s2560" xml:space="preserve">Mais il tombe à-peu-près ſelon la ligne <lb/>A, B. </s> <s xml:id="echoid-s2561" xml:space="preserve">ce qui fait une différence d’environ <lb/>1400 lieues; </s> <s xml:id="echoid-s2562" xml:space="preserve">car on peut compter 1400 <lb/>lieues communes de France du point R à <lb/>l’Equateur de la Terre B.</s> <s xml:id="echoid-s2563" xml:space="preserve">; donc ce tour-<lb/>billon n’éxiſte pas.</s> <s xml:id="echoid-s2564" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2565" xml:space="preserve">3<emph style="super">0</emph>. </s> <s xml:id="echoid-s2566" xml:space="preserve">Si ce tourbillon de matiere autour de <lb/>la Terre, & </s> <s xml:id="echoid-s2567" xml:space="preserve">ces autres prétendus tourbil-<lb/>lons autour de Jupiter & </s> <s xml:id="echoid-s2568" xml:space="preserve">de Saturne, &</s> <s xml:id="echoid-s2569" xml:space="preserve">c. <lb/></s> <s xml:id="echoid-s2570" xml:space="preserve">éxiſtoient, tous ces tourbillons immenſes <lb/>de matiere ſubtile, roulant ſi rapidement <lb/>dans des directions différentes, ne pour-<lb/>roient jamais laiſſer venir à nous, en ligne <lb/>droite, un rayon de lumiere dardé d’une <pb o="200" file="0222" n="223" rhead="DE LA PHILOSOPHIE"/> Etoile. </s> <s xml:id="echoid-s2571" xml:space="preserve">Il eſt prouvé que ces rayons arri-<lb/>vent en très - peu de tems par rapport au <lb/>chemin immenſe qu’ils font; </s> <s xml:id="echoid-s2572" xml:space="preserve">donc ces tour-<lb/>billons n’éxiſtent pas.</s> <s xml:id="echoid-s2573" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2574" xml:space="preserve">4<emph style="super">0</emph>. </s> <s xml:id="echoid-s2575" xml:space="preserve">Si ces tourbillons emportoient les Pla-<lb/>netes d’Occident en Orient, les Cometes, <lb/>qui traverſent en tout ſens ces eſpaces d’O-<lb/>rient en Occident & </s> <s xml:id="echoid-s2576" xml:space="preserve">du Nord au Sud, ne <lb/>les pourroient jamais traverſer. </s> <s xml:id="echoid-s2577" xml:space="preserve">Et quand <lb/>on ſuppoſeroit que les Cometes n’ont point <lb/>été en effet du Nord au Sud, ni d’Orient en <lb/>Occident, on ne gagneroit rien par cette <lb/>évaſion, car on ſait que quand une Come-<lb/>te ſe trouve dans la région de Mars, de <lb/>Jupiter, de Saturne, elle va incompara-<lb/>blement plus vîte que Mars, que Jupiter, <lb/>que Saturne; </s> <s xml:id="echoid-s2578" xml:space="preserve">donc elle ne peut-être em-<lb/>portée, par la même couche du fluide qui <lb/>eſt ſuppoſé emporter ces Planetes; </s> <s xml:id="echoid-s2579" xml:space="preserve">donc <lb/>ces tourbillons n’éxiſtent pas.</s> <s xml:id="echoid-s2580" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2581" xml:space="preserve">5<emph style="super">0</emph>. </s> <s xml:id="echoid-s2582" xml:space="preserve">Ces prétendus tourbillons ſeroient ou <lb/>auſſi denſes, auſſi maſſifs que les Planetes, <lb/>ou bien ils ſeroient plus denſes, ou enfin <lb/>moins denſes. </s> <s xml:id="echoid-s2583" xml:space="preserve">Dans le premier cas, la <lb/>matiere prétendue, qui entoure la Lune & </s> <s xml:id="echoid-s2584" xml:space="preserve"><lb/>la Terre, étant ſuppoſée denſe comme un <lb/>égal volume de Terre, nous éprouverions <pb o="201" file="0223" n="224" rhead="DE NEUTON."/> pour lever un pied cubique de Marbre, <lb/>p r exemple, la même réſiſtance que ſi <lb/>nous avions à lever une colomne de Mar-<lb/>bre d’un pied de baſe, qui auroit pour ſa <lb/>longueur la diſtance de la Terre à la Lune. <lb/></s> <s xml:id="echoid-s2585" xml:space="preserve">Dans le deuxième cas, la matiere fluide <lb/>étant plus grave que la Terre, notre Glo-<lb/>be nageroit ſur ce fluide, comme un Vaiſ-<lb/>ſeau nage ſu@ l’Eau, & </s> <s xml:id="echoid-s2586" xml:space="preserve">ne pourroit être <lb/>plongé, comme on le prétend, dans cette <lb/>matiere ſubtile. </s> <s xml:id="echoid-s2587" xml:space="preserve">Dans le troiſième cas, le <lb/>fluide étant moins denſe, moins peſant que <lb/>la Terre, ce fluide ne pourroit jamais la <lb/>ſoutenir, par la raiſon que l’Eau ne peut <lb/>ſoutenir le fer, ni rien de ce qui peſe plus <lb/>qu’elle; </s> <s xml:id="echoid-s2588" xml:space="preserve">donc ces tourbillons n’éxiſtent pas.</s> <s xml:id="echoid-s2589" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2590" xml:space="preserve">6<emph style="super">0</emph>. </s> <s xml:id="echoid-s2591" xml:space="preserve">Si ces fluides imaginaires éxiſtoient, <lb/>tout l’ordre des Aſtres ſeroit interverti: <lb/></s> <s xml:id="echoid-s2592" xml:space="preserve">le Soleil qui tourne ſur lui-même, perdroit <lb/>bien-tôt de ſon mouvement à force de ren-<lb/>contrer ce fluide; </s> <s xml:id="echoid-s2593" xml:space="preserve">& </s> <s xml:id="echoid-s2594" xml:space="preserve">aucune des Planetes <lb/>ne ſuivroit la route qu’elle tient, n’auroit le <lb/>mouvement qu’elle a, n’auroit bien-tôt au-<lb/>cun mouvement.</s> <s xml:id="echoid-s2595" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2596" xml:space="preserve">7<emph style="super">0</emph>. </s> <s xml:id="echoid-s2597" xml:space="preserve">Les Planetes emportées dans ces tour-<lb/>billons ſuppoſés ne pourroient ſe mouvoir <lb/>que circulairement, puiſque ces tourbil- <pb o="202" file="0224" n="225" rhead="DE LA PHILOSOPHIE"/> lons, à égales diſtances du centre, ſe-<lb/>roient également denſes; </s> <s xml:id="echoid-s2598" xml:space="preserve">mais les Planetes <lb/>ſe meuvent dans des Ellipſes; </s> <s xml:id="echoid-s2599" xml:space="preserve">donc elles <lb/>ne peuvent être portées par des tourbillons; <lb/></s> <s xml:id="echoid-s2600" xml:space="preserve">donc, &</s> <s xml:id="echoid-s2601" xml:space="preserve">c.</s> <s xml:id="echoid-s2602" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2603" xml:space="preserve">8<emph style="super">0</emph>. </s> <s xml:id="echoid-s2604" xml:space="preserve">La Terre a ſon Orbite qu’elle par-<lb/>court entre celui de Venus & </s> <s xml:id="echoid-s2605" xml:space="preserve">celui de <lb/>Mars: </s> <s xml:id="echoid-s2606" xml:space="preserve">tous ces Orbites ſont elliptiques, & </s> <s xml:id="echoid-s2607" xml:space="preserve"><lb/>ont le Soleil pour centre: </s> <s xml:id="echoid-s2608" xml:space="preserve">or quand Mars, <lb/>& </s> <s xml:id="echoid-s2609" xml:space="preserve">Venus & </s> <s xml:id="echoid-s2610" xml:space="preserve">la Terre ſont plus près l’un de <lb/>l’autre, alors la matiere du torrent préten-<lb/>du, qui emporte la Terre, ſeroit beaucoup <lb/>plus reſſerrée: </s> <s xml:id="echoid-s2611" xml:space="preserve">cette matiere ſubtile devroit <lb/>précipiter ſon cours, comme un Fleuve <lb/>rétreci dans ſes bords, ou coulant ſous les <lb/>arches d’un Pont: </s> <s xml:id="echoid-s2612" xml:space="preserve">alors ce fluide devroit <lb/>emporter la Terre d’une rapidité bien plus <lb/>grande qu’en toute autre poſition; </s> <s xml:id="echoid-s2613" xml:space="preserve">mais <lb/>au contraire c’eſt dans ce tems-là même <lb/>que le mouvement de la Terre eſt plus <lb/>ralenti.</s> <s xml:id="echoid-s2614" xml:space="preserve"/> </p> <pb o="203" file="0225" n="226" rhead="DE NEUTON."/> <figure> <image file="0225-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0225-01"/> </figure> <p> <s xml:id="echoid-s2615" xml:space="preserve">Quand Mars paroît dans le Signe des Poif-<lb/>ſons, Mars, la Terre & </s> <s xml:id="echoid-s2616" xml:space="preserve">Venus ſont à-peu-<lb/>près dans cette proximité que vous voyez: <lb/></s> <s xml:id="echoid-s2617" xml:space="preserve">alors le Soleil paroît retarder de quelque <lb/>minutes, c’eſt-à-dire que c’eſt la Terre qui <lb/>retarde; </s> <s xml:id="echoid-s2618" xml:space="preserve">il eſt donc démontré impoſſible <lb/>qu’il y ait là un torrent de matiere qui em-<lb/>porte les Planetes; </s> <s xml:id="echoid-s2619" xml:space="preserve">donc ce tourbillon n’é-<lb/>xiſte pas.</s> <s xml:id="echoid-s2620" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2621" xml:space="preserve">9<emph style="super">0</emph>. </s> <s xml:id="echoid-s2622" xml:space="preserve">Parmi des démonſtrations plus re-<lb/>cherchées, qui anéantiſſent les tourbillons, <lb/>nous choiſirons celle-ci. </s> <s xml:id="echoid-s2623" xml:space="preserve">Par une des gran- <pb o="204" file="0226" n="227" rhead="DE LA PHIL OSOPHIE"/> des loix de Kepler, toute Planete décrit <lb/>des aires égales en tems égaux: </s> <s xml:id="echoid-s2624" xml:space="preserve">par une <lb/>autre loi non moins ſûre, chaque Planete <lb/>fait ſa révolution autour du Soleil en telle <lb/>ſorte, que ſi, par exemple, ſa moyenne <lb/>diſtance au Soleil eſt 10. </s> <s xml:id="echoid-s2625" xml:space="preserve">prenez le cube de <lb/>ce nombre, ce qui fera 1000.</s> <s xml:id="echoid-s2626" xml:space="preserve">, & </s> <s xml:id="echoid-s2627" xml:space="preserve">le tems <lb/>de la révolution de cette Planete autour du <lb/>Soleil ſera proportionné à la racine quar-<lb/>rée de ce nombre 1000. </s> <s xml:id="echoid-s2628" xml:space="preserve">Or s’il y avoit des <lb/>couches de matiere qui portaſſent des Pla-<lb/>netes, ces couches ne pourroient ſuivre <lb/>ces loix; </s> <s xml:id="echoid-s2629" xml:space="preserve">car il faudroit que les vîteſſes de <lb/>ces torrents fuſſent à la fois proportionelles <lb/>à leur diſtances au Soleil, & </s> <s xml:id="echoid-s2630" xml:space="preserve">aux racines <lb/>quarrées de ces diſtances; </s> <s xml:id="echoid-s2631" xml:space="preserve">ce qui eſt incom-<lb/>patible.</s> <s xml:id="echoid-s2632" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2633" xml:space="preserve">Pour comble enſin, tout le monde voit <lb/>ce qui arriveroit à deux fluides circulant <lb/>l’un vis-à-vis de l’autre. </s> <s xml:id="echoid-s2634" xml:space="preserve">Ils ſe conſondroient <lb/>néceſſairement & </s> <s xml:id="echoid-s2635" xml:space="preserve">formeroient le Chaos au <lb/>lieu de le débrouiller. </s> <s xml:id="echoid-s2636" xml:space="preserve">Cela ſeul auroit <lb/>jetté ſur le Syſtême Cartéſien un ridicule <lb/>qui l’eût accablé, ſi le goût de la nouveauté, <lb/>& </s> <s xml:id="echoid-s2637" xml:space="preserve">le peu d’uſage où l’on étoit alors d’exa-<lb/>miner, n’avoient prévalu.</s> <s xml:id="echoid-s2638" xml:space="preserve"/> </p> <pb o="205" file="0227" n="228" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s2639" xml:space="preserve">Il faut prouver à préſent que le Plein, <lb/>dans lequel ces tourbillons ſont ſuppoſés ſe <lb/>mouvoir, eſt auſſi impoſſible que ces tour-<lb/>billons.</s> <s xml:id="echoid-s2640" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2641" xml:space="preserve">1<emph style="super">0</emph>. </s> <s xml:id="echoid-s2642" xml:space="preserve">Un ſeul rayon de lumiere, qui ne Preuve <lb/> <anchor type="note" xlink:label="note-0227-01a" xlink:href="note-0227-01"/> peſe pas, à beaucoup près, la cent - milliè-<lb/>me partie d’un grain, auroit à déranger <lb/>tout l’Univers, ſi elle avoit à s’ouvrir un <lb/>chemin juſqu’à nous à travers un eſpace <lb/>immenſe, dont chaque point réſiſteroit par <lb/>lui-même, & </s> <s xml:id="echoid-s2643" xml:space="preserve">par toute la ligne dont il ſe-<lb/>roit preſſé.</s> <s xml:id="echoid-s2644" xml:space="preserve"/> </p> <div xml:id="echoid-div122" type="float" level="2" n="2"> <note position="right" xlink:label="note-0227-01" xlink:href="note-0227-01a" xml:space="preserve">Preuve <lb/>contre <lb/>le Plein.</note> </div> <p> <s xml:id="echoid-s2645" xml:space="preserve">2<emph style="super">0</emph>. </s> <s xml:id="echoid-s2646" xml:space="preserve">Soient ces deux corps durs A, B: </s> <s xml:id="echoid-s2647" xml:space="preserve">(nous <lb/>avons déja prouvé qu’il faut qu’il y ait des <lb/>corps durs) ils ſe touchent par une ſurface, <lb/>& </s> <s xml:id="echoid-s2648" xml:space="preserve">ſont ſuppoſés entourés d’un fluidé qui les <lb/>preſſe de tous côtés: </s> <s xml:id="echoid-s2649" xml:space="preserve">or, quand on les ſé-<lb/>pare, il eſt clair que la prétendue matie-<lb/>re ſubtile arrive plutôt au point A, où on <lb/>les ſépare, qu’au point B;</s> <s xml:id="echoid-s2650" xml:space="preserve"/> </p> <pb o="206" file="0228" n="229" rhead="DE LA PHILOSOPHIE"/> <figure> <image file="0228-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0228-01"/> </figure> <p> <s xml:id="echoid-s2651" xml:space="preserve">Donc il y a un moment où B ſera vui-<lb/>de; </s> <s xml:id="echoid-s2652" xml:space="preserve">donc même dans le Syſtême de la ma-<lb/>tiere ſubtile, il y a du vuide, c’eſt-à-dire <lb/>de l’eſpace.</s> <s xml:id="echoid-s2653" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2654" xml:space="preserve">3<emph style="super">0</emph>. </s> <s xml:id="echoid-s2655" xml:space="preserve">S’il n’y avoit point de vuide & </s> <s xml:id="echoid-s2656" xml:space="preserve">d’eſpa-<lb/>ce, il n’y auroit point de mouvement, mê-<lb/>me dans le Syſtême de Deſcartes. </s> <s xml:id="echoid-s2657" xml:space="preserve">Il ſup-<lb/>poſe que Dieu créa l’Univers plein & </s> <s xml:id="echoid-s2658" xml:space="preserve">con-<lb/>ſiſtant en petits cubes: </s> <s xml:id="echoid-s2659" xml:space="preserve">ſoit donc un nom-<lb/>bre donné de cubes repréſentant l’Uni-<lb/>vers, ſans qu’il y ait entre eux le moindre <lb/>intervalle: </s> <s xml:id="echoid-s2660" xml:space="preserve">il eſt évident qu’il faut qu’un <lb/>d’eux ſorte de la place qu’il occupoit, car <lb/>ſi chacun reſte dans ſa place, il n’y a point <lb/>de mouvement, puiſque le mouvement con-<lb/>ſiſte à ſortir de ſa place, à paſſer d’un point <lb/>de l’eſpace dans un autre point de l’eſpace; <lb/></s> <s xml:id="echoid-s2661" xml:space="preserve">or qui ne voit que l’un de ces cubes ne <pb o="207" file="0229" n="230" rhead="DE NEUTON."/> peut quitter ſa place ſans la laiſſer vuide á <lb/>l’inſtant qu’il en ſort, car il eſt clair que <lb/>ce cube en tournant ſur lui-même doit pré-<lb/>ſenter ſon angle au cube qui le touche, a-<lb/>vant que l’angle ſoit briſé? </s> <s xml:id="echoid-s2662" xml:space="preserve">donc alors il y <lb/>a de l’eſpace entre ces deux cubes; </s> <s xml:id="echoid-s2663" xml:space="preserve">donc <lb/>dans le Syſtême de Deſcartes même, il ne <lb/>peut y avoir de mouvement ſans vuide.</s> <s xml:id="echoid-s2664" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2665" xml:space="preserve">4<emph style="super">0</emph>. </s> <s xml:id="echoid-s2666" xml:space="preserve">Si tout étoit plein, comme le veut <lb/>Deſcartes, nous éprouverions nous-mêmes <lb/>en marchant une réſiſtance infinie, au lieu <lb/>que nous n’éprouvons que celle des fluides <lb/>dans leſquelles nous ſommes, par exemple, <lb/>celle de l’eau qui nous réſiſte 860. </s> <s xml:id="echoid-s2667" xml:space="preserve">fois plus <lb/>que celle de l’air, celle du mercure qui ré-<lb/>ſiſte environ 14000. </s> <s xml:id="echoid-s2668" xml:space="preserve">fois plus que l’air; </s> <s xml:id="echoid-s2669" xml:space="preserve">or les <lb/>réſiſtances des fluides ſont comme les quar-<lb/>rés des vîteſſes; </s> <s xml:id="echoid-s2670" xml:space="preserve">c’eſt-à-dire, ſi un homme <lb/>parcourt dans une tierce un pied d’eſpace <lb/>du mercure qui lui réſiſte 14000. </s> <s xml:id="echoid-s2671" xml:space="preserve">fois plus <lb/>que l’air, ſi cet homme dans la ſeconde <lb/>tierce a le double de cette vîteſſe, ce mer-<lb/>cure lui réſiſtera dans la ſeconde tierce com-<lb/>me le quarré de 2. </s> <s xml:id="echoid-s2672" xml:space="preserve">multiplié par 14000.</s> <s xml:id="echoid-s2673" xml:space="preserve">, <lb/>réſiſtance 56000. </s> <s xml:id="echoid-s2674" xml:space="preserve">fois plus forte que celle de <lb/>l’air qui réſiſte alors à nos mouvemens; </s> <s xml:id="echoid-s2675" xml:space="preserve">donc <lb/>ſi tout étoit plein, il ſeroit abſolument im- <pb o="208" file="0230" n="231" rhead="DE LA PHILOSOPHIE"/> poſſible de faire un pas, de reſpirer, <lb/>&</s> <s xml:id="echoid-s2676" xml:space="preserve">c.</s> <s xml:id="echoid-s2677" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2678" xml:space="preserve">5<emph style="super">0</emph>. </s> <s xml:id="echoid-s2679" xml:space="preserve">On a voulu éluder la force de cette <lb/>démonſtration; </s> <s xml:id="echoid-s2680" xml:space="preserve">mais on ne peut répondre <lb/>à une démonſtration que par une erreur. <lb/></s> <s xml:id="echoid-s2681" xml:space="preserve">On prétend que ce torrent infini de matie-<lb/>re ſubtile pénétrant tous les pores des corps, <lb/>ne peut en arrêter le mouvement. </s> <s xml:id="echoid-s2682" xml:space="preserve">On ne <lb/>fait pas réflexion que tout mobile, qui ſe <lb/>meut dans un fluide, éprouve d’autant plus <lb/>de réſiſtance, qu’il oppoſe plus de ſurface <lb/>à ce fluide: </s> <s xml:id="echoid-s2683" xml:space="preserve">or plus un corps a de trous <lb/>plus il a de ſurface: </s> <s xml:id="echoid-s2684" xml:space="preserve">ainſi la prétendue <lb/>matiere ſubtile en choquant tout l’intérieur <lb/>d’un corps, s’oppoſeroit bien davantage au <lb/>mouvement de ce corps, qu’en ne touchant <lb/>que ſa ſuperficie extérieure; </s> <s xml:id="echoid-s2685" xml:space="preserve">& </s> <s xml:id="echoid-s2686" xml:space="preserve">cela eſt en-<lb/>core démontré en rigueur.</s> <s xml:id="echoid-s2687" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2688" xml:space="preserve">6<emph style="super">0</emph>. </s> <s xml:id="echoid-s2689" xml:space="preserve">Dans le Plein tous les corps ſeroient <lb/>également peſants; </s> <s xml:id="echoid-s2690" xml:space="preserve">il eſt impoſſible de con-<lb/>cevoir qu’un corps peſe ſur moi, me preſſe, <lb/>que par ſa maſſe une livre de poudre d’or <lb/>peſe autant ſur ma main, qu’un morceau d’or <lb/>d’une livre. </s> <s xml:id="echoid-s2691" xml:space="preserve">En vain les Cartéſiens répon-<lb/>dent que la matiere ſubtile pénétrant les in-<lb/>terſtices des corps ne peſe point, & </s> <s xml:id="echoid-s2692" xml:space="preserve">qu’il <lb/>ne faut compter pour peſant que ce qui n’eſt <pb o="209" file="0231" n="232" rhead="DE NEUTON."/> point matiere ſubtile: </s> <s xml:id="echoid-s2693" xml:space="preserve">cette opinion de <lb/>Deſcartes n’eſt chez lui qu’une pure contra-<lb/>diction, car ſelon lui cette prétendue ma-<lb/>tieré ſubtile fait ſeule la peſanteur des corps, <lb/>en les repouſſant vers la Terre; </s> <s xml:id="echoid-s2694" xml:space="preserve">donc elle <lb/>peſe elle-même ſur ces corps; </s> <s xml:id="echoid-s2695" xml:space="preserve">donc, ſi elle <lb/>peſe, il n’y a pas plus de raiſon pourquoi <lb/>un corps ſera plus peſant qu’un autre, puiſ-<lb/>que tout étant plein, tout aura également <lb/>de maſſe, ſoit ſolide, ſoit fluide; </s> <s xml:id="echoid-s2696" xml:space="preserve">donc le <lb/>Plein eſt une chimére; </s> <s xml:id="echoid-s2697" xml:space="preserve">donc il y a du vui-<lb/>de; </s> <s xml:id="echoid-s2698" xml:space="preserve">donc rien ne ſe peut faire dans la Na-<lb/>ture ſans vuide; </s> <s xml:id="echoid-s2699" xml:space="preserve">donc la peſanteur n’eſt pas <lb/>l’effet d’un prétendu tourbillon imaginé dans <lb/>le Plein.</s> <s xml:id="echoid-s2700" xml:space="preserve"/> </p> <figure> <image file="0231-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0231-01"/> </figure> <pb file="0232" n="233"/> <figure> <image file="0232-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0232-01"/> </figure> </div> <div xml:id="echoid-div124" type="section" level="1" n="26"> <head xml:id="echoid-head44" xml:space="preserve">CHAPITRE DIX-SEPT.</head> <head xml:id="echoid-head45" xml:space="preserve">Ce que c’eſt que le Vuide, & l’Eſpace, ſans lequel <lb/>il n’y auroit ni peſanteur ni mouvement.</head> <p> <s xml:id="echoid-s2701" xml:space="preserve">CEUX qui ne peuvent concevoir le Vui-<lb/> <anchor type="note" xlink:label="note-0232-01a" xlink:href="note-0232-01"/> de, objectent que ce Vuide ne ſeroit <lb/>rien, que le rien ne peut avoir des pro-<lb/>prietés, & </s> <s xml:id="echoid-s2702" xml:space="preserve">qu’ainſi il ne ſe pourroit rien <lb/>opérer dans le Vuide.</s> <s xml:id="echoid-s2703" xml:space="preserve"/> </p> <div xml:id="echoid-div124" type="float" level="2" n="1"> <note position="left" xlink:label="note-0232-01" xlink:href="note-0232-01a" xml:space="preserve">Diffi-<lb/>culté <lb/>contre <lb/>le Vai-<lb/>de.</note> </div> <p> <s xml:id="echoid-s2704" xml:space="preserve">On répond qu’il n’eſt pas vrai que le <lb/> <anchor type="note" xlink:label="note-0232-02a" xlink:href="note-0232-02"/> Vuide ſoit rien; </s> <s xml:id="echoid-s2705" xml:space="preserve">il eſt le lieu des corps, il eſt <lb/>l’eſpace, il a des proprietés, il eſt étendu <pb o="211" file="0233" n="234" rhead="DENEUTON."/> en longueur, largueur & </s> <s xml:id="echoid-s2706" xml:space="preserve">profondeur, il eſt <lb/>pénétrable, il eſt inſéparable, &</s> <s xml:id="echoid-s2707" xml:space="preserve">c. </s> <s xml:id="echoid-s2708" xml:space="preserve">Il eſt <lb/>vrai que je ne peux pas me faire dans le <lb/>cerveau une image de l’Eſpace étendu, com-<lb/>me je m’en fais une du Corps étendu; </s> <s xml:id="echoid-s2709" xml:space="preserve">mais <lb/>je me ſuis démontré que cet Eſpace éxiſte. <lb/></s> <s xml:id="echoid-s2710" xml:space="preserve">Je ne puis en Géométrie me repréſenter une <lb/>infinité de cercles paſſant entre un cercle & </s> <s xml:id="echoid-s2711" xml:space="preserve"><lb/>une tangente; </s> <s xml:id="echoid-s2712" xml:space="preserve">mais je me ſuis démontré <lb/>cependant que la choſe eſt vraie en Géo-<lb/>métrie, & </s> <s xml:id="echoid-s2713" xml:space="preserve">cela ſuffit. </s> <s xml:id="echoid-s2714" xml:space="preserve">Je ne puis conce-<lb/>voir ce que c’eſt qui penſe en moi, je ſuis <lb/>cependant convaincu que quelque choſe <lb/>penſe en moi. </s> <s xml:id="echoid-s2715" xml:space="preserve">De même je me démontre <lb/>l’impoſſibilité du Plein & </s> <s xml:id="echoid-s2716" xml:space="preserve">la néceſſité du <lb/>Vuide, ſans avoir une image du Vuide; </s> <s xml:id="echoid-s2717" xml:space="preserve">car <lb/>je n’ai d’image que de ce qui eſt corporel, <lb/>& </s> <s xml:id="echoid-s2718" xml:space="preserve">l’Eſpace n’eſt point corporel. </s> <s xml:id="echoid-s2719" xml:space="preserve">Autre cho-<lb/>ſe eſt ſe repréſenter une image, autre cho-<lb/>ſe eſt concevoir une vérité; </s> <s xml:id="echoid-s2720" xml:space="preserve">je conçois <lb/>très-bien l’Eſpace, & </s> <s xml:id="echoid-s2721" xml:space="preserve">les Philoſophes Epi-<lb/>curiens, qui n’avoient guère raiſon qu’en <lb/>cela, le concevoient très-bien.</s> <s xml:id="echoid-s2722" xml:space="preserve"/> </p> <div xml:id="echoid-div125" type="float" level="2" n="2"> <note position="left" xlink:label="note-0232-02" xlink:href="note-0232-02a" xml:space="preserve">Répon-<lb/>ſe,</note> </div> <p> <s xml:id="echoid-s2723" xml:space="preserve">Il n’y avoit d’autre réponſe à cet Argu-<lb/>ment que de dire que la Matiere eſt infi-<lb/>nie; </s> <s xml:id="echoid-s2724" xml:space="preserve">c’eſt ce que pluſieurs Philoſophes ont <pb o="212" file="0234" n="235" rhead="DELA PHILOSOPHIE"/> aſſûré, & </s> <s xml:id="echoid-s2725" xml:space="preserve">ce que Deſcartes a renouvellé <lb/>après eux.</s> <s xml:id="echoid-s2726" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2727" xml:space="preserve">Mais ſurquoi imagine-t-on que la Matie-<lb/> <anchor type="note" xlink:label="note-0234-01a" xlink:href="note-0234-01"/> re eſt infinie? </s> <s xml:id="echoid-s2728" xml:space="preserve">Sur une autre ſuppoſition que <lb/>l’on s’eſt plû de faire. </s> <s xml:id="echoid-s2729" xml:space="preserve">On dit: </s> <s xml:id="echoid-s2730" xml:space="preserve">l’Etendue <lb/>& </s> <s xml:id="echoid-s2731" xml:space="preserve">la Matiere ſont la même choſe: </s> <s xml:id="echoid-s2732" xml:space="preserve">on ne <lb/>peut concevoir que l’Etendue ſoit finie; <lb/></s> <s xml:id="echoid-s2733" xml:space="preserve">donc il faut admettre la Matiere infinie.</s> <s xml:id="echoid-s2734" xml:space="preserve"/> </p> <div xml:id="echoid-div126" type="float" level="2" n="3"> <note position="left" xlink:label="note-0234-01" xlink:href="note-0234-01a" xml:space="preserve">La Ma-<lb/>tiére <lb/>n’eſt pas <lb/>infinie.</note> </div> <p> <s xml:id="echoid-s2735" xml:space="preserve">Cela prouve combien on s’égare, quand <lb/>on ne raiſonne que ſur des ſuppoſitions. </s> <s xml:id="echoid-s2736" xml:space="preserve">Il <lb/>eſt faux que l’Etendue & </s> <s xml:id="echoid-s2737" xml:space="preserve">la Matiere ſoient <lb/>la même choſe: </s> <s xml:id="echoid-s2738" xml:space="preserve">toute matiere eſt étendue; <lb/></s> <s xml:id="echoid-s2739" xml:space="preserve">mais toute étendue n’eſt pas matiere. </s> <s xml:id="echoid-s2740" xml:space="preserve">Deſ-<lb/>cartes en avançant que l’Etendue ne peut-<lb/>être que de la matiere, diſoit une choſe bien <lb/>peu Philoſophique, car nous ne ſavons point <lb/>du tout ce que c’eſt que Matiere; </s> <s xml:id="echoid-s2741" xml:space="preserve">nous en <lb/>connoiſſons ſeulement quelques proprietés, <lb/>& </s> <s xml:id="echoid-s2742" xml:space="preserve">perſonne ne peut nier qu’il ne ſoit poſſi-<lb/>ble qu’il éxiſte des millions d’autres ſubſtan-<lb/>ces étendues, différentes de ce que nous <lb/>appellons Matiere; </s> <s xml:id="echoid-s2743" xml:space="preserve">or ces ſubſtances où <lb/>ſeront-elles, ſinon dans l’Eſpace?</s> <s xml:id="echoid-s2744" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2745" xml:space="preserve">Outre cette faute, Deſcartes ſe contre- <pb o="213" file="0235" n="236" rhead="DE NEUTON."/> diſoit encore, car il admettoit un Dieu; </s> <s xml:id="echoid-s2746" xml:space="preserve">or <lb/>où eſt Dieu? </s> <s xml:id="echoid-s2747" xml:space="preserve">Il n’eſt pas dans un point ma-<lb/>thématique, il eſt immenſe; </s> <s xml:id="echoid-s2748" xml:space="preserve">qu’eſt-ce que <lb/>ſon immenſité, ſinon l’Eſpace immenſe?</s> <s xml:id="echoid-s2749" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2750" xml:space="preserve">A l’égard de l’in finité prétendue de la Ma-<lb/>tiere, cette idée eſt auſſi peu fondée que <lb/>les tourbillons. </s> <s xml:id="echoid-s2751" xml:space="preserve">Nous avons vu que le <lb/>Vuide eſt d’une néceſſité abſolue dans l’or-<lb/>dre des choſes, & </s> <s xml:id="echoid-s2752" xml:space="preserve">qu’ainſi la Matiere ne rem-<lb/>pliſſant point tout l’Eſpace, elle n’eſt point <lb/>infinie; </s> <s xml:id="echoid-s2753" xml:space="preserve">mais, qu’entend-on par une Matiere <lb/>infinie? </s> <s xml:id="echoid-s2754" xml:space="preserve">car le mot d’indéfinie, dont Deſcar-<lb/> <anchor type="note" xlink:label="note-0235-01a" xlink:href="note-0235-01"/> tes s’eſt ſervi, ou revient au méme, ou ne <lb/>ſignifie rien. </s> <s xml:id="echoid-s2755" xml:space="preserve">Entend-on que la Matiere eſt <lb/>infinie eſſentiellement par ſa nature? </s> <s xml:id="echoid-s2756" xml:space="preserve">En ce <lb/>cas elle eſt donc Dieu? </s> <s xml:id="echoid-s2757" xml:space="preserve">Entend - on que <lb/>Dieu l’a créée infinie? </s> <s xml:id="echoid-s2758" xml:space="preserve">D’oú le ſauroit-on? <lb/></s> <s xml:id="echoid-s2759" xml:space="preserve">Entend on que l’Etendue & </s> <s xml:id="echoid-s2760" xml:space="preserve">la Matiere ſont <lb/>la même choſe? </s> <s xml:id="echoid-s2761" xml:space="preserve">C’eſt un argument dont on <lb/>a prouvé aſſez la fauſſeté.</s> <s xml:id="echoid-s2762" xml:space="preserve"/> </p> <div xml:id="echoid-div127" type="float" level="2" n="4"> <note position="right" xlink:label="note-0235-01" xlink:href="note-0235-01a" xml:space="preserve">Diſcuſ-<lb/>ſion de <lb/>cette <lb/>Vérité.</note> </div> <p> <s xml:id="echoid-s2763" xml:space="preserve">L’éxiſtence de la Matiere infinie eſt, au <lb/>fond, une contradiction dans les termes. </s> <s xml:id="echoid-s2764" xml:space="preserve">Mais <lb/>dira-t-on, vous admettez un Eſpace immen-<lb/>ſe, infini; </s> <s xml:id="echoid-s2765" xml:space="preserve">pourquoi n’en ferez-vous pas <lb/>autant de la Matiere? </s> <s xml:id="echoid-s2766" xml:space="preserve">Voici la différence:</s> <s xml:id="echoid-s2767" xml:space="preserve"> <pb o="214" file="0236" n="237" rhead="DE LA PHILOSOPHIE"/> L’Eſpace éxiſte néceſſairement, parce que <lb/>Dieu éxiſte néceſſairement; </s> <s xml:id="echoid-s2768" xml:space="preserve">il eſt im-<lb/>menſe, il eſt comme la durée, un mode, <lb/>une proprieté infinie d’un Etre néceſſaire, <lb/>infini. </s> <s xml:id="echoid-s2769" xml:space="preserve">La Matiere n’eſt rien de tout cela: <lb/></s> <s xml:id="echoid-s2770" xml:space="preserve">elle n’éxiſte point néceſſairement: </s> <s xml:id="echoid-s2771" xml:space="preserve">& </s> <s xml:id="echoid-s2772" xml:space="preserve">ſi cette <lb/>ſubſtance étoit infinie, elle ſeroit ou une <lb/>proprieté eſſentielle de Dieu, ou Dieu mê-<lb/>me: </s> <s xml:id="echoid-s2773" xml:space="preserve">or elle n’eſt ni l’un ni l’autre; </s> <s xml:id="echoid-s2774" xml:space="preserve">elle n’eſt <lb/>donc pas infinie & </s> <s xml:id="echoid-s2775" xml:space="preserve">ne ſauroit l’être.</s> <s xml:id="echoid-s2776" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2777" xml:space="preserve">Je conclurai ce Chapitre par une remar-<lb/> <anchor type="note" xlink:label="note-0236-01a" xlink:href="note-0236-01"/> que qui me paroît mériter beaucoup d’at-<lb/>tention. </s> <s xml:id="echoid-s2778" xml:space="preserve">Deſcartes admettoit un Dieu <lb/>Créateur & </s> <s xml:id="echoid-s2779" xml:space="preserve">Cauſe de tout: </s> <s xml:id="echoid-s2780" xml:space="preserve">mais il nioit la <lb/>poſſibilité du Vuide: </s> <s xml:id="echoid-s2781" xml:space="preserve">Epicure nioit qu’il y <lb/>eût un Dieu Créateur & </s> <s xml:id="echoid-s2782" xml:space="preserve">Cauſe de tout, & </s> <s xml:id="echoid-s2783" xml:space="preserve"><lb/>il admettoit le Vuide; </s> <s xml:id="echoid-s2784" xml:space="preserve">or c’étoit Deſcartes <lb/>qui par ſes principes devoit nier un Dieu <lb/>Créateur, & </s> <s xml:id="echoid-s2785" xml:space="preserve">c’étoit Epicure qui devoit l’ad-<lb/>mettre. </s> <s xml:id="echoid-s2786" xml:space="preserve">En voici la preuve évidente.</s> <s xml:id="echoid-s2787" xml:space="preserve"/> </p> <div xml:id="echoid-div128" type="float" level="2" n="5"> <note position="left" xlink:label="note-0236-01" xlink:href="note-0236-01a" xml:space="preserve">Remar-<lb/>que ſin-<lb/>guliére.</note> </div> <p> <s xml:id="echoid-s2788" xml:space="preserve">Si le Vuide étoit impoſſible, ſi la Matiere <lb/>étoit infinie, ſi l’Etendue & </s> <s xml:id="echoid-s2789" xml:space="preserve">la Matiree é-<lb/>toient la même choſe, il faudroit que la <lb/>Matiere fût néceſſaire: </s> <s xml:id="echoid-s2790" xml:space="preserve">or ſi la Matiere étoit <lb/>néceſſaire, elle éxiſteroit par elle-même d’une <lb/>néceſſité abſolue, inhérente dans ſa nature <pb o="215" file="0237" n="238" rhead="DE NEUTON."/> primordiale, antécédente à tout; </s> <s xml:id="echoid-s2791" xml:space="preserve">donc elle <lb/>ſeroit Dieu; </s> <s xml:id="echoid-s2792" xml:space="preserve">donc celui qui admet l’impoſſi-<lb/>bilité du Vuide, doit, s’il raiſonne conſé-<lb/>quemment, ne point admettre d’autre Dieu <lb/>que la Matiere.</s> <s xml:id="echoid-s2793" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2794" xml:space="preserve">Au contraire, s’il y a du vuide, la Ma-<lb/>tiere n’eſt donc point un Etre néceſſaire, <lb/>éxiſtant par lui-même, &</s> <s xml:id="echoid-s2795" xml:space="preserve">c.</s> <s xml:id="echoid-s2796" xml:space="preserve">; donc elle a été <lb/>créée; </s> <s xml:id="echoid-s2797" xml:space="preserve">donc il y a un Dieu; </s> <s xml:id="echoid-s2798" xml:space="preserve">donc c’étoit <lb/>à Epicure à croire un Dieu, & </s> <s xml:id="echoid-s2799" xml:space="preserve">c’étoit à Deſ-<lb/>cartes à le nier. </s> <s xml:id="echoid-s2800" xml:space="preserve">Pourquoi donc au con-<lb/>traire Deſcartes a-t il toujours parlé de l’éxiſ-<lb/>tence d’un Etre Créateur & </s> <s xml:id="echoid-s2801" xml:space="preserve">Conſervateur, <lb/>& </s> <s xml:id="echoid-s2802" xml:space="preserve">Epicure l’a - t - il rejetté? </s> <s xml:id="echoid-s2803" xml:space="preserve">C’eſt que les <lb/>hommes dans leurs ſentimens, comme dans <lb/>leur conduite, ſuivent rarement leurs prin-<lb/>cipes, & </s> <s xml:id="echoid-s2804" xml:space="preserve">que leurs Syſtêmes ainſi que leurs <lb/>vies ſont des contradictions.</s> <s xml:id="echoid-s2805" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2806" xml:space="preserve">Nous voyons de tout ce qui précéde que <lb/> <anchor type="note" xlink:label="note-0237-01a" xlink:href="note-0237-01"/> la Matiere eſt finie, qu’il y a du vuide, <lb/>c’eſt-à-dire, de l’eſpace, & </s> <s xml:id="echoid-s2807" xml:space="preserve">même incom-<lb/>parablement plus d’eſpace que de matiere <lb/>dans notre Monde; </s> <s xml:id="echoid-s2808" xml:space="preserve">car il y a beau-<lb/>coup plus de pores que de ſolides. </s> <s xml:id="echoid-s2809" xml:space="preserve">Nous <lb/>concluons que le Plein eſt impoſſible, que <pb o="216" file="0238" n="239" rhead="DE LA PHILOSOPHIE"/> les tourbillons de matiere ſubtile le ſont pa-<lb/>reillement; </s> <s xml:id="echoid-s2810" xml:space="preserve">qu’ainſi la cauſe que Deſcartes <lb/>aſſignoit à la peſanteur & </s> <s xml:id="echoid-s2811" xml:space="preserve">au mouvement <lb/>eſt une chimére.</s> <s xml:id="echoid-s2812" xml:space="preserve"/> </p> <div xml:id="echoid-div129" type="float" level="2" n="6"> <note position="right" xlink:label="note-0237-01" xlink:href="note-0237-01a" xml:space="preserve">Conclu-<lb/>ſion.</note> </div> <p> <s xml:id="echoid-s2813" xml:space="preserve">Nous venons de nous appercevoir par <lb/>l’expérience dans la Machine pneuma-<lb/>tique qu’il faut qu’il y ait une force qui <lb/>faſſe deſcendre les corps vers le cen-<lb/>tre de la Terre, c’eſt - à - dire, qui leur <lb/>donne la peſanteur, & </s> <s xml:id="echoid-s2814" xml:space="preserve">que cette force doit <lb/>agir en raiſon de la maſſe des corps; </s> <s xml:id="echoid-s2815" xml:space="preserve">il faut <lb/>maintenant voir quels ſont les effets de cette <lb/>force, car ſi nous en découvrons les effets, <lb/>il eſt évident qu’elle éxiſte. </s> <s xml:id="echoid-s2816" xml:space="preserve">N’allons donc <lb/>point d’abord imaginer des Cauſes & </s> <s xml:id="echoid-s2817" xml:space="preserve">faire <lb/>des Hypothèſes: </s> <s xml:id="echoid-s2818" xml:space="preserve">c’eſt le ſûr moyen de s’é-<lb/>garer: </s> <s xml:id="echoid-s2819" xml:space="preserve">ſuivons pas à pas, ce qui ſe paſſe <lb/>réellement dans la Nature; </s> <s xml:id="echoid-s2820" xml:space="preserve">nous ſommes <lb/>des Voyageurs arrivés à l’Embouchure d’un <lb/>Fleuve, il faut le remonter avant que d’i-<lb/>maginer où eſt ſa ſource.</s> <s xml:id="echoid-s2821" xml:space="preserve"/> </p> <pb file="0239" n="240"/> <figure> <image file="0239-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0239-01"/> </figure> </div> <div xml:id="echoid-div131" type="section" level="1" n="27"> <head xml:id="echoid-head46" xml:space="preserve">CHAPITRE DIX-HUIT.</head> <head xml:id="echoid-head47" style="it" xml:space="preserve">Gravitation démontrée par les découvertes de <lb/>Galilée & de Neuton; que la Lune parcourt <lb/>ſon Orbite par la force de cette gravitation.</head> <p> <s xml:id="echoid-s2822" xml:space="preserve">GALILE’E le reſtaurateur de la Raiſon <lb/> <anchor type="note" xlink:label="note-0239-01a" xlink:href="note-0239-01"/> en Italie, découvrit cette importante <lb/>propoſition, que les Corps graves qui deſ-<lb/>cendent ſur la Terre (faiſant abſtraction <lb/>de la petite réſiſtance de l’air) ont un <lb/>mouvement accéléré dans une proportion <lb/>dont je vais tâcher de donner une idée net-<lb/>te.</s> <s xml:id="echoid-s2823" xml:space="preserve"/> </p> <div xml:id="echoid-div131" type="float" level="2" n="1"> <note position="right" xlink:label="note-0239-01" xlink:href="note-0239-01a" xml:space="preserve">Loix de <lb/>la chûte <lb/>des <lb/>corps <lb/>trou-<lb/>vées pat<unsure/> <lb/>Galilée.</note> </div> <pb o="218" file="0240" n="241" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s2824" xml:space="preserve">Un Corps abandonné à lui-même du haut <lb/>d’une Tour, parcourt, dans la premiere ſe-<lb/>conde de tems, un eſpace qui s’eſt trou-<lb/>vé être de 15 pieds de Paris, ſelon les dé-<lb/>couvertes d’Hugens inventeur en Mathé-<lb/>matiques. </s> <s xml:id="echoid-s2825" xml:space="preserve">On croyoit avant Galilée que <lb/>ce Corps pendant deux ſecondes auroit par-<lb/>couru ſeulement deux fois le même eſpace, <lb/>& </s> <s xml:id="echoid-s2826" xml:space="preserve">qu’ainſi il feroit 150 pieds en dix ſecon-<lb/>des, & </s> <s xml:id="echoid-s2827" xml:space="preserve">neuf cens pieds en une minute: </s> <s xml:id="echoid-s2828" xml:space="preserve">c’é-<lb/>toit là l’opinion générale, & </s> <s xml:id="echoid-s2829" xml:space="preserve">même fort <lb/>vraiſemblable à qui n’examine pas de près; <lb/></s> <s xml:id="echoid-s2830" xml:space="preserve">cependant il eſt vrai qu’en une minute ce <lb/>corps auroit fait un chemin de cinquante-<lb/>quatre mille pieds, & </s> <s xml:id="echoid-s2831" xml:space="preserve">deux cens ſeize <lb/>mille pieds en deux minutes.</s> <s xml:id="echoid-s2832" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2833" xml:space="preserve">Voici comment ce progrés, qui étonne <lb/>d’abord l’imagination, s’opére néceſſairement <lb/>& </s> <s xml:id="echoid-s2834" xml:space="preserve">avec ſimplicité. </s> <s xml:id="echoid-s2835" xml:space="preserve">Un Corps eſt précipité <lb/>par ſon propre poids: </s> <s xml:id="echoid-s2836" xml:space="preserve">cette force quel-<lb/>conque qui l’anime à deſcendre de quinze <lb/>pieds dans la premiere ſeconde, agit éga-<lb/>lement à tous les inſtans, car rien n’ayant <lb/>changé, il faut qu’elle ſoit toujours la mê-<lb/>me; </s> <s xml:id="echoid-s2837" xml:space="preserve">ainſi à la deuxième ſeconde le Corps <pb o="219" file="0241" n="242" rhead="DE NEUTON."/> aurala force qu’il a acquiſe à chaque inſtant <lb/>de la premie@e ſeconde, & </s> <s xml:id="echoid-s2838" xml:space="preserve">la force qu’il é-<lb/>prouve chaque inſtant de la deuxième. </s> <s xml:id="echoid-s2839" xml:space="preserve">Or <lb/>par la force qui l’animoit à la premiere ſe-<lb/>conde il parcouroit quinze pieds, il a donc <lb/>encore cette force quand il deſcend la deu-<lb/>xième ſeconde. </s> <s xml:id="echoid-s2840" xml:space="preserve">Il a outre cela la force de <lb/>quinze autres pieds qu’il acquéroit à meſu-<lb/>re qu’il deſcendoit dans cette premiere ſe-<lb/>conde, cela fait trente: </s> <s xml:id="echoid-s2841" xml:space="preserve">il faut (rien n’a-<lb/>yant changé) que dans le tems de cette <lb/>deuxième ſeconde, il ait encore la force de <lb/>parcourir quinze pieds, cela fait quarante-<lb/>cinq; </s> <s xml:id="echoid-s2842" xml:space="preserve">par la même raiſon le Corps parcourra <lb/>ſoixante-quinze pieds dans la troiſième ſe-<lb/>conde, & </s> <s xml:id="echoid-s2843" xml:space="preserve">ainſi du reſte.</s> <s xml:id="echoid-s2844" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2845" xml:space="preserve">De là il ſuit 1<emph style="super">0</emph>. </s> <s xml:id="echoid-s2846" xml:space="preserve">que le mobile acquiert en <lb/>tems égaux infiniment petits des degrés in-<lb/>finiment petits de vîteſſe, leſquels accélé-<lb/>rent ſon mouvement vers le centre de la <lb/>Terre, tant qu’il ne trouve pas de réſiſ-<lb/>tance.</s> <s xml:id="echoid-s2847" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2848" xml:space="preserve">2<emph style="super">0</emph>. </s> <s xml:id="echoid-s2849" xml:space="preserve">Que les vîteſſes qu’il acquiert ſont <lb/>comme les tems qu’il employe à deſcen-<lb/>dre.</s> <s xml:id="echoid-s2850" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2851" xml:space="preserve">3<emph style="super">0</emph>. </s> <s xml:id="echoid-s2852" xml:space="preserve">Que les eſpaces qu’il parcourt ſont <pb o="220" file="0242" n="243" rhead="DE LA PHILOSOPHIE"/> comme les quarrés de ces tems ou de ces <lb/>vîteſſes.</s> <s xml:id="echoid-s2853" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2854" xml:space="preserve">4<emph style="super">0</emph>. </s> <s xml:id="echoid-s2855" xml:space="preserve">Que la progreſſion des eſpaces par-<lb/>courus par ce mobile ſont comme les nom-<lb/>bres impairs 1, 3, 5, 7. </s> <s xml:id="echoid-s2856" xml:space="preserve">Cette connoiſ-<lb/>ſance néceſſaire de ce Phénomêne qui arri-<lb/>ve autour de nous à tous les inſtans, va être <lb/>rendue ſenſible à ceux même qui ſeroient <lb/>d’abord un peu embarraſſés de tous ces rap-<lb/>ports; </s> <s xml:id="echoid-s2857" xml:space="preserve">il ne faut qu’un peu d’attention en <lb/>jettant les yeux ſur cette petite table que <lb/>chaque Lecteur peut augmenter à fon gré.</s> <s xml:id="echoid-s2858" xml:space="preserve"/> </p> <pb o="221" file="0243" n="244" rhead="DE NEUTON."/> <note position="right" xml:space="preserve"> <lb/>Tems \\ dans \\ les \\ quels le \\ mobile \\ tombe. # Eſpa- \\ ces \\ qu’il \\ par- \\ court \\ en \\ chaque \\ tems. # Eſpaces parcourus \\ ſont comme les \\ quarrés des tems. # Nombres \\ impairs, \\ qui mar- \\ quent la \\ progreſ- \\ ſion du \\ mouve- \\ ment, & \\ les eſpa- \\ ces par- \\ courus. <lb/>I<emph style="super">re</emph>. Se \\ conde, \\ une vî- \\ teſſe: # Le \\ Corps \\ deſ- \\ cend \\ de 15 \\ pieds: # Le quarré d’un eſt \\ un, le corps par- \\ court 15. pieds. # Une fois \\ quinze, <lb/>2m<emph style="super">e</emph>. \\ Secon- \\ de, \\ deux \\ vîteſ- \\ ſes: # Le \\ Corps \\ par- \\ court \\ 45. \\ pieds: # Le quarré de deux \\ ſecondes, ou de \\ deux vîteſſes eſt \\ quatre: quatre fois \\ quinze font 60; \\ donc le corps a \\ parcouru 60. pieds, \\ c’eſt-à dire, 15. \\ dans la premiere \\ ſeconde, & 45. dans \\ la deuxième. # Trois \\ fois \\ quinze ; \\ ainſi la \\ progreſ- \\ ſion eſt \\ d’un à 3. \\ dans cette \\ ſeconde. <lb/>3m<emph style="super">e</emph>. \\ Se- \\ conde, \\ trois \\ vîteſ- \\ ſes. # Le \\ Corps \\ par- \\ court \\ 75. \\ pieds. # Le quarté de 3. \\ ſecondes eſt neuf: \\ or neuf fois 15. \\ font 135; donc le \\ corps a parcouru \\ dans les trois ſe- \\ condes 135. pieds. # Cinq fois \\ 15. pieds; \\ ainſi la \\ progreſ- \\ ſion eſt \\ viſible \\ ment ſe- \\ lon les \\ nombres \\ impairs \\ 1. 3. 5. & 9<unsure/>1</note> <pb o="222" file="0244" n="245" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s2859" xml:space="preserve">Il eſt clair d’abord qu’à chaque inſtant in-<lb/>finiment petit, le mobile re(ç)oit un mouve-<lb/>ment accéléré, puiſque, par l’énoncé même <lb/>de la propoſition & </s> <s xml:id="echoid-s2860" xml:space="preserve">par l’expérience, ce <lb/>mouvement augmente continuellement. </s> <s xml:id="echoid-s2861" xml:space="preserve">Par <lb/>cette petite Table un coup d’œil démontre-<lb/>ra, qu’au bout d’une minute le mobile aura <lb/>parcouru cinquante-quatre mille pieds, car <lb/>54000. </s> <s xml:id="echoid-s2862" xml:space="preserve">pieds font le quarré de ſoixante ſe-<lb/>condes, multiplié par quinze; </s> <s xml:id="echoid-s2863" xml:space="preserve">or quinze <lb/>multiplié par le quarré de ſoixante, qui eſt <lb/>3600. </s> <s xml:id="echoid-s2864" xml:space="preserve">donne cinquante-quatre mille.</s> <s xml:id="echoid-s2865" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2866" xml:space="preserve">De ces Expériences il naiſſoit une nou-<lb/>velle conjecture, à la vérité bien fondée, <lb/>mais qui requéroit pourtant une démon-<lb/>ſtration particuliére. </s> <s xml:id="echoid-s2867" xml:space="preserve">Car, voyant qu’un <lb/>corps, par une peſanteur toujours égale, <lb/>faiſoit ſoixante fois autant de chemin au <lb/>bout de 60 minutes, qu’il en faiſoit pen-<lb/>dant la premiére minute, on préſuma que la <lb/>peſanteur elle-même devoit varier en raiſon <lb/>quelconque des diſtances du centre de la <lb/>Terre.</s> <s xml:id="echoid-s2868" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2869" xml:space="preserve">Cela fit auſſi ſoup(ç)onner deſlors à quel-<lb/>que<unsure/>s grands Génies, qui cherchoient une <pb o="223" file="0245" n="246" rhead="DE NEUTON."/> route nouvelle, & </s> <s xml:id="echoid-s2870" xml:space="preserve">entr’autres au fameux <lb/>Bacon Chancelier d’Angleterre, qu’il y avoit <lb/>une gravitation, une attraction des Corps <lb/>au centre de la Terre, & </s> <s xml:id="echoid-s2871" xml:space="preserve">de ce centre aux <lb/>Corps. </s> <s xml:id="echoid-s2872" xml:space="preserve">Il propoſoit dans ſon excellent Li-<lb/>vre Novum Scientiarum Organum, qu’on fît <lb/>des expériences avec des Pendules ſur les <lb/>plus hautes Tours & </s> <s xml:id="echoid-s2873" xml:space="preserve">aux profondeurs les <lb/>plus grandes; </s> <s xml:id="echoid-s2874" xml:space="preserve">car, diſoit-il, ſi les mêmes <lb/>Pendules font de plus rapides vibrations au <lb/>ſond d’un Puits que ſur une Tour, il faut <lb/>conclure que la peſanteur, qui eſt le princi-<lb/>pe de ces vibrations, ſera beaucoup plus <lb/>forte au centre de la Terre, dont ce Puits <lb/>eſt plus proche. </s> <s xml:id="echoid-s2875" xml:space="preserve">Il eſſaya auſſi de faire deſ-<lb/>cendre des mobiles de différentes éléva-<lb/>tions, & </s> <s xml:id="echoid-s2876" xml:space="preserve">d’obſerver s’ils deſcendroient de <lb/>moins de quinze pieds dans la premiére ſe-<lb/>conde; </s> <s xml:id="echoid-s2877" xml:space="preserve">mais il ne parut jamais de variation <lb/>dans ces expériences, les hauteurs & </s> <s xml:id="echoid-s2878" xml:space="preserve">les <lb/>profondeurs où on les faiſoit étant trop pe-<lb/>tites.</s> <s xml:id="echoid-s2879" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2880" xml:space="preserve">On reſtoit donc dans l’incertitude, & </s> <s xml:id="echoid-s2881" xml:space="preserve">l’i-<lb/>dée de cette force agiſſant du centre de la <lb/>Terre demeuroit un ſoup(ç)on vague.</s> <s xml:id="echoid-s2882" xml:space="preserve"/> </p> <pb o="224" file="0246" n="247" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s2883" xml:space="preserve">Deſeartes en eut connoiſſance: </s> <s xml:id="echoid-s2884" xml:space="preserve">il en par-<lb/>le même en traitant de la peſanteur; </s> <s xml:id="echoid-s2885" xml:space="preserve">mais <lb/>les expériences qui devoient éclaircir cette <lb/>grande queſtion manquoient encore. </s> <s xml:id="echoid-s2886" xml:space="preserve">Le <lb/>Syſtéme des tourbillons entraînoit ce Génie <lb/>ſublime & </s> <s xml:id="echoid-s2887" xml:space="preserve">vaſte: </s> <s xml:id="echoid-s2888" xml:space="preserve">il vouloit en créant ſon <lb/>Univers, donner la direction de tout à ſa <lb/>Matiere ſubtile: </s> <s xml:id="echoid-s2889" xml:space="preserve">il en fit la diſpenſatrice de <lb/>tout mouvement & </s> <s xml:id="echoid-s2890" xml:space="preserve">de toute peſanteur; </s> <s xml:id="echoid-s2891" xml:space="preserve">pe-<lb/>tit à petit l’Europe adopta ſon Syſtême fau-<lb/>te de mieux.</s> <s xml:id="echoid-s2892" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2893" xml:space="preserve">Enfin en 1672. </s> <s xml:id="echoid-s2894" xml:space="preserve">Mr. </s> <s xml:id="echoid-s2895" xml:space="preserve">Richer dans un Voya-<lb/> <anchor type="note" xlink:label="note-0246-01a" xlink:href="note-0246-01"/> ge à la Cayenne près de la Ligne, entrepris <lb/>par ordre de Louïs XIV. </s> <s xml:id="echoid-s2896" xml:space="preserve">ſous les auſpices <lb/>de Colbert le Pere de tous les Arts: </s> <s xml:id="echoid-s2897" xml:space="preserve">Richer, <lb/>dis-je, parmi beaucoup d’obſervations, trou-<lb/>va que le Pendule de ſon Horloge ne faiſoit <lb/>plus ſes oſcillations, ſes vibrations auſſi fré-<lb/>quentes que dans la Latitude de Paris, & </s> <s xml:id="echoid-s2898" xml:space="preserve"><lb/>qu’il falloit abſolument racourcir le Pendu-<lb/>le d’une ligne & </s> <s xml:id="echoid-s2899" xml:space="preserve">de plus d’un quart.</s> <s xml:id="echoid-s2900" xml:space="preserve"/> </p> <div xml:id="echoid-div132" type="float" level="2" n="2"> <note position="left" xlink:label="note-0246-01" xlink:href="note-0246-01a" xml:space="preserve">Expé-<lb/>rience <lb/>faite <lb/>par des <lb/>Acadé-<lb/>miciens, <lb/>laquelle <lb/>conduit <lb/>à cette <lb/>décou <lb/>verte.</note> </div> <p> <s xml:id="echoid-s2901" xml:space="preserve">La Phyſique & </s> <s xml:id="echoid-s2902" xml:space="preserve">la Géométrie n’étoient <lb/>pas alors, à beaucoup près, ſi cultivées qu’el-<lb/>les le ſont aujourd’hui. </s> <s xml:id="echoid-s2903" xml:space="preserve">Quel homme eût <pb o="225" file="0247" n="248" rhead="DE NEUTON."/> pu croire que de cette remarque ſi petite <lb/>en apparence, & </s> <s xml:id="echoid-s2904" xml:space="preserve">que d’une ligne de plus <lb/>ou de moins, puſſent ſortir les plus grandes <lb/>vérités Phyſiques? </s> <s xml:id="echoid-s2905" xml:space="preserve">On trouva d’abord, qu’il <lb/>falloit néceſſairement que la peſanteur fût <lb/>moindre ſous l’Equateur, que dans notre La-<lb/>titude, puiſque la ſeule peſanteur fait l’oſ-<lb/>cillation d’un pendule.</s> <s xml:id="echoid-s2906" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2907" xml:space="preserve">On vit par conſéquent que, puiſque la <lb/>peſanteur des Corps étoit d’autant moins <lb/>forte, que ces Corps ſont plus éloignés du <lb/>centre de la Terre, il falloit abſolument <lb/>que la Région de l’Equateur fût beaucoup <lb/> <anchor type="note" xlink:label="note-0247-01a" xlink:href="note-0247-01"/> plus élevée que la nôtre, plus éloignée du <lb/>centre, & </s> <s xml:id="echoid-s2908" xml:space="preserve">qu’ainſi la Terre ne pouvoit être <lb/>une Sphére. </s> <s xml:id="echoid-s2909" xml:space="preserve">Beaucoup de Philoſophes fi-<lb/>rent à propos de ces découvertes ce que <lb/>font tous les hommes, à qui il faut changer <lb/>d’opinion; </s> <s xml:id="echoid-s2910" xml:space="preserve">ils combattirent la Vérité nou-<lb/>velle. </s> <s xml:id="echoid-s2911" xml:space="preserve">Une partie des Docteurs juſqu’au <lb/>XV. </s> <s xml:id="echoid-s2912" xml:space="preserve">Siècle avoit cru la Terre plate, plus <lb/>longue d’Orient en Occident que du Mi-<lb/>di au Septentrion, & </s> <s xml:id="echoid-s2913" xml:space="preserve">couverte du Ciel <lb/>comme d’une Tente en demi-voute. </s> <s xml:id="echoid-s2914" xml:space="preserve">Leur <lb/>opinion leur paroiſſoit d’autant plus ſûre <lb/>qu’ils la croyoient fondée ſur la Bible. </s> <s xml:id="echoid-s2915" xml:space="preserve">Peu <pb o="226" file="0248" n="249" rhead="DE LA PHILOSOPHIE"/> de tems avant la découverte de l’Amérique, <lb/>un Evêque d’Avila traitoit l’opinion de la <lb/>rondeur de la Terre, d’impieté, & </s> <s xml:id="echoid-s2916" xml:space="preserve">d’ab-<lb/>ſurdité. </s> <s xml:id="echoid-s2917" xml:space="preserve">Enfin la Raiſon & </s> <s xml:id="echoid-s2918" xml:space="preserve">le Voyage de <lb/>Chriſtophe Colomb rendirent à la Terre ſon <lb/>ancienne forme ſphérique, que les Chaldéens <lb/>& </s> <s xml:id="echoid-s2919" xml:space="preserve">les Egyptiens lui avoient donnée. </s> <s xml:id="echoid-s2920" xml:space="preserve">Alors <lb/>on paſſa d’une extrémité à l’autre; </s> <s xml:id="echoid-s2921" xml:space="preserve">on crut <lb/>la Terre une Sphére parfaite, comme on <lb/>croyoit que les Etoiles faiſoient leur révo-<lb/>lution dans un vrai cercle.</s> <s xml:id="echoid-s2922" xml:space="preserve"/> </p> <div xml:id="echoid-div133" type="float" level="2" n="3"> <note position="right" xlink:label="note-0247-01" xlink:href="note-0247-01a" xml:space="preserve">La Ter-<lb/>re plus <lb/>haute à <lb/>propor-<lb/>tion à <lb/>l’Equa-<lb/>teur <lb/>qu’au <lb/>Pole.</note> </div> <p> <s xml:id="echoid-s2923" xml:space="preserve">Cependant du moment que l’on commen-<lb/>ça à bien ſavoir que notre Globe tourne ſur <lb/>lui-même en vingt-quatre heures, on auroit <lb/>du juger de cela ſeul, qu’une forme entiére-<lb/>ment ronde ne peut lui appartenir. </s> <s xml:id="echoid-s2924" xml:space="preserve">On n’a-<lb/>voit qu’à conſiderer que le mouvement de <lb/>rotation en vingt-quatre heures doit élever <lb/>les Eaux de la Mer: </s> <s xml:id="echoid-s2925" xml:space="preserve">que ces Eaux éle-<lb/>vêes plus que le reſte du Globe devroient à <lb/>tout moment retomber ſur les Terres de la <lb/>Région de l’Equateur & </s> <s xml:id="echoid-s2926" xml:space="preserve">les inonder: </s> <s xml:id="echoid-s2927" xml:space="preserve">or <lb/>elles n’y retombent pas; </s> <s xml:id="echoid-s2928" xml:space="preserve">donc la Terre ſo-<lb/>lide y doit être élevée comme les Eaux. </s> <s xml:id="echoid-s2929" xml:space="preserve">Ce <lb/>raiſonnement ſi ſimple, ſi naturel, étoit écha-<lb/>pé aux plus grands Génies; </s> <s xml:id="echoid-s2930" xml:space="preserve">preuve certaine <pb o="227" file="0249" n="250" rhead="DE NEUTON."/> du préjugé qui n’avoit pas même permis ce <lb/>leger examen. </s> <s xml:id="echoid-s2931" xml:space="preserve">On conteſta encore l’expé-<lb/>rience même de Richer: </s> <s xml:id="echoid-s2932" xml:space="preserve">on prétendit que <lb/>nos Pendules ne faiſoient leurs vibrations ſi <lb/>promptes vers l’Equateur, que parce que <lb/>la chaleur allongeoit ce métal: </s> <s xml:id="echoid-s2933" xml:space="preserve">on vit que <lb/>la chaleur du plus brûlant Eté l’allonge d’u. <lb/></s> <s xml:id="echoid-s2934" xml:space="preserve">ne ligne ſur trente pieds de longueur; </s> <s xml:id="echoid-s2935" xml:space="preserve">& </s> <s xml:id="echoid-s2936" xml:space="preserve">il <lb/>s’agiſſoit ici d’une ligne & </s> <s xml:id="echoid-s2937" xml:space="preserve">un quart, d’une <lb/>ligne & </s> <s xml:id="echoid-s2938" xml:space="preserve">demie, ou meme de deux lignes ſur <lb/>une verge de fer longue de 3 pieds 8 li-<lb/>gnes.</s> <s xml:id="echoid-s2939" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2940" xml:space="preserve">Quelques années après, Mrs. </s> <s xml:id="echoid-s2941" xml:space="preserve">Deshayes, <lb/>Varin, Feuillée, Couplet, repétérent vers <lb/>l’Equateur la même expérience du Pendu-<lb/>le; </s> <s xml:id="echoid-s2942" xml:space="preserve">il le fallut toujours racourcir, quoique <lb/>la chaleur fût très-ſouvent moins grande <lb/>ſous la Ligne même, qu’à quinze ou vingt <lb/>degrès de la Ligne Equinoxiale. </s> <s xml:id="echoid-s2943" xml:space="preserve">Cette ex-<lb/>périence vient d’être confirmée de nouveau <lb/>par les Académiciens qui ſont à préſent au <lb/>Pérou; </s> <s xml:id="echoid-s2944" xml:space="preserve">& </s> <s xml:id="echoid-s2945" xml:space="preserve">on apprend dans le moment que <lb/>vers Quito, dans un tems où il geloit, il <lb/>a fallu racourcir le Pendule à ſecondes d’en-<lb/>viron deux lignes.</s> <s xml:id="echoid-s2946" xml:space="preserve"/> </p> <pb o="228" file="0250" n="251" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s2947" xml:space="preserve">Tandis qu’on trouvoit ainſi de nouvelles <lb/>vérités ſous la Ligne, Mr. </s> <s xml:id="echoid-s2948" xml:space="preserve">Picart par les <lb/>mêmes ordres avoit donné en 1669 une me-<lb/>ſure de la Terre, en traçant une petite par-<lb/>tie de la Méridienne de la France. </s> <s xml:id="echoid-s2949" xml:space="preserve">Elle <lb/>ne donnoit pas à la vérité une meſure auſſi <lb/>exacte de notre Globe qu’on l’auroit eue, ſi <lb/>l’on en avoit meſuré des degrés en France, & </s> <s xml:id="echoid-s2950" xml:space="preserve"><lb/>vers l’Equateur & </s> <s xml:id="echoid-s2951" xml:space="preserve">vers le Cercle Polaire; <lb/></s> <s xml:id="echoid-s2952" xml:space="preserve">mais cette différence ſera trop petite pour <lb/>être comptée dans les choſes dont nous al-<lb/>lons parler.</s> <s xml:id="echoid-s2953" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2954" xml:space="preserve">Ces découvertes étoient néceſſaires pour <lb/>fonder la Théorie de Neuton. </s> <s xml:id="echoid-s2955" xml:space="preserve">On ſe croit <lb/>obligé ici de rapporter ſur ces découvertes <lb/>& </s> <s xml:id="echoid-s2956" xml:space="preserve">ſur cette Théorie une Anecdote qui ne <lb/>ſera pas ſans utilité dans l’Hiſtoire de l’Eſ-<lb/>prit humain, & </s> <s xml:id="echoid-s2957" xml:space="preserve">qui ſervira à faire connoî-<lb/>tre combien l’exactitude eſt néceſſaire dans <lb/>les Sciences & </s> <s xml:id="echoid-s2958" xml:space="preserve">combien Neuton cherchoit <lb/>ſincérement la Vérité.</s> <s xml:id="echoid-s2959" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2960" xml:space="preserve">Il avoit jetté dès l’année 1666 les fonde-<lb/> <anchor type="note" xlink:label="note-0250-01a" xlink:href="note-0250-01"/> mens de ſon admirable Syſtême de la gra-<lb/>vitation; </s> <s xml:id="echoid-s2961" xml:space="preserve">mais il falloit pour que ce Syſtê- <pb o="229" file="0251" n="252" rhead="DE NEUTON."/> me ſe trouvât vrai dans toutes ſes parties, & </s> <s xml:id="echoid-s2962" xml:space="preserve"><lb/>ſur-tout pour tirer du mouvement de la Lu-<lb/>ne les concluſions que nous allons voir; </s> <s xml:id="echoid-s2963" xml:space="preserve">il <lb/>falloit, dis-je, que les degrés de Latitude <lb/>fuſſent chacun environ de vingt-cinq lieues <lb/>communes de France, & </s> <s xml:id="echoid-s2964" xml:space="preserve">de près de ſoixan-<lb/>te & </s> <s xml:id="echoid-s2965" xml:space="preserve">dix milles d’Angleterre.</s> <s xml:id="echoid-s2966" xml:space="preserve"/> </p> <div xml:id="echoid-div134" type="float" level="2" n="4"> <note position="left" xlink:label="note-0250-01" xlink:href="note-0250-01a" xml:space="preserve">Anec-<lb/>dote <lb/>ſur ces <lb/>décou-<lb/>vertes.</note> </div> <p> <s xml:id="echoid-s2967" xml:space="preserve">Dès l’année 1636: </s> <s xml:id="echoid-s2968" xml:space="preserve">Norwood Mathéma-<lb/>ticien Anglais avoit fait, par pure curioſité, <lb/>depuis Londres juſqu’à Yorck, vers le Nord <lb/>d’Angleterre, les mêmes opérations que <lb/>les bienfaits du Miniſtère de France firent <lb/>entreprendre depuis par Picart en 1669, <lb/>vers le Nord de Paris, dans un moindre <lb/>eſpace de terrain.</s> <s xml:id="echoid-s2969" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2970" xml:space="preserve">Les degrés de Norwood ſe trouvoient, à <lb/>très-peu de choſe près, de 70 milles d’An-<lb/>gleterre, & </s> <s xml:id="echoid-s2971" xml:space="preserve">de 25 lieues communes de Fran-<lb/>ce; </s> <s xml:id="echoid-s2972" xml:space="preserve">c’étoit préciſément la meſure que Neu-<lb/>ton avoit devinée par ſa Théorie, & </s> <s xml:id="echoid-s2973" xml:space="preserve">qui pou-<lb/>voit ſeule la juſtifier.</s> <s xml:id="echoid-s2974" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2975" xml:space="preserve">Mais ce qui paroîtra étonnant, c’eſt qu’en <lb/>1666, & </s> <s xml:id="echoid-s2976" xml:space="preserve">même pluſieurs années après, <lb/>Neuton ne ſavoit rien des meſures de Nor- <pb o="230" file="0252" n="253" rhead="DE LA PHILOSOPHIE"/> wood, priſes plus de 30 ans auparavant. <lb/></s> <s xml:id="echoid-s2977" xml:space="preserve">Les malheurs qui avoient affligé l’Angleter-<lb/>re, avoient été auſſi funeſtes aux Sciences <lb/>qu’à l’Etat. </s> <s xml:id="echoid-s2978" xml:space="preserve">La découverte de Norwood é-<lb/>toit enſévelie dans l’oubli; </s> <s xml:id="echoid-s2979" xml:space="preserve">on s’en tenoit à <lb/>la meſure fautive des Pilotes, qui par leur <lb/>eſtime vague comptoient 60 milles ſeule-<lb/>ment pour un degré de Latitude. </s> <s xml:id="echoid-s2980" xml:space="preserve">Neuton <lb/>retiré à la Campagne pendant la peſte de <lb/>1666, n’étant point à portée d’être inſtruit <lb/>des meſures de Norwood, s’en tenoit à <lb/>cette fauſſe meſure des 60 milles.</s> <s xml:id="echoid-s2981" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2982" xml:space="preserve">Ce fut par cette fauſſe meſure qu’il re-<lb/>chercha, comme nous l’allons dire, ſi le <lb/>même pouvoir qui fait graviter ici les corps <lb/>vers le centre de la Terre, retient la Lune <lb/>dans ſon Orbite. </s> <s xml:id="echoid-s2983" xml:space="preserve">Il ſe trouva aſſez loin des <lb/>concluſions, où il ſeroit parvenu avec une <lb/>meſure plus exacte de la Terre, & </s> <s xml:id="echoid-s2984" xml:space="preserve">il eut la <lb/>bonne foi d’abandonner ſa recherche.</s> <s xml:id="echoid-s2985" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2986" xml:space="preserve">Il la reprit quelques années après, ſur les <lb/>meſures de Picart, & </s> <s xml:id="echoid-s2987" xml:space="preserve">il s’y confirma enco-<lb/>re davantage en 1683. </s> <s xml:id="echoid-s2988" xml:space="preserve">par les meſures plus <lb/>exactes de Caſſini, la Hire, Chazelles & </s> <s xml:id="echoid-s2989" xml:space="preserve">Va-<lb/>rin, qui encouragés par Colbert embraſſé- <pb o="231" file="0253" n="254" rhead="DE NEUTON."/> rent un plus grand terrain que Picart.</s> <s xml:id="echoid-s2990" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2991" xml:space="preserve">Ces Académiciens pouſſérent la Méri-<lb/>dienne juſqu’en Auvergne; </s> <s xml:id="echoid-s2992" xml:space="preserve">mais Colbert <lb/>étant mort, Louvois, qui lui ſuccéda dans <lb/>le Département del’Académie, & </s> <s xml:id="echoid-s2993" xml:space="preserve">non dans <lb/>ſon goût pour les Sciences, interrompit un <lb/>peu ce grand travail.</s> <s xml:id="echoid-s2994" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s2995" xml:space="preserve">Ce ne fut guère que vers ce tems-là que <lb/>Neuton eut connoiſſance des opérations de <lb/>Norwood; </s> <s xml:id="echoid-s2996" xml:space="preserve">il vit avec étonnement que ces <lb/>meſures étoient les mêmes que celles de <lb/>Picart & </s> <s xml:id="echoid-s2997" xml:space="preserve">de Caſſini, à cela près, que le de-<lb/>gré meſuré par Norwood ſurpaſſoit celui de <lb/>Picart de 240 toiſes, & </s> <s xml:id="echoid-s2998" xml:space="preserve">ne ſurpaſſoit ce-<lb/>lui de Caſſini que de huit. </s> <s xml:id="echoid-s2999" xml:space="preserve">Neuton attri-<lb/>buoit ce petit excédant de huit toiſes par <lb/>degré à la figure de la Terre, qu’il croyoit <lb/>être celle d’un Sphéroïde applati vers les <lb/>Poles; </s> <s xml:id="echoid-s3000" xml:space="preserve">& </s> <s xml:id="echoid-s3001" xml:space="preserve">il jugeoit que Norwood en tirant <lb/>ſa Méridienne dans des Régions plus Sep-<lb/>tentrionales que la nôtre, avoit du trouver <lb/>ſes degrés plus grands que ceux de Caſſini, <lb/>puiſqu’il ſuppoſoit la courbe du terrain me-<lb/>ſurée par Norwood plus longue. </s> <s xml:id="echoid-s3002" xml:space="preserve">Quoi qu’il <lb/>on ſoit, voici la ſublime Théorie qu’il tira <pb o="232" file="0254" n="255" rhead="DE LA PHILOSOPHIE"/> de ces meſures, & </s> <s xml:id="echoid-s3003" xml:space="preserve">des découvertes du grand <lb/>Galilée.</s> <s xml:id="echoid-s3004" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3005" xml:space="preserve">La peſanteur ſur notre Globe eſt en rai-<lb/> <anchor type="note" xlink:label="note-0254-01a" xlink:href="note-0254-01"/> ſon réciproque des quarrés des diſtances des <lb/>corps peſants du centre de la Terre; </s> <s xml:id="echoid-s3006" xml:space="preserve">ainſi <lb/>plus ces diſtances augmentent, plus la pe-<lb/>ſanteur diminue.</s> <s xml:id="echoid-s3007" xml:space="preserve"/> </p> <div xml:id="echoid-div135" type="float" level="2" n="5"> <note position="left" xlink:label="note-0254-01" xlink:href="note-0254-01a" xml:space="preserve">Théo-<lb/>rie tirée <lb/>de ces <lb/>décou-<lb/>vertes.</note> </div> <p> <s xml:id="echoid-s3008" xml:space="preserve">La force qui fait la peſanteur ne dépend <lb/>point des tourbillons de Matiere ſubtile, <lb/>dont l’exiſtence eſt démontrée fauſſe.</s> <s xml:id="echoid-s3009" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3010" xml:space="preserve">Cette force, telle qu’elle ſoit, agit ſur <lb/>tous les corps, non ſelon leurs ſurfaces; </s> <s xml:id="echoid-s3011" xml:space="preserve">mais <lb/>ſelon leurs maſſes. </s> <s xml:id="echoid-s3012" xml:space="preserve">Si elle agit à une diſtan-<lb/>ce, elle doit agir à toutes les diſtances; </s> <s xml:id="echoid-s3013" xml:space="preserve">ſi <lb/>elle agit en raiſon inverſe du quarré de ces <lb/>diſtances, elle doit toujours agir ſuivant <lb/>cette proportion ſur les corps connus, quand <lb/>ils ne ſont pas au point de contact, je veux <lb/>dire, le plus près qu’il eſt poſſible d’être, <lb/>ſans être unis.</s> <s xml:id="echoid-s3014" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3015" xml:space="preserve">Si, ſuivant cette proportion, cette force <lb/>fait parcourir ſur notre Globe 54000 pieds <lb/>en 60 ſecondes, un corps qui ſera environ <pb o="233" file="0255" n="256" rhead="DE NEUTON."/> à ſoixante rayons du centre de la Terre, <lb/>devra en 60 ſecondes tomber ſeulement de <lb/>quinze pieds de Paris ou environ.</s> <s xml:id="echoid-s3016" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3017" xml:space="preserve">La Lune dans ſon moyen mouvement eſt <lb/> <anchor type="note" xlink:label="note-0255-01a" xlink:href="note-0255-01"/> éloignée du centre de la Terre d’environ <lb/>ſoixante rayons du Globe de la Terre: </s> <s xml:id="echoid-s3018" xml:space="preserve">or <lb/>par les meſures priſes en France on connoît <lb/>combien de pieds contient l’Orbite que dé-<lb/>crit la Lune; </s> <s xml:id="echoid-s3019" xml:space="preserve">on ſait par-là que dans ſon <lb/>moyen mouvement elle décrit 187961 <lb/>pieds de Paris en une minute.</s> <s xml:id="echoid-s3020" xml:space="preserve"/> </p> <div xml:id="echoid-div136" type="float" level="2" n="6"> <note position="right" xlink:label="note-0255-01" xlink:href="note-0255-01a" xml:space="preserve">La mê-<lb/>me cau-<lb/>ſe qui <lb/>fait <lb/>tomber <lb/>les <lb/>corps <lb/>ſur la <lb/>Terre, <lb/>dirige la <lb/>Lune <lb/>autour <lb/>de la <lb/>Terre.</note> </div> <figure> <image file="0255-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0255-01"/> </figure> <p> <s xml:id="echoid-s3021" xml:space="preserve">La Lune dans ſon moyen mouvement, <lb/>eſt tombée de A, en B, elle a donc obéï <pb o="234" file="0256" n="257" rhead="DE LA PHIL OSOPHIE"/> à la force de projectile, qui la pouſſe dans la <lb/>tangente A, C, & </s> <s xml:id="echoid-s3022" xml:space="preserve">à la force, qui la feroit <lb/>deſcendre ſuivant la ligne A, D. </s> <s xml:id="echoid-s3023" xml:space="preserve">égale à B, <lb/>C: </s> <s xml:id="echoid-s3024" xml:space="preserve">ôtez la force qui la dirige de A, en C, <lb/>reſtera une force qui pourra être évaluée <lb/>par la ligne C, B: </s> <s xml:id="echoid-s3025" xml:space="preserve">cette ligne C, B. </s> <s xml:id="echoid-s3026" xml:space="preserve">eſt <lb/>égale à la ligne A, D; </s> <s xml:id="echoid-s3027" xml:space="preserve">mais il eſt dé-<lb/>montré que la courbe A, B. </s> <s xml:id="echoid-s3028" xml:space="preserve">valant <lb/>187961. </s> <s xml:id="echoid-s3029" xml:space="preserve">pieds, la ligne A, D. </s> <s xml:id="echoid-s3030" xml:space="preserve">ou C, <lb/>B. </s> <s xml:id="echoid-s3031" xml:space="preserve">en vaudra ſeulement quinze; </s> <s xml:id="echoid-s3032" xml:space="preserve">donc <lb/>que la Lune ſoit tombée en B, ou en D, <lb/>c’eſt ici la méme choſe, elle auroit par-<lb/>couru 15. </s> <s xml:id="echoid-s3033" xml:space="preserve">pieds en une minute de C, en <lb/>B; </s> <s xml:id="echoid-s3034" xml:space="preserve">donc elle auroit parcouru 15. </s> <s xml:id="echoid-s3035" xml:space="preserve">pieds <lb/>auſſi de A, en D. </s> <s xml:id="echoid-s3036" xml:space="preserve">en une minute. </s> <s xml:id="echoid-s3037" xml:space="preserve">Mais <lb/>en parcourant cet eſpace en une minute, <lb/>elle fait préciſément 3600 fois moins de <lb/>chemin qu’un mobile n’en feroit ici ſur la <lb/>Terre: </s> <s xml:id="echoid-s3038" xml:space="preserve">3600. </s> <s xml:id="echoid-s3039" xml:space="preserve">eſt juſte le quarré de ſa diſ-<lb/>tance; </s> <s xml:id="echoid-s3040" xml:space="preserve">donc la gravitation qui agit ici ſur <lb/>tous les corps, agit auſſi entre la Terre & </s> <s xml:id="echoid-s3041" xml:space="preserve"><lb/>la Lune préciſément dans ce rapport de <lb/>la raiſon inverſe du quarré des diſtances.</s> <s xml:id="echoid-s3042" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3043" xml:space="preserve">Mais ſi cette puiſſance qui anime les <lb/>corps, dirige la Lune dans ſon Orbite, el-<lb/>le doit auſſi diriger la Terre dans le ſien, <pb o="235" file="0257" n="258" rhead="DE NEUTON."/> & </s> <s xml:id="echoid-s3044" xml:space="preserve">l’effet qu’elle opére ſur la Planete de <lb/>la Lune, elle doit l’opérer ſur la Planete <lb/>de la Terre. </s> <s xml:id="echoid-s3045" xml:space="preserve">Car ce pouvoir eſt par-tout <lb/>le même: </s> <s xml:id="echoid-s3046" xml:space="preserve">toutes les autres Planetes doi-<lb/>vent lui être ſoumiſes, le Soleil doit auſſi <lb/>éprouver ſa loi: </s> <s xml:id="echoid-s3047" xml:space="preserve">& </s> <s xml:id="echoid-s3048" xml:space="preserve">s’il n’y a aucun mou-<lb/>vement des Planetes les unes à l’égard des <lb/>autres, qui ne ſoit l’effet néceſſaire de <lb/>cette puiſſance, il faut avouer alors que <lb/>toute la Nature la démontre; </s> <s xml:id="echoid-s3049" xml:space="preserve">c’eſt ce que <lb/>nous allons obſerver plus amplement.</s> <s xml:id="echoid-s3050" xml:space="preserve"/> </p> <figure> <image file="0257-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0257-01"/> </figure> <pb file="0258" n="259"/> <figure> <image file="0258-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0258-01"/> </figure> </div> <div xml:id="echoid-div138" type="section" level="1" n="28"> <head xml:id="echoid-head48" xml:space="preserve">CHAPITRE DIX-NEUF.</head> <head xml:id="echoid-head49" style="it" xml:space="preserve">Q<unsure/>ue la gravitation & l’attraction dirigent tou-<lb/>tes les Planetes dans leurs Cours.</head> <p> <s xml:id="echoid-s3051" xml:space="preserve">PReſque toute la Théorie de la peſanteur <lb/> <anchor type="note" xlink:label="note-0258-01a" xlink:href="note-0258-01"/> chez Deſcartes eſt fondée ſur cette loi <lb/>de la Nature, que tout corps qui ſe meut en <lb/>ligne courbe, tend à s’éloigner de ſon cen-<lb/>tre en une ligne droite, qui toucheroit la <lb/>courbe en un point. </s> <s xml:id="echoid-s3052" xml:space="preserve">Telle eſt la fronde <lb/>qui en s’échapant de la main au point B, <lb/>ſuivroit cette ligne B, C.</s> <s xml:id="echoid-s3053" xml:space="preserve"/> </p> <div xml:id="echoid-div138" type="float" level="2" n="1"> <note position="left" xlink:label="note-0258-01" xlink:href="note-0258-01a" xml:space="preserve">Com-<lb/>menton <lb/>doit en-<lb/>tendre, <lb/>la Théo-<lb/>rie de <lb/>la pe-<lb/>ſanteur <lb/>chez <lb/>Deſcar-<lb/>tes.</note> </div> <pb o="237" file="0259" n="260" rhead="DE NEUTON."/> <figure> <image file="0259-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0259-01"/> </figure> <p> <s xml:id="echoid-s3054" xml:space="preserve">Tous les corps en tournant avec la Terre <lb/>font ainſi un effort pour s’éloigner du cen-<lb/>tre; </s> <s xml:id="echoid-s3055" xml:space="preserve">mais la Matiere ſubtile faiſant un bien <lb/>plus grand effort repouſſe, diſoit-on, tous <lb/>les autres corps.</s> <s xml:id="echoid-s3056" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3057" xml:space="preserve">Il eſt aiſé de voir que ce n’étoit point à <lb/>la Matiere ſubtile à faire ce plus grand ef-<lb/>fort, & </s> <s xml:id="echoid-s3058" xml:space="preserve">à s’éloigner du centre du tourbil-<lb/>lon prétendu, plutôt que les autres corps; <lb/></s> <s xml:id="echoid-s3059" xml:space="preserve">au contraire c’étoit ſa nature (ſuppoſé qu’el-<lb/>éxiſtât) d’aller au centre de ſon mouve-<lb/>ment, & </s> <s xml:id="echoid-s3060" xml:space="preserve">de laiſſer aller à la circonférence <pb o="238" file="0260" n="261" rhead="DE LA PHIL OSOPHIE"/> tous les corps qui auroient eu plus de maſ-<lb/>ſe. </s> <s xml:id="echoid-s3061" xml:space="preserve">C’eſt en effet ce qui arrive ſur une ta-<lb/>ble qui tourne en rond, lorſque dans un tu-<lb/>be pratiqué dans cette table, on a mêlé plu-<lb/>ſieurs poudres & </s> <s xml:id="echoid-s3062" xml:space="preserve">pluſieurs liqueurs de pe-<lb/>ſanteurs ſpécifiques différentes; </s> <s xml:id="echoid-s3063" xml:space="preserve">tout ce qui <lb/>a plus de maſſe s’éloigne du centre, tout ce <lb/>qui a moins de maſſe s’en approche. </s> <s xml:id="echoid-s3064" xml:space="preserve">Telle <lb/>eſt la loi de la Nature; </s> <s xml:id="echoid-s3065" xml:space="preserve">& </s> <s xml:id="echoid-s3066" xml:space="preserve">lorſque Deſcartes <lb/>a fait circuler à la circonférence ſa préten-<lb/>due Matiere ſubtile, il a commencé par vio-<lb/>ler cette loi des forces centrifuges, qu’il po-<lb/>ſoit pour ſon premier principe. </s> <s xml:id="echoid-s3067" xml:space="preserve">Il a eu <lb/>beau imaginer que Dieu avoit créé des <lb/>dés tournans les uns ſur les autres: </s> <s xml:id="echoid-s3068" xml:space="preserve">que la <lb/>raclure de ces dés qui faiſoit ſa Matiere <lb/>ſubtile, s’échapant de tous les côtés, acqué-<lb/>roit par-là plus de vîteſſe: </s> <s xml:id="echoid-s3069" xml:space="preserve">que le centre <lb/>d’un tourbillon s’encroutoit, &</s> <s xml:id="echoid-s3070" xml:space="preserve">c.</s> <s xml:id="echoid-s3071" xml:space="preserve">; il s’en <lb/>falloit bien que ces imaginations rectifiaſ-<lb/>ſent cette erreur.</s> <s xml:id="echoid-s3072" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3073" xml:space="preserve">Sans perdre plus de tems à combattre ces <lb/>Etres de raiſon, ſuivons les loix de la Mé-<lb/>canique qui opére dans la Nature. </s> <s xml:id="echoid-s3074" xml:space="preserve">Un <lb/>corps qui ſe meut circulairement, prend en <lb/>cette maniere, à chaque point de la courbe <pb o="239" file="0261" n="262" rhead="DE NEUTON."/> qu’il décrit, une direction qui l’éloigneroit <lb/>du Cercle, en lui faiſant ſuivre une ligne <lb/>droite.</s> <s xml:id="echoid-s3075" xml:space="preserve"/> </p> <figure> <image file="0261-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0261-01"/> </figure> <p> <s xml:id="echoid-s3076" xml:space="preserve">Cela eſt vrai. </s> <s xml:id="echoid-s3077" xml:space="preserve">Mais il faut prendre garde <lb/>que ce corps ne s’éloigneroit ainſi du cen-<lb/>tre, que par cet autre grand Principe: </s> <s xml:id="echoid-s3078" xml:space="preserve">que <lb/>tout corps étant indifférent de lui-même au <lb/>repos & </s> <s xml:id="echoid-s3079" xml:space="preserve">au mouvement, & </s> <s xml:id="echoid-s3080" xml:space="preserve">ayant cette iner-<lb/>tie qui eſt un attribut de la Matiere, ſuit <lb/>néceſſairement la ligne dans laquelle il eſt mu. <lb/></s> <s xml:id="echoid-s3081" xml:space="preserve">Or tout corps qui tourne autour d’un cen-<lb/>tre, ſuit à chaque inſtant une ligne droite <lb/>infiniment petite, qui deviendroit une droi-<lb/>te infiniment longue, s’il ne rencontroit <pb o="240" file="0262" n="263" rhead="DE LA PHILOSOPHIE"/> point d’obſtacle. </s> <s xml:id="echoid-s3082" xml:space="preserve">Le réſultat de ce princi-<lb/>pe, réduit à ſa juſte valeur, n’eſt donc au-<lb/>tre choſe, ſinon qu’un corps qui ſuit une <lb/>ligne droite, ſuivra toujours une ligne droi-<lb/>te; </s> <s xml:id="echoid-s3083" xml:space="preserve">donc il faut une autre force pour lui <lb/>faire décrire une courbe; </s> <s xml:id="echoid-s3084" xml:space="preserve">donc cette autre <lb/>force, par laquelle il décrit la courbe le fe-<lb/>roit tomber au centre à chaque inſtant, en <lb/>cas que ce mouvement de projectile en li-<lb/>gne droite ceſſat. </s> <s xml:id="echoid-s3085" xml:space="preserve">A la vérité de moment <lb/>en moment ce corps iroit en A, en B, en <lb/>C. </s> <s xml:id="echoid-s3086" xml:space="preserve">s’il s’échapoit;</s> <s xml:id="echoid-s3087" xml:space="preserve"/> </p> <figure> <image file="0262-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0262-01"/> </figure> <p> <s xml:id="echoid-s3088" xml:space="preserve">Mais auſſi de moment en moment il re-<lb/>tomberoit de A, de B, de C. </s> <s xml:id="echoid-s3089" xml:space="preserve">au centre;</s> <s xml:id="echoid-s3090" xml:space="preserve"> <pb o="241" file="0263" n="264" rhead="DE NEUTON."/> parce que ſon mouvement eſt compoſé de <lb/>deux ſortes de mouvemens, du mouvement de <lb/>projectile en ligne droite, & </s> <s xml:id="echoid-s3091" xml:space="preserve">du mouvement <lb/>imprimé auſſi en ligne droite par la force <lb/>centripète, force par laquelle il iroit au cen-<lb/> <anchor type="note" xlink:label="note-0263-01a" xlink:href="note-0263-01"/> tre. </s> <s xml:id="echoid-s3092" xml:space="preserve">Ainſi de cela même que le corps décriroit <lb/>ces tangentes A, B, C. </s> <s xml:id="echoid-s3093" xml:space="preserve">il eſt démontré qu’il <lb/>y a un pouvoir qui le retire de ces tangen-<lb/>tes à l’inſtant même qu’il les commence. </s> <s xml:id="echoid-s3094" xml:space="preserve">Il <lb/>faut donc abſolument conſiderer tout corps <lb/>ſe mouvant dans une courbe, comme mu <lb/>par deux puiſſances, dont l’une eſt celle <lb/>qui lui feroit parcourir des tangentes, & </s> <s xml:id="echoid-s3095" xml:space="preserve"><lb/>qu’on nomme la force centrifuge, ou plu-<lb/>tôt la force d’inertie, d’inactivité, par la-<lb/>quelle un corps ſuit toujours une droite s’il <lb/>n’en eſt empêché; </s> <s xml:id="echoid-s3096" xml:space="preserve">& </s> <s xml:id="echoid-s3097" xml:space="preserve">l’autre force qui reti-<lb/>re le corps vers le centre, laquelle on <lb/>nomme la force contripète, & </s> <s xml:id="echoid-s3098" xml:space="preserve">qui eſt la vé-<lb/>ritable force.</s> <s xml:id="echoid-s3099" xml:space="preserve"/> </p> <div xml:id="echoid-div139" type="float" level="2" n="2"> <note position="right" xlink:label="note-0263-01" xlink:href="note-0263-01a" xml:space="preserve">Ce que <lb/>c’eſt que <lb/>la force <lb/>centri-<lb/>fuge, & <lb/>la force <lb/>centri-<lb/>pète.</note> </div> <pb o="242" file="0264" n="265" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s3100" xml:space="preserve">C’eſt ainſi qu’un corps mu ſelon la ligne <lb/>horiſontale G, E. </s> <s xml:id="echoid-s3101" xml:space="preserve">& </s> <s xml:id="echoid-s3102" xml:space="preserve">ſelon la ligne perpen-<lb/>diculaire G, F. </s> <s xml:id="echoid-s3103" xml:space="preserve">obéït à chaque inſtant à ces <lb/>deux puiſſances en parcourant la diagonale <lb/>G, H.</s> <s xml:id="echoid-s3104" xml:space="preserve"/> </p> <figure> <image file="0264-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0264-01"/> </figure> <p> <s xml:id="echoid-s3105" xml:space="preserve">De l’établiſſement de cette force centri-<lb/>pète, il réſulte d’abord cette démonſtra-<lb/>tion, que tout mobile qui ſe meut dans un <lb/>cercle, ou dans une ellipſe, ou dans une <lb/>courbe quelconque, ſe meut autour d’un <lb/>centre auquel il tend.</s> <s xml:id="echoid-s3106" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3107" xml:space="preserve">Il ſuit encore que ce mobile, quelques <lb/>portions de courbe qu’il parcoure, décrira <lb/>dans ſes plus grands arcs & </s> <s xml:id="echoid-s3108" xml:space="preserve">dans ſes plus <lb/>petits arcs, des aires égales en tems égaux.</s> <s xml:id="echoid-s3109" xml:space="preserve"> <pb o="243" file="0265" n="266" rhead="DE NEUTON."/> Si, par exemple, un mobile en une minu-<lb/>te borde l’eſpace A, C, B. </s> <s xml:id="echoid-s3110" xml:space="preserve">qui contiendra <lb/>cent milles d’aire, il doit border en deux <lb/>minutes un autre eſpace B, C, D. </s> <s xml:id="echoid-s3111" xml:space="preserve">de deux <lb/>cens milles.</s> <s xml:id="echoid-s3112" xml:space="preserve"/> </p> <figure> <image file="0265-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0265-01"/> </figure> <p> <s xml:id="echoid-s3113" xml:space="preserve">Cette Loi inviolablement obſervée par <lb/>toutes les Planetes, & </s> <s xml:id="echoid-s3114" xml:space="preserve">inconnue à toute <lb/>l’Antiquité, fut découverte il y a près <lb/>de 150. </s> <s xml:id="echoid-s3115" xml:space="preserve">ans par Kepler, qui a mérité le <lb/>nom de Législateur en Aſtronomie, mal-<lb/>gré ſes erreurs Philoſophiques. </s> <s xml:id="echoid-s3116" xml:space="preserve">Il ne pou-<lb/>voit ſavoir encore la raiſon de cette rè-<lb/>gle à laquelle les corps céleſtes ſont aſſu-<lb/>jettis. </s> <s xml:id="echoid-s3117" xml:space="preserve">L’extrême ſagacité de Kepler trou-<lb/>va l’effet dont le génie de Neuton a trou-<lb/>vé la cauſe.</s> <s xml:id="echoid-s3118" xml:space="preserve"/> </p> <pb o="244" file="0266" n="267" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s3119" xml:space="preserve">Je vais donner ici la ſubſtance de la <lb/>Démonſtration de Neuton: </s> <s xml:id="echoid-s3120" xml:space="preserve">elle ſera aiſé-<lb/>ment compriſe par tout Lecteur attentif; <lb/></s> <s xml:id="echoid-s3121" xml:space="preserve">car les hommes ont une Géométrie natu-<lb/>relle dans l’eſprit, qui leur fait ſaiſir les <lb/>rapports, quand ils ne ſont pas trop com-<lb/>pliqués. </s> <s xml:id="echoid-s3122" xml:space="preserve">On trouvera la Démonſtration <lb/>plus étendue en Notes.</s> <s xml:id="echoid-s3123" xml:space="preserve"/> </p> <figure> <image file="0266-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0266-01"/> </figure> <p> <s xml:id="echoid-s3124" xml:space="preserve">Que le corps A. </s> <s xml:id="echoid-s3125" xml:space="preserve">ſoit mu en B. </s> <s xml:id="echoid-s3126" xml:space="preserve">en un eſpa-<lb/>ce de tems très-petit: </s> <s xml:id="echoid-s3127" xml:space="preserve">au bout d’un pareil eſpa-<lb/>ce, un mouvement également continué (car <lb/>il n’y a ici nulle accélération) le feroit ve-<lb/>nir en C; </s> <s xml:id="echoid-s3128" xml:space="preserve">mais en B. </s> <s xml:id="echoid-s3129" xml:space="preserve">il trouve une force qui <lb/>le pouſſe dans la ligne B, H, S.</s> <s xml:id="echoid-s3130" xml:space="preserve">; il ne ſuit <lb/>donc ni ce chemin B, H, S. </s> <s xml:id="echoid-s3131" xml:space="preserve">ni ce chemin <lb/>A, B, C; </s> <s xml:id="echoid-s3132" xml:space="preserve">tirez ce parallélogramme C, D.</s> <s xml:id="echoid-s3133" xml:space="preserve"> <pb o="245" file="0267" n="268" rhead="DE NEUTON"/> B, H. </s> <s xml:id="echoid-s3134" xml:space="preserve">alors le mobile étant mu par la force</s> </p> </div> <div xml:id="echoid-div141" type="section" level="1" n="29"> <head xml:id="echoid-head50" xml:space="preserve"><emph style="sc">De’ monstration.</emph></head> <p style="it"> <s xml:id="echoid-s3135" xml:space="preserve">Que tout mobile attiré par une force centripète <lb/>décrit dans une ligne courbe des aires éga. <lb/></s> <s xml:id="echoid-s3136" xml:space="preserve">les en tems égaux (1).</s> <s xml:id="echoid-s3137" xml:space="preserve"/> </p> <figure> <image file="0267-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0267-01"/> </figure> <p> <s xml:id="echoid-s3138" xml:space="preserve">(1) Tout corps ſe meut d’un mouvement uniforme, <lb/>quand il n’y a point de force accélératrice; </s> <s xml:id="echoid-s3139" xml:space="preserve">donc le <lb/>corps A. </s> <s xml:id="echoid-s3140" xml:space="preserve">mu en ligne droite dans le premier tems de <lb/>A, en B. </s> <s xml:id="echoid-s3141" xml:space="preserve">ira en pareil tems de B, en C. </s> <s xml:id="echoid-s3142" xml:space="preserve">de C, en Z. <lb/></s> <s xml:id="echoid-s3143" xml:space="preserve">Ces eſpaces conçus égaux, la force centripète dans <lb/>le ſecond tems donne à ce corps en B. </s> <s xml:id="echoid-s3144" xml:space="preserve">un mouve-<lb/>ment quelconque, & </s> <s xml:id="echoid-s3145" xml:space="preserve">le corps au lieu d’aller en C. </s> <s xml:id="echoid-s3146" xml:space="preserve">va <lb/>en H.</s> <s xml:id="echoid-s3147" xml:space="preserve">; quelle direction a-t-il eue différente de B, C.</s> <s xml:id="echoid-s3148" xml:space="preserve">? <lb/>Tirez les 4. </s> <s xml:id="echoid-s3149" xml:space="preserve">lignes C, H. </s> <s xml:id="echoid-s3150" xml:space="preserve">G, B. </s> <s xml:id="echoid-s3151" xml:space="preserve">C, B. </s> <s xml:id="echoid-s3152" xml:space="preserve">G, H. </s> <s xml:id="echoid-s3153" xml:space="preserve">le <lb/>mobile a ſuivi la diagonale B, H. </s> <s xml:id="echoid-s3154" xml:space="preserve">de ce parallélo-<lb/>gramme.</s> <s xml:id="echoid-s3155" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3156" xml:space="preserve">Or les 2. </s> <s xml:id="echoid-s3157" xml:space="preserve">côtés B, C. </s> <s xml:id="echoid-s3158" xml:space="preserve">B, G. </s> <s xml:id="echoid-s3159" xml:space="preserve">du parallélogramme <lb/>ſont dans le même plan que le triangle A, B, S. </s> <s xml:id="echoid-s3160" xml:space="preserve">donc <lb/>les forces ſont dirigées vers G, S. </s> <s xml:id="echoid-s3161" xml:space="preserve">& </s> <s xml:id="echoid-s3162" xml:space="preserve">vers la droite A, <lb/>B, C, Z.</s> <s xml:id="echoid-s3163" xml:space="preserve"> <pb o="246" file="0268" n="269" rhead="DE LA PHILOSOPHIE"/> B, C. </s> <s xml:id="echoid-s3164" xml:space="preserve">& </s> <s xml:id="echoid-s3165" xml:space="preserve">par la force B, H. </s> <s xml:id="echoid-s3166" xml:space="preserve">s’en va ſelon</s> </p> <p> <s xml:id="echoid-s3167" xml:space="preserve">Les triangles S, H, B. </s> <s xml:id="echoid-s3168" xml:space="preserve">S, C, B. </s> <s xml:id="echoid-s3169" xml:space="preserve">ſont égaux, puiſ-<lb/>qu’ils ſont ſur la même baſe S, B. </s> <s xml:id="echoid-s3170" xml:space="preserve">& </s> <s xml:id="echoid-s3171" xml:space="preserve">entre les parallel-<lb/>les H, C. </s> <s xml:id="echoid-s3172" xml:space="preserve">G, B; </s> <s xml:id="echoid-s3173" xml:space="preserve">mais S, B, A. </s> <s xml:id="echoid-s3174" xml:space="preserve">S, H, B. </s> <s xml:id="echoid-s3175" xml:space="preserve">ſont égaux, <lb/>ayant même baſe & </s> <s xml:id="echoid-s3176" xml:space="preserve">même hauteur; </s> <s xml:id="echoid-s3177" xml:space="preserve">donc S, B, A. </s> <s xml:id="echoid-s3178" xml:space="preserve">S, <lb/>H, B. </s> <s xml:id="echoid-s3179" xml:space="preserve">ſont auſſi égaux.</s> <s xml:id="echoid-s3180" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3181" xml:space="preserve">Il faut en dire autant des triangles S, T, H. </s> <s xml:id="echoid-s3182" xml:space="preserve">S, D, H; <lb/></s> <s xml:id="echoid-s3183" xml:space="preserve">donc tous ces triangles ſont égaux. </s> <s xml:id="echoid-s3184" xml:space="preserve">Diminuez la hau-<lb/>teur à l’infini, le corps à chaque moment infiniment petit <lb/>décrira la courbe, de laquelle toutes les lignes tendent <lb/>au point S.</s> <s xml:id="echoid-s3185" xml:space="preserve">; donc dans tous les cas les aires de ces <lb/>triangles ſont proportionelles aux tems.</s> <s xml:id="echoid-s3186" xml:space="preserve"/> </p> </div> <div xml:id="echoid-div142" type="section" level="1" n="30"> <head xml:id="echoid-head51" xml:space="preserve"><emph style="sc">Demonstration.</emph></head> <p style="it"> <s xml:id="echoid-s3187" xml:space="preserve">Que tout corps dans une courbe décrivant des <lb/>triangles égaux autour d’un point, eſt mu par <lb/>la force contripète autour de ce point (2).</s> <s xml:id="echoid-s3188" xml:space="preserve"/> </p> <figure> <image file="0268-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0268-01"/> </figure> <p> <s xml:id="echoid-s3189" xml:space="preserve">(2) Que cette courbe ſoit divifée en parties égales <lb/>A, B. </s> <s xml:id="echoid-s3190" xml:space="preserve">B, H. </s> <s xml:id="echoid-s3191" xml:space="preserve">H, F. </s> <s xml:id="echoid-s3192" xml:space="preserve">infiniment petites, décrites en tems <lb/>égaux; </s> <s xml:id="echoid-s3193" xml:space="preserve">ſoit conçue la force agir aux points B, H, F.</s> <s xml:id="echoid-s3194" xml:space="preserve"/> </p> <pb o="247" file="0269" n="270" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s3195" xml:space="preserve">la diagonale B, D. </s> <s xml:id="echoid-s3196" xml:space="preserve">Or cette ligne B, D. <lb/></s> <s xml:id="echoid-s3197" xml:space="preserve">& </s> <s xml:id="echoid-s3198" xml:space="preserve">cette ligne B, A. </s> <s xml:id="echoid-s3199" xml:space="preserve">conçues infiniment <lb/>petites ſont les naiſſances d’une courbe, &</s> <s xml:id="echoid-s3200" xml:space="preserve">c.</s> <s xml:id="echoid-s3201" xml:space="preserve">; <lb/>donc ce corps ſe doit mouvoir dans une <lb/>courbe.</s> <s xml:id="echoid-s3202" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3203" xml:space="preserve">Il doit border des eſpaces égaux en tems <lb/> <anchor type="note" xlink:label="note-0269-01a" xlink:href="note-0269-01"/> égaux, car l’eſpace du triangle S, B, A. </s> <s xml:id="echoid-s3204" xml:space="preserve">eſt <lb/>égal à l’eſpace du triangle S, B, D. </s> <s xml:id="echoid-s3205" xml:space="preserve">: </s> <s xml:id="echoid-s3206" xml:space="preserve">ces trian-<lb/>gles ſont égaux; </s> <s xml:id="echoid-s3207" xml:space="preserve">donc ces aires ſont égales; <lb/></s> <s xml:id="echoid-s3208" xml:space="preserve">donc tout corps qui parcourt des aires éga-<lb/>les en tems égaux dans une courbe, fait ſa <lb/>révolution autour du centre des forces au-<lb/>quel il tend; </s> <s xml:id="echoid-s3209" xml:space="preserve">done<unsure/> les Planetes tendent <lb/>vers le Soleil, tournent autour du Soleil, &</s> <s xml:id="echoid-s3210" xml:space="preserve"/> </p> <div xml:id="echoid-div142" type="float" level="2" n="1"> <note position="right" xlink:label="note-0269-01" xlink:href="note-0269-01a" xml:space="preserve">Cette <lb/>démonſ-<lb/>tration <lb/>prouve <lb/>que le <lb/>Soleil eſt <lb/>le centre <lb/>del’Uni-<lb/>vers & <lb/>non la <lb/>Terre.</note> </div> <p> <s xml:id="echoid-s3211" xml:space="preserve">ſoit A, B. </s> <s xml:id="echoid-s3212" xml:space="preserve">prolongée en C. </s> <s xml:id="echoid-s3213" xml:space="preserve">ſoit B, H. </s> <s xml:id="echoid-s3214" xml:space="preserve">prolongée en <lb/>T. </s> <s xml:id="echoid-s3215" xml:space="preserve">le triangle S, A, B. </s> <s xml:id="echoid-s3216" xml:space="preserve">ſera égal au triangle S, B, H. <lb/></s> <s xml:id="echoid-s3217" xml:space="preserve">car A, B. </s> <s xml:id="echoid-s3218" xml:space="preserve">eſt égal à B, C; </s> <s xml:id="echoid-s3219" xml:space="preserve">donc S, B, H. </s> <s xml:id="echoid-s3220" xml:space="preserve">eſt égal à S, <lb/>B, C; </s> <s xml:id="echoid-s3221" xml:space="preserve">donc la force en B, G. </s> <s xml:id="echoid-s3222" xml:space="preserve">eſt parallelle à C, H; </s> <s xml:id="echoid-s3223" xml:space="preserve">mais <lb/>cette ligne B, G. </s> <s xml:id="echoid-s3224" xml:space="preserve">parallelle à C, H. </s> <s xml:id="echoid-s3225" xml:space="preserve">eſt la ligne B, G, S. </s> <s xml:id="echoid-s3226" xml:space="preserve"><lb/>tendante au centre. </s> <s xml:id="echoid-s3227" xml:space="preserve">Le corps en H. </s> <s xml:id="echoid-s3228" xml:space="preserve">eſt dirigé par la <lb/>force centripète ſelon une ligne parallelle à F, T. </s> <s xml:id="echoid-s3229" xml:space="preserve">de <lb/>même qu’au point B. </s> <s xml:id="echoid-s3230" xml:space="preserve">il étoit dirigé par cette même <lb/>force dans une ligne parallelle à C, H. </s> <s xml:id="echoid-s3231" xml:space="preserve">Or la ligne paral-<lb/>lelle à C, H. </s> <s xml:id="echoid-s3232" xml:space="preserve">tend en S.</s> <s xml:id="echoid-s3233" xml:space="preserve">; donc la ligne parallelle à F, <lb/>T. </s> <s xml:id="echoid-s3234" xml:space="preserve">tendra auſſi en S.</s> <s xml:id="echoid-s3235" xml:space="preserve">; donc toutes les lignes ainſi tirées <lb/>tendront au point S.</s> <s xml:id="echoid-s3236" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3237" xml:space="preserve">Concevez maintenant en S. </s> <s xml:id="echoid-s3238" xml:space="preserve">des triangles ſemblables <lb/>à ceux ci-deſſus; </s> <s xml:id="echoid-s3239" xml:space="preserve">plus ces triangles ci-deſſus ſeront pe-<lb/>tits, plus les triangles en S. </s> <s xml:id="echoid-s3240" xml:space="preserve">approcheront d’un point <lb/>Phyſique, lequel point S. </s> <s xml:id="echoid-s3241" xml:space="preserve">ſera le centre des forces.</s> <s xml:id="echoid-s3242" xml:space="preserve"/> </p> <pb o="248" file="0270" n="271" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s3243" xml:space="preserve">non autour de la Terre. </s> <s xml:id="echoid-s3244" xml:space="preserve">Car en prenant la <lb/>Terre pour centre, leurs aires ſont inéga-<lb/>les par rapport aux tems, & </s> <s xml:id="echoid-s3245" xml:space="preserve">en prenant le <lb/>Soleil pour centre, ces aires ſe trouvent <lb/>toujours proportionnelles aux tems; </s> <s xml:id="echoid-s3246" xml:space="preserve">ſi vous <lb/>en exceptez les petits dérangemens cauſés <lb/>par la gravitation même des Planétes.</s> <s xml:id="echoid-s3247" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3248" xml:space="preserve">Pour bien entendre encore ce que c’eſt <lb/>que ces aires proportionnelles aux tems, & </s> <s xml:id="echoid-s3249" xml:space="preserve"><lb/>pour voir d’un coup d’œil l’avantage que <lb/>vous tirez de cette connoiſſance, regardez <lb/>la Terre emportée dans ſon ellipſe autour <lb/>du Soleil S. </s> <s xml:id="echoid-s3250" xml:space="preserve">ſon centre. </s> <s xml:id="echoid-s3251" xml:space="preserve">Quand elle va de B, <lb/>en D. </s> <s xml:id="echoid-s3252" xml:space="preserve">elle ballaye un auſſi grand eſpace que <lb/>quand elle parcourt ce grand arc H. </s> <s xml:id="echoid-s3253" xml:space="preserve">K: </s> <s xml:id="echoid-s3254" xml:space="preserve">le <lb/>Secteur H, K. </s> <s xml:id="echoid-s3255" xml:space="preserve">regagne en largeur ce que le <lb/>Secteur B, S, D. </s> <s xml:id="echoid-s3256" xml:space="preserve">a en longueur. </s> <s xml:id="echoid-s3257" xml:space="preserve">Pour faire <lb/>l’aire de ces Secteurs égale en tems égaux, <lb/>il faut que le corps vers H, K. </s> <s xml:id="echoid-s3258" xml:space="preserve">aille plus vîte <lb/>que vers B, D. </s> <s xml:id="echoid-s3259" xml:space="preserve">Ainſi la Terre & </s> <s xml:id="echoid-s3260" xml:space="preserve">toute Pla-<lb/>néte ſe meut plus vîte dans ſon périhélie, <lb/>qui eſt la courbe la plus voiſine du Soleil S, <lb/>que dans ſon aphélie, qui eſt la courbe la <lb/>plus éloignée de ce même foyer S.</s> <s xml:id="echoid-s3261" xml:space="preserve"/> </p> <pb o="249" file="0271" n="272" rhead="DE NEUTON."/> <figure> <image file="0271-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0271-01"/> </figure> <p> <s xml:id="echoid-s3262" xml:space="preserve">On connoît donc quel eſt le centre d’une <lb/>Planéte, & </s> <s xml:id="echoid-s3263" xml:space="preserve">quelle figure elle décrit dans <lb/>ſon orbite par les aires qu’elle parcourt; <lb/></s> <s xml:id="echoid-s3264" xml:space="preserve">on connoît que toute Planéte, lorſqu’elle <lb/>eſt plus éloignée du centre de ſon mouve-<lb/> <anchor type="note" xlink:label="note-0271-01a" xlink:href="note-0271-01"/> ment, gravite moins vers ce centre. </s> <s xml:id="echoid-s3265" xml:space="preserve">Ainſi <lb/>la Terre étant plus près du Soleil d’un tren-<lb/>tième, c’eſt-à-dire, d’un million de lieues, <lb/>pendant notre Hyver que pendant notre <lb/>Eté, eſt plus attirée auſſi en Hyver; </s> <s xml:id="echoid-s3266" xml:space="preserve">ainſi <lb/>elle va plus vîte alors par la raiſon de ſa <lb/>courbe; </s> <s xml:id="echoid-s3267" xml:space="preserve">ainſi nous avons huit jours & </s> <s xml:id="echoid-s3268" xml:space="preserve">demi <lb/>d’Eté plus que d’Hyver, & </s> <s xml:id="echoid-s3269" xml:space="preserve">le Soleil paroît <lb/>dans les Signes Septentrionaux huit jours <lb/>& </s> <s xml:id="echoid-s3270" xml:space="preserve">demi de plus que dans les Méridionaux.</s> <s xml:id="echoid-s3271" xml:space="preserve"> <pb o="250" file="0272" n="273" rhead="DE LA PHILOSOPHIE"/> Puis donc que toute Planéte ſuit, par rap-<lb/>port au Soleil, ſon centre, cette Loi de <lb/>gravitation que la Lune éprouve par rap-<lb/>port à la Terre, & </s> <s xml:id="echoid-s3272" xml:space="preserve">à laquelle tous les corps <lb/>ſont ſoumis en tombant ſur la Terre, il eſt <lb/>démontré que cette gravitation, cette at-<lb/>traction, agit ſur tous les corps que nous <lb/>connoiſſons.</s> <s xml:id="echoid-s3273" xml:space="preserve"/> </p> <div xml:id="echoid-div143" type="float" level="2" n="2"> <note position="right" xlink:label="note-0271-01" xlink:href="note-0271-01a" xml:space="preserve">C’eſt <lb/>pour les <lb/>raiſons <lb/>précé-<lb/>dentes <lb/>que <lb/>nous <lb/>avons <lb/>plus <lb/>d’Eté <lb/>que <lb/>d’Hy-<lb/>ver.</note> </div> <p> <s xml:id="echoid-s3274" xml:space="preserve">Mais une autre puiſſante Démonſtration <lb/>de cette Vérité, eſt la Loi que ſuivent reſ-<lb/>pectivement toutes les Planétes dans leurs <lb/>cours & </s> <s xml:id="echoid-s3275" xml:space="preserve">dans leurs diſtances; </s> <s xml:id="echoid-s3276" xml:space="preserve">c’eſt ce qu’il <lb/>faut bien examiner.</s> <s xml:id="echoid-s3277" xml:space="preserve"/> </p> <figure> <image file="0272-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0272-01"/> </figure> <pb file="0273" n="274"/> <figure> <image file="0273-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0273-01"/> </figure> </div> <div xml:id="echoid-div145" type="section" level="1" n="31"> <head xml:id="echoid-head52" xml:space="preserve">CHAPITRE VINGT.</head> <p style="it"> <s xml:id="echoid-s3278" xml:space="preserve">Démonſtration des loix de la gravitation, tirée <lb/>des règles de Kepler; </s> <s xml:id="echoid-s3279" xml:space="preserve">qu’une de ces loix <lb/>de Kepler démontrẽ<unsure/> le mouvement <lb/>de la Terre.</s> <s xml:id="echoid-s3280" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3281" xml:space="preserve">KEPLER trouva encore cette admira-<lb/> <anchor type="note" xlink:label="note-0273-01a" xlink:href="note-0273-01"/> ble règle, dont je vais donner un <lb/>exemple avant que de donner la définition, <lb/>pour rendre la choſe plus ſenſible & </s> <s xml:id="echoid-s3282" xml:space="preserve">plus <lb/>aiſée.</s> <s xml:id="echoid-s3283" xml:space="preserve"/> </p> <div xml:id="echoid-div145" type="float" level="2" n="1"> <note position="right" xlink:label="note-0273-01" xlink:href="note-0273-01a" xml:space="preserve">Grande <lb/>règle de <lb/>Kepler.</note> </div> <pb o="252" file="0274" n="275" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s3284" xml:space="preserve">Jupiter a 4. </s> <s xml:id="echoid-s3285" xml:space="preserve">Satellites qui tournent au-<lb/>tour de lui: </s> <s xml:id="echoid-s3286" xml:space="preserve">le plus proche eſt éloigné de <lb/>2. </s> <s xml:id="echoid-s3287" xml:space="preserve">Diamétres de Jupiter & </s> <s xml:id="echoid-s3288" xml:space="preserve">5. </s> <s xml:id="echoid-s3289" xml:space="preserve">ſixièmes, & </s> <s xml:id="echoid-s3290" xml:space="preserve"><lb/>il fait ſon tour en 42. </s> <s xml:id="echoid-s3291" xml:space="preserve">heures: </s> <s xml:id="echoid-s3292" xml:space="preserve">le dernier <lb/>tourne autour de Jupiter en 402. </s> <s xml:id="echoid-s3293" xml:space="preserve">heures; <lb/></s> <s xml:id="echoid-s3294" xml:space="preserve">je veux ſavoir à quelle diſtance ce dernier <lb/>Satellite eſt du centre de Jupiter. </s> <s xml:id="echoid-s3295" xml:space="preserve">Pour y <lb/>parvenir, je fais cette règle. </s> <s xml:id="echoid-s3296" xml:space="preserve">Comme le <lb/>quarré de 42. </s> <s xml:id="echoid-s3297" xml:space="preserve">heures, révolution du ier. </s> <s xml:id="echoid-s3298" xml:space="preserve"><lb/>Satellite, eſt au quarré de 402. </s> <s xml:id="echoid-s3299" xml:space="preserve">heures, ré-<lb/>volution du dernier; </s> <s xml:id="echoid-s3300" xml:space="preserve">ainſi le cube de deux <lb/>Diamétres & </s> <s xml:id="echoid-s3301" xml:space="preserve">{5/6} eſt à un 4<emph style="super">e</emph>. </s> <s xml:id="echoid-s3302" xml:space="preserve">terme. </s> <s xml:id="echoid-s3303" xml:space="preserve">Ce 4<emph style="super">e</emph>. </s> <s xml:id="echoid-s3304" xml:space="preserve"><lb/>terme étant trouvé, j’en extrais la racine <lb/>cube, cette racine cube ſe trouve 12. </s> <s xml:id="echoid-s3305" xml:space="preserve">{2/3}.</s> <s xml:id="echoid-s3306" xml:space="preserve">; <lb/>ainſi je dis que le 4<emph style="super">e</emph>. </s> <s xml:id="echoid-s3307" xml:space="preserve">Satellite eſt éloigné <lb/>du centre de Jupiter de 12. </s> <s xml:id="echoid-s3308" xml:space="preserve">Diamétres de <lb/>Jupiter & </s> <s xml:id="echoid-s3309" xml:space="preserve">{2/3}.</s> <s xml:id="echoid-s3310" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3311" xml:space="preserve">Je fais la même règle pour toutes les Pla-<lb/>nétes qui tournent autour du Soleil. </s> <s xml:id="echoid-s3312" xml:space="preserve">Je <lb/>dis: </s> <s xml:id="echoid-s3313" xml:space="preserve">Venus tourne en 224. </s> <s xml:id="echoid-s3314" xml:space="preserve">jours, & </s> <s xml:id="echoid-s3315" xml:space="preserve">la <lb/>Terre en 365; </s> <s xml:id="echoid-s3316" xml:space="preserve">la Terre eſt à 30000000. <lb/></s> <s xml:id="echoid-s3317" xml:space="preserve">de lieues du Soleil, à combien de lieues <lb/>ſera Venus? </s> <s xml:id="echoid-s3318" xml:space="preserve">Je dis: </s> <s xml:id="echoid-s3319" xml:space="preserve">comme le quarré <lb/>de l’année de la Terre eſt au quarré de l’an-<lb/>née de Venus, ainſi le cube de la diſtance <pb o="253" file="0275" n="276" rhead="DE NEUTON."/> moyenne de la Terre eſt à un 4e. </s> <s xml:id="echoid-s3320" xml:space="preserve">ter-<lb/>me dont la racine cubique ſera environ <lb/>21700000. </s> <s xml:id="echoid-s3321" xml:space="preserve">de lieues, qui font la diſtance <lb/>moyenne de Venus au Soleil; </s> <s xml:id="echoid-s3322" xml:space="preserve">j’en dis <lb/>autant de la Terre & </s> <s xml:id="echoid-s3323" xml:space="preserve">de Saturne, &</s> <s xml:id="echoid-s3324" xml:space="preserve">c.</s> <s xml:id="echoid-s3325" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3326" xml:space="preserve">Cette loi eſt donc, que le quarré d’une <lb/>révolution d’une Planete eſt toujours au <lb/>quarré des révolutions des autres Planetes, <lb/>comme le cube de ſa diſtance eſt aux cubes <lb/>des diſtances des autres, au centre commun.</s> <s xml:id="echoid-s3327" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3328" xml:space="preserve">Kepler qui trouva cette proportion, étoit <lb/> <anchor type="note" xlink:label="note-0275-01a" xlink:href="note-0275-01"/> bien loin d’en trouver la raiſon. </s> <s xml:id="echoid-s3329" xml:space="preserve">Moins bon <lb/>Philoſophe qu’ Aſtronome admirable, il dit <lb/>(au 4<emph style="super">e</emph>. </s> <s xml:id="echoid-s3330" xml:space="preserve">Liv. </s> <s xml:id="echoid-s3331" xml:space="preserve">de ſon Epitome) que le So-<lb/>leil a une ame, non pas une ame intelligen-<lb/>te animum, mais une ame végétante, agiſ-<lb/>ſante, animam: </s> <s xml:id="echoid-s3332" xml:space="preserve">qu’en tournant ſur lui-mê-<lb/>me il attire à ſoi les Planetes; </s> <s xml:id="echoid-s3333" xml:space="preserve">mais que <lb/>les Planetes ne tombent pas dans le Soleil, <lb/>parce qu’elles font auſſi une révolution ſur <lb/>leur axe. </s> <s xml:id="echoid-s3334" xml:space="preserve">En faiſant cette révolution, dit-<lb/>il, elles préſentent au Soleil tantôt un côté <lb/>ami, tantôt un côté ennemi: </s> <s xml:id="echoid-s3335" xml:space="preserve">le côté ami <lb/>eſt attiré, & </s> <s xml:id="echoid-s3336" xml:space="preserve">le côté ennemi eſt repouſſé <pb o="254" file="0276" n="277" rhead="DE LA PHILOSOPHIE"/> ce qui produit le cours annuel des Planetes <lb/>dans des Ellipſes.</s> <s xml:id="echoid-s3337" xml:space="preserve"/> </p> <div xml:id="echoid-div146" type="float" level="2" n="2"> <note position="right" xlink:label="note-0275-01" xlink:href="note-0275-01a" xml:space="preserve">Raiſonas <lb/>indi-<lb/>gnes <lb/>d’un <lb/>Philoſo-<lb/>phe <lb/>données <lb/>par <lb/>Kepler <lb/>de cette <lb/>loi ad-<lb/>mirable.</note> </div> <p> <s xml:id="echoid-s3338" xml:space="preserve">Il faut avouer pour l’humiliation de la <lb/>Philoſophie, que c’eſt de ce raiſonnement <lb/>ſi peu Philoſophique, qu’il avoit conclu <lb/>que le Soleil devoit tourner ſur ſon axe: <lb/></s> <s xml:id="echoid-s3339" xml:space="preserve">l’erreur le couduiſit par hazard à la vérité; </s> <s xml:id="echoid-s3340" xml:space="preserve"><lb/>il devina la rotation du Soleil ſur lui-même <lb/>plus de 15. </s> <s xml:id="echoid-s3341" xml:space="preserve">ans avant que les yeux de Ga-<lb/>lilée la reconnuſſent à l’aide des Teleſco-<lb/>pes.</s> <s xml:id="echoid-s3342" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3343" xml:space="preserve">Kepler ajoute dans ſon même Epitome <lb/>p. </s> <s xml:id="echoid-s3344" xml:space="preserve">495. </s> <s xml:id="echoid-s3345" xml:space="preserve">que la maſſe du Soleil, la maſſe de <lb/>tout l’Ether, & </s> <s xml:id="echoid-s3346" xml:space="preserve">la maſſe des Sphéres des <lb/>Etoiles fixes ſont parfaitement égales; </s> <s xml:id="echoid-s3347" xml:space="preserve">& </s> <s xml:id="echoid-s3348" xml:space="preserve"><lb/>que ce ſont les 3. </s> <s xml:id="echoid-s3349" xml:space="preserve">Symboles de la Très-Sain-<lb/>te Trinité.</s> <s xml:id="echoid-s3350" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3351" xml:space="preserve">Le Lecteur qui en liſant ces Elémens, <lb/>aura vu de ſi grandes réveries, à côté de <lb/>ſi ſublimes vérités, dans un auſſi grand <lb/>homme que Kepler, dans un auſſi profond <lb/>Mathématicien que Kirker, ne doit point <lb/>en être ſurpris: </s> <s xml:id="echoid-s3352" xml:space="preserve">on peut être un Génie en <lb/>fait de calcul & </s> <s xml:id="echoid-s3353" xml:space="preserve">d’obſervations, & </s> <s xml:id="echoid-s3354" xml:space="preserve">ſe ſer- <pb o="255" file="0277" n="278" rhead="DE NEUTON."/> vir mal quelquefois de ſa raiſon pour le <lb/>reſte; </s> <s xml:id="echoid-s3355" xml:space="preserve">il y a tels Eſprits qui ont beſoin de <lb/>s’appuyer ſur la Géométrie, & </s> <s xml:id="echoid-s3356" xml:space="preserve">qui tombent <lb/>quand ils veulent marcher ſeuls. </s> <s xml:id="echoid-s3357" xml:space="preserve">Il n’eſt <lb/>donc pas étonnant que Kepler, en décou-<lb/>vrant ces loix de l’Aſtronomie, n’ait pas <lb/>connu la raiſon de ces loix.</s> <s xml:id="echoid-s3358" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3359" xml:space="preserve">Cette raiſon eſt, que la force centripète <lb/> <anchor type="note" xlink:label="note-0277-01a" xlink:href="note-0277-01"/> eſt préciſément en proportion inverſe du <lb/>quarré de la diſtance du centre de mouve-<lb/>ment, vers lequel ces forces ſont dirigées; <lb/></s> <s xml:id="echoid-s3360" xml:space="preserve">c’eſt ce qu’il faut ſuivre attentivement. </s> <s xml:id="echoid-s3361" xml:space="preserve">Il <lb/>faut bien entendre, qu’en un mot cette loi <lb/>de la gravitation eſt telle, que tout corps <lb/>qui approche 3. </s> <s xml:id="echoid-s3362" xml:space="preserve">fois plus du centre de ſon <lb/>mouvement, gravite 9. </s> <s xml:id="echoid-s3363" xml:space="preserve">fois davantage: </s> <s xml:id="echoid-s3364" xml:space="preserve">que <lb/>s’il s’éloigne 3. </s> <s xml:id="echoid-s3365" xml:space="preserve">fois plus, il gravitera 9. </s> <s xml:id="echoid-s3366" xml:space="preserve"><lb/>fois moins; </s> <s xml:id="echoid-s3367" xml:space="preserve">& </s> <s xml:id="echoid-s3368" xml:space="preserve">que s’il s’éloigne 100. </s> <s xml:id="echoid-s3369" xml:space="preserve">fois <lb/>plus, il gravitera 10000. </s> <s xml:id="echoid-s3370" xml:space="preserve">fois moins.</s> <s xml:id="echoid-s3371" xml:space="preserve"/> </p> <div xml:id="echoid-div147" type="float" level="2" n="3"> <note position="right" xlink:label="note-0277-01" xlink:href="note-0277-01a" xml:space="preserve">Raiſon <lb/>vérita-<lb/>ble de <lb/>cette loi <lb/>trouvée <lb/>par <lb/>Neuton.</note> </div> <p> <s xml:id="echoid-s3372" xml:space="preserve">Un corps ſe mouvant circulairement au-<lb/>tour d’un centre, peſe donc en raiſon in-<lb/>verſe du quarré de ſa diſtance actuelle au <lb/>centre, comme auſſi en raiſon directe de ſa <lb/>maſſe; </s> <s xml:id="echoid-s3373" xml:space="preserve">or il eſt démontré que c’eſt la gra-<lb/>vitation qui le fait tourner autour de ce <pb o="256" file="0278" n="279" rhead="DE LA PHILOSOPHIE"/> centre, puiſque ſans cette gravitation, il <lb/>s’en éloigneroit en décrivant une tangente. <lb/></s> <s xml:id="echoid-s3374" xml:space="preserve">Cette gravitation agira donc plus fortement <lb/>ſur un mobile, qui tournera plus vîte autour <lb/>de ce centre; </s> <s xml:id="echoid-s3375" xml:space="preserve">& </s> <s xml:id="echoid-s3376" xml:space="preserve">plus ce mobile ſera éloi-<lb/>gné, plus il tournera lentement, car alors <lb/>il peſera bien moins.</s> <s xml:id="echoid-s3377" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3378" xml:space="preserve">C’eſt par cette raiſon que la Terre, quoi-<lb/>que 1170. </s> <s xml:id="echoid-s3379" xml:space="preserve">fois plus petite que Jupiter, ne <lb/>peſe pourtant ſur le Soleil que 8. </s> <s xml:id="echoid-s3380" xml:space="preserve">fois moins <lb/>que Jupiter; </s> <s xml:id="echoid-s3381" xml:space="preserve">& </s> <s xml:id="echoid-s3382" xml:space="preserve">cela en raiſon directe des <lb/>maſſes, & </s> <s xml:id="echoid-s3383" xml:space="preserve">en raiſon inverſe des quarrés des <lb/>diſtances de ces Planetes au Soleil.</s> <s xml:id="echoid-s3384" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3385" xml:space="preserve">Voilà donc cette loi de la gravitation en <lb/> <anchor type="note" xlink:label="note-0278-01a" xlink:href="note-0278-01"/> raiſon du quarré des diſtances, démontrée</s> </p> <div xml:id="echoid-div148" type="float" level="2" n="4"> <note position="left" xlink:label="note-0278-01" xlink:href="note-0278-01a" xml:space="preserve">Récapi-<lb/>tulation <lb/>des <lb/>preuves <lb/>de la <lb/>gravita-<lb/>tion.</note> </div> <p> <s xml:id="echoid-s3386" xml:space="preserve">1<emph style="super">0</emph>. </s> <s xml:id="echoid-s3387" xml:space="preserve">Par l’Orbite que décrit la Lune, & </s> <s xml:id="echoid-s3388" xml:space="preserve"><lb/>par ſon éloignement de la Terre, ſon cen-<lb/>tre:</s> <s xml:id="echoid-s3389" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3390" xml:space="preserve">2<emph style="super">0</emph>. </s> <s xml:id="echoid-s3391" xml:space="preserve">Par le chemin de chaque Planete au-<lb/>tour du Soleil dans une Ellipſe;</s> <s xml:id="echoid-s3392" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3393" xml:space="preserve">3<emph style="super">0</emph>. </s> <s xml:id="echoid-s3394" xml:space="preserve">Par la comparaiſon des diſtances & </s> <s xml:id="echoid-s3395" xml:space="preserve"><lb/>des révolutions de toutes les Planetes au-<lb/>tour de leur centre commun.</s> <s xml:id="echoid-s3396" xml:space="preserve"/> </p> <pb o="257" file="0279" n="280" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s3397" xml:space="preserve">Il ne ſera pas inutile de remarquer que <lb/> <anchor type="note" xlink:label="note-0279-01a" xlink:href="note-0279-01"/> cette même règle de Kepler, qui ſert à con-<lb/>firmer la découverte de Neuton touchant <lb/>la gravitation, confirme auſſi le Syſtême de <lb/>Copernic ſur le mouvement de la Terre. <lb/></s> <s xml:id="echoid-s3398" xml:space="preserve">On peut dire que Kepler par cette ſeule <lb/>règle a démontré ce qu’on avoit trouvé a-<lb/>vant lui, & </s> <s xml:id="echoid-s3399" xml:space="preserve">a ouvert le chemin aux vérités <lb/>qu’on devoit découvrir un jour. </s> <s xml:id="echoid-s3400" xml:space="preserve">Car d’un <lb/>côté il eſt démontré que ſi la loi des for-<lb/>ces centripètes n’avoit pas lieu, la règle <lb/>de Kepler ſeroit impoſſible; </s> <s xml:id="echoid-s3401" xml:space="preserve">de l’autre il eſt <lb/>démontré que ſuivant cette même règle, ſi <lb/>le Soleil tournoit autour de la Terre, il <lb/>faudroit dire: </s> <s xml:id="echoid-s3402" xml:space="preserve">Comme la révolution de la <lb/>Lune autour de la Terre en un mois, eſt à <lb/>la révolution prétendue du Soleil autour de <lb/>la Terre en un an, ainſi la racine quar-<lb/>rée du cube de la diſtance de la Lune à la <lb/>Terre, eſt à la racine quarrée du cube de la <lb/>diſtance du Soleil à la Terre. </s> <s xml:id="echoid-s3403" xml:space="preserve">Par ce cal-<lb/>cul on trouveroit que le Soleil n’eſt qu’à <lb/>510000. </s> <s xml:id="echoid-s3404" xml:space="preserve">lieues de nous; </s> <s xml:id="echoid-s3405" xml:space="preserve">mais il eſt prouvé <lb/>qu’il en eſt au moins à environ 30. </s> <s xml:id="echoid-s3406" xml:space="preserve">millions <lb/>de lieues; </s> <s xml:id="echoid-s3407" xml:space="preserve">ainſi donc le mouvement de la <lb/>Terre a été démontré en rigueur par Kep- <pb o="258" file="0280" n="281" rhead="DE LA PHILOSOPHIE"/> ler. </s> <s xml:id="echoid-s3408" xml:space="preserve">Voici encore une démonſtration bien <lb/>ſimple tirée des mêmes théorêmes.</s> <s xml:id="echoid-s3409" xml:space="preserve"/> </p> <div xml:id="echoid-div149" type="float" level="2" n="5"> <note position="right" xlink:label="note-0279-01" xlink:href="note-0279-01a" xml:space="preserve">Ces dé-<lb/>couver-<lb/>tes de <lb/>Kepler <lb/>& de <lb/>Neuton <lb/>ſervent <lb/>à dé-<lb/>montrer <lb/>que c’eſt <lb/>la Terre <lb/>qui <lb/>tourne <lb/>autour <lb/>du So-<lb/>leil.</note> </div> <p> <s xml:id="echoid-s3410" xml:space="preserve">Si la Terre étoit le centre du mouvement <lb/> <anchor type="note" xlink:label="note-0280-01a" xlink:href="note-0280-01"/> du Soleil, comme elle l’eſt du mouvement <lb/>de la Lune, la révolution du Soleil ſeroit <lb/>de 475. </s> <s xml:id="echoid-s3411" xml:space="preserve">ans, au lieu d’une année; </s> <s xml:id="echoid-s3412" xml:space="preserve">car l’é-<lb/>loignement moyen où le Soleil eſt de la <lb/>Terre, eſt à l’éloignement moyen où la <lb/>Lune eſt de la Terre, comme 337. </s> <s xml:id="echoid-s3413" xml:space="preserve">eſt à <lb/>un: </s> <s xml:id="echoid-s3414" xml:space="preserve">or le cube de la diſtance de la Lune <lb/>eſt 1.</s> <s xml:id="echoid-s3415" xml:space="preserve">, le cube de la diſtance du Soleil <lb/>38272753: </s> <s xml:id="echoid-s3416" xml:space="preserve">achevez la règle, & </s> <s xml:id="echoid-s3417" xml:space="preserve">dites: <lb/></s> <s xml:id="echoid-s3418" xml:space="preserve">Comme le cube 1. </s> <s xml:id="echoid-s3419" xml:space="preserve">eſt à ce nombre cubé <lb/>38272753. </s> <s xml:id="echoid-s3420" xml:space="preserve">ainſi le quarré de 28. </s> <s xml:id="echoid-s3421" xml:space="preserve">qui eſt la <lb/>révolution périodique de la Lune eſt à un <lb/>4<emph style="super">e</emph>. </s> <s xml:id="echoid-s3422" xml:space="preserve">nombre: </s> <s xml:id="echoid-s3423" xml:space="preserve">vous trouverez que le Soleil <lb/>mettroit 475. </s> <s xml:id="echoid-s3424" xml:space="preserve">ans au lieu d’une année à <lb/>tourner autour de la Terre; </s> <s xml:id="echoid-s3425" xml:space="preserve">il eſt donc dé-<lb/>montré que c’eſt la Terre qui tourne.</s> <s xml:id="echoid-s3426" xml:space="preserve"/> </p> <div xml:id="echoid-div150" type="float" level="2" n="6"> <note position="left" xlink:label="note-0280-01" xlink:href="note-0280-01a" xml:space="preserve">Dé-<lb/>monſ-<lb/>tration <lb/>du mou-<lb/>vement <lb/>de la <lb/>Terre <lb/>tirée des <lb/>mêmes <lb/>loix.</note> </div> <p> <s xml:id="echoid-s3427" xml:space="preserve">Il ſemble d’autant plus à propos de pla-<lb/>cer ici ces Démonſtrations, qu’il y a en-<lb/>core des hommes deſtinez à inſtruire les au-<lb/>tres en Italie, en Eſpagne, & </s> <s xml:id="echoid-s3428" xml:space="preserve">même en <lb/>France, qui doutent, ou qui affectent de <lb/>douter du mouvement de la Terre.</s> <s xml:id="echoid-s3429" xml:space="preserve"/> </p> <pb o="259" file="0281" n="282" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s3430" xml:space="preserve">Il eſt donc prouvé par la loi de Kepler <lb/>& </s> <s xml:id="echoid-s3431" xml:space="preserve">par celle de Neuton, que chaque Pla-<lb/>nete gravite vers le Soleil, centre de l’Or-<lb/>bite qu’elles décrivent: </s> <s xml:id="echoid-s3432" xml:space="preserve">ces loix s’accom-<lb/>pliſſent dans Jupiter par rapport à Jupiter, <lb/>leur centre: </s> <s xml:id="echoid-s3433" xml:space="preserve">dans les Lunes de Saturne par <lb/>rapport à Saturne, dans la nôtre par rap-<lb/>port à nous: </s> <s xml:id="echoid-s3434" xml:space="preserve">toutes ces Planetes ſecondai-<lb/>res qui roulent autour de leur Planete cen-<lb/>trale gravitent auſſi avec leur Planete cen-<lb/>trale vers le Soleil; </s> <s xml:id="echoid-s3435" xml:space="preserve">ainſi la Lune entraînée <lb/>autour de la Terre par la force centripète, <lb/>eſt en même tems attirée par le Soleil au-<lb/>tour duquel elle fait auſſi ſa révolution. </s> <s xml:id="echoid-s3436" xml:space="preserve">Il <lb/>n’y a aucune varieté dans le cours de la <lb/>Lune, dans ſes diſtances de la Terre, dans <lb/>la figure de ſon Orbite, tantôt aprochante <lb/>de l’ellipſe, tantôt du cercle, &</s> <s xml:id="echoid-s3437" xml:space="preserve">c. </s> <s xml:id="echoid-s3438" xml:space="preserve">qui ne <lb/>ſoit une ſuite de la gravitation en raiſon <lb/>des changemens de ſa diſtance à la Terre, <lb/>& </s> <s xml:id="echoid-s3439" xml:space="preserve">de ſa diſtance au Soleil.</s> <s xml:id="echoid-s3440" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3441" xml:space="preserve">Si elle ne parcourt pas exactement dans <lb/>ſon Orbite des aires égales en tems égaux; <lb/></s> <s xml:id="echoid-s3442" xml:space="preserve">Mr. </s> <s xml:id="echoid-s3443" xml:space="preserve">Neuton a calculé tous les cas où cette <lb/>inégalité ſe trouve: </s> <s xml:id="echoid-s3444" xml:space="preserve">tous dépendent de l’at- <pb o="260" file="0282" n="283" rhead="DE LA PHILOSOPHIE"/> traction du Soleil; </s> <s xml:id="echoid-s3445" xml:space="preserve">il attire ces 2. </s> <s xml:id="echoid-s3446" xml:space="preserve">Globes <lb/>en raiſon directe de leurs maſſes, & </s> <s xml:id="echoid-s3447" xml:space="preserve">en <lb/>raiſon inverſe du quarré de leurs diſtances. <lb/></s> <s xml:id="echoid-s3448" xml:space="preserve">Nous allons voir que la moindre variation <lb/>de la Lune eſt un effet néceſſaire de ces <lb/>pouvoirs combinez.</s> <s xml:id="echoid-s3449" xml:space="preserve"/> </p> <figure> <image file="0282-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0282-01"/> </figure> <pb file="0283" n="284"/> <figure> <image file="0283-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0283-01"/> </figure> </div> <div xml:id="echoid-div152" type="section" level="1" n="32"> <head xml:id="echoid-head53" xml:space="preserve"><emph style="bf">CHAPITRE VINGT-UN.</emph></head> <head xml:id="echoid-head54" style="it" xml:space="preserve">Nouvelles preuves de l’attraction. Que les in-<lb/>égalités du mouvement & de l’Orbite de <lb/>la Lune ſont néceſſairement les <lb/>effets de l’attraction.</head> <p> <s xml:id="echoid-s3450" xml:space="preserve">LA Lune n’a qu’un ſeul mouvement égal, <lb/>c’eſt ſa rotation autour d’elle-même <lb/>ſur ſon axe, & </s> <s xml:id="echoid-s3451" xml:space="preserve">c’eſt le ſeul dont nous ne <lb/>nous appercevons pas: </s> <s xml:id="echoid-s3452" xml:space="preserve">c’eſt ce mouvement <lb/>qui nous préſente toujours à - peu - près le <lb/>même diſque de la Lune; </s> <s xml:id="echoid-s3453" xml:space="preserve">de ſorte qu’en <pb o="262" file="0284" n="285" rhead="DE LA PHILOSOPHIE"/> tournant réellement ſur elle-même, elle pa-<lb/>roît ne point tourner du tout, & </s> <s xml:id="echoid-s3454" xml:space="preserve">avoir ſeu-<lb/>lement un petit mouvement de balancement, <lb/>de libration, qu’elle n’a point, & </s> <s xml:id="echoid-s3455" xml:space="preserve">que tou-<lb/>te l’Antiquité lui attribuoit.</s> <s xml:id="echoid-s3456" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3457" xml:space="preserve">Tous ſes autres mouvemens autour de la <lb/>Terre ſont inégaux, & </s> <s xml:id="echoid-s3458" xml:space="preserve">doivent l’être ſi la <lb/>règle de la gravitation eſt vraye. </s> <s xml:id="echoid-s3459" xml:space="preserve">La Lune <lb/>dans ſon cours d’un mois eſt néceſſairement <lb/>plus près du Soleil dans un certain point, <lb/>& </s> <s xml:id="echoid-s3460" xml:space="preserve">dans un certain tems de ſon cours: </s> <s xml:id="echoid-s3461" xml:space="preserve">or <lb/>dans ce point & </s> <s xml:id="echoid-s3462" xml:space="preserve">dans ce tems ſa maſſe <lb/>demeure la même: </s> <s xml:id="echoid-s3463" xml:space="preserve">ſa diſtance étant ſeule-<lb/>ment changée, l’attraction du Soleil doit <lb/>changer en raiſon reverſée du quarré de <lb/>cette diſtance: </s> <s xml:id="echoid-s3464" xml:space="preserve">le cours de la Lune doit <lb/>donc changer, elle doit donc aller plus vîte <lb/>en certains tems que l’attraction ſeule de la <lb/>Terre ne la feroit aller; </s> <s xml:id="echoid-s3465" xml:space="preserve">or par l’attraction <lb/>de la Terre elle doit parcourir des aires é-<lb/>gales en tems égaux, comme vous l’avez <lb/>déja obſervé au Chapitre 19.</s> <s xml:id="echoid-s3466" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3467" xml:space="preserve">On ne peut s’empêcher d’admirer avec <lb/>quelle ſagacité Neuton a démêlé toutes ces <lb/>inégalités, réglé la marche de cette Plane- <pb o="263" file="0285" n="286" rhead="DE NEUTON."/> te, qui s’étoit dérobée à toutes les recher-<lb/>ches des Aſtronomes; </s> <s xml:id="echoid-s3468" xml:space="preserve">c’eſt-là ſur-tout qu’on <lb/>peut dire:</s> <s xml:id="echoid-s3469" xml:space="preserve"/> </p> <p style="it"> <s xml:id="echoid-s3470" xml:space="preserve">Nec propius fas eſt mortali attingere Divos.</s> <s xml:id="echoid-s3471" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3472" xml:space="preserve">Entre les exemples qu’on peut choiſir, pre-<lb/> <anchor type="note" xlink:label="note-0285-01a" xlink:href="note-0285-01"/> nons celui-ci: </s> <s xml:id="echoid-s3473" xml:space="preserve">Soit A. </s> <s xml:id="echoid-s3474" xml:space="preserve">la Lune: </s> <s xml:id="echoid-s3475" xml:space="preserve">A, B, N, Q. <lb/></s> <s xml:id="echoid-s3476" xml:space="preserve">l’Orbite de la Lune: </s> <s xml:id="echoid-s3477" xml:space="preserve">S. </s> <s xml:id="echoid-s3478" xml:space="preserve">le Soleil; </s> <s xml:id="echoid-s3479" xml:space="preserve">B. </s> <s xml:id="echoid-s3480" xml:space="preserve">l’en-<lb/>droit où la Lune ſe trouve dans ſon dernier <lb/>quartier <anchor type="note" xlink:href="" symbol="(*)"/>.</s> <s xml:id="echoid-s3481" xml:space="preserve"/> </p> <div xml:id="echoid-div152" type="float" level="2" n="1"> <note position="right" xlink:label="note-0285-01" xlink:href="note-0285-01a" xml:space="preserve">Exem-<lb/>ple en <lb/>preuve.</note> </div> <note symbol="(*)" position="foot" xml:space="preserve"> On a laiſſé ce blanc, & renvoyé la ſuite du Tex-<lb/>te avec la Figure aux pages ſuivantes, pour la commo-<lb/>dité du Lecteur.</note> <pb o="264" file="0286" n="287" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s3482" xml:space="preserve">Elle eſt alors manifeſtement à la même <lb/>diſtance du Soleil qu’eſt la Terre. </s> <s xml:id="echoid-s3483" xml:space="preserve">La <lb/>différence de l’obliquité de la ligne de <lb/>direction de la Lune au Soleil étant comp-<lb/>tée pour rien, la gravitation de la Terre <lb/>& </s> <s xml:id="echoid-s3484" xml:space="preserve">de la Lune vers le Soleil eſt donc la mê-<lb/>me. </s> <s xml:id="echoid-s3485" xml:space="preserve">Cependant la Terre avance dans ſa <lb/>route annuelle de T. </s> <s xml:id="echoid-s3486" xml:space="preserve">en V. </s> <s xml:id="echoid-s3487" xml:space="preserve">& </s> <s xml:id="echoid-s3488" xml:space="preserve">la Lune dans <lb/>ſon cours d’un mois avance en Z.</s> <s xml:id="echoid-s3489" xml:space="preserve">: or en Z. <lb/></s> <s xml:id="echoid-s3490" xml:space="preserve">il eſt manifeſte qu’elle eſt plus attirée par le <lb/>Soleil S. </s> <s xml:id="echoid-s3491" xml:space="preserve">dont elle ſe trouve plus proche <lb/>que la Terre; </s> <s xml:id="echoid-s3492" xml:space="preserve">ſon mouvement ſera donc <lb/>accéléré de Z. </s> <s xml:id="echoid-s3493" xml:space="preserve">vers N.</s> <s xml:id="echoid-s3494" xml:space="preserve">; l’Orbite qu’elle <lb/>décrit ſera donc changée, mais comment <lb/>ſera - t - elle changée? </s> <s xml:id="echoid-s3495" xml:space="preserve">En s’aplatiſſ<unsure/>ant un <lb/>peu, en devenant plus approchante d’une <lb/>droite depuis Z. </s> <s xml:id="echoid-s3496" xml:space="preserve">vers N.</s> <s xml:id="echoid-s3497" xml:space="preserve">; ainſi donc de <lb/>moment en moment la gravitation change <lb/>le cours & </s> <s xml:id="echoid-s3498" xml:space="preserve">la forme de l’Ellipſe, dans la-<lb/>quelle ſe meut cette Planete.</s> <s xml:id="echoid-s3499" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3500" xml:space="preserve">Par la même raiſon la Lune doit retar-<lb/>der ſon cours, & </s> <s xml:id="echoid-s3501" xml:space="preserve">changer encore la figure <lb/>de l’Orbite qu’elle décrit, lorſqu’elle re-<lb/>paſſe de la conjonction N. </s> <s xml:id="echoid-s3502" xml:space="preserve">à ſon premier <lb/>quartier Q; </s> <s xml:id="echoid-s3503" xml:space="preserve">car puiſque de ſon dernier <pb file="0287" n="288"/> <anchor type="figure" xlink:label="fig-0287-01a" xlink:href="fig-0287-01"/> <pb file="0288" n="289"/> <pb o="265" file="0289" n="290" rhead="DE NEUTON."/> quartier elle accéléroit ſon cours en apla-<lb/>tiſſant ſa courbe vers ſa conjonction N. <lb/></s> <s xml:id="echoid-s3504" xml:space="preserve">elle doit retarder ce même cours en remon-<lb/>tant de la conjonction vers ſon premier <lb/>quartier.</s> <s xml:id="echoid-s3505" xml:space="preserve"/> </p> <div xml:id="echoid-div153" type="float" level="2" n="2"> <figure xlink:label="fig-0287-01" xlink:href="fig-0287-01a"> <image file="0287-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0287-01"/> </figure> </div> <p> <s xml:id="echoid-s3506" xml:space="preserve">Mais lorſque la Lune remonte de ce pre-<lb/>mier quartier vers ſon plein A. </s> <s xml:id="echoid-s3507" xml:space="preserve">elle eſt alors <lb/>plus loin du Soleil qui l’attire d’autant <lb/>moins, elle gravite plus vers la Terre. <lb/></s> <s xml:id="echoid-s3508" xml:space="preserve">Alors la Lune accélérant ſon mouvement, <lb/>la courbe qu’elle décrit s’applatit encore un <lb/>peu comme dans la conjonction; </s> <s xml:id="echoid-s3509" xml:space="preserve">& </s> <s xml:id="echoid-s3510" xml:space="preserve">c’eſt-là <lb/>l’unique raiſon pour laquelle la Lune eſt <lb/>plus loin de nous dans ſes quartiers, que <lb/>dans ſa conjonction & </s> <s xml:id="echoid-s3511" xml:space="preserve">dans ſon oppoſition. </s> <s xml:id="echoid-s3512" xml:space="preserve"><lb/>La courbe qu’elle décrit eſt une eſpèce d’o-<lb/>vale approchant du cercle à - peu - près en <lb/>cette maniere.</s> <s xml:id="echoid-s3513" xml:space="preserve"/> </p> <pb o="266" file="0290" n="291" rhead="DE LA PHILOSOPHIE"/> <figure> <image file="0290-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0290-01"/> </figure> <p> <s xml:id="echoid-s3514" xml:space="preserve">Ainſi donc le Soleil, dont elle s’approche, <lb/>ou s’éloigne à chaque inſtant, doit à cha-<lb/>que inſtant varier le cours de cette Planete.</s> <s xml:id="echoid-s3515" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3516" xml:space="preserve">Elle a ſon apogée & </s> <s xml:id="echoid-s3517" xml:space="preserve">ſon périgée, ſa <lb/> <anchor type="note" xlink:label="note-0290-01a" xlink:href="note-0290-01"/> plus grande & </s> <s xml:id="echoid-s3518" xml:space="preserve">ſa plus petite diſtance de la <lb/>Terre; </s> <s xml:id="echoid-s3519" xml:space="preserve">mais les points, les places de cet <lb/>apogée & </s> <s xml:id="echoid-s3520" xml:space="preserve">de ce périgée, doivent changer.</s> <s xml:id="echoid-s3521" xml:space="preserve"/> </p> <div xml:id="echoid-div154" type="float" level="2" n="3"> <note position="left" xlink:label="note-0290-01" xlink:href="note-0290-01a" xml:space="preserve">Inégali-<lb/>tés du <lb/>cours de <lb/>la Lune, <lb/>toutes <lb/>cauſées <lb/>par l’at-<lb/>traction.</note> </div> <p> <s xml:id="echoid-s3522" xml:space="preserve">Elle a ſes nœuds, c’eſt-à-dire, les points <lb/>où l’Orbite qu’elle parcourt, rencontre <lb/>préciſément l’Orbite de la Terre; </s> <s xml:id="echoid-s3523" xml:space="preserve">mais ces <lb/>nœuds, ces points d’interſection, doivent <lb/>toujours changer auſſi.</s> <s xml:id="echoid-s3524" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3525" xml:space="preserve">Elle a ſon Equateur incliné à l’Equateur <pb o="267" file="0291" n="292" rhead="DE NEUTON."/> de la Terre; </s> <s xml:id="echoid-s3526" xml:space="preserve">mais cet Equateur, tantôt plus <lb/>tantôt moins attiré, doit changer ſon incli-<lb/>naiſon.</s> <s xml:id="echoid-s3527" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3528" xml:space="preserve">Elle ſuit la Terre malgré toutes ces va-<lb/>rietés: </s> <s xml:id="echoid-s3529" xml:space="preserve">elle l’accompagne dans ſa courſe an-<lb/>nuelle; </s> <s xml:id="echoid-s3530" xml:space="preserve">mais la Terre dans cette courſe ſe <lb/>trouve d’un million de lieues plus voiſine <lb/>du Soleil en Hyver qu’en Eté. </s> <s xml:id="echoid-s3531" xml:space="preserve">Qu’arrive-<lb/>t-il alors indépendemment de toutes ces au-<lb/>tres variations ? </s> <s xml:id="echoid-s3532" xml:space="preserve">L’attraction de la Terre <lb/>agit plus pleinement ſur la Lune en Eté: </s> <s xml:id="echoid-s3533" xml:space="preserve">a-<lb/>lors la Lune acheve ſon cours d’un mois un <lb/>peu plus vîte; </s> <s xml:id="echoid-s3534" xml:space="preserve">mais en Hyver au contraire, <lb/>la Terre elle-même plus attirée par le So-<lb/>leil, & </s> <s xml:id="echoid-s3535" xml:space="preserve">allant plus rapidement qu’en Eté, <lb/>laiſſe ralentir le cours de la Lune, & </s> <s xml:id="echoid-s3536" xml:space="preserve">les <lb/>mois d’Hyver de la Lune ſont un peu plus <lb/>longs que ſes mois d’Eté. </s> <s xml:id="echoid-s3537" xml:space="preserve">Ce peu que nous <lb/>en diſons ſuffira pour donner une idée gé-<lb/>nérale de ces changemens.</s> <s xml:id="echoid-s3538" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3539" xml:space="preserve">Si quelqu’un faiſoit ici la difficulté que <lb/>j’ai entendu propoſer quelquefois, com-<lb/>ment la Lune étant plus attirée par la So-<lb/>leil, ne tombe pas alors dans cet Aſtre? </s> <s xml:id="echoid-s3540" xml:space="preserve">Il <lb/>n’a d’abord qu’à conſiderer que la force de <pb o="268" file="0292" n="293" rhead="DE LA PHILOSOPHIE"/> gravitation qui dirige la Lune autour de la <lb/>Terre eſt ſeulement diminuée ici par l’ac-<lb/>tion du Soleil; </s> <s xml:id="echoid-s3541" xml:space="preserve">nous verrons de plus à l’ar-<lb/>ticle des Cometes, pourquoi un corps qui ſe <lb/>meut en une Ellipſe & </s> <s xml:id="echoid-s3542" xml:space="preserve">qui s’approche de <lb/>ſon foyer ne tombe point cependant dans <lb/>ce foyer.</s> <s xml:id="echoid-s3543" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3544" xml:space="preserve">De ces inégalités du cours de la Lune, <lb/> <anchor type="note" xlink:label="note-0292-01a" xlink:href="note-0292-01"/> cauſées par l’attraction, vous conclurez a-<lb/>vec raiſon, que deux Planetes quelconques, <lb/>aſſez voiſines, aſſez groſſes pour agir l’une <lb/>ſur l’autre ſenſiblement, ne pourront ja-<lb/>mais tourner dans des cercles autour du <lb/>Soleil, ni même dans des Ellipſes abſolu-<lb/>ment réguliéres. </s> <s xml:id="echoid-s3545" xml:space="preserve">Ainſi les courbes que décri-<lb/>vent Jupiter & </s> <s xml:id="echoid-s3546" xml:space="preserve">Saturne, éprouvent, par <lb/>exemple, des variations ſenſibles, quand <lb/>ces Aftres ſont en conjonction: </s> <s xml:id="echoid-s3547" xml:space="preserve">quand, é-<lb/>tant le plus près l’un de l’autre qu’il eſt poſ-<lb/>ſible, & </s> <s xml:id="echoid-s3548" xml:space="preserve">le plus loin du Soleil, leur action <lb/>mutuelle augmente, & </s> <s xml:id="echoid-s3549" xml:space="preserve">celle du Soleil fur <lb/>eux diminue.</s> <s xml:id="echoid-s3550" xml:space="preserve"/> </p> <div xml:id="echoid-div155" type="float" level="2" n="4"> <note position="left" xlink:label="note-0292-01" xlink:href="note-0292-01a" xml:space="preserve">Déduc-<lb/>tion de <lb/>ces vé-<lb/>rités.</note> </div> <p> <s xml:id="echoid-s3551" xml:space="preserve">Cette gravitation augmentée & </s> <s xml:id="echoid-s3552" xml:space="preserve">affoiblie <lb/> <anchor type="note" xlink:label="note-0292-02a" xlink:href="note-0292-02"/> ſelon les diſtances, affignoit donc néceſſai- <pb o="269" file="0293" n="294" rhead="DE NEUTON."/> rement une figure elliplique irréguliére au <lb/> <anchor type="note" xlink:label="note-0293-01a" xlink:href="note-0293-01"/> chemin de la plûpart des Planetes; </s> <s xml:id="echoid-s3553" xml:space="preserve">ainſi la <lb/>loi de la gravitation n’eſt point l’effet du <lb/>cours des Aſtres, mais l’orbite qu’ils décri-<lb/>vent eſt l’effet de la gravitation. </s> <s xml:id="echoid-s3554" xml:space="preserve">Si cette <lb/>gravitation n’étoit pas comme elle eſt en <lb/>raiſon inverſe des quarrés des diſtances, <lb/>l’Univers ne pourroit ſubſiſter dans l’ordre <lb/>où il eſt.</s> <s xml:id="echoid-s3555" xml:space="preserve"/> </p> <div xml:id="echoid-div156" type="float" level="2" n="5"> <note position="left" xlink:label="note-0292-02" xlink:href="note-0292-02a" xml:space="preserve">La gra-<lb/>vitation <lb/>n’eſt</note> <note position="right" xlink:label="note-0293-01" xlink:href="note-0293-01a" xml:space="preserve">point <lb/>l’effet <lb/>du cours <lb/>des Af-<lb/>tres, <lb/>mais <lb/>leur <lb/>cours eſt <lb/>l’effet <lb/>de la <lb/>gravita-<lb/>tion.</note> </div> <p> <s xml:id="echoid-s3556" xml:space="preserve">Si les Satellites de Jupiter & </s> <s xml:id="echoid-s3557" xml:space="preserve">de Saturne <lb/>font leur révolution dans des courbes qui <lb/>ſont plus approchantes du cercle, c’eſt qu’é-<lb/>tant très - proches des groſſes Planetes qui <lb/>ſont leur centre, & </s> <s xml:id="echoid-s3558" xml:space="preserve">très - loin du Soleil, <lb/>l’action du Soleil ne peut changer le cours <lb/>de ces Satellites, comme elle change le <lb/>cours de notre Lune; </s> <s xml:id="echoid-s3559" xml:space="preserve">il eſt donc prouvé <lb/>que la gravitation, dont le nom ſeul ſem-<lb/>bloit un ſi étrange paradoxe, eſt une loi <lb/>néceſſaire dans la conſtitution du Monde; <lb/></s> <s xml:id="echoid-s3560" xml:space="preserve">tant ce qui eſt peu vraiſemblable eſt vrai <lb/>quelquefois.</s> <s xml:id="echoid-s3561" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3562" xml:space="preserve">Souvenons-nous ici combien il ſembloit <lb/>abſurde autrefois que la figure de la Terre <pb o="270" file="0294" n="295" rhead="DE LA PHILOSOPHIE"/> ne fût pas ſphérique, & </s> <s xml:id="echoid-s3563" xml:space="preserve">cependant il eſt <lb/>prouvé, comme nous l’avons vu, que la <lb/>Terre ne peut avoir une forme entiére-<lb/>ment ſphérique; </s> <s xml:id="echoid-s3564" xml:space="preserve">il en eſt ainſi de la gravi-<lb/>tation.</s> <s xml:id="echoid-s3565" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3566" xml:space="preserve">Il n’y a pas à préſent de bon Phyſicien <lb/>qui ne reconnoiſſe & </s> <s xml:id="echoid-s3567" xml:space="preserve">la règle de Kepler, & </s> <s xml:id="echoid-s3568" xml:space="preserve"><lb/>la néceſſité d’admettre une gravitation telle <lb/>que Neuton l’a prouvée; </s> <s xml:id="echoid-s3569" xml:space="preserve">mais il y a enco-<lb/>re des Philoſophes attachés à leurs tourbil-<lb/>lons de Matiere ſubtile, qui voudroient <lb/>concilier ces tourbillons imaginaires avec <lb/>ces Vérités démontrées.</s> <s xml:id="echoid-s3570" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3571" xml:space="preserve">Nous avons déja vu combien ces tour-<lb/> <anchor type="note" xlink:label="note-0294-01a" xlink:href="note-0294-01"/> billons ſont inadmiſſibles; </s> <s xml:id="echoid-s3572" xml:space="preserve">mais cette gra-<lb/>vitation même ne fournit-elle pas une nou-<lb/>velle démonſtration contr’eux? </s> <s xml:id="echoid-s3573" xml:space="preserve">Car ſuppoſé <lb/>que ces tourbillons exiſtaſſent, ils ne pour-<lb/>roient tourner autour d’un centre que par <lb/>les loix de cette gravitation même; </s> <s xml:id="echoid-s3574" xml:space="preserve">il fau-<lb/>droit donc recourir à cette gravitation, <lb/>comme à la cauſe de ces tourbillons, & </s> <s xml:id="echoid-s3575" xml:space="preserve"><lb/>non pas aux tourbillons prétendus, comme <lb/>à la cauſe de la gravitation.</s> <s xml:id="echoid-s3576" xml:space="preserve"/> </p> <div xml:id="echoid-div157" type="float" level="2" n="6"> <note position="left" xlink:label="note-0294-01" xlink:href="note-0294-01a" xml:space="preserve">Cette <lb/>gravita-<lb/>tion, <lb/>cette at-<lb/>traction, <lb/>peut ê. <lb/>tre un <lb/>premier <lb/>Principe <lb/>établi <lb/>dans la <lb/>Nature.</note> </div> <pb o="371" file="0295" n="296" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s3577" xml:space="preserve">Si étant forcé enfin d’abandonner ces <lb/>tourbillons imaginaires, on ſe réduit à dire, <lb/>que cette gravitation, cette attraction, <lb/>dépend de quelqu’autre cauſe connue, de <lb/>quelqu’autre proprieté ſecrette de la Ma-<lb/>tiere: </s> <s xml:id="echoid-s3578" xml:space="preserve">ou cette autre proprieté ſera elle-<lb/>même l’effet d’une autre proprieté, ou bien <lb/>ſera une cauſe primordiale, un premier <lb/>principe établi par l’Auteur de la Nature; <lb/></s> <s xml:id="echoid-s3579" xml:space="preserve">or pourquoi l’attraction de la Matiere ne <lb/>ſera-t-elle pas elle-même ce premier prin-<lb/>cipe?</s> <s xml:id="echoid-s3580" xml:space="preserve"/> </p> <figure> <image file="0295-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0295-01"/> </figure> <pb o="272" file="0296" n="297" rhead="CHAPITRE VINGT-DEUX."/> <figure> <image file="0296-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0296-01"/> </figure> </div> <div xml:id="echoid-div159" type="section" level="1" n="33"> <head xml:id="echoid-head55" style="it" xml:space="preserve">Nouvelles preuves & nouveaux effets de la gra-<lb/>vitation: que ce pouvoir eft dans cbaque <lb/>partie de la Matiere; Découvertes <lb/>dépendantes de ce principe.</head> <p> <s xml:id="echoid-s3581" xml:space="preserve">REcueillons de toutes ces notions que la <lb/>force centripète, l’attraction, la gra-<lb/>vitation, eſt le Principe indubitable & </s> <s xml:id="echoid-s3582" xml:space="preserve">du <lb/>cours des Planetes, & </s> <s xml:id="echoid-s3583" xml:space="preserve">de la chûte de <lb/>tous les corps, & </s> <s xml:id="echoid-s3584" xml:space="preserve">de cette peſanteur que <lb/>nous éprouvons dans les corps. </s> <s xml:id="echoid-s3585" xml:space="preserve">Cette for-<lb/>ce centripète, cette attraction, n’eſt &</s> <s xml:id="echoid-s3586" xml:space="preserve"> <pb o="273" file="0297" n="298" rhead="DE NEUTON."/> ne peut être le ſimple pouvoir d’un corps <lb/>d’en appeller un autre à lui: </s> <s xml:id="echoid-s3587" xml:space="preserve">nous la con-<lb/>ſidèrons ici comme une force dont ré-<lb/>ſulte le mouvement autour d’un centre; <lb/></s> <s xml:id="echoid-s3588" xml:space="preserve">cette force fait graviter le Soleil vers le <lb/>centre des Planetes, comme les Planetes <lb/>gravitent vers le Soleil, & </s> <s xml:id="echoid-s3589" xml:space="preserve">attire la Ter-<lb/>re vers la Lune, comme la Lune vers la <lb/>Terre.</s> <s xml:id="echoid-s3590" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3591" xml:space="preserve">Une des loix primitives du mouvement <lb/>eſt encore une nouvelle Démonſtration <lb/>de cette Vérité: </s> <s xml:id="echoid-s3592" xml:space="preserve">cette loi eſt que la réac-<lb/>tion eſt égale à l’action; </s> <s xml:id="echoid-s3593" xml:space="preserve">ainſi ſi le So-<lb/>leil gravite ſur les Planetes, les Planetes <lb/>gravitent ſur lui, & </s> <s xml:id="echoid-s3594" xml:space="preserve">nous verrons au com-<lb/>mencement du Chapitre ſuivant en quel-<lb/>le maniere cette grande loi s’opére.</s> <s xml:id="echoid-s3595" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3596" xml:space="preserve">Or cette gravitation agiſſant néceſſaire-<lb/>ment en raiſon directe de la maſſe, & </s> <s xml:id="echoid-s3597" xml:space="preserve">le So-<lb/>leil étant environ 760 fois plus gros que <lb/>toutes les Planetes miſes enſemble, (ſans <lb/>compter les Satellites de Jupiter, & </s> <s xml:id="echoid-s3598" xml:space="preserve">l’an-<lb/>neau & </s> <s xml:id="echoid-s3599" xml:space="preserve">les Lunes de Saturne) il faut que <lb/>le Soleil ſoit leur centre de gravitation;</s> <s xml:id="echoid-s3600" xml:space="preserve"> <pb o="274" file="0298" n="299" rhead="DE LA PHILOSOPHIE"/> ainſi il faut qu’elles tournent toutes au-<lb/>tour du Soleil.</s> <s xml:id="echoid-s3601" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3602" xml:space="preserve">Remarquons ſoigneuſement que, quand <lb/> <anchor type="note" xlink:label="note-0298-01a" xlink:href="note-0298-01"/> nous diſons que le pouvoir de gravitation <lb/>agit en raiſon directe des maſſes, nous enten-<lb/>dons toujours que ce pouvoir de la gravi-<lb/>tation agit d’autant plus ſur un corps, que <lb/>ce corps a plus de parties, & </s> <s xml:id="echoid-s3603" xml:space="preserve">nous l’avons <lb/>démontré en faiſant voir qu’un brin de pail-<lb/>le deſcend auſſi vîte dans la Machine pur-<lb/>gée d’air, qu’une livre d’or. </s> <s xml:id="echoid-s3604" xml:space="preserve">Nous avons <lb/>dit (en faiſant abſtraction de la petite ré-<lb/>ſiſtance de l’air) qu’une balle de plomb, <lb/>par exemple, tombe de 15. </s> <s xml:id="echoid-s3605" xml:space="preserve">pieds ſur la Ter-<lb/>re en une ſeconde: </s> <s xml:id="echoid-s3606" xml:space="preserve">nous avons démontré <lb/>que cette même balle tomberoit de 15. </s> <s xml:id="echoid-s3607" xml:space="preserve">pieds <lb/>en une minute, ſi elle étoit à 60. </s> <s xml:id="echoid-s3608" xml:space="preserve">rayons de <lb/>la Terre comme eſt la Lune; </s> <s xml:id="echoid-s3609" xml:space="preserve">donc le pou-<lb/>voir de la Terre ſur la Lune eſt au pouvoir <lb/>qu’elle auroit ſur une balle de plomb trans-<lb/>portée à l’élévation de la Lune, comme le <lb/>corps ſolide de la Lune ſeroit avec le corps <lb/>ſolide de cette petite balle. </s> <s xml:id="echoid-s3610" xml:space="preserve">C’eſt en cet-<lb/>te proportion que le Soleil agit ſur toutes <lb/>les Planetes; </s> <s xml:id="echoid-s3611" xml:space="preserve">il attire Jupiter & </s> <s xml:id="echoid-s3612" xml:space="preserve">Saturne, & </s> <s xml:id="echoid-s3613" xml:space="preserve"><lb/>les Satellites de Jupiter & </s> <s xml:id="echoid-s3614" xml:space="preserve">de Saturne, en <pb o="275" file="0299" n="300" rhead="DE NEUTON."/> raiſon directe de la matiere ſolide, qui eſt <lb/>dans les Satellites de Jupiter & </s> <s xml:id="echoid-s3615" xml:space="preserve">de Saturne, <lb/>& </s> <s xml:id="echoid-s3616" xml:space="preserve">de celle qui eſt dans Saturne & </s> <s xml:id="echoid-s3617" xml:space="preserve">dans Ju-<lb/>piter.</s> <s xml:id="echoid-s3618" xml:space="preserve"/> </p> <div xml:id="echoid-div159" type="float" level="2" n="1"> <note position="left" xlink:label="note-0298-01" xlink:href="note-0298-01a" xml:space="preserve">Remar-<lb/>que gé-<lb/>nérale <lb/>& im-<lb/>portan-<lb/>te ſur le <lb/>principe <lb/>de l’at-<lb/>traction.</note> </div> <p> <s xml:id="echoid-s3619" xml:space="preserve">De-là il découle une Vérité inconteſta-<lb/>ble, que cette gravitation n’eſt pas ſeule-<lb/>ment dans la maſſe totale de chaque Plane-<lb/>te, mais dans chaque partie de cette maſ-<lb/>ſe; </s> <s xml:id="echoid-s3620" xml:space="preserve">& </s> <s xml:id="echoid-s3621" xml:space="preserve">qu’ainſi il n’y a pas un atome de ma-<lb/>tiere dans l’Univers, qui ne ſoit revêtu de <lb/>cette proprieté.</s> <s xml:id="echoid-s3622" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3623" xml:space="preserve">Nous choiſirons ici la maniere la plus <lb/> <anchor type="note" xlink:label="note-0299-01a" xlink:href="note-0299-01"/> ſimple dont Neuton a démontré que cette <lb/>gravitation eſt également dans chaque ato-<lb/>me. </s> <s xml:id="echoid-s3624" xml:space="preserve">Si toutes les parties d’un Globe n’a-<lb/>voient pas également cette proprieté: </s> <s xml:id="echoid-s3625" xml:space="preserve">s’il <lb/>y en avoit de plus foibles & </s> <s xml:id="echoid-s3626" xml:space="preserve">de plus fortes, <lb/>la Planete en tournant ſur elle-même préſen-<lb/>teroit néceſſairement des côtés plus foibles, <lb/>& </s> <s xml:id="echoid-s3627" xml:space="preserve">enſuite des côtés plus forts à pareille diſ-<lb/>tance; </s> <s xml:id="echoid-s3628" xml:space="preserve">ainſi les mêmes corps dans toutes <lb/>les occaſions poſſibles éprouvent tantôt un <lb/>degré de gravitation, tantôt un autre à pa-<lb/>reille diſtance; </s> <s xml:id="echoid-s3629" xml:space="preserve">la loi de la raiſon inverſe <lb/>des quarrés des diſtances & </s> <s xml:id="echoid-s3630" xml:space="preserve">la loi de Kepler <pb o="276" file="0300" n="301" rhead="DE LA PHIL OSOPHIE"/> ſeroient toujours interverties; </s> <s xml:id="echoid-s3631" xml:space="preserve">or elles ne <lb/>le ſont pas; </s> <s xml:id="echoid-s3632" xml:space="preserve">donc il n’y a dans toutes les <lb/>Planetes aucune partie moins gravitante <lb/>qu’une autre.</s> <s xml:id="echoid-s3633" xml:space="preserve"/> </p> <div xml:id="echoid-div160" type="float" level="2" n="2"> <note position="right" xlink:label="note-0299-01" xlink:href="note-0299-01a" xml:space="preserve">La gra-<lb/>vita-<lb/>tion, <lb/>l’attrac-<lb/>tion, eſt <lb/>dans <lb/>toutes <lb/>les par-<lb/>ties de <lb/>la ma-<lb/>tiere <lb/>égale-<lb/>ment.</note> </div> <p> <s xml:id="echoid-s3634" xml:space="preserve">En voici encore une Démonſtration. </s> <s xml:id="echoid-s3635" xml:space="preserve">S’il <lb/>y avoit des corps en qui cette proprieté fût <lb/>différente, il y auroit des corps qui tom-<lb/>beroient plus lentement & </s> <s xml:id="echoid-s3636" xml:space="preserve">d’autres plus vî-<lb/>te dans la Machine du vuide: </s> <s xml:id="echoid-s3637" xml:space="preserve">or tous les <lb/>corps tombent dans le même-tems, tous les <lb/>pendules mêmes font dans l’air de pareilles <lb/>vibrations à égale longueur: </s> <s xml:id="echoid-s3638" xml:space="preserve">les pendules <lb/>d’or, d’argent, de fer, de bois d’Erable, de <lb/>verre, font leurs vibrations en tems égaux; <lb/></s> <s xml:id="echoid-s3639" xml:space="preserve">donc tous les corps ont cette proprieté de <lb/>la gravitation préciſément dans le même de-<lb/>gré, c’eſt-à-dire, préciſément comme leurs <lb/>maſſes; </s> <s xml:id="echoid-s3640" xml:space="preserve">de ſorte que la gravitation agit com-<lb/>me 100. </s> <s xml:id="echoid-s3641" xml:space="preserve">ſur 100. </s> <s xml:id="echoid-s3642" xml:space="preserve">atomes, & </s> <s xml:id="echoid-s3643" xml:space="preserve">comme 10. </s> <s xml:id="echoid-s3644" xml:space="preserve">ſur <lb/>10. </s> <s xml:id="echoid-s3645" xml:space="preserve">atomes.</s> <s xml:id="echoid-s3646" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3647" xml:space="preserve">De Vérité en Vérité on s’éleve inſenſi-<lb/>blement à des connoiſſances qui ſembloient <lb/>être hors de la ſphére de l’Eſprit humain.</s> <s xml:id="echoid-s3648" xml:space="preserve"/> </p> <pb o="277" file="0301" n="302" rhead="DE NEUTON"/> <p> <s xml:id="echoid-s3649" xml:space="preserve">Neuton a oſé calculer à l’aide des ſeules <lb/> <anchor type="note" xlink:label="note-0301-01a" xlink:href="note-0301-01"/> loix de la gravitation, quelle doit être la <lb/>peſanteur des corps dans d’autres Globes <lb/>que le nôtre: </s> <s xml:id="echoid-s3650" xml:space="preserve">ce que doit peſer dans la Lu-<lb/>ne, dans Saturne, dans le Soleil, le même <lb/>corps que nous appellons ici une livre; </s> <s xml:id="echoid-s3651" xml:space="preserve">& </s> <s xml:id="echoid-s3652" xml:space="preserve"><lb/>comme ces différentes peſanteurs dépen-<lb/>dent directement de la maſſe des Globes, <lb/>il a fallu calculer quelle doit être la maſſe <lb/>de ces Aſtres. </s> <s xml:id="echoid-s3653" xml:space="preserve">Qu’on diſe après cela que <lb/>la gravitation, l’attraction, eſt une qualité <lb/>occulte: </s> <s xml:id="echoid-s3654" xml:space="preserve">qu’on oſe appeller de ce nom une <lb/>loi univerſelle, qui conduit à de ſi étonnan-<lb/>tes découvertes.</s> <s xml:id="echoid-s3655" xml:space="preserve"/> </p> <div xml:id="echoid-div161" type="float" level="2" n="3"> <note position="right" xlink:label="note-0301-01" xlink:href="note-0301-01a" xml:space="preserve">Calcul <lb/>hardi & <lb/>admira-<lb/>ble de <lb/>Neuton.<unsure/></note> </div> <p> <s xml:id="echoid-s3656" xml:space="preserve">Il n’eſt rien de plus aiſé que de connoî-<lb/>tre la groſſeur d’un Aſtre quelconque, dès <lb/>qu’on connoît ſon diametre; </s> <s xml:id="echoid-s3657" xml:space="preserve">car le produit <lb/>de la circonférence du grand Cercle par le <lb/>diametre donne la ſurface de l’Aſtre, & </s> <s xml:id="echoid-s3658" xml:space="preserve">le <lb/>tiers du produit de cette ſurface par lerayon <lb/>fait la groſſeur.</s> <s xml:id="echoid-s3659" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3660" xml:space="preserve">Mais en connoiſſant cette groſſeur, on <lb/>ne connoît point du tout la maſſe, c’eſt-à-<lb/>dire, la quantité de la matiere que l’Aſtre <pb o="278" file="0302" n="303" rhead="DE LA PHILOSOPHIE"/> contient; </s> <s xml:id="echoid-s3661" xml:space="preserve">on ne le peut ſavoir que par cette <lb/>admirable découverte des loix de la gravi-<lb/>tation.</s> <s xml:id="echoid-s3662" xml:space="preserve"/> </p> <p style="it"> <s xml:id="echoid-s3663" xml:space="preserve">1<emph style="super">0</emph>. </s> <s xml:id="echoid-s3664" xml:space="preserve">Luand on dit denſité, quantité de ma-<lb/> <anchor type="note" xlink:label="note-0302-01a" xlink:href="note-0302-01"/> tiere, dans un Globe quelconque, on entend que <lb/>la matiere de ce Globe eſt homogène; </s> <s xml:id="echoid-s3665" xml:space="preserve">par exem-<lb/>ple, que tout pied cubique de cette matiere eſt <lb/>également peſant.</s> <s xml:id="echoid-s3666" xml:space="preserve"/> </p> <div xml:id="echoid-div162" type="float" level="2" n="4"> <note position="left" xlink:label="note-0302-01" xlink:href="note-0302-01a" xml:space="preserve">Com-<lb/>ment on <lb/>peut <lb/>connol<unsure/>-<lb/>tre la <lb/>quanti-<lb/>té de <lb/>matiere <lb/>d’un Aſ-<lb/>tre, & <lb/>ce que <lb/>les mê<unsure/>-<lb/>mes <lb/>corps <lb/>peſent <lb/>ſur les <lb/>divers <lb/>Aſtres.</note> </div> <p style="it"> <s xml:id="echoid-s3667" xml:space="preserve">2<emph style="super">0</emph>. </s> <s xml:id="echoid-s3668" xml:space="preserve">Tout Globe attire en raiſon directe de ſa <lb/>maſſe; </s> <s xml:id="echoid-s3669" xml:space="preserve">ainſi toutes choſes égales, un Globe qui <lb/>aura 10. </s> <s xml:id="echoid-s3670" xml:space="preserve">fois plus de maſſe, attirera 10. </s> <s xml:id="echoid-s3671" xml:space="preserve">fois <lb/>davantage qu’un corps 10. </s> <s xml:id="echoid-s3672" xml:space="preserve">fois moins maſſiſ<unsure/> <lb/>n’attirera à pareille diſtance.</s> <s xml:id="echoid-s3673" xml:space="preserve"/> </p> <p style="it"> <s xml:id="echoid-s3674" xml:space="preserve">3<emph style="super">0</emph>. </s> <s xml:id="echoid-s3675" xml:space="preserve">Il faut abſolument conſiderer la groſſeur, <lb/>la circonférence de ce Globe quelconque; </s> <s xml:id="echoid-s3676" xml:space="preserve">car plus <lb/>la circonférence eſt grande, plus la diſtance au <lb/>centre augmente, & </s> <s xml:id="echoid-s3677" xml:space="preserve">il attire en raiſon renver-<lb/>ſée du quarré de cette diſtance. </s> <s xml:id="echoid-s3678" xml:space="preserve">Exemple, ſi le <lb/>diametre de la Planete A. </s> <s xml:id="echoid-s3679" xml:space="preserve">eſt 4. </s> <s xml:id="echoid-s3680" xml:space="preserve">fois plus grand <lb/>que celui de la Planete B. </s> <s xml:id="echoid-s3681" xml:space="preserve">toutes deux ayant <lb/>également de matiere, la Planete A. </s> <s xml:id="echoid-s3682" xml:space="preserve">attirera <lb/>les corps à ſa ſuperficie 16. </s> <s xml:id="echoid-s3683" xml:space="preserve">fois moins que la <lb/>Planete B. </s> <s xml:id="echoid-s3684" xml:space="preserve">& </s> <s xml:id="echoid-s3685" xml:space="preserve">ce qui peſera une livre ſur la <lb/>Planete A. </s> <s xml:id="echoid-s3686" xml:space="preserve">peſera 16. </s> <s xml:id="echoid-s3687" xml:space="preserve">livres ſur la Plane-<lb/>te B.</s> <s xml:id="echoid-s3688" xml:space="preserve"/> </p> <p style="it"> <s xml:id="echoid-s3689" xml:space="preserve">4<emph style="super">0</emph>. </s> <s xml:id="echoid-s3690" xml:space="preserve">Il faut ſavoir ſur - tout en combien de <pb o="279" file="0303" n="304" rhead="DE NEUTON."/> tems les mobiles attirés par ce Globe duquel <lb/>on cherche la denſité, font leur révolution au-<lb/>tour de ce Globe; </s> <s xml:id="echoid-s3691" xml:space="preserve">car, comme nous l’avons <lb/>vu au Chapitre 19. </s> <s xml:id="echoid-s3692" xml:space="preserve">tout corps circulant au-<lb/>tour d’un autre, gravite d’autant plus qu’il <lb/>tourne plus vîte; </s> <s xml:id="echoid-s3693" xml:space="preserve">or il ne gravite davantage <lb/>que par l’une de ces deux raiſons, ou parce <lb/>qu’il s’approche plus du centre qui l’attire, <lb/>ou parce que ce centre attirant contient plus <lb/>de matiere. </s> <s xml:id="echoid-s3694" xml:space="preserve">Si donc je veux ſavoir la den-<lb/>ſité du Soleil par rapport à la denſité de no-<lb/>tre Terre, je dois comparer le tems de la ré-<lb/>volution d’une Planete comme Venus autour <lb/>du Soleil, avec le cours de la Lune autour <lb/>de notre Terre, & </s> <s xml:id="echoid-s3695" xml:space="preserve">la diſtance de Venus au <lb/>Soleil avec la diſtance de la Lune à la Terre.</s> <s xml:id="echoid-s3696" xml:space="preserve"/> </p> <p style="it"> <s xml:id="echoid-s3697" xml:space="preserve">5<emph style="super">0</emph>. </s> <s xml:id="echoid-s3698" xml:space="preserve">Voici comme je procéde. </s> <s xml:id="echoid-s3699" xml:space="preserve">La quantité <lb/>de matiere du Soleil, par rapport à celle de <lb/>la Terre, eſt comme le cube de la diſtance <lb/>de Venus au centre du Soleil eſt au cube de <lb/>la diſtance de la Lune au centre de la Ter-<lb/>re (prenant la diſtance de Venus au Soleil 257. <lb/></s> <s xml:id="echoid-s3700" xml:space="preserve">fois plus grande que celle de la Lune à la Ter-<lb/>re), & </s> <s xml:id="echoid-s3701" xml:space="preserve">auſſi en raiſon réciproque du quar-<lb/>ré du tems périodique de Venus autour du Soleil, <lb/>au quarré du tems périodique de la Lune autour <lb/>de la Terre.</s> <s xml:id="echoid-s3702" xml:space="preserve"/> </p> <pb o="280" file="0304" n="305" rhead="DE LA PHILOSOPHIE"/> <p style="it"> <s xml:id="echoid-s3703" xml:space="preserve">Cette opération faite, en ſuppoſant toujours <lb/>que le Soleil eſt à la Terre en groſſeur comme un <lb/>million à l’unité, & </s> <s xml:id="echoid-s3704" xml:space="preserve">en comptant rondement, <lb/>vous trouverez que le Soleil, plus gros que la <lb/>Terre un million de fois, n’a que 250000. <lb/></s> <s xml:id="echoid-s3705" xml:space="preserve">fois ou environ plus de matiere.</s> <s xml:id="echoid-s3706" xml:space="preserve"/> </p> <p style="it"> <s xml:id="echoid-s3707" xml:space="preserve">Cela ſuppoſé, je veux ſavoir quelle propor-<lb/>tion ſe trouve entre la force de la gravitation à <lb/>la ſurface du Soleil, & </s> <s xml:id="echoid-s3708" xml:space="preserve">cette même force à la <lb/>ſurface de la Terre; </s> <s xml:id="echoid-s3709" xml:space="preserve">je veux ſavoir en un mot <lb/>combien peſe ſur le Soleil ce qui peſe ici une li-<lb/>vre.</s> <s xml:id="echoid-s3710" xml:space="preserve"/> </p> <p style="it"> <s xml:id="echoid-s3711" xml:space="preserve">Pour y parvenir, je dis: </s> <s xml:id="echoid-s3712" xml:space="preserve">La force de cette <lb/>gravitation dépend directement de la denſité des <lb/>Globes attirants, & </s> <s xml:id="echoid-s3713" xml:space="preserve">de la diſiance du centre de <lb/>ces Globes aux corps peſants ſur ces Globes: </s> <s xml:id="echoid-s3714" xml:space="preserve">or <lb/>les corps peſants ſe trouvants à la ſuperficie du <lb/>Globe, leur diſtance eſt préciſément le rayon du <lb/>Globe; </s> <s xml:id="echoid-s3715" xml:space="preserve">mais le rayon du Globe de la Terre eſt <lb/>à celui du Soleil comme 1. </s> <s xml:id="echoid-s3716" xml:space="preserve">eſt à 100. </s> <s xml:id="echoid-s3717" xml:space="preserve">& </s> <s xml:id="echoid-s3718" xml:space="preserve">la den-<lb/>ſité reſpective de la Terre eſt à celle du Soleil <lb/>comme 4. </s> <s xml:id="echoid-s3719" xml:space="preserve">eſt à 1. </s> <s xml:id="echoid-s3720" xml:space="preserve">Dites donc: </s> <s xml:id="echoid-s3721" xml:space="preserve">comme 100, <lb/>rayon du Soleil multiplié par un, eſt à 4, den-<lb/>ſité de la Terre multipliée par 1. </s> <s xml:id="echoid-s3722" xml:space="preserve">ainſi eſt la <pb o="281" file="0305" n="306" rhead="DE NEUTON."/> peſanteur des corps ſur la ſurface du Soleil à la <lb/>peſanteur des même corps ſur la ſurface de la <lb/>Terre: </s> <s xml:id="echoid-s3723" xml:space="preserve">ce rapport de 100. </s> <s xml:id="echoid-s3724" xml:space="preserve">à 4. </s> <s xml:id="echoid-s3725" xml:space="preserve">réduit aux plus <lb/>petits termes, eſt comme 25. </s> <s xml:id="echoid-s3726" xml:space="preserve">à 1. </s> <s xml:id="echoid-s3727" xml:space="preserve">; </s> <s xml:id="echoid-s3728" xml:space="preserve">donc une <lb/>livre peſe 25. </s> <s xml:id="echoid-s3729" xml:space="preserve">livres ſur la ſurface du Soleil, ce <lb/>que je cherchois.</s> <s xml:id="echoid-s3730" xml:space="preserve"/> </p> <p style="it"> <s xml:id="echoid-s3731" xml:space="preserve">J’ai ſuppoſé ici les denſités reſpectives de la <lb/>Terre & </s> <s xml:id="echoid-s3732" xml:space="preserve">du Soleil comme 4. </s> <s xml:id="echoid-s3733" xml:space="preserve">& </s> <s xml:id="echoid-s3734" xml:space="preserve">1.</s> <s xml:id="echoid-s3735" xml:space="preserve">, mais ce <lb/>n’eſt pas tout-à-fait 4; </s> <s xml:id="echoid-s3736" xml:space="preserve">auſſi la peſanteur des <lb/>corps ſur la ſurface du Soleil eſt à celle des <lb/>corps ſur la Terre environ comme 27.</s> <s xml:id="echoid-s3737" xml:space="preserve">, & </s> <s xml:id="echoid-s3738" xml:space="preserve">non <lb/>pas comme 25. </s> <s xml:id="echoid-s3739" xml:space="preserve">à 1.</s> <s xml:id="echoid-s3740" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3741" xml:space="preserve">On ne peut avoir les mêmes notions de <lb/>toutes les Planetes, car celles qui n’ont <lb/>point de Lunes, point de Satellites, man-<lb/>quant de Planetes de comparaiſon, ne peu-<lb/>vent être ſoumiſes à nos recherches; </s> <s xml:id="echoid-s3742" xml:space="preserve">ainſi <lb/>nous ne ſavons point le rapport de gravi-<lb/>tation qui eſt entre Mercure, Mars, Ve-<lb/>nus & </s> <s xml:id="echoid-s3743" xml:space="preserve">nous, mais nous ſavons celui des <lb/>autres Planetes.</s> <s xml:id="echoid-s3744" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3745" xml:space="preserve">Je vais donner une petite Théorie de tout <lb/>notre Monde Planétaire, tel que les décou-<lb/>vertes de Neuton ſervent à le faire connoî- <pb o="282" file="0306" n="307" rhead="DE LA PHILOSOPHIE"/> tre; </s> <s xml:id="echoid-s3746" xml:space="preserve">ceux qui voudront ſe rendre une rai-<lb/>ſon plus approfondie de ces calculs, liront <lb/>Neuton lui-même, ou Grégory, ou Mr. <lb/></s> <s xml:id="echoid-s3747" xml:space="preserve">de Graveſande. </s> <s xml:id="echoid-s3748" xml:space="preserve">Il faut ſeulement avertir <lb/>qu’en ſuivant les proportions découvertes <lb/>par Neuton, nous nous ſommes attachés <lb/>au calcul Aſtronomique de l’Obſervatoire <lb/>de Paris. </s> <s xml:id="echoid-s3749" xml:space="preserve">Quel que ſoit le calcul, les pro-<lb/>portions & </s> <s xml:id="echoid-s3750" xml:space="preserve">les preuves ſont les mêmes.</s> <s xml:id="echoid-s3751" xml:space="preserve"/> </p> <figure> <image file="0306-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0306-01"/> </figure> <pb file="0307" n="308"/> <figure> <image file="0307-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0307-01"/> </figure> </div> <div xml:id="echoid-div164" type="section" level="1" n="34"> <head xml:id="echoid-head56" xml:space="preserve">CHAPITRE VINGT-TROIS.</head> <head xml:id="echoid-head57" style="it" xml:space="preserve">Théorie de notre Monde Planétaire.</head> <head xml:id="echoid-head58" xml:space="preserve"><emph style="sc">Le</emph> <emph style="sc">Soleil</emph>.</head> <p> <s xml:id="echoid-s3752" xml:space="preserve">LE Soleil eſt au centre de notre Monde <lb/>Planétaire & </s> <s xml:id="echoid-s3753" xml:space="preserve">doit y être néceſſaire-<lb/>ment. </s> <s xml:id="echoid-s3754" xml:space="preserve">Ce n’eſt pas que le point du milieu <lb/>du Soleil ſoit préciſément le centre de l’U-<lb/>nivers; </s> <s xml:id="echoid-s3755" xml:space="preserve">mais ce point central vers lequel <lb/>notre Univers gravite, eſt néceſſairement <lb/>dans le corps de cet Aſtre, & </s> <s xml:id="echoid-s3756" xml:space="preserve">toutes les <lb/>Planetes, ayant reçu unefois le mouvement <pb o="284" file="0308" n="309" rhead="DE LA PHILOSOPHIE"/> de projectile, doivent toutes tourner au-<lb/>tour de ce point, qui eſt dans le Soleil. </s> <s xml:id="echoid-s3757" xml:space="preserve">En <lb/>voici la preuve.</s> <s xml:id="echoid-s3758" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3759" xml:space="preserve">Soient ces deux Globes A. </s> <s xml:id="echoid-s3760" xml:space="preserve">& </s> <s xml:id="echoid-s3761" xml:space="preserve">B. </s> <s xml:id="echoid-s3762" xml:space="preserve">le plus <lb/>grand repréſentant le Soleil, le plus petit <lb/>repréſentant une Planete quelquonque. </s> <s xml:id="echoid-s3763" xml:space="preserve">S’ils <lb/>ſont abandonnés l’un & </s> <s xml:id="echoid-s3764" xml:space="preserve">l’autre à la loi de <lb/>la gravitation, & </s> <s xml:id="echoid-s3765" xml:space="preserve">libres de tout autre mou-<lb/>vement, ils ſeront attirés en raiſon directe <lb/>de leurs maſſes: </s> <s xml:id="echoid-s3766" xml:space="preserve">ils ſeront déterminés en <lb/>ligne perpendiculaire l’un vers l’autre; </s> <s xml:id="echoid-s3767" xml:space="preserve">& </s> <s xml:id="echoid-s3768" xml:space="preserve"><lb/>A. </s> <s xml:id="echoid-s3769" xml:space="preserve">plus gros un million de fois que B. </s> <s xml:id="echoid-s3770" xml:space="preserve">for-<lb/>cera B. </s> <s xml:id="echoid-s3771" xml:space="preserve">à ſe jetter vers lui un million de <lb/>fois plus vîte que le Globe A. </s> <s xml:id="echoid-s3772" xml:space="preserve">n’ira vers B.</s> <s xml:id="echoid-s3773" xml:space="preserve"/> </p> <figure> <image file="0308-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0308-01"/> </figure> <pb o="285" file="0309" n="310" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s3774" xml:space="preserve">Mais qu’ils ayent l’un & </s> <s xml:id="echoid-s3775" xml:space="preserve">l’autre un mou-<lb/>vement de projectile en raiſon de leurs <lb/>maſſes, la Planete en B, C. </s> <s xml:id="echoid-s3776" xml:space="preserve">le Soleil en A, <lb/>D.</s> <s xml:id="echoid-s3777" xml:space="preserve">: alors la Planete obéït à 2. </s> <s xml:id="echoid-s3778" xml:space="preserve">mouvemens: <lb/></s> <s xml:id="echoid-s3779" xml:space="preserve"> <anchor type="note" xlink:label="note-0309-01a" xlink:href="note-0309-01"/> elle ſuit la ligne B, C. </s> <s xml:id="echoid-s3780" xml:space="preserve">& </s> <s xml:id="echoid-s3781" xml:space="preserve">gravite en même-<lb/>tems vers le Soleil ſuivant la ligne B, A; <lb/></s> <s xml:id="echoid-s3782" xml:space="preserve">elle parcourera donc la ligne courbe B, F. </s> <s xml:id="echoid-s3783" xml:space="preserve"><lb/>le Soleil de même ſuivra la ligne A, E; </s> <s xml:id="echoid-s3784" xml:space="preserve">& </s> <s xml:id="echoid-s3785" xml:space="preserve"><lb/>gravitant l’un vers l’autre, ils tourneront au-<lb/>tour d’un centre commun. </s> <s xml:id="echoid-s3786" xml:space="preserve">Mais le Soleil <lb/>ſurpaſſant un million de fois la Terre en <lb/>groſſeur, & </s> <s xml:id="echoid-s3787" xml:space="preserve">la courbe A, E. </s> <s xml:id="echoid-s3788" xml:space="preserve">qu’il décrira <lb/>étant un million de fois plus petite que celle <lb/>que décrit la Terre, ce centre commun eſt <lb/>néceſſairement preſqu’au milieu du So-<lb/>leil.</s> <s xml:id="echoid-s3789" xml:space="preserve"/> </p> <div xml:id="echoid-div164" type="float" level="2" n="1"> <note position="right" xlink:label="note-0309-01" xlink:href="note-0309-01a" xml:space="preserve">Dé-<lb/>monſ-<lb/>tration <lb/>du mou-<lb/>vement <lb/>de la <lb/>Terre <lb/>autour <lb/>du So-<lb/>leil <lb/>tirée de <lb/>la gravi-<lb/>tation.</note> </div> <p> <s xml:id="echoid-s3790" xml:space="preserve">Il eſt démontré encore par-là que la Ter-<lb/>re & </s> <s xml:id="echoid-s3791" xml:space="preserve">les Planetes tournent autour de cet Aſ-<lb/>tre; </s> <s xml:id="echoid-s3792" xml:space="preserve">& </s> <s xml:id="echoid-s3793" xml:space="preserve">cette démonſtration eſt d’autant plus <lb/>belle & </s> <s xml:id="echoid-s3794" xml:space="preserve">plus puiſſante, qu’elle eſt indépen-<lb/>dante de toute obſervation, & </s> <s xml:id="echoid-s3795" xml:space="preserve">fondée <lb/>ſur la Mécanique primordiale du Mon-<lb/>de.</s> <s xml:id="echoid-s3796" xml:space="preserve"/> </p> <pb o="286" file="0310" n="311" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s3797" xml:space="preserve">Si l’on fait le Diametre du Soleil égal à <lb/> <anchor type="note" xlink:label="note-0310-01a" xlink:href="note-0310-01"/> cent Diametres de la Terre, & </s> <s xml:id="echoid-s3798" xml:space="preserve">ſi par con-<lb/>ſéquent il ſurpaſſe un million de fois la Ter-<lb/>re en groſſeur, il eſt 760. </s> <s xml:id="echoid-s3799" xml:space="preserve">fois plus gros que <lb/>toutes les Planetes enſemble, en ne comp-<lb/>tant ni les Satellites de Jupiter ni l’Anneau <lb/>de Saturne. </s> <s xml:id="echoid-s3800" xml:space="preserve">Il gravite vers les Planetes & </s> <s xml:id="echoid-s3801" xml:space="preserve"><lb/>les fait graviter toutes vers lui; </s> <s xml:id="echoid-s3802" xml:space="preserve">c’eſt cette <lb/>gravitation qui les fait circuler en les reti-<lb/>rant de la tangente, & </s> <s xml:id="echoid-s3803" xml:space="preserve">l’attraction que le <lb/>Soleil exerce ſur elles, ſurpaſſe celles qu’el-<lb/>les exercent ſur lui, autant qu’il les ſurpaſſe <lb/>en quantité de matiere. </s> <s xml:id="echoid-s3804" xml:space="preserve">Ne perdez jamais <lb/>de vûe que cette attraction réciproque n’eſt <lb/>autre choſe que la loi des mobiles gravitants <lb/>tous & </s> <s xml:id="echoid-s3805" xml:space="preserve">tournants tous vers un centre com-<lb/>mun.</s> <s xml:id="echoid-s3806" xml:space="preserve"/> </p> <div xml:id="echoid-div165" type="float" level="2" n="2"> <note position="left" xlink:label="note-0310-01" xlink:href="note-0310-01a" xml:space="preserve">Groſ-<lb/>ſeur du <lb/>Soleil.</note> </div> <p> <s xml:id="echoid-s3807" xml:space="preserve">Le Soleil tourne donc ſur ce centre com-<lb/> <anchor type="note" xlink:label="note-0310-02a" xlink:href="note-0310-02"/> mun, c’eſt-à-dire ſur lui-même en 25. </s> <s xml:id="echoid-s3808" xml:space="preserve">jours <lb/>& </s> <s xml:id="echoid-s3809" xml:space="preserve">{1/2}. </s> <s xml:id="echoid-s3810" xml:space="preserve">ſon point de milieu eſt toujours un peu <lb/>éloigné de ce centre commun de gravité, & </s> <s xml:id="echoid-s3811" xml:space="preserve"><lb/>le corps du Soleil s’en éloigne à proportion <lb/>que pluſieurs Planetes en conjonction l’atti-<lb/>rent vers elles; </s> <s xml:id="echoid-s3812" xml:space="preserve">mais quand toutes les Pla-<lb/>netes ſe trouveroient d’un côté & </s> <s xml:id="echoid-s3813" xml:space="preserve">le Soleil <pb o="287" file="0311" n="312" rhead="DE NEUTON."/> d’un autre, le centre commun de gravité <lb/>du Monde Planétaire ſortiroit à peine du <lb/>Soleil, & </s> <s xml:id="echoid-s3814" xml:space="preserve">leurs forces réunies pourroient <lb/>à peine déranger & </s> <s xml:id="echoid-s3815" xml:space="preserve">remuer le Soleil d’un <lb/>Diametre entier.</s> <s xml:id="echoid-s3816" xml:space="preserve"/> </p> <div xml:id="echoid-div166" type="float" level="2" n="3"> <note position="left" xlink:label="note-0310-02" xlink:href="note-0310-02a" xml:space="preserve">Il tour-<lb/>ne ſur <lb/>lui mê-<lb/>me au-<lb/>tour du <lb/>centre <lb/>com <lb/>mun du <lb/>Monde <lb/>plané-<lb/>taire.</note> </div> <p> <s xml:id="echoid-s3817" xml:space="preserve">Il change donc réellement de place à tout <lb/> <anchor type="note" xlink:label="note-0311-01a" xlink:href="note-0311-01"/> moment, à meſure qu’il eſt plus ou moins <lb/>attiré par les Planetes: </s> <s xml:id="echoid-s3818" xml:space="preserve">& </s> <s xml:id="echoid-s3819" xml:space="preserve">ce petit appro-<lb/>chement du Soleil rétablit le dérangement <lb/>que les Planetes opérent les unes ſur les au-<lb/>tres; </s> <s xml:id="echoid-s3820" xml:space="preserve">ainſi le dérangement continuel de <lb/>cet Aſtre entretient l’ordre de la Natu-<lb/>re.</s> <s xml:id="echoid-s3821" xml:space="preserve"/> </p> <div xml:id="echoid-div167" type="float" level="2" n="4"> <note position="right" xlink:label="note-0311-01" xlink:href="note-0311-01a" xml:space="preserve">Il chan-<lb/>ge tou-<lb/>jours de <lb/>place.</note> </div> <p> <s xml:id="echoid-s3822" xml:space="preserve">Quoiqu’il ſurpaſſe un million de fois la <lb/>Terre en groſſeur, il n’a pas un mil-<lb/>lion plus de matiere, comme on l’a déja <lb/>dit.</s> <s xml:id="echoid-s3823" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3824" xml:space="preserve">S’il étoit en effet un million de fois plus <lb/>ſolide, plus plein que la Terre, l’ordre du <lb/>Monde ne ſeroit pas tel qu’il eſt; </s> <s xml:id="echoid-s3825" xml:space="preserve">car les ré-<lb/>volutions des Planetes & </s> <s xml:id="echoid-s3826" xml:space="preserve">leurs diſtances à <lb/>leur centre dépendent de leur gravitation, <lb/>& </s> <s xml:id="echoid-s3827" xml:space="preserve">leur gravitation dépend en raiſon directe <pb o="288" file="0312" n="313" rhead="DE LA PHILOSOPHIE"/> de la quantité de la matiere du Globe où <lb/>eſt leur centre; </s> <s xml:id="echoid-s3828" xml:space="preserve">donc ſi le Soleil ſurpaſſoit à <lb/>un tel excès notre Terre & </s> <s xml:id="echoid-s3829" xml:space="preserve">notre Lune en <lb/>matiere ſolide, ces Planetes ſeroient beau-<lb/>coup plus attirées, & </s> <s xml:id="echoid-s3830" xml:space="preserve">leurs Ellipſes très-<lb/>dérangées.</s> <s xml:id="echoid-s3831" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3832" xml:space="preserve">En ſecond lieu la matiere du Soleil ne <lb/>peut-être comme ſa groſſeur; </s> <s xml:id="echoid-s3833" xml:space="preserve">car ce Globe <lb/>étant tout en feu, la rarefaction eſt néceſ-<lb/> <anchor type="note" xlink:label="note-0312-01a" xlink:href="note-0312-01"/> ſairement fort grande, & </s> <s xml:id="echoid-s3834" xml:space="preserve">la matiere eſt d’au-<lb/>tant moindre que la rarefaction eſt plus <lb/>forte.</s> <s xml:id="echoid-s3835" xml:space="preserve"/> </p> <div xml:id="echoid-div168" type="float" level="2" n="5"> <note position="left" xlink:label="note-0312-01" xlink:href="note-0312-01a" xml:space="preserve">Sa den-<lb/>ſité.</note> </div> <p> <s xml:id="echoid-s3836" xml:space="preserve">Par les loix de la gravitation il paroît que <lb/>le Soleil n’a que 250000. </s> <s xml:id="echoid-s3837" xml:space="preserve">fois plus de matie-<lb/>re que la Terre; </s> <s xml:id="echoid-s3838" xml:space="preserve">or le Soleil un million plus <lb/>gros n’étant que le quart d’un million plus <lb/>matériel, la Terre un million de fois plus pe-<lb/>tite aura donc à proportion 4. </s> <s xml:id="echoid-s3839" xml:space="preserve">fois plus de <lb/>matiere que le Soleil, & </s> <s xml:id="echoid-s3840" xml:space="preserve">ſera quatre fois <lb/>plus denſe.</s> <s xml:id="echoid-s3841" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3842" xml:space="preserve">Le même corps en ce cas, qui peſe ſur <lb/>la ſurſace de la Terre comme une livre, pe-<lb/>ſeroit ſur la ſurface du Soleil comme 25.</s> <s xml:id="echoid-s3843" xml:space="preserve"> <pb o="289" file="0313" n="314" rhead="DE NEUTON."/> livres; </s> <s xml:id="echoid-s3844" xml:space="preserve">mais cette proportion eſt de 27. </s> <s xml:id="echoid-s3845" xml:space="preserve">à <lb/>l’unité, parce que la Terre n’eſt pas en ef-<lb/>fet 4. </s> <s xml:id="echoid-s3846" xml:space="preserve">fois plus denſe.</s> <s xml:id="echoid-s3847" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3848" xml:space="preserve">Le même corps qui tombe ici de 15. </s> <s xml:id="echoid-s3849" xml:space="preserve">pieds <lb/> <anchor type="note" xlink:label="note-0313-01a" xlink:href="note-0313-01"/> dans la 1<emph style="super">ere</emph>. </s> <s xml:id="echoid-s3850" xml:space="preserve">ſeconde, tombera d’environ <lb/>413. </s> <s xml:id="echoid-s3851" xml:space="preserve">pieds ſur la ſurface du Soleil, toutes <lb/>choſes d’ailleurs égales.</s> <s xml:id="echoid-s3852" xml:space="preserve"/> </p> <div xml:id="echoid-div169" type="float" level="2" n="6"> <note position="right" xlink:label="note-0313-01" xlink:href="note-0313-01a" xml:space="preserve">En <lb/>quelle <lb/>propor-<lb/>tion les <lb/>corps <lb/>tombent <lb/>ſur le <lb/>Soleil.</note> </div> <p> <s xml:id="echoid-s3853" xml:space="preserve">Le Soleil perd toujours, ſelon Neuton, <lb/>un peu de ſa ſubſtance, & </s> <s xml:id="echoid-s3854" xml:space="preserve">ſeroit dans la <lb/>ſuite des ſiècles réduit à rien, ſi les Come-<lb/>tes, qui tombent de tems en tems dans ſa <lb/>Sphére, ne ſervoient à réparer ſes pertes; <lb/></s> <s xml:id="echoid-s3855" xml:space="preserve">car tout s’altére & </s> <s xml:id="echoid-s3856" xml:space="preserve">tout ſe répare dans l’U-<lb/>nivers.</s> <s xml:id="echoid-s3857" xml:space="preserve"/> </p> </div> <div xml:id="echoid-div171" type="section" level="1" n="35"> <head xml:id="echoid-head59" xml:space="preserve"><emph style="sc">Mercure</emph>.</head> <p> <s xml:id="echoid-s3858" xml:space="preserve">Depuis le Soleil juſqu’à onze à douze mil-<lb/>lions de nos lieues ou environ, il ne paroît <lb/>aucun Globe.</s> <s xml:id="echoid-s3859" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3860" xml:space="preserve">A 11. </s> <s xml:id="echoid-s3861" xml:space="preserve">ou 12. </s> <s xml:id="echoid-s3862" xml:space="preserve">millions de nos lieues du So-<lb/>leil eſt Mercure dans ſa moyenne diſtance. <lb/></s> <s xml:id="echoid-s3863" xml:space="preserve">C’eſt la plus excentrique de toutes les Pla-<lb/>netes: </s> <s xml:id="echoid-s3864" xml:space="preserve">elle tourne dans une Ellipſe qui la <pb o="290" file="0314" n="315" rhead="DE LA PHILOSOPHIE"/> met dans ſon périhélie près d’un tiers plus <lb/>près que dans ſon aphélie; </s> <s xml:id="echoid-s3865" xml:space="preserve">telle eſt à-peu-<lb/>près la courbe qu’elle décrit.</s> <s xml:id="echoid-s3866" xml:space="preserve"/> </p> <figure> <image file="0314-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0314-01"/> </figure> <p> <s xml:id="echoid-s3867" xml:space="preserve">Mercure eſt à-peu-près 27. </s> <s xml:id="echoid-s3868" xml:space="preserve">fois plus pe-<lb/>tit que la Terre; </s> <s xml:id="echoid-s3869" xml:space="preserve">il tourne autour du Soleil <lb/>en 88. </s> <s xml:id="echoid-s3870" xml:space="preserve">jours, ce qui fait ſon année.</s> <s xml:id="echoid-s3871" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3872" xml:space="preserve">Sa révolution ſur lui-même qui fait ſon <lb/> <anchor type="note" xlink:label="note-0314-01a" xlink:href="note-0314-01"/> jour eſt inconnue; </s> <s xml:id="echoid-s3873" xml:space="preserve">on ne peut aſſigner ni <lb/>ſa peſanteur, ni ſa denſité. </s> <s xml:id="echoid-s3874" xml:space="preserve">On ſait ſeule-<lb/>ment que ſi Mercure eſt préciſément une <lb/>Terre comme la nôtre, il faut que la ma-<lb/>tiere de ce Globe ſoit environ 8. </s> <s xml:id="echoid-s3875" xml:space="preserve">fois plus <lb/>denſe que la nôtre, pour que tout n’y ſoit <lb/>pas dans un degré d’efferveſcence qui tue-<lb/>roit en un inſtant des Animaux de notre <lb/>eſpèce, & </s> <s xml:id="echoid-s3876" xml:space="preserve">qui feroit évaporer toute matie- <pb o="291" file="0315" n="316" rhead="DE NEUTON."/> re de la conſiſtence de eaux de notre Glo-<lb/>be.</s> <s xml:id="echoid-s3877" xml:space="preserve"/> </p> <div xml:id="echoid-div171" type="float" level="2" n="1"> <note position="left" xlink:label="note-0314-01" xlink:href="note-0314-01a" xml:space="preserve">Idée de <lb/>Neuton <lb/>ſur la <lb/>denſité <lb/>du corps <lb/>de Mer-<lb/>cure.</note> </div> <p> <s xml:id="echoid-s3878" xml:space="preserve">Voici la preuve de cette aſſertion. </s> <s xml:id="echoid-s3879" xml:space="preserve">Mer-<lb/>cure reçoit environ 7. </s> <s xml:id="echoid-s3880" xml:space="preserve">fois plus de lumiere <lb/>que nous, à raiſon du quarré des diſtances, <lb/>parce qu’il eſt environ 2. </s> <s xml:id="echoid-s3881" xml:space="preserve">fois {2/3} plus près du <lb/>centre de la lumiere & </s> <s xml:id="echoid-s3882" xml:space="preserve">de la chaleur; </s> <s xml:id="echoid-s3883" xml:space="preserve">donc <lb/>il eſt 7. </s> <s xml:id="echoid-s3884" xml:space="preserve">fois plus étouffé, toutes choſes éga-<lb/>les. </s> <s xml:id="echoid-s3885" xml:space="preserve">Or ſur notre Terre la grande chaleur <lb/>de l’Eté étant augmentée environ 7. </s> <s xml:id="echoid-s3886" xml:space="preserve">à 8. <lb/></s> <s xml:id="echoid-s3887" xml:space="preserve">fois, fait incontinent bouillir l’eau à gros <lb/>bouillons; </s> <s xml:id="echoid-s3888" xml:space="preserve">donc il faudroit que tout fût en-<lb/>viron 7. </s> <s xml:id="echoid-s3889" xml:space="preserve">fois plus denſe qu’il n’eſt, pour ré-<lb/>ſiſter à 7. </s> <s xml:id="echoid-s3890" xml:space="preserve">ou 8. </s> <s xml:id="echoid-s3891" xml:space="preserve">fois plus de chaleur que le <lb/>plus brûlant Eté n’en donne dans nos Cli-<lb/>mats; </s> <s xml:id="echoid-s3892" xml:space="preserve">donc Mercure doit être au moins 7. </s> <s xml:id="echoid-s3893" xml:space="preserve"><lb/>fois plus denſe que notre Terre, pour que <lb/>les mêmes choſes qui ſont dans notre Ter-<lb/>re puiſſent ſubſiſter dans le Globe de Mer-<lb/>cure, toutes choſes égales. </s> <s xml:id="echoid-s3894" xml:space="preserve">Au reſte, ſi <lb/>Mercure reçoit environ 7. </s> <s xml:id="echoid-s3895" xml:space="preserve">fois plus de <lb/>rayons que notre Globe, parce qu’il eſt en-<lb/>viron 2. </s> <s xml:id="echoid-s3896" xml:space="preserve">fois {2/3} plus près du Soleil, par la <lb/>même raiſon le Soleil paroît, de Mercure, <lb/>environ 7. </s> <s xml:id="echoid-s3897" xml:space="preserve">fois plus grand, que de notre <lb/>Terre.</s> <s xml:id="echoid-s3898" xml:space="preserve"/> </p> <pb o="292" file="0316" n="317" rhead="DE LA PHILOSOPHIE"/> </div> <div xml:id="echoid-div173" type="section" level="1" n="36"> <head xml:id="echoid-head60" xml:space="preserve"><emph style="sc">Venus.</emph></head> <p> <s xml:id="echoid-s3899" xml:space="preserve">Après Mercure eſt Venus à 21. </s> <s xml:id="echoid-s3900" xml:space="preserve">ou 22. </s> <s xml:id="echoid-s3901" xml:space="preserve">mil-<lb/>lions de lieues du Soleil dans ſa diſtance mo-<lb/>yenne; </s> <s xml:id="echoid-s3902" xml:space="preserve">elle eſt groſſe comme la Terre, ſon <lb/>année eſt de 224. </s> <s xml:id="echoid-s3903" xml:space="preserve">jours. </s> <s xml:id="echoid-s3904" xml:space="preserve">On ne ſait pas <lb/>encore ce que c’eſt que ſon jour, c’eſt-à-<lb/>dire, ſa révolution ſur elle-même. </s> <s xml:id="echoid-s3905" xml:space="preserve">De très-<lb/>grands Aſtronomes croyent ce jour de 23. <lb/></s> <s xml:id="echoid-s3906" xml:space="preserve">heures, d’autres le croyent de 25. </s> <s xml:id="echoid-s3907" xml:space="preserve">de nos <lb/>jours. </s> <s xml:id="echoid-s3908" xml:space="preserve">On n’a pas pu encore faire des ob-<lb/>ſervations aſſez ſûres pour ſavoir de quel <lb/>côté eſt l’erreur; </s> <s xml:id="echoid-s3909" xml:space="preserve">mais cette erreur, en tout <lb/>cas, ne peut-etre qu’une mépriſe des yeux, <lb/>une erreur d’obſervation, & </s> <s xml:id="echoid-s3910" xml:space="preserve">non de raiſon-<lb/>nement.</s> <s xml:id="echoid-s3911" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3912" xml:space="preserve">L’Ellipſe que Venus parcourt dans ſon <lb/>année eſt moins excentrique que celle de <lb/>Mercure; </s> <s xml:id="echoid-s3913" xml:space="preserve">on peut ſe former quelqu’idée <lb/>du chemin de ces 2. </s> <s xml:id="echoid-s3914" xml:space="preserve">Planetes autour du So-<lb/>leil par cette figure.</s> <s xml:id="echoid-s3915" xml:space="preserve"/> </p> <pb o="293" file="0317" n="318" rhead="DE NEUTON."/> <figure> <image file="0317-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0317-01"/> </figure> <p> <s xml:id="echoid-s3916" xml:space="preserve">Il n’eſt pas hors de propos de remarquer ici <lb/> <anchor type="note" xlink:label="note-0317-01a" xlink:href="note-0317-01"/> que Venus & </s> <s xml:id="echoid-s3917" xml:space="preserve">Mercure ont par rapport à <lb/>nous des Phaſes différentes ainſi que la Lu-<lb/>ne. </s> <s xml:id="echoid-s3918" xml:space="preserve">On reprochoit autrefois à Copernic, <lb/>que dans ſon Syſtême ces Phaſes devoient <lb/>paroître, & </s> <s xml:id="echoid-s3919" xml:space="preserve">on concluoit que ſon Syſtême <lb/>étoit faux, parce qu’on ne les appercevoit <lb/>pas. </s> <s xml:id="echoid-s3920" xml:space="preserve">Si Venus & </s> <s xml:id="echoid-s3921" xml:space="preserve">Mercure, lui diſoit-on, <lb/>tournent autour du Soleil, & </s> <s xml:id="echoid-s3922" xml:space="preserve">que nous tour-<lb/>nions dans un plus grand cercle, nous de-<lb/>vons voir Mercure & </s> <s xml:id="echoid-s3923" xml:space="preserve">Venus, tantôt pleins <lb/>tantôt en croiſſant, &</s> <s xml:id="echoid-s3924" xml:space="preserve">c.</s> <s xml:id="echoid-s3925" xml:space="preserve">; mais c’eſt ce que <lb/>nous ne voyons jamais. </s> <s xml:id="echoid-s3926" xml:space="preserve">C’eſt pourtant ce <lb/>qui arrive, leur diſoit Copernic, & </s> <s xml:id="echoid-s3927" xml:space="preserve">c’eſt-<lb/>ce que vous verrez, ſi vous trouvez jamais <lb/>un moyen de perfectionner votre vûe. </s> <s xml:id="echoid-s3928" xml:space="preserve">L’in-<lb/>vention des Teleſcopes & </s> <s xml:id="echoid-s3929" xml:space="preserve">les obſervations <lb/>de Galilée ſervirent bien-tôt à accomplir la <pb o="294" file="0318" n="319" rhead="DE LA PHILOSOPHIE"/> prédiction de Copernic. </s> <s xml:id="echoid-s3930" xml:space="preserve">Au reſte, on ne <lb/>peut rien aſſigner ſur la maſſe de Venus & </s> <s xml:id="echoid-s3931" xml:space="preserve"><lb/>ſur la peſanteur des corps dans cette Pla-<lb/>nete.</s> <s xml:id="echoid-s3932" xml:space="preserve"/> </p> <div xml:id="echoid-div173" type="float" level="2" n="1"> <note position="right" xlink:label="note-0317-01" xlink:href="note-0317-01a" xml:space="preserve">Prédic-<lb/>tion de <lb/>Coper-<lb/>nic ſur <lb/>les Pha-<lb/>ſes de <lb/>Venus.</note> </div> </div> <div xml:id="echoid-div175" type="section" level="1" n="37"> <head xml:id="echoid-head61" xml:space="preserve"><emph style="sc">La</emph> <emph style="sc">Terre.</emph></head> <p> <s xml:id="echoid-s3933" xml:space="preserve">Après Venus eſt notre Terre placée à <lb/>30. </s> <s xml:id="echoid-s3934" xml:space="preserve">millions de lieues du Soleil, ou environ, <lb/>au moins dans ſa moyenne diſtance.</s> <s xml:id="echoid-s3935" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3936" xml:space="preserve">Elle eſt à-peu-près un million de fois plus <lb/>petite que le Soleil: </s> <s xml:id="echoid-s3937" xml:space="preserve">elle gravite vers lui, <lb/>& </s> <s xml:id="echoid-s3938" xml:space="preserve">tourne autour de lui dans une Ellipſe en <lb/>365. </s> <s xml:id="echoid-s3939" xml:space="preserve">jours, 5. </s> <s xml:id="echoid-s3940" xml:space="preserve">heures & </s> <s xml:id="echoid-s3941" xml:space="preserve">48. </s> <s xml:id="echoid-s3942" xml:space="preserve">minutes; </s> <s xml:id="echoid-s3943" xml:space="preserve">& </s> <s xml:id="echoid-s3944" xml:space="preserve"><lb/>fait au moins 180. </s> <s xml:id="echoid-s3945" xml:space="preserve">millions de lieues par an. <lb/></s> <s xml:id="echoid-s3946" xml:space="preserve">L’Ellipſe qu’elle parcourt eſt très-dérangée <lb/>par l’action de la Lune ſur elle, & </s> <s xml:id="echoid-s3947" xml:space="preserve">tandis <lb/>que le centre commun de la Terre & </s> <s xml:id="echoid-s3948" xml:space="preserve">de la <lb/>Lune décrit une Ellipſe véritable, la Ter-<lb/>re décrit en effet cette courbe à chaque <lb/>Lunaiſon.</s> <s xml:id="echoid-s3949" xml:space="preserve"/> </p> <pb o="295" file="0319" n="320" rhead="DE NEUTON."/> <figure> <image file="0319-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0319-01"/> </figure> <p> <s xml:id="echoid-s3950" xml:space="preserve">Son mouvement de rotation ſur ſon axe <lb/> <anchor type="note" xlink:label="note-0319-01a" xlink:href="note-0319-01"/> d’Occident en Orient conſtitue ſon jour de <lb/>23. </s> <s xml:id="echoid-s3951" xml:space="preserve">heures, 56. </s> <s xml:id="echoid-s3952" xml:space="preserve">minutes. </s> <s xml:id="echoid-s3953" xml:space="preserve">Ce mouvement <lb/>n’eſt point l’effet de la gravitation. </s> <s xml:id="echoid-s3954" xml:space="preserve">Il pa-<lb/>roît ſur-tout impoſſible de recourir ici à cet-<lb/>te raiſon ſuffiſante dont parle le grand Phi-<lb/>loſophe Leibnitz. </s> <s xml:id="echoid-s3955" xml:space="preserve">Il faut abſolument avouer <lb/>que les Planetes & </s> <s xml:id="echoid-s3956" xml:space="preserve">le Soleil pouvoient tour-<lb/>ner d’Orient en Occident; </s> <s xml:id="echoid-s3957" xml:space="preserve">donc il faut con-<lb/>venir que cette rotation d’Occident en O-<lb/>rient eſt l’effet de la volonté libre du Créa-<lb/>teur, & </s> <s xml:id="echoid-s3958" xml:space="preserve">que cette volonté libre eſt l’uni-<lb/>que raiſon ſuffiſante de cette rotation.</s> <s xml:id="echoid-s3959" xml:space="preserve"/> </p> <div xml:id="echoid-div175" type="float" level="2" n="1"> <note position="right" xlink:label="note-0319-01" xlink:href="note-0319-01a" xml:space="preserve">Quelle <lb/>eſt la <lb/>cauſe <lb/>de la <lb/>rotation <lb/>journa-<lb/>liére de <lb/>la Ter-<lb/>re.</note> </div> <p> <s xml:id="echoid-s3960" xml:space="preserve">La Terre a un autre mouvement que ſes <lb/>Poles achevent en 25920. </s> <s xml:id="echoid-s3961" xml:space="preserve">années: </s> <s xml:id="echoid-s3962" xml:space="preserve">c’eſt la <lb/>gravitation vers le Soleil & </s> <s xml:id="echoid-s3963" xml:space="preserve">vers la Lune <lb/>qui cauſe évidemment ce mouvement; </s> <s xml:id="echoid-s3964" xml:space="preserve">ce <lb/>que nous prouverons dans le Chapitre ſui-<lb/>vant.</s> <s xml:id="echoid-s3965" xml:space="preserve"/> </p> <pb o="296" file="0320" n="321" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s3966" xml:space="preserve">La Terre éprouve encore une révolution <lb/>beaucoup plus étrange, dont la cauſe eſt plus <lb/>cachée, dont la longueur étonne l’imagina-<lb/>tion, & </s> <s xml:id="echoid-s3967" xml:space="preserve">qui ſembleroit promettre au Gen-<lb/>re Humain une durée que l’on n’oſeroit <lb/>concevoir. </s> <s xml:id="echoid-s3968" xml:space="preserve">Cette période eſt ſelon toutes <lb/>les apparences d’un million neuf cens qua-<lb/>rante-quatre mille ans. </s> <s xml:id="echoid-s3969" xml:space="preserve">C’eſt ici le lieu <lb/>d’inſérer ce qu’on ſait de cette étonnante <lb/>découverte avant que de finir le Chapitre de <lb/>la Terre.</s> <s xml:id="echoid-s3970" xml:space="preserve"/> </p> </div> <div xml:id="echoid-div177" type="section" level="1" n="38"> <head xml:id="echoid-head62" xml:space="preserve"><emph style="sc">Digression</emph></head> <head xml:id="echoid-head63" style="it" xml:space="preserve">Sur la Période de 1944000. ans nouvelle-<lb/>ment découverte.</head> <p> <s xml:id="echoid-s3971" xml:space="preserve">L’Egypte & </s> <s xml:id="echoid-s3972" xml:space="preserve">une partie de l’Aſie, d’où <lb/>nous ſont venues toutes les Sciences qui <lb/>ſemblent circuler dans l’Univers, conſer-<lb/>voient autrefois une Tradition immémoria-<lb/>le, vague, incertaine, mais qui ne pou-<lb/>voit être ſans fondement. </s> <s xml:id="echoid-s3973" xml:space="preserve">On diſoit qu’il <lb/>s’étoit fait des changemens prodigieux dans <lb/>notre Globe, & </s> <s xml:id="echoid-s3974" xml:space="preserve">dans le Ciel par rapport à <lb/>notre Globe. </s> <s xml:id="echoid-s3975" xml:space="preserve">La ſeule inſpection de la Ter- <pb o="297" file="0321" n="322" rhead="DE NEUTON."/> re donnoit un grand poids à cette opi-<lb/>nion.</s> <s xml:id="echoid-s3976" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3977" xml:space="preserve">On voit que les Eaux ont ſucceſſivement <lb/>couvert & </s> <s xml:id="echoid-s3978" xml:space="preserve">abandonné les lits qui les con-<lb/>tiennent; </s> <s xml:id="echoid-s3979" xml:space="preserve">des Végétaux, des Poiſſons des <lb/>Indes, trouvés dans les pétrifications de no-<lb/>notre Europe, des Coquillages entaſſés ſur <lb/>des Montagnes, rendent aſſez témoignage à <lb/>cette ancienne Vérité.</s> <s xml:id="echoid-s3980" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3981" xml:space="preserve">Ovide en expoſant la Philoſophie de Pi-<lb/>thagore, & </s> <s xml:id="echoid-s3982" xml:space="preserve">en faiſant parler ce Philoſo-<lb/>phe inſtruit par les Sages de l’Aſie, parloit <lb/>au nom de tous les Philoſophes d’Orient, <lb/>lorſqu’il diſoit:</s> <s xml:id="echoid-s3983" xml:space="preserve"/> </p> <p style="it"> <s xml:id="echoid-s3984" xml:space="preserve">Nil equidem durare diu ſub imagine eâdem <lb/>Crediderim; </s> <s xml:id="echoid-s3985" xml:space="preserve">ſic ad ferrum veniſtis ab auro <lb/>Sæcula, ſic toties verſa eſt fortuna locorum. <lb/></s> <s xml:id="echoid-s3986" xml:space="preserve">Vidi ego quod fuerat quondam ſolidiſſima Tellus <lb/>Eſſe Fretum: </s> <s xml:id="echoid-s3987" xml:space="preserve">vidi factas ex Æquore Terras: </s> <s xml:id="echoid-s3988" xml:space="preserve"><lb/>Et procul à pelago Concbæ jacuere marinæ: </s> <s xml:id="echoid-s3989" xml:space="preserve"><lb/>Quodque fuit Campus Vallem decurſus aquarum <lb/>Fecit; </s> <s xml:id="echoid-s3990" xml:space="preserve">& </s> <s xml:id="echoid-s3991" xml:space="preserve">eluvie Mons eſt deductus in Æquor, <lb/>Eque paludoſa ſiccis bumus aret arenis.</s> <s xml:id="echoid-s3992" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s3993" xml:space="preserve">On peut rendre ainſi le ſens de ces Vers.</s> <s xml:id="echoid-s3994" xml:space="preserve"/> </p> <pb o="298" file="0322" n="323" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s3995" xml:space="preserve">Le Tems qui donne à tout le mouvement & </s> <s xml:id="echoid-s3996" xml:space="preserve"><lb/>l’être,</s> </p> <p> <s xml:id="echoid-s3997" xml:space="preserve">Produit, acroît, détruit, fait mourir, fait <lb/>renaître,</s> </p> <p> <s xml:id="echoid-s3998" xml:space="preserve">Change tout dans les Cieux, ſur la Terre & </s> <s xml:id="echoid-s3999" xml:space="preserve"><lb/>dans l’Air;</s> <s xml:id="echoid-s4000" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4001" xml:space="preserve">L’Age d’Or à ſon tour ſuivra l’Age de Fer:</s> <s xml:id="echoid-s4002" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4003" xml:space="preserve">Flore embellit des Champs l’aridité ſauvage:</s> <s xml:id="echoid-s4004" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4005" xml:space="preserve">La Mer change ſon lit, ſon flux & </s> <s xml:id="echoid-s4006" xml:space="preserve">ſon riva-<lb/>ge:</s> <s xml:id="echoid-s4007" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4008" xml:space="preserve">Le limon qui nous porte eſt né du ſein des <lb/>Eaux:</s> <s xml:id="echoid-s4009" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4010" xml:space="preserve">Le Caucaſe eſt ſemé du débris des Vaiſſeaux:</s> <s xml:id="echoid-s4011" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4012" xml:space="preserve">Bien-tôt la main du Tems applanit les Mon-<lb/>tagnes,</s> </p> <p> <s xml:id="echoid-s4013" xml:space="preserve">Il creuſe les Vallons, il étend les Campa-<lb/>gnes;</s> <s xml:id="echoid-s4014" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4015" xml:space="preserve">Tandis que l’Eternel, le Souverain des tems,</s> </p> <p> <s xml:id="echoid-s4016" xml:space="preserve">Eſt ſeul inébranlable en ces grands change-<lb/>mens.</s> <s xml:id="echoid-s4017" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4018" xml:space="preserve">Voilà quelle étoit l’opinion de l’Orient, <lb/>& </s> <s xml:id="echoid-s4019" xml:space="preserve">ce n’eſt pas lui faire tort de la rappor-<lb/>ter en vers, ancien langage de la Philoſo-<lb/>phie.</s> <s xml:id="echoid-s4020" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4021" xml:space="preserve">A ces témoignages que la Nature donne <lb/>de tant de révolutions qui ont changé la fa-<lb/>ce de la Terre, ſe joignoit cette idée des <lb/>anciens Egyptiens, Peuple autrefois Géo- <pb o="299" file="0323" n="324" rhead="DE NEUTON."/> metre & </s> <s xml:id="echoid-s4022" xml:space="preserve">Aſtronome, avant que la Super-<lb/>ſtition & </s> <s xml:id="echoid-s4023" xml:space="preserve">la Molleſſe en euſſent fait un Peu-<lb/>ple mépriſable. </s> <s xml:id="echoid-s4024" xml:space="preserve">Cette idée étoit que le So-<lb/>leil s’étoit levé pendant des Siècles à l’Oc-<lb/>cident; </s> <s xml:id="echoid-s4025" xml:space="preserve">il eſt vrai que c’étoit une Tradi-<lb/>tion auſſi obſcure que les Hiéroglyphes. <lb/></s> <s xml:id="echoid-s4026" xml:space="preserve">Hérodote, qu’on peut regarder comme un <lb/>Auteur trop récent, & </s> <s xml:id="echoid-s4027" xml:space="preserve">par conſéquent de <lb/>trop peu de poids à l’égard de telles Anti-<lb/>quités, rapporte au Livre d’Euterpe que, <lb/>ſelon les Prêtres Egyptiens, le Soleil dans <lb/>l’eſpace de onze mille trois cens quarante ans, <lb/>(& </s> <s xml:id="echoid-s4028" xml:space="preserve">les années des Egyptiens étoient de <lb/>365. </s> <s xml:id="echoid-s4029" xml:space="preserve">jours) s’étoit levé deux fois où il ſe <lb/>couche, & </s> <s xml:id="echoid-s4030" xml:space="preserve">s’étoit couché deux fois où il <lb/>ſe leve, ſans qu’il y eût eu le moindre chan-<lb/>gement en Egypte, malgré cette variation <lb/>du cours du Soleil.</s> <s xml:id="echoid-s4031" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4032" xml:space="preserve">Ou les Prêtres qui avoient raconté cet <lb/>Evénement à Hérodote, s’étoient bien mal <lb/>expliqués, ou Hérodote les avoit bien mal <lb/>entendus. </s> <s xml:id="echoid-s4033" xml:space="preserve">Car que le Soleil eût changé ſon <lb/>cours, c’étoit une Tradition qui pouvoit <lb/>être probable pour des Philoſophes; </s> <s xml:id="echoid-s4034" xml:space="preserve">mais <lb/>qu’en onze mille & </s> <s xml:id="echoid-s4035" xml:space="preserve">quelques années, les <lb/>Points cardinaux euſſent changé deux fois, <pb o="300" file="0324" n="325" rhead="DE LA PHILOSOPHIE"/> cela étoit impoſſible. </s> <s xml:id="echoid-s4036" xml:space="preserve">Ces deux révolutions, <lb/>comme nous l’allons voir, ne pourroient s’o-<lb/>pérer qu’en près de quatre millions d’années. <lb/></s> <s xml:id="echoid-s4037" xml:space="preserve">La révolution entiére des Poles de l’Eclip-<lb/>tique ou de l’Equateur s’acheve en près de <lb/>1944000. </s> <s xml:id="echoid-s4038" xml:space="preserve">années, & </s> <s xml:id="echoid-s4039" xml:space="preserve">cette révolution de <lb/>l’Ecliptique & </s> <s xml:id="echoid-s4040" xml:space="preserve">de l’Equateur peut ſeule, à <lb/>l’aide du mouvement journalier de la Terre, <lb/>tourner notre Globe ſucceſſivement à l’O-<lb/>rient, au Midi, à l’Occident, au Septen-<lb/>trion. </s> <s xml:id="echoid-s4041" xml:space="preserve">Ainſi ce n’eſt que dans une Période <lb/>de deux fois 1944000. </s> <s xml:id="echoid-s4042" xml:space="preserve">années que notre <lb/>Globe peut voir deux fois le Soleil ſe coucher <lb/>à l’Occident, & </s> <s xml:id="echoid-s4043" xml:space="preserve">non pas en 110. </s> <s xml:id="echoid-s4044" xml:space="preserve">Siècles <lb/>ſeulement, ſelon le rapport vague des Prê-<lb/>tres de Thèbes, & </s> <s xml:id="echoid-s4045" xml:space="preserve">d’Hérodote, le Pere de <lb/>l’Hiſtoire & </s> <s xml:id="echoid-s4046" xml:space="preserve">du menſonge.</s> <s xml:id="echoid-s4047" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4048" xml:space="preserve">Il eſt encore impoſſible que ce change-<lb/>ment ſe fût fait ſans que l’Egypte s’en fût <lb/>reſſentie; </s> <s xml:id="echoid-s4049" xml:space="preserve">car ſi la Terre en tournant jour-<lb/>nellement ſur elle-même eût ſucceſſivement <lb/>fourni ſon année d’Occident en Orient, puis <lb/>du Nord au Sud, d’Orient en Occident, <lb/>du Sud au Nord en ſe relevant ſur ſon axe, <lb/>on voit clairement que l’Egypte eût changé <lb/>de poſition comme tous les Climats de la <pb o="301" file="0325" n="326" rhead="DE NEUTON."/> Terre. </s> <s xml:id="echoid-s4050" xml:space="preserve">Les pluyes qui tombent aujour-<lb/>d’hui depuis ſi long-tems du Tropique du <lb/>Capricorne, & </s> <s xml:id="echoid-s4051" xml:space="preserve">qui fertiliſent l’Egypte en <lb/>groſſiſſant le Nil, auroient ceſſé. </s> <s xml:id="echoid-s4052" xml:space="preserve">Le ter-<lb/>rain de l’Egypte ſe fût trouvé dans une Zo-<lb/>ne glaciale, le Nil & </s> <s xml:id="echoid-s4053" xml:space="preserve">l’Egypte auroient <lb/>diſparu.</s> <s xml:id="echoid-s4054" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4055" xml:space="preserve">Platon, Diogène de Laërce & </s> <s xml:id="echoid-s4056" xml:space="preserve">Plutarque <lb/>ne parlent pas plus intelligiblement de cette <lb/>révolution; </s> <s xml:id="echoid-s4057" xml:space="preserve">mais enfin ils en parlent, ils <lb/>ſont des témoins qui reſtent encore d’une <lb/>Tradition preſque perdue.</s> <s xml:id="echoid-s4058" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4059" xml:space="preserve">Voici quelque choſe de plus frappant & </s> <s xml:id="echoid-s4060" xml:space="preserve"><lb/>de plus circonſtancié. </s> <s xml:id="echoid-s4061" xml:space="preserve">Les Philoſophes de <lb/>Babylone comptoient, au tems de l’entrée <lb/>d’Aléxandre dans leur Ville, quatre cens <lb/>trente mille ans depuis leurs premiéres Ob-<lb/>ſervations Aſtronomiques, l’Année Baby-<lb/>lonienne n’étant que de 360. </s> <s xml:id="echoid-s4062" xml:space="preserve">jours; </s> <s xml:id="echoid-s4063" xml:space="preserve">mais <lb/>cette Epoque de 403000. </s> <s xml:id="echoid-s4064" xml:space="preserve">ans a été regar-<lb/>dée comme un Monument de la vanité d’u-<lb/>ne Nation vaincue, qui vouloit, ſelon la <lb/>coutume de tous les Peuples & </s> <s xml:id="echoid-s4065" xml:space="preserve">de tous les <lb/>Particuliers, regagner par ſon antiquité la <lb/>gloire qu’elle perdoit par ſa foibleſſe.</s> <s xml:id="echoid-s4066" xml:space="preserve"/> </p> <pb o="302" file="0326" n="327" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s4067" xml:space="preserve">Enfin les Sciences ayant été apportées <lb/>parmi nous, & </s> <s xml:id="echoid-s4068" xml:space="preserve">s’étant peu-à-peu cultivées, <lb/>le Chevalier de Louville, diſtingué parmi <lb/>la foule de ceux qui ont fait honneur au <lb/>Siècle de Louïs XIV. </s> <s xml:id="echoid-s4069" xml:space="preserve">alla exprès à Marſeil-<lb/>le en 1714. </s> <s xml:id="echoid-s4070" xml:space="preserve">pour voir ſi l’obliquité de l’E-<lb/>cliptique y paroiſſoit la même qu’elle avoit <lb/>été obſervée & </s> <s xml:id="echoid-s4071" xml:space="preserve">fixée par Pitheas, il y avoit <lb/>plus de 2000. </s> <s xml:id="echoid-s4072" xml:space="preserve">ans. </s> <s xml:id="echoid-s4073" xml:space="preserve">Il trouva cette obliquité <lb/>de l’Ecliptique, c’eſt-à-dire, l’angle formé <lb/>par l’axe de l’Equateur & </s> <s xml:id="echoid-s4074" xml:space="preserve">par l’axe de l’E-<lb/>cliptique, moindre de 20. </s> <s xml:id="echoid-s4075" xml:space="preserve">minutes que Pi-<lb/>theas ne l’avoit trouvé. </s> <s xml:id="echoid-s4076" xml:space="preserve">Quel rapport de cet <lb/>angle diminué de 20. </s> <s xml:id="echoid-s4077" xml:space="preserve">minutes avec l’opi-<lb/>nion de l’ancienne Egypte? </s> <s xml:id="echoid-s4078" xml:space="preserve">avecles 403000. <lb/></s> <s xml:id="echoid-s4079" xml:space="preserve">ans dont ſe vantoit Babylone? </s> <s xml:id="echoid-s4080" xml:space="preserve">avec une Pé-<lb/>riode du Monde de près de deux millions <lb/>d’années, & </s> <s xml:id="echoid-s4081" xml:space="preserve">méme, ſelon l’Obſervation du <lb/>Chevalier de Louville, de plus de deux mil-<lb/>lions? </s> <s xml:id="echoid-s4082" xml:space="preserve">Il faut voir l’uſage qu’il en fit, & </s> <s xml:id="echoid-s4083" xml:space="preserve"><lb/>comment il en doit réſulter un jour une Aſ-<lb/>tronomie toute nouvelle.</s> <s xml:id="echoid-s4084" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4085" xml:space="preserve">Si l’angle que l’axe de l’Equateur fait a-<lb/>vec l’axe de l’Ecliptique eſt plus petit au-<lb/>jourd’hui de 20. </s> <s xml:id="echoid-s4086" xml:space="preserve">minutes, qu’il ne l’étoit il y a <pb o="303" file="0327" n="328" rhead="DE NEUTON."/> 2000. </s> <s xml:id="echoid-s4087" xml:space="preserve">ans, l’axe de la Terre en ſe rele-<lb/>vant ſur le Plan de l’Ecliptique, s’en ap-<lb/>proche d’un degré entier en 6000. </s> <s xml:id="echoid-s4088" xml:space="preserve">ans.</s> <s xml:id="echoid-s4089" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4090" xml:space="preserve">Que cet angle, P. </s> <s xml:id="echoid-s4091" xml:space="preserve">E. </s> <s xml:id="echoid-s4092" xml:space="preserve">ſoit, par exemple, d’en-<lb/>viron 23. </s> <s xml:id="echoid-s4093" xml:space="preserve">degrés & </s> <s xml:id="echoid-s4094" xml:space="preserve">{1/2} aujourd’hui, & </s> <s xml:id="echoid-s4095" xml:space="preserve">qu’il dé-<lb/>croiſſe toujours juſqu’ à ce qu’il devienne nul, <lb/>& </s> <s xml:id="echoid-s4096" xml:space="preserve">qu’il recommence enſuite pour accroître <lb/>& </s> <s xml:id="echoid-s4097" xml:space="preserve">décroître encore, il arrivera certainement <lb/>que dans 23. </s> <s xml:id="echoid-s4098" xml:space="preserve">fois & </s> <s xml:id="echoid-s4099" xml:space="preserve">{1/2}. </s> <s xml:id="echoid-s4100" xml:space="preserve">ſix mille ans, c’eſt-<lb/>à-dire, dans 141000. </s> <s xml:id="echoid-s4101" xml:space="preserve">années, notre Eclip-<lb/>tique & </s> <s xml:id="echoid-s4102" xml:space="preserve">notre Equateur coïncideront dans <lb/>tous leurs points: </s> <s xml:id="echoid-s4103" xml:space="preserve">le Soleil ſera dans l’Equa-<lb/>teur, ou du-moins s’en éloignera très-peu <lb/>pendant pluſieurs Siècles; </s> <s xml:id="echoid-s4104" xml:space="preserve">les Jours, les <lb/>Nuits, les Saiſons ſeront égaux ſur toute <lb/>la Terre. </s> <s xml:id="echoid-s4105" xml:space="preserve">Il ſe trouve ſelon le calcul de <lb/>l’Aſtronome Français, calcul un peu réfor-<lb/>mé depuis, que l’axe de l’Ecliptique avoit <lb/>été perpendiculaire à celui de l’Equateur, <lb/>il y a environ 399000. </s> <s xml:id="echoid-s4106" xml:space="preserve">de nos années, ſup-<lb/>poſé que le Monde eût exiſté alors. </s> <s xml:id="echoid-s4107" xml:space="preserve">Otez <lb/>de ce nombre le tems qui s’eſt écoulé de-<lb/>puis l’entrée triomphante d’Aléxandre dans <lb/>Babylone, on verra avec étonnement que <lb/>ce calcul ſe rapporte aſſez juſte avec les <lb/>403000. </s> <s xml:id="echoid-s4108" xml:space="preserve">années de 360. </s> <s xml:id="echoid-s4109" xml:space="preserve">jours que comp- <pb o="304" file="0328" n="329" rhead="DE LA PHILOSOPHIE"/> toient les Babyloniens: </s> <s xml:id="echoid-s4110" xml:space="preserve">on verra qu’ils com-<lb/>mençoient ce compte préciſément au point <lb/>où le Pole de la Terre avoit regardé le Bé-<lb/>lier, & </s> <s xml:id="echoid-s4111" xml:space="preserve">où la Terre dans ſa courſe annuelle <lb/>avoit été du Midi au Nord; </s> <s xml:id="echoid-s4112" xml:space="preserve">enfin où le So-<lb/>leil ſe levoit & </s> <s xml:id="echoid-s4113" xml:space="preserve">ſe couchoit aux Régions <lb/>du Ciel où ſont aujourd’hui les Poles.</s> <s xml:id="echoid-s4114" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4115" xml:space="preserve">Il y a quelque apparence que les Aſtro-<lb/>nomes Chaldéens avoient fait la même opé-<lb/>ration, & </s> <s xml:id="echoid-s4116" xml:space="preserve">par conſéquent le même raiſon-<lb/>nement que le Philoſophe Français: </s> <s xml:id="echoid-s4117" xml:space="preserve">ils a-<lb/>voient meſuré l’obliquité de l’Ecliptique, <lb/>ils l’avoient trouvée décroiſſante: </s> <s xml:id="echoid-s4118" xml:space="preserve">& </s> <s xml:id="echoid-s4119" xml:space="preserve">remon-<lb/>tant par leurs calculs juſqu’ à un Point Car-<lb/>dinal, ils avoient compté du point où l’E-<lb/>cliptique & </s> <s xml:id="echoid-s4120" xml:space="preserve">l’Equateur avoient fait un angle <lb/>de 90. </s> <s xml:id="echoid-s4121" xml:space="preserve">degrés; </s> <s xml:id="echoid-s4122" xml:space="preserve">point qu’on pourroit conſi-<lb/>dérer comme le commencement, ou la fin, <lb/>ou la moitié, ou le quart de cette Période <lb/>énorme.</s> <s xml:id="echoid-s4123" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4124" xml:space="preserve">Par-là l’Enigme des Egyptiens étoit dé-<lb/>brouillée, le compte des Chaldéens juſtifié, <lb/>le rapport d’Hérodote éclairci, & </s> <s xml:id="echoid-s4125" xml:space="preserve">l’Univers <lb/>flatté d’un long avenir, dont la durée plaît à <lb/>l’imagination des hommes; </s> <s xml:id="echoid-s4126" xml:space="preserve">quoique cette <pb o="305" file="0329" n="330" rhead="DE NEUTON."/> comparaiſon faſſe encore paroître notre vie <lb/>plus courte.</s> <s xml:id="echoid-s4127" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4128" xml:space="preserve">On s’oppoſa beaucoup à cette découver-<lb/>te du Chevalier de Louville, & </s> <s xml:id="echoid-s4129" xml:space="preserve">parce qu’el-<lb/>le étoit bien étrange, & </s> <s xml:id="echoid-s4130" xml:space="preserve">parce qu’elle ne <lb/>ſembloit pas encore aſſez conſtatée. </s> <s xml:id="echoid-s4131" xml:space="preserve">Un A-<lb/>cadémicien avoit, dans un Voyage en Egyp-<lb/>te, meſuré une Pyramide: </s> <s xml:id="echoid-s4132" xml:space="preserve">il en avoit trouvé <lb/>les 4. </s> <s xml:id="echoid-s4133" xml:space="preserve">faces expoſées aux 4. </s> <s xml:id="echoid-s4134" xml:space="preserve">Points Cardi-<lb/>naux; </s> <s xml:id="echoid-s4135" xml:space="preserve">donc les Meridiens, diſoit-on, n’a-<lb/>voient pas changé depuis tant de Siècles; <lb/></s> <s xml:id="echoid-s4136" xml:space="preserve">donc l’obliquité de l’Ecliptique, qui par ſa <lb/>diminution eût du changer tous les Méri-<lb/>diens, n’avoit pas en effet diminué. </s> <s xml:id="echoid-s4137" xml:space="preserve">Mais <lb/>ces Pyramides n’étoient point une Barriére <lb/>invincible à ces découvertes nouvelles; </s> <s xml:id="echoid-s4138" xml:space="preserve">car <lb/>étoit-on bien ſûr que les Architectes de la <lb/>Pyramide ne ſe fuſſent pas trompés de quel-<lb/>ques minutes? </s> <s xml:id="echoid-s4139" xml:space="preserve">La plus inſenſible aberration, <lb/>en poſant une pierre, eût ſuffi ſeule pour <lb/>opérer cette erreur. </s> <s xml:id="echoid-s4140" xml:space="preserve">D’ailleurs, l’Académi-<lb/>cien n’avoit-il pas négligé cette petite dif-<lb/>férence, qui peut ſe trouver entre les Points <lb/>où le Soleil doit marquer les Equinoxes & </s> <s xml:id="echoid-s4141" xml:space="preserve"><lb/>les Solſtices ſur cette Pyramide, ſuppoſé <lb/>que rien n’ait changé, & </s> <s xml:id="echoid-s4142" xml:space="preserve">les Points où il <pb o="306" file="0330" n="331" rhead="DE LA PHILOSOPHIE"/> les marque en effet? </s> <s xml:id="echoid-s4143" xml:space="preserve">N’auroit il pas pu ſe <lb/>tromper dans les fables de l’Egypte où il <lb/>opéroit par pure curioſité, puiſque Ticho-<lb/>Brahé lui-méme s’étoit trompé de 18. </s> <s xml:id="echoid-s4144" xml:space="preserve">minu-<lb/>tes dans la poſition de la Méridienne d’U-<lb/>ranibourg, de ſa Ville du Ciel, où il rappor-<lb/>toit toutes ſes Obſervations; </s> <s xml:id="echoid-s4145" xml:space="preserve">mais Ticho-<lb/>Brahé s’étoit-il en effet trompé de 18. </s> <s xml:id="echoid-s4146" xml:space="preserve">minu-<lb/>tes, comme on le prétend? </s> <s xml:id="echoid-s4147" xml:space="preserve">Ne ſe pouvoit-<lb/>il pas encore, que cette différence trouvée <lb/>entre la vraye Méridienne d’Uranibourg <lb/>& </s> <s xml:id="echoid-s4148" xml:space="preserve">celle de Ticho-Brahé, vint en partie du <lb/>changement même du Ciel, & </s> <s xml:id="echoid-s4149" xml:space="preserve">en partie des <lb/>erreurs preſqu’inévitables, commiſes & </s> <s xml:id="echoid-s4150" xml:space="preserve">par <lb/>Ticho-Brahé & </s> <s xml:id="echoid-s4151" xml:space="preserve">par ceux qui l’ont corrigé?</s> <s xml:id="echoid-s4152" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4153" xml:space="preserve">Mais auſſi le Chevalier de Louville s’étoit <lb/>pu tromper lui-même, & </s> <s xml:id="echoid-s4154" xml:space="preserve">avoir vu un dé-<lb/>croiſſement d’obliquité qui n’exiſte point. <lb/></s> <s xml:id="echoid-s4155" xml:space="preserve">Pitheas ſur-tout étoit vraiſemblablement la <lb/>ſource de toutes ces erreurs: </s> <s xml:id="echoid-s4156" xml:space="preserve">il avoit obſer-<lb/>vé comme la plûpart des Anciens avec peu <lb/>d’exactitude: </s> <s xml:id="echoid-s4157" xml:space="preserve">il étoit donc de la prudence, <lb/>aveclaquelle on procéde aujourd’hui en Phy-<lb/>ſique, d’attendre de nouveaux éclairciſſe-<lb/>mens; </s> <s xml:id="echoid-s4158" xml:space="preserve">ainſi le petit nombre qui peut juger de <lb/>ce grand différend demeura dans le ſilence.</s> <s xml:id="echoid-s4159" xml:space="preserve"/> </p> <pb o="307" file="0331" n="332" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s4160" xml:space="preserve">Enfin, en 1734. </s> <s xml:id="echoid-s4161" xml:space="preserve">M. </s> <s xml:id="echoid-s4162" xml:space="preserve">Godin (l’un des Phi-<lb/>loſophes que l’amour de la Vérité vient de <lb/>conduire au Pérou) reprit le fil de ces dé-<lb/>couvertes: </s> <s xml:id="echoid-s4163" xml:space="preserve">il ne s’agit plus ici de l’examen <lb/>d’une Pyramide ſur laquelle il reſtera tou-<lb/>jours des difficultés; </s> <s xml:id="echoid-s4164" xml:space="preserve">il faut partir de la fa-<lb/>meuſe Méridienne tracée en 1655. </s> <s xml:id="echoid-s4165" xml:space="preserve">par Do-<lb/>minique Caſſini dans l’Egliſe de St. </s> <s xml:id="echoid-s4166" xml:space="preserve">Pétrone, <lb/>avec une préciſion dont on eſt plus ſûr que <lb/>de celle des Architectes des Pyramides. </s> <s xml:id="echoid-s4167" xml:space="preserve">L’o-<lb/>bliquité de l’Ecliptique qui en réſultoit eſt <lb/>de 23. </s> <s xml:id="echoid-s4168" xml:space="preserve">d. </s> <s xml:id="echoid-s4169" xml:space="preserve">29’. </s> <s xml:id="echoid-s4170" xml:space="preserve">15". </s> <s xml:id="echoid-s4171" xml:space="preserve">mais on ne peut plus <lb/>douter par les dernieres Obſervations, que <lb/>cet angle de l’Ecliptique & </s> <s xml:id="echoid-s4172" xml:space="preserve">de l’Equateur <lb/>ne ſoit à préſent de 23. </s> <s xml:id="echoid-s4173" xml:space="preserve">d. </s> <s xml:id="echoid-s4174" xml:space="preserve">28’. </s> <s xml:id="echoid-s4175" xml:space="preserve">20". </s> <s xml:id="echoid-s4176" xml:space="preserve">à-peu-<lb/>près, à moins que les réfractions, qui en-<lb/>trent dans la détermination de la hauteur <lb/>du Pole faite par l’Etoile Polaire, & </s> <s xml:id="echoid-s4177" xml:space="preserve">par <lb/>conſéquent auſſi dans celle de l’élévation de <lb/>l’Equateur & </s> <s xml:id="echoid-s4178" xml:space="preserve">de l’obliquité de l’Ecliptique, <lb/>ne ſoient un peu changées depuis ce tems: <lb/></s> <s xml:id="echoid-s4179" xml:space="preserve">changement qu’on commence à ſoupçonner <lb/>par la différence des élévations du Pole, <lb/>trouvées dans les mêmes Villes après quel-<lb/>que eſpace de tems, comme dans celles de <lb/>Londres, d’Amſterdam & </s> <s xml:id="echoid-s4180" xml:space="preserve">de Coppenhague;</s> <s xml:id="echoid-s4181" xml:space="preserve"> <pb o="308" file="0332" n="333" rhead="DE LA PHILOSOPHIE"/> quoique ces Obſervations ne ſuffiſent pas <lb/>encore pour nous aſſûrer entiérement, que <lb/>de ſiècle en ſiècle l’air ſe trouve tantôt <lb/>plus, tantôt moins tranſparent. </s> <s xml:id="echoid-s4182" xml:space="preserve">Il eſt vrai <lb/>qu’on a découvert depuis peu, & </s> <s xml:id="echoid-s4183" xml:space="preserve">démontré <lb/>infailliblement, que les réfractions de deux <lb/>endroits, meme à très-peu de diſtance l’un <lb/>de l’autre, peuvent différer quelqueſois au <lb/>delà de l’opinion ; </s> <s xml:id="echoid-s4184" xml:space="preserve">ce qui oblige à préſent <lb/>un Obſervateur exact de bien déterminer, <lb/>avant toutes choſes, les réfractions de ſon <lb/>Horizon, s’il veut que ſes obſervations <lb/>ſoient accréditées; </s> <s xml:id="echoid-s4185" xml:space="preserve">mais l’on ſait auſſi que, <lb/>ſelon l’expérience de Mr. </s> <s xml:id="echoid-s4186" xml:space="preserve">Huygens, en laiſ-<lb/>ſant une Lunette dans une ſituation con-<lb/>ſtante, & </s> <s xml:id="echoid-s4187" xml:space="preserve">dirigée vers la pointe de quel-<lb/>que Clocher élevé, depuis midi juſqu’au <lb/>ſoir, l’on y verra cette pointe toujours plus <lb/>élevée ſur le déclin du jour, qu’à midi, & </s> <s xml:id="echoid-s4188" xml:space="preserve"><lb/>que par conſéquent l’air peut changer de <lb/>tranſparence. </s> <s xml:id="echoid-s4189" xml:space="preserve">Cependant comme tout cela ne <lb/>contribue rien à un changement, tel que ce-<lb/>lui qu’on pourroit ſoupçonner de ſe mêler au <lb/>Phénomêne de cette queſtion, on auroit <lb/>tort d’admettre un fait auſſi douteux, vû <lb/>qu’on n’en a point encore de preuves con-<lb/>vaincantes, ni de raiſons Phyſiques.</s> <s xml:id="echoid-s4190" xml:space="preserve"/> </p> <pb o="309" file="0333" n="334" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s4191" xml:space="preserve">A l’égard des Pyramides d’Egypte, & </s> <s xml:id="echoid-s4192" xml:space="preserve">de <lb/>la conſtance des Méridiens, qui ſemble <lb/>contraire à cette mobilité des Poles de l’E-<lb/>quateur, il eſt à propos de remarquer en-<lb/>core, qu’en ſuppoſant la figure de la Terre, <lb/>non pas ſphéroïde, comme elle l’eſt vérita-<lb/>blement, mais exactement ſphérique, ce <lb/>mouvement du Plan de l’Equateur & </s> <s xml:id="echoid-s4193" xml:space="preserve">de ſes <lb/>Poles, ſe peut concevoir de deux manieres. <lb/></s> <s xml:id="echoid-s4194" xml:space="preserve">Car, ou la plûpart des Places, ſituées à préſent <lb/>ſous l’Equateur, auront après quelques ſiè-<lb/>cles une Latitude Méridionale ou Septen-<lb/>trionale, l’Equateur les ayant quittées pour <lb/>s’approcher del’Ecliptique, (auquel cas tous <lb/>les Méridiens ſeront dérangés, & </s> <s xml:id="echoid-s4195" xml:space="preserve">deux Vil-<lb/>les quelconques, ſans avoir changé de pla-<lb/>ce, de diſtance, ni de leur premiére ſitua-<lb/>tion ſur la Terre, auront pourtant changé <lb/>de Rumb, l’une à l’égard de l’autre); </s> <s xml:id="echoid-s4196" xml:space="preserve">ou l’E-<lb/>quateur n’abandonnera jamais les Places, qui <lb/>ont été de tout tems ſituées ſous lui, mais <lb/>ſon Plan tournera avec elles autour de l’E-<lb/>cliptique, ſans qu’il ſe faſſe jamais aucun <lb/>changement dans les Méridiens, leur con-<lb/>ſtance ne prouvant pas la même choſe con-<lb/>tre le mouvement de l’Equateur que dans <pb o="310" file="0334" n="335" rhead="DE LA PHILOSOPHIE"/> la premiére ſuppoſition. </s> <s xml:id="echoid-s4197" xml:space="preserve">Au contraire re-<lb/>prenant la figure ſphéroïde de la Terre, qui <lb/>eſt la véritable, il eſt clair que ſes parties <lb/>ſolides ſe ſoutenant & </s> <s xml:id="echoid-s4198" xml:space="preserve">ne ſe pouvant pas <lb/>quitter les unes les autres, les plus éloignées <lb/>du Centre de la Terre demeureront toujours <lb/>dans le même éloignement, & </s> <s xml:id="echoid-s4199" xml:space="preserve">que par con-<lb/>ſéquent la circonſérence de l’Equateur, qui <lb/>les a une fois environnées, ne les quittera <lb/>jamais; </s> <s xml:id="echoid-s4200" xml:space="preserve">de ſorte que le Plan de l’Equateur, <lb/>tant mobile qu’immobile, ne ſauroit jamais <lb/>apporter aucun dérangement aux Méridiens. <lb/></s> <s xml:id="echoid-s4201" xml:space="preserve">On voit par-là que, quoique les Architectes <lb/>Egyptiens ayent eu ordre d’aſſeoir les Py-<lb/>ramides parallèement aux quatre Points <lb/>Cardinaux du Monde, & </s> <s xml:id="echoid-s4202" xml:space="preserve">qu’ils ayent exé-<lb/>cuté cet ordre avec la derniere exactitude, <lb/>cela n’empêche pas que l’angle de l’inter-<lb/>ſection de l’Equateur & </s> <s xml:id="echoid-s4203" xml:space="preserve">de l’Ecliptique ne <lb/>puiſſe toujours varier autant que l’on vou-<lb/>dra.</s> <s xml:id="echoid-s4204" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4205" xml:space="preserve">Rien ne fait plus de plaiſir que de voir <lb/>rétablir le crédit des Vérités les plus reſpec-<lb/>tables par leur ancienneté, après avoir été <lb/>miſes en conteſtation dans des Siècles auſſi <lb/>circonſpects & </s> <s xml:id="echoid-s4206" xml:space="preserve">auſſi peu crédules qu’eſt le <pb o="311" file="0335" n="336" rhead="DE NEUTON."/> nôtre; </s> <s xml:id="echoid-s4207" xml:space="preserve">mais il faut avouer néanmoins, que <lb/>ſi les Egyptiens & </s> <s xml:id="echoid-s4208" xml:space="preserve">les Babyloniens ont été <lb/>les premiers à découvrir le décroiſſement <lb/>de cette obliquité, ils l’ont découvert par <lb/>des raiſonnemens bien moins fondés, que ne <lb/>ſont ceux par leſquels nous leur attribuons <lb/>cette découverte. </s> <s xml:id="echoid-s4209" xml:space="preserve">Hérodote publia ſon Hif <lb/>toire environ cent ans après qu’Anaximan-<lb/>dre de Milet eut trouvé, le premier, le <lb/>moyen de meſurer l’obliquité de l’Eclipti-<lb/>que: </s> <s xml:id="echoid-s4210" xml:space="preserve">& </s> <s xml:id="echoid-s4211" xml:space="preserve">cette invention ayant paſſé peu a-<lb/>près en Egypte par les Voyages de Cléoſtra-<lb/>te , d’Harpale & </s> <s xml:id="echoid-s4212" xml:space="preserve">d’Eudoxe, les Egyp-<lb/>tiens, qui ne manquérent pas de trouver <lb/>cette obliquité plus petite que ne l’avoit <lb/>trouvée Anaximandre, s’en prévalurent <lb/>pour en faire honneur à leur Nation; </s> <s xml:id="echoid-s4213" xml:space="preserve">com-<lb/>me ſi la diminution & </s> <s xml:id="echoid-s4214" xml:space="preserve">par conſéquent la <lb/>meſure de l’obliquité de l’Ecliptique avoient <lb/>été connues chez eux pendant des milliers <lb/>d’années, dans le tems que cette derniére <lb/>venoit ſeulement d’être découverte parmi <lb/>les Grecs. </s> <s xml:id="echoid-s4215" xml:space="preserve">Nous avons dit ci-deſſus à-peu-<lb/>près la même choſe des Babyloniens, qui <lb/>également jaloux des Egyptiens & </s> <s xml:id="echoid-s4216" xml:space="preserve">des <lb/>Grecs, ont remonté, par un pareil calcul, <lb/>juſqu’à une antiquite incomparablement <pb o="312" file="0336" n="337" rhead="DE LA PHILOSOPHIE"/> plus abſurde que n’eſt celle des Egyptiens.</s> <s xml:id="echoid-s4217" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4218" xml:space="preserve">Mais, ſoit que ce mouvement de l’Equa-<lb/>teur exiſte, ſoit qu’il n’exiſte pas, il eſt <lb/>toujours certain, qu’il ne peut-etre produit <lb/>par aucun méchaniſme de ceux qui ſont <lb/>tombés dans la penſée du ſavant Newton. <lb/></s> <s xml:id="echoid-s4219" xml:space="preserve">Le mouvement qui reſſemble plus naturel-<lb/>lement à celui de l’axe de la Terre, eſt la <lb/>variation de l’inclinaiſon de l’Orbe de la <lb/>Lune, qui eſt de 5. </s> <s xml:id="echoid-s4220" xml:space="preserve">deg. </s> <s xml:id="echoid-s4221" xml:space="preserve">18. </s> <s xml:id="echoid-s4222" xml:space="preserve">ou 19. </s> <s xml:id="echoid-s4223" xml:space="preserve">min. </s> <s xml:id="echoid-s4224" xml:space="preserve"><lb/>quand les Nœuds de la Lune ſe trouvent en <lb/>conjonction, ou en oppoſition avec le So-<lb/>leil, & </s> <s xml:id="echoid-s4225" xml:space="preserve">de 5. </s> <s xml:id="echoid-s4226" xml:space="preserve">deg. </s> <s xml:id="echoid-s4227" xml:space="preserve">ſeulement, quand ces <lb/>mêmes Nœuds ſont dans les Quadratures. </s> <s xml:id="echoid-s4228" xml:space="preserve"><lb/>Il eſt vrai que, par une analogie naturelle, <lb/>ce grand Philoſophe attribue à l’axe de la <lb/>Terre un petit mouvement alternatif, par <lb/>lequel l’angle de l’interſection de l’Eclip-<lb/>tique & </s> <s xml:id="echoid-s4229" xml:space="preserve">de l’Equinoxiale ſe trouvant <lb/>dans les Equinoxes, par exemple, de 23. </s> <s xml:id="echoid-s4230" xml:space="preserve"><lb/>deg. </s> <s xml:id="echoid-s4231" xml:space="preserve">29. </s> <s xml:id="echoid-s4232" xml:space="preserve">min. </s> <s xml:id="echoid-s4233" xml:space="preserve">s’étrecit en approchant des <lb/>Solſtices, & </s> <s xml:id="echoid-s4234" xml:space="preserve">s’élargit derechef depuis les <lb/>Solſtices juſqu’aux Equinoxes; </s> <s xml:id="echoid-s4235" xml:space="preserve">de ſorte <lb/>qu’aux Solſtices, cet angle, dans ſa plus <lb/>petite dimenſion, eſt de 23. </s> <s xml:id="echoid-s4236" xml:space="preserve">deg. </s> <s xml:id="echoid-s4237" xml:space="preserve">29. </s> <s xml:id="echoid-s4238" xml:space="preserve">min. </s> <s xml:id="echoid-s4239" xml:space="preserve"><lb/>moins quelques ſecondes.</s> <s xml:id="echoid-s4240" xml:space="preserve"/> </p> <pb o="313" file="0337" n="338" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s4241" xml:space="preserve">Mais ces alternatives de diminution & </s> <s xml:id="echoid-s4242" xml:space="preserve"><lb/>d’accroiſſement ne produiſent point de mou-<lb/>vement circulaire du Plan de l’Equinoxiale, <lb/>d’un Pole de l’Ecliptique à l’autre. </s> <s xml:id="echoid-s4243" xml:space="preserve">Il faut <lb/>donc, que cette circulation dépende de <lb/>quelqu’autre raiſon inconnue juſqu’à préſent, <lb/>qu’il faut tâcher de découvrir, au cas que <lb/>ce Phénomêne ſoit réel.</s> <s xml:id="echoid-s4244" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4245" xml:space="preserve">Pour que la diminution de cet angle é-<lb/>gale toujours ſon accroiſſement, il faut que <lb/>le centre abſolu de peſanteur de toute la <lb/>maſſe de la Terre ſoit le même que le <lb/>centre géométrique de ſa figure ſphéroïde; <lb/></s> <s xml:id="echoid-s4246" xml:space="preserve">mais il ſe peut bien faire que cela ne ſoit <lb/>pas. </s> <s xml:id="echoid-s4247" xml:space="preserve">Car, ſi la Terre eſt tant ſoit peu plus <lb/>matérielle du côté Boréal de l’Equateur, <lb/>que du côté Méridional, & </s> <s xml:id="echoid-s4248" xml:space="preserve">qu’il arrive au <lb/>dedans de cette Planete, ou à ſa ſurface, <lb/>quelque changement, qui diminue la quan-<lb/>tité de matiére dans un endroit & </s> <s xml:id="echoid-s4249" xml:space="preserve">qui l’aug-<lb/>mente dans un autre, il eſt évident, que <lb/>la ſurface extérieure de la Terre & </s> <s xml:id="echoid-s4250" xml:space="preserve">le cen-<lb/>tre commun de la peſanteur de toute ſa <lb/>maſſe changeront de poſition, l’un à l’égard <lb/>de l’autre; </s> <s xml:id="echoid-s4251" xml:space="preserve">& </s> <s xml:id="echoid-s4252" xml:space="preserve">comme le centre géométrique <pb o="314" file="0338" n="339" rhead="DE LA PHILOSOPHIE"/> de ſa ſurſace ſphéroïde extérieure demeure <lb/>toujours le même, il eſt néceſſaire que ce cen-<lb/>tre change auſſi de poſition, à l’égard de celui <lb/>de peſanteur, dès que quelque raiſon conſtan-<lb/>te, ou non conſtante, ôte quelque peu de <lb/>matiere en quelqu’endroit, pour le porter <lb/>ailleurs. </s> <s xml:id="echoid-s4253" xml:space="preserve">Or les deux centres, ſavoir le géo-<lb/>métrique de la figure ovale de la Terre & </s> <s xml:id="echoid-s4254" xml:space="preserve"><lb/>celui de ſa peſanteur générale, doivent né-<lb/>ceſſairement être dans le même axe de ſon <lb/>tournoyement, ſi ce tournoyement doit ê-<lb/>tre égal & </s> <s xml:id="echoid-s4255" xml:space="preserve">uniforme pendant 24. </s> <s xml:id="echoid-s4256" xml:space="preserve">heures, <lb/>ſans s’accélérer & </s> <s xml:id="echoid-s4257" xml:space="preserve">ſe retarder par repriſes; <lb/></s> <s xml:id="echoid-s4258" xml:space="preserve">ce qui ſeroit contraire à l’expérience.</s> <s xml:id="echoid-s4259" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4260" xml:space="preserve">Pour effectuer donc ce mouvement du <lb/>Plan de l’Equateur, il ſuffit qu’il y ait, au-<lb/>dedans de la Terre, une matiere, qui en <lb/>circulant continuellement, mais lentement, <lb/>déplace toujours le centre commun de pe-<lb/>ſanteur, par rapport à la ſurface de la Ter-<lb/>re, parce que l’axe du tournoyement ſuivra <lb/>toujours le même chemin de ce centre.</s> <s xml:id="echoid-s4261" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4262" xml:space="preserve">Si cette matiere ne circulepas, mais qu’elle <lb/>ait un mouvement irrégulier & </s> <s xml:id="echoid-s4263" xml:space="preserve">très petit, <lb/>le Plan de l’Equateur changera auſſi de poſi- <pb o="315" file="0339" n="340" rhead="DE NEUTON."/> tion avec l’Ecliptique, mais ſans règle cer-<lb/>taine, & </s> <s xml:id="echoid-s4264" xml:space="preserve">pourra être tantôt plus près, tan-<lb/>tôt plus loin d’elle; </s> <s xml:id="echoid-s4265" xml:space="preserve">ce qui ſeroit peut-être <lb/>plus vraiſemblable qu’une circulation par-<lb/>faite. </s> <s xml:id="echoid-s4266" xml:space="preserve">Mais tout ce raiſonnement n’aura <lb/>lieu que lorſqu’il ſera démontré d’une ma-<lb/>niere tout-à-fait inconteſtable, que l’appro-<lb/>chement de l’Equateur & </s> <s xml:id="echoid-s4267" xml:space="preserve">de l’Ecliptique, <lb/>dont les plus habiles Obſervateurs préten-<lb/>dent s’appercevoir aujourd’hui, eſt réel: </s> <s xml:id="echoid-s4268" xml:space="preserve">& </s> <s xml:id="echoid-s4269" xml:space="preserve"><lb/>qu’il n’y a point d’illuſion, ni de la part des <lb/>réfractions, ni des Inſtrumens, dans une af-<lb/>faire qui eſt encore ſi delicate, & </s> <s xml:id="echoid-s4270" xml:space="preserve">ſi peu <lb/>ſenſible dans les obſervations modernes, où <lb/>il ne s’agit encore que de quelques ſecondes <lb/>de diminution; </s> <s xml:id="echoid-s4271" xml:space="preserve">de ſorte que ce ne ſera <lb/>qu’après pluſieurs Siècles d’obſervations <lb/>continuées, que l’on pourra dire, avec une <lb/>pleine certitude, ſi l’obliquité eſt variable, <lb/>ou comment elle l’eſt.</s> <s xml:id="echoid-s4272" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4273" xml:space="preserve">Le moyen le plus court & </s> <s xml:id="echoid-s4274" xml:space="preserve">le plus ſûr de <lb/>terminer cette queſtion, ſeroit de meſurer <lb/>exactement l’élévation du Pole des ruïnes <lb/>de l’ancienne Ville de Syène en Egypte. <lb/></s> <s xml:id="echoid-s4275" xml:space="preserve">L’on ſait, au rapport de Strabon dans le <lb/>dernier Livre de ſa Géographie, que cette <pb o="316" file="0340" n="341" rhead="DE LA PHILOSOPHIE"/> Ville étoit ſituée préciſément ſous le Tro-<lb/>pique de Cancer, & </s> <s xml:id="echoid-s4276" xml:space="preserve">qu’il y avoit un Puits <lb/>très-profond, dans lequel on ne voyoit ja-<lb/>mais l’image du Soleil, qu’au point de Mi-<lb/>di, aux Solſtices d’Eté, le Soleil donnant <lb/>verticalement ſur la ſurface Horizontale de <lb/>l’eau, au bas du Puits. </s> <s xml:id="echoid-s4277" xml:space="preserve">Strabon ajoute au <lb/>même endroit, qu’en partant de la Gréce, <lb/>cette Ville étoit la premiére que l’on ren-<lb/>controit, où les Gnomons, ou des Colomnes <lb/>érigées verticalement n’euſſent point d’om-<lb/>bre Méridienne une fois dans l’année, ſavoir <lb/>au Solſtice d’Eté; </s> <s xml:id="echoid-s4278" xml:space="preserve">de ſorte que voilà deux <lb/>preuves différentes, qui nous aſſûrent que <lb/>du tems de Strabon, ou quelque tems avant <lb/>lui, le Tropique du Cancer a paſſé par le <lb/>point vertical de cette Ville.</s> <s xml:id="echoid-s4279" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4280" xml:space="preserve">Or ſi en meſurant à préſent la Latitude de <lb/>l’endroit, où a été autrefois cette Place, on y <lb/>trouvoit le Pole Septentrional élevé de 23. <lb/></s> <s xml:id="echoid-s4281" xml:space="preserve">deg. </s> <s xml:id="echoid-s4282" xml:space="preserve">49. </s> <s xml:id="echoid-s4283" xml:space="preserve">min. </s> <s xml:id="echoid-s4284" xml:space="preserve">ou davantage, ce ſeroit .</s> <s xml:id="echoid-s4285" xml:space="preserve">une <lb/>preuve indubitable que Mr. </s> <s xml:id="echoid-s4286" xml:space="preserve">le Chevalier de <lb/>Louville avoit trouvé la vérité, & </s> <s xml:id="echoid-s4287" xml:space="preserve">que l’obli-<lb/>quité de l’Ecliptique étoit diminuée de 20. </s> <s xml:id="echoid-s4288" xml:space="preserve"><lb/>min. </s> <s xml:id="echoid-s4289" xml:space="preserve">pendant près de 18. </s> <s xml:id="echoid-s4290" xml:space="preserve">ſiècles. </s> <s xml:id="echoid-s4291" xml:space="preserve">Je dis de 23. </s> <s xml:id="echoid-s4292" xml:space="preserve"><lb/>deg. </s> <s xml:id="echoid-s4293" xml:space="preserve">49. </s> <s xml:id="echoid-s4294" xml:space="preserve">min. </s> <s xml:id="echoid-s4295" xml:space="preserve">ou davantage, car la Tour de <pb o="317" file="0341" n="342" rhead="DE NEUTON."/> Syène étant déja renommée, à cauſe de la <lb/>propriété dont nous venons de parler, du <lb/>tems du Prophête Ezéchiel, qui en fait men-<lb/>tion au Chap. </s> <s xml:id="echoid-s4296" xml:space="preserve">29. </s> <s xml:id="echoid-s4297" xml:space="preserve">de ſa Prophétie, il eſt appa-<lb/>rent que ſi l’obliquité de l’Ecliptique étoit <lb/>variable, elle auroit encore diminué de 5. <lb/></s> <s xml:id="echoid-s4298" xml:space="preserve">à 6. </s> <s xml:id="echoid-s4299" xml:space="preserve">minutes, dans la même proportion, <lb/>depuis le tems de ce Prophête juſqu’à celui <lb/>de Strabon, pendant plus de cinq Siècles, <lb/>ſans compter ce qu’il pourroit y avoir de <lb/>diminution depuis la fondation de cette <lb/>Tour juſqu’au tems de ce Prophête.</s> <s xml:id="echoid-s4300" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4301" xml:space="preserve">Mais ſi au contraire on n’y trouvoit le Pole <lb/>élevé que de 23. </s> <s xml:id="echoid-s4302" xml:space="preserve">deg. </s> <s xml:id="echoid-s4303" xml:space="preserve">& </s> <s xml:id="echoid-s4304" xml:space="preserve">demi, ou environ, il <lb/>faudroit conclure, ſans héſiter, que, pen-<lb/>dant toute cette ſuite de Siècles, l’obliquité <lb/>en queſtion a été conſtamment la même, <lb/>ou que ſa diminution n’a rien eu de conſi-<lb/>dérable; </s> <s xml:id="echoid-s4305" xml:space="preserve">& </s> <s xml:id="echoid-s4306" xml:space="preserve">que l’eſpace compris entre l’E-<lb/>quinoxiale & </s> <s xml:id="echoid-s4307" xml:space="preserve">l’Ecliptique ne s’eſt que peu, <lb/>ou point rétreci. </s> <s xml:id="echoid-s4308" xml:space="preserve">Toute la difficulté ne <lb/>conſiſteroit qu’à bien découvrir la ſituation <lb/>de cette ancienne Ville au voiſinage du Nil <lb/>& </s> <s xml:id="echoid-s4309" xml:space="preserve">de l’Iſle Eléphantine. </s> <s xml:id="echoid-s4310" xml:space="preserve">Ce ſeroit le moyen <lb/>de prévenir les ſoins de la Poſtérité, & </s> <s xml:id="echoid-s4311" xml:space="preserve">de <lb/>ſe faire un mérite auprès d’elle, en lui pré- <pb o="318" file="0342" n="343" rhead="DE LA PHILOSOPHIE"/> ſentant des Démonſtrations achevées d’une <lb/>vérité, dont l’éclairciſſement pourra lui <lb/>coûter pluſieurs ſiècles.</s> <s xml:id="echoid-s4312" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4313" xml:space="preserve">Le dénombrement que nous avons entre-<lb/>pris de faire ici des principales particulari-<lb/>tés qui regardent la Terre, par rapport au <lb/>rang qu’elle tient parmi les Planetes, nous <lb/>engage à examiner les preuves de ſa figure <lb/>ſphéroïde que nous avons ſuppoſée vérita-<lb/>ble, & </s> <s xml:id="echoid-s4314" xml:space="preserve">de faire voir l’impoſſibilité du chan-<lb/>gement des Méridiens. </s> <s xml:id="echoid-s4315" xml:space="preserve">Nous en avons dé-<lb/>ja donné une idée générale au Chapitre <lb/>XVIII. </s> <s xml:id="echoid-s4316" xml:space="preserve">lorſque, par rapport à l’étendue & </s> <s xml:id="echoid-s4317" xml:space="preserve"><lb/>aux divers degrés de la peſanteur, nous a-<lb/>vons fait mention de l’inondation des Eaux <lb/>vers les Régions de l’Equateur, qui devoit <lb/>réſulter néceſſairement du tournoyement de <lb/>la Terre autour de ſon axe, ſi elle étoit <lb/>exactement ſphérique. </s> <s xml:id="echoid-s4318" xml:space="preserve">Mais comme ce n’é-<lb/>toit pas là le lieu de prouver que cette dif-<lb/>férence étoit aſſez ſenſible pour pouvoir <lb/>être meſurée, nous allons faire voir ici ce <lb/>qui en eſt.</s> <s xml:id="echoid-s4319" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4320" xml:space="preserve">Les preuves, dont nous nous ſervirons, <lb/>ſont tirées en partio des raiſonnemens de <pb o="319" file="0343" n="344" rhead="DE NEUTON."/> Phyſique, & </s> <s xml:id="echoid-s4321" xml:space="preserve">en partie de l’Expérience mê-<lb/>me. </s> <s xml:id="echoid-s4322" xml:space="preserve">Les raiſonnemens de Phyſique, qui <lb/>nous prouvent la néceſſité de cette figure, <lb/>ne ſuppoſent pour tout Principe, que le <lb/>mouvement journalier de la Terre, de 23. <lb/></s> <s xml:id="echoid-s4323" xml:space="preserve">heures 56. </s> <s xml:id="echoid-s4324" xml:space="preserve">minutes. </s> <s xml:id="echoid-s4325" xml:space="preserve">Si la Terre eſt exacte-<lb/>ment ſphérique, la vîteſſe du tournoyement <lb/>de tous les Corps peſants ſous l’Equateur <lb/>diminuera leur peſanteur, ou la vîteſſe de <lb/>leur chûte, à meſure qu’elle différera moins <lb/>de celle qu’il faudroit pour faire circuler <lb/>tous les corps peſants ſous l’Equateur, ſans <lb/>pouvoir jamais tomber, ou s’approcher du <lb/>centre de la Terre; </s> <s xml:id="echoid-s4326" xml:space="preserve">ou pour faire que tout <lb/>ce qu’ily a de corps ſous l’Equateur, fuſſent <lb/>autant de Satellites, qui tournaſſent par <lb/>leur mouvement journalier dans la circon-<lb/>férence de l’Equateur, comme fait la Lune <lb/>dans ſon Orbite. </s> <s xml:id="echoid-s4327" xml:space="preserve">Or en diſant par une Rè-<lb/>gle de Trois: </s> <s xml:id="echoid-s4328" xml:space="preserve">Comme le cube de la diſtance <lb/>de la Lune, de 60. </s> <s xml:id="echoid-s4329" xml:space="preserve">ſémi-diametres de la <lb/>Terre, eſt au cube d’un ſeul de ces ſémi-dia-<lb/>metres, de même le quarré de 39343 minutes, <lb/>qui font un mois périodique de la Lune, eſt <lb/>au quarré des minutes de la révolution des <lb/>Satellites, ou des corps peſants, dans la <lb/>circonférence de l’Equateur terreſtre, ſi <pb o="320" file="0344" n="345" rhead="DE LA PHILOSOPHIE"/> l’on vouloit que la force centrifuge contre-<lb/>balançât exactement la peſanteur. </s> <s xml:id="echoid-s4330" xml:space="preserve">On trou-<lb/>ve pour le réſultat de ce calcul 84. </s> <s xml:id="echoid-s4331" xml:space="preserve">{2/5} de mi-<lb/>nutes de révolution; </s> <s xml:id="echoid-s4332" xml:space="preserve">de ſorte que ſi le jour <lb/>des Etoiles étoit de 84 {2/5} de minutes, au lieu <lb/>qu’il eſt de 23. </s> <s xml:id="echoid-s4333" xml:space="preserve">heures 56. </s> <s xml:id="echoid-s4334" xml:space="preserve">min. </s> <s xml:id="echoid-s4335" xml:space="preserve">qui eſt 17. <lb/></s> <s xml:id="echoid-s4336" xml:space="preserve">fois plus grand, il n’y auroit ſous l’Equa-<lb/>teur, ni chûte, ni poids des corps.</s> <s xml:id="echoid-s4337" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4338" xml:space="preserve">On trouve le même nombre de 84 {2/5} de <lb/>minutes, ſans ſe ſervir de la Lune, en ſui-<lb/>vant le Théorême de Mr. </s> <s xml:id="echoid-s4339" xml:space="preserve">Huygens, par <lb/>lequel il a trouvé qu’un corps, pour tour-<lb/>ner circulairement, d’une force centrifuge <lb/>égale à ſon propre poids, doit faire tout le <lb/>tour du Cercle en autant de tems, qu’un <lb/>Pendule, de la longueur du rayon du mê-<lb/>me Cercle, employeroit à faire deux vibra-<lb/>tions. </s> <s xml:id="echoid-s4340" xml:space="preserve">Or pour faire l’application de ce <lb/>Théorême au Cercle de l’Equateur, & </s> <s xml:id="echoid-s4341" xml:space="preserve">au <lb/>ſémi-diametre de la Terre, il faut ſeule-<lb/>ment dire: </s> <s xml:id="echoid-s4342" xml:space="preserve">Comme 3. </s> <s xml:id="echoid-s4343" xml:space="preserve">pieds, & </s> <s xml:id="echoid-s4344" xml:space="preserve">{17/288} d’un <lb/>pied, longueur du Pendule d’une ſeconde, <lb/>ſont au quarré d’une ſeconde, ainſi 19615800 <lb/>pieds du ſémi-diametre de la Terre, ſelon <lb/>la meſure de Mr. </s> <s xml:id="echoid-s4345" xml:space="preserve">Picart, ſont à 6412430, <lb/>qui eſt le quarré de 2532. </s> <s xml:id="echoid-s4346" xml:space="preserve">ſecondes, ou de <pb o="321" file="0345" n="346" rhead="DE NEUTON."/> 42. </s> <s xml:id="echoid-s4347" xml:space="preserve">min. </s> <s xml:id="echoid-s4348" xml:space="preserve">12. </s> <s xml:id="echoid-s4349" xml:space="preserve">ſecondes. </s> <s xml:id="echoid-s4350" xml:space="preserve">Un Pendule de la <lb/>longueur du ſémi-diametre de la Terre, fe-<lb/>roit donc chaque vibration en 42. </s> <s xml:id="echoid-s4351" xml:space="preserve">min. </s> <s xml:id="echoid-s4352" xml:space="preserve">12. <lb/></s> <s xml:id="echoid-s4353" xml:space="preserve">ſecondes; </s> <s xml:id="echoid-s4354" xml:space="preserve">& </s> <s xml:id="echoid-s4355" xml:space="preserve">par conſéquent pour égaler la <lb/>peſanteur à la force centrifuge de la rota-<lb/>tion journaliére ſous l’Equateur, il faudroit <lb/>que cette rotation s’achevât en 84. </s> <s xml:id="echoid-s4356" xml:space="preserve">min. </s> <s xml:id="echoid-s4357" xml:space="preserve">24. </s> <s xml:id="echoid-s4358" xml:space="preserve"><lb/>ſecondes.</s> <s xml:id="echoid-s4359" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4360" xml:space="preserve">Mais, comme elle ſe trouve 17. </s> <s xml:id="echoid-s4361" xml:space="preserve">fois <lb/>plus lente, il eſt évident qu’en ſuppoſant <lb/>la ſurface de la Terre exactement ſphé-<lb/>rique, la peſanteur ſous l’Equateur excéde <lb/>ſa diminution, ou la force centrifuge, 17. <lb/></s> <s xml:id="echoid-s4362" xml:space="preserve">fois 17 fois, c’eſt-à-dire 289. </s> <s xml:id="echoid-s4363" xml:space="preserve">fois, & </s> <s xml:id="echoid-s4364" xml:space="preserve">par-<lb/>là la vîteſſe de la chûte des corps, ſous l’E-<lb/>quateur, ſeroit à celle de leur chûte ſous les <lb/>Poles, comme 288 ſont à 289; </s> <s xml:id="echoid-s4365" xml:space="preserve">& </s> <s xml:id="echoid-s4366" xml:space="preserve">un Pen-<lb/>dule d’une ſeconde, qui feroit ſous le Pole <lb/>86400. </s> <s xml:id="echoid-s4367" xml:space="preserve">vibrations pendant un jour Solaire, <lb/>n’en feroit ſous l’Equateur qu’environ <lb/>86250. </s> <s xml:id="echoid-s4368" xml:space="preserve">tout de même que le Pendule d’une <lb/>ſeconde de Paris, étant tranſporté ſous l’E-<lb/>quateur, & </s> <s xml:id="echoid-s4369" xml:space="preserve">y faiſant ſes chûtes curvilignes, <lb/>ou ſes vibrations un peu plus lentes qu’ici, <lb/>retarderoit par jour de 2. </s> <s xml:id="echoid-s4370" xml:space="preserve">min. </s> <s xml:id="echoid-s4371" xml:space="preserve">5. </s> <s xml:id="echoid-s4372" xml:space="preserve">ſecondes, <lb/>ou environ.</s> <s xml:id="echoid-s4373" xml:space="preserve"/> </p> <pb o="322" file="0346" n="347" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s4374" xml:space="preserve">L’expérience de Mr. </s> <s xml:id="echoid-s4375" xml:space="preserve">Richer faite dans <lb/>l’Iſle de Caïenne, celle de Mr. </s> <s xml:id="echoid-s4376" xml:space="preserve">Halley dans <lb/>l’Iſle de Ste. </s> <s xml:id="echoid-s4377" xml:space="preserve">Hélène, & </s> <s xml:id="echoid-s4378" xml:space="preserve">celles de ceux dont <lb/>on peut voir les noms à la page 227. </s> <s xml:id="echoid-s4379" xml:space="preserve">de cet-<lb/>te Edition, ayant vérifié, à quelques cir-<lb/>conſtances près, cette diminution de la pe-<lb/>ſanteur ſous l’Equateur, qui eſt une conſé-<lb/>quence néceſſaire & </s> <s xml:id="echoid-s4380" xml:space="preserve">indubitable du mouve-<lb/>ment journalier de la Terre; </s> <s xml:id="echoid-s4381" xml:space="preserve">il nous reſte à <lb/>voir le dérangement que cauſeroient ſur ſa <lb/>ſurface les forces centrifuges de ce même <lb/>mouvement ſous les Cercles parallèles de l’E-<lb/>quateur, ſi la Terre étoit exactement <lb/>ſphérique.</s> <s xml:id="echoid-s4382" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4383" xml:space="preserve">Tout le monde ſait qu’une Balance exac-<lb/>te étant ſuſpendue par ſon milieu, & </s> <s xml:id="echoid-s4384" xml:space="preserve">de-<lb/>meurant en repos, les Baſſins, ou des Poids <lb/>égaux ſuſpendus par des cordelettes à ſes <lb/>deux extrémités, font prendre à ces cor-<lb/>delettes, ou plutôt à leurs milieux, des ſi-<lb/>tuations perpendiculaires à leurs Horizons, <lb/>& </s> <s xml:id="echoid-s4385" xml:space="preserve">qui tendent directement au centre de la <lb/>Terre. </s> <s xml:id="echoid-s4386" xml:space="preserve">Mais ſi l’on donne à cette Balance <lb/>un mouvement circulaire, dont le centre <lb/>ſoit le point de ſuſpenſion de la Balance, <pb o="323" file="0347" n="348" rhead="DE NEUTON."/> on verra d’abord que les Baſſins, ou les <lb/>poids, s’éloigneront de la perpendiculaire, <lb/>à proportion de la vîteſſe du mouvement <lb/>circulaire; </s> <s xml:id="echoid-s4387" xml:space="preserve">de ſorte que les cordelettes ne <lb/>ſuivront plus la direction ordinaire de la pe-<lb/>ſanteur vers le centre de la Terre.</s> <s xml:id="echoid-s4388" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4389" xml:space="preserve">Figurons-nous à préſent une grande Balan-<lb/>ce curviligne, dont le milieu ſoit ſuſpendu <lb/>à l’un des Poles de la Terre, & </s> <s xml:id="echoid-s4390" xml:space="preserve">dont les deux <lb/>extrémités s’étendent juſqu’à égale élévation <lb/>du même Pole, de part & </s> <s xml:id="echoid-s4391" xml:space="preserve">d’autre; </s> <s xml:id="echoid-s4392" xml:space="preserve">il eſt <lb/>évident que ſi la figure ſphérique de la Ter-<lb/>re (qui eſt-ce que nous examinons) tourne <lb/>autour de ſon axe, & </s> <s xml:id="echoid-s4393" xml:space="preserve">qu’elle emporte en <lb/>même tems cette Balance curviligne, par <lb/>un mouvement circulaire autour du même <lb/>axe, les poids qui étant en repos devroient <lb/>converger vers le centre de la Terre, s’é-<lb/>loigneront un peu de cette convergence & </s> <s xml:id="echoid-s4394" xml:space="preserve"><lb/>des perpendiculaires, de part & </s> <s xml:id="echoid-s4395" xml:space="preserve">d’autre. <lb/></s> <s xml:id="echoid-s4396" xml:space="preserve">Ainſi le Sinus du petit angle de déviation, <lb/>compris entre la perpendiculaire & </s> <s xml:id="echoid-s4397" xml:space="preserve">la nou-<lb/>velle direction du poids, ſera bien près de <lb/>{1/289} du produit du Sinus, & </s> <s xml:id="echoid-s4398" xml:space="preserve">du Co-Sinus de <lb/>l’élévation du Pole, diviſé par le rayon.</s> <s xml:id="echoid-s4399" xml:space="preserve"/> </p> <pb o="324" file="0348" n="349" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s4400" xml:space="preserve">On voit clairement que ſans imaginer <lb/>cette Balance curviligne, ce raiſonnement <lb/>peut également s’appliquer à toutes les li-<lb/>gnes à plomb, qui ſe trouvent ſur la ſurface <lb/>de la Terre. </s> <s xml:id="echoid-s4401" xml:space="preserve">C’eſt de cette maniére qu’on <lb/>trouve qu’à Paris, & </s> <s xml:id="echoid-s4402" xml:space="preserve">en cent autres en-<lb/>droits de même Latitude, qu’un Pendule <lb/>en repos ne tendroit pas perpendiculaire-<lb/>ment à l’Horizon, mais feroit avec la per-<lb/>pendiculaire un angle de près de ſix minu-<lb/>tes, ce qui ſeroit aſſez ſenſible, ſi la Terre <lb/>étoit exactement ſphérique; </s> <s xml:id="echoid-s4403" xml:space="preserve">cependant com-<lb/>me en nul endroit du Monde on ne trouve <lb/>aucune déviation, c’eſt une preuve ſuffiſante <lb/>que la face de la Terre eſt telle, qu’il faut <lb/>qu’elle ſoit, pour que la direction de la pe-<lb/>ſanteur ſoit perpendiculaire, ce qui ne ſe <lb/>peut que dans une figure ſphéroïde.</s> <s xml:id="echoid-s4404" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4405" xml:space="preserve">Cette figure ſphéroïde produit encore un <lb/>autre changement à l’égard de la peſanteur, <lb/>mais de peu de conſéquence. </s> <s xml:id="echoid-s4406" xml:space="preserve">L’on ſait que, <lb/>ſans conſidérer la diminution de la peſanteur, <lb/>dont nous venons de parler, la peſanteur <lb/>elle-même varie encore ſelon la diverſité <lb/>des diſtances du centre de la Terre, quand <lb/>même il n’y auroit point de rotation. </s> <s xml:id="echoid-s4407" xml:space="preserve">C’eſt <pb o="325" file="0349" n="350" rhead="DE NEUTON."/> ce qui fait que les expériences des Pendules <lb/>tranſportés en différens Climats, ne répon-<lb/>dent pas dans la derniére préciſion au cal-<lb/>cul que nous avons donné ci-deſſus, quoi-<lb/>qu’elles prouvent toutes en général que la <lb/>peſanteur différe ſenſiblement, & </s> <s xml:id="echoid-s4408" xml:space="preserve">qu’elle <lb/>eſt toujours moins forte vers l’Equateur, <lb/>que vers les Poles. </s> <s xml:id="echoid-s4409" xml:space="preserve">C’eſt auſſi ce qui parta-<lb/>ge les ſentimens des plus grands Géomé-<lb/>tres ſur la proportion de l’axe de la rota-<lb/>tion de la Terre au diametre de ſon Equa-<lb/>teur. </s> <s xml:id="echoid-s4410" xml:space="preserve">Mr. </s> <s xml:id="echoid-s4411" xml:space="preserve">Huygens & </s> <s xml:id="echoid-s4412" xml:space="preserve">après lui Jaques <lb/>Herman dans ſon excellent Ouvrage de <lb/>la Phoronomie, ont déterminé cette pro-<lb/>portion, comme de 577. </s> <s xml:id="echoid-s4413" xml:space="preserve">à 578.</s> <s xml:id="echoid-s4414" xml:space="preserve">; mais <lb/>Neuton nous la donne de 229. </s> <s xml:id="echoid-s4415" xml:space="preserve">à 230, en-<lb/>viron triple de la précédente. </s> <s xml:id="echoid-s4416" xml:space="preserve">La différen-<lb/>ce de ces meſures ne provient que de ce <lb/>que Mr. </s> <s xml:id="echoid-s4417" xml:space="preserve">Huygens n’a conſidéré la peſanteur <lb/>que comme une force qui pouſſe les corps <lb/>vers un ſeul centre; </s> <s xml:id="echoid-s4418" xml:space="preserve">au lieu que Neuton l’a <lb/>conſidérée comme une force par laquelle <lb/>tous les corps & </s> <s xml:id="echoid-s4419" xml:space="preserve">toutes les particules de la <lb/>Terre, juſqu’aux plus petites, ſont tirées <lb/>les unes vers les autres.</s> <s xml:id="echoid-s4420" xml:space="preserve"/> </p> <pb o="326" file="0350" n="351" rhead="DE LA PHILOSOPHIE"/> </div> <div xml:id="echoid-div178" type="section" level="1" n="39"> <head xml:id="echoid-head64" xml:space="preserve"><emph style="sc">Mars.</emph></head> <p> <s xml:id="echoid-s4421" xml:space="preserve">La quatrième Planete de notre Syſtême <lb/>eſt Mars. </s> <s xml:id="echoid-s4422" xml:space="preserve">Sa moyenne diſtance du Soleil <lb/>eſt de 46. </s> <s xml:id="echoid-s4423" xml:space="preserve">millions de lieues. </s> <s xml:id="echoid-s4424" xml:space="preserve">De toutes les <lb/>Planetes ſupérieures, c’eſt celle qui a la <lb/>plus grande excentricité, auſſi n’en con-<lb/>noît-on point parmi tous les Corps céleſtes, <lb/>dont la grandeur apparente ſoit plus varia-<lb/>ble; </s> <s xml:id="echoid-s4425" xml:space="preserve">de ſorte que ſa plus grande Phaſe ex-<lb/>céde juſqu’à 7. </s> <s xml:id="echoid-s4426" xml:space="preserve">fois la plus petite. </s> <s xml:id="echoid-s4427" xml:space="preserve">Au mois <lb/>d’Août 1719. </s> <s xml:id="echoid-s4428" xml:space="preserve">Mars étant oppoſé au Soleil, <lb/>à 2 ou 3 degrés ſeulement de diſtance de <lb/>ſon périhélie, l’on ſe ſouvient encore que <lb/>pluſieurs perſonnes, qui n’avoient aucune <lb/>teinture d’Aſtronomie, furent étonnées de <lb/>le voir, & </s> <s xml:id="echoid-s4429" xml:space="preserve">le prirent pour une Comete, ou <lb/>un nouvel Aſtre, qui venoit de naître <lb/>dans le Ciel, comme on a fait de Vénus <lb/>l’année derniere, lorſqu’au mois de Mai <lb/>ayant atteint ſa plus grande hauteur Méri-<lb/>dienne au commencement du Cancer, & </s> <s xml:id="echoid-s4430" xml:space="preserve"><lb/>étant encore aſſez loin du Soleil pour n’être <lb/>point éclipſée par ſon éclat, elle lança ſes <lb/>rayons par le chemin le plus court de la <lb/>partie Boréale de l’Atmoſphére.</s> <s xml:id="echoid-s4431" xml:space="preserve"/> </p> <pb o="327" file="0351" n="352" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s4432" xml:space="preserve">Comme la grande excentricité de Mars <lb/>rend ſon mouvement apparent fort inégal, <lb/>c’eſt de lui principalement que Kepler s’eſt <lb/>fervi, pour examiner & </s> <s xml:id="echoid-s4433" xml:space="preserve">vérifier la découver-<lb/>te qu’il avoit faite de l’égalité des aires par-<lb/>courues par chaque Planete en particulier, <lb/>en tems égaux; </s> <s xml:id="echoid-s4434" xml:space="preserve">& </s> <s xml:id="echoid-s4435" xml:space="preserve">c’eſt auſſi par lui, qu’il <lb/>a reconnu & </s> <s xml:id="echoid-s4436" xml:space="preserve">prouvé la néceſſité qu’il y a-<lb/>voit de n’admettre par tout le Ciel que des <lb/>excentricités plus petites, environ de la <lb/>moitié de celles qui avoient été établies <lb/>par les Anciens.</s> <s xml:id="echoid-s4437" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4438" xml:space="preserve">De toutes les Planetes, Mars eſt encore <lb/>celle qui a la plus grande Atmoſphére, à <lb/>proportion de ſon noyau, du moins à ce <lb/>qu’on en connoît juſqu’à préſent; </s> <s xml:id="echoid-s4439" xml:space="preserve">ce qui ſe <lb/>prouve par le changement de couleur d’une <lb/>Fixe obſervée par Mr. </s> <s xml:id="echoid-s4440" xml:space="preserve">Römer, en appro-<lb/>chant & </s> <s xml:id="echoid-s4441" xml:space="preserve">en quittant le diſque de Mars, la-<lb/>quelle pâlit ſenſiblement à l’approche de ce <lb/>diſque, étant encore éloignée de lui des <lb/>deux tiers du diametre du même diſque, & </s> <s xml:id="echoid-s4442" xml:space="preserve"><lb/>qui étant ſortie de derriére le corps opaque <lb/>de Mars, ne recouvra la vivacité naturelle <lb/>& </s> <s xml:id="echoid-s4443" xml:space="preserve">ordinaire de ſa lumiére qu’à la diſtan- <pb o="328" file="0352" n="353" rhead="DE LIA PHILOSOPHIE"/> ce des deux tiers du même diametre.</s> <s xml:id="echoid-s4444" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4445" xml:space="preserve">Sans l’Etoile de Mars nous ignorerions <lb/>tout-à-fait l’éloignement & </s> <s xml:id="echoid-s4446" xml:space="preserve">la véritable <lb/>grandeur des Corps céleſtes; </s> <s xml:id="echoid-s4447" xml:space="preserve">& </s> <s xml:id="echoid-s4448" xml:space="preserve">c’eſt le cé-<lb/>lèbre Mr. </s> <s xml:id="echoid-s4449" xml:space="preserve">Caſſini le Pere, qui s’eſt aviſé le <lb/>premier, de ſe ſervir des diſtances appa-<lb/>rentes de cette Planete d’avec les Fixes <lb/>prochaines, lorſqu’elle eſt oppoſée au So-<lb/>leil, pour trouver la véritable dimenſion <lb/>de notre Syſtême. </s> <s xml:id="echoid-s4450" xml:space="preserve">Sa parallaxe horizonta-<lb/>le, qui dans cette ſituation eſt aſſez grande <lb/>pour être obſervée & </s> <s xml:id="echoid-s4451" xml:space="preserve">calculée ſans qu’il y <lb/>ait à craindre aucune erreur trop ſenſible, <lb/>ſavoir de 26 à 27. </s> <s xml:id="echoid-s4452" xml:space="preserve">ſecondes dans ſon péri-<lb/>hélie, nous donne le moyen de calculer les <lb/>parallaxes horizontales du Soleil & </s> <s xml:id="echoid-s4453" xml:space="preserve">des au-<lb/>tres Planetes, qui ne peuvent être obſervées <lb/>par elles-mêmes, à cauſe de leur petiteſſe. <lb/></s> <s xml:id="echoid-s4454" xml:space="preserve">Par les taches de Mars, que nous repréſen-<lb/>tons ici de la maniere, dont elles ont apparu <lb/>en 1719. </s> <s xml:id="echoid-s4455" xml:space="preserve">l’on a découvert & </s> <s xml:id="echoid-s4456" xml:space="preserve">l’on s’eſt con-<lb/>vaincu, qu’il tourne autour d’un axe toujours <lb/>parallèle à lui-même, (comme celui de la <lb/>Terre) en 24 heures, 40 minutes;</s> <s xml:id="echoid-s4457" xml:space="preserve"/> </p> <pb o="329" file="0353" n="354" rhead="DE NEUTON."/> <figure> <image file="0353-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0353-01"/> </figure> <p> <s xml:id="echoid-s4458" xml:space="preserve">Ou que 36 révolutions de Mars autour <lb/>de ſon axe égalent 37 révolutions de la Ter-<lb/>re autour du ſien.</s> <s xml:id="echoid-s4459" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4460" xml:space="preserve">Les taches de cette Planete ſemblent ê-<lb/> <anchor type="note" xlink:label="note-0353-01a" xlink:href="note-0353-01"/> tre plus variables que celles de toutes les <lb/>autres. </s> <s xml:id="echoid-s4461" xml:space="preserve">Les bandes obſcures qu’on a ob-<lb/>ſervées en 1704. </s> <s xml:id="echoid-s4462" xml:space="preserve">1717. </s> <s xml:id="echoid-s4463" xml:space="preserve">& </s> <s xml:id="echoid-s4464" xml:space="preserve">1719. </s> <s xml:id="echoid-s4465" xml:space="preserve">ne convien-<lb/>nent point entr’elles, ni par rapport à leur <lb/>ſituation, ni par rapport à leur figure. </s> <s xml:id="echoid-s4466" xml:space="preserve">En <lb/>1704. </s> <s xml:id="echoid-s4467" xml:space="preserve">& </s> <s xml:id="echoid-s4468" xml:space="preserve">1717. </s> <s xml:id="echoid-s4469" xml:space="preserve">on a vu une bande obſcure <lb/>occupant plus d’un hémiſphére de Mars, a-<lb/>vec cette différence qu’en 1704. </s> <s xml:id="echoid-s4470" xml:space="preserve">elle avoit <lb/>au milieu une pointe, qui ne s’y trouvoit <pb o="330" file="0354" n="355" rhead="DE LA PHILOSOPHIE"/> point en 1717. </s> <s xml:id="echoid-s4471" xml:space="preserve">& </s> <s xml:id="echoid-s4472" xml:space="preserve">qu’en 1717. </s> <s xml:id="echoid-s4473" xml:space="preserve">elle étoit <lb/>plus éloignée de l’équateur de Mars, & </s> <s xml:id="echoid-s4474" xml:space="preserve"><lb/>plus près de ſon pole Méridional qu’en <lb/>1704. </s> <s xml:id="echoid-s4475" xml:space="preserve">En 1719. </s> <s xml:id="echoid-s4476" xml:space="preserve">on a trouvé une bande <lb/>coudée, formée ſeulement après le mois de <lb/>Juillet, dont la partie la plus Méridionale, <lb/>par rapport à nos yeux, s’étendoit oblique-<lb/>ment ſur la moitié de l’hémiſphére de Mars, <lb/>& </s> <s xml:id="echoid-s4477" xml:space="preserve">égaloit environ un quart de Cercle, pre-<lb/>nant ſon commencement entre le pole Méri-<lb/>dional & </s> <s xml:id="echoid-s4478" xml:space="preserve">l’équateur de Mars, & </s> <s xml:id="echoid-s4479" xml:space="preserve">finiſſant <lb/>entre ſon équateur & </s> <s xml:id="echoid-s4480" xml:space="preserve">ſon pole Septentrio-<lb/>nal, où les deux parties de cette bande, en <lb/>ſe joignant, faiſoient un angle, comme <lb/>cela ſe voit Figure 2. </s> <s xml:id="echoid-s4481" xml:space="preserve">Le 13. </s> <s xml:id="echoid-s4482" xml:space="preserve">de Juillet d’au-<lb/>paravant on n’avoit obſervé qu’une ſeule <lb/>bande obſcure rectiligne, telle qu’on la voit <lb/>Figure 1.</s> <s xml:id="echoid-s4483" xml:space="preserve"/> </p> <div xml:id="echoid-div178" type="float" level="2" n="1"> <note position="right" xlink:label="note-0353-01" xlink:href="note-0353-01a" xml:space="preserve">Remar-<lb/>ques ſur <lb/>les ta-<lb/>ches de <lb/>Mars.</note> </div> <p> <s xml:id="echoid-s4484" xml:space="preserve">Outre ces bandes obſcures, on avoit dé-<lb/>couvert des taches conſuſes de figure fort <lb/>irréguliére, comme dans les Fig. </s> <s xml:id="echoid-s4485" xml:space="preserve">3. </s> <s xml:id="echoid-s4486" xml:space="preserve">&</s> <s xml:id="echoid-s4487" xml:space="preserve">. 4. </s> <s xml:id="echoid-s4488" xml:space="preserve">qui <lb/>n’étoient auſſi que temporaires, & </s> <s xml:id="echoid-s4489" xml:space="preserve">qui n’a-<lb/>voient preſque rien de commun avec celles <lb/>qu’on avoit obſervées auparavant, que leur <lb/>inconſtance.</s> <s xml:id="echoid-s4490" xml:space="preserve"/> </p> <pb o="331" file="0355" n="356" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s4491" xml:space="preserve">Mais les taches les plus conſidérables <lb/>de cette Planete ſont celles, qui s’ob-<lb/>ſervent proche de ſes deux poles, dont <lb/>cependant on n’en voit jamais qu’une à la <lb/>fois, & </s> <s xml:id="echoid-s4492" xml:space="preserve">qui ſont ordinairement plus claires <lb/>que le reſte du corps. </s> <s xml:id="echoid-s4493" xml:space="preserve">Il y a près de 70 <lb/>ans, que ces taches-là ſont connues, & </s> <s xml:id="echoid-s4494" xml:space="preserve"><lb/>qu’on en voit preſque toujours l’une ou <lb/>l’autre, ce qui prouve qu’elles ſont per-<lb/>manentes, & </s> <s xml:id="echoid-s4495" xml:space="preserve">que les viciſſitudes d’appari-<lb/>tion & </s> <s xml:id="echoid-s4496" xml:space="preserve">d’occultation qu’elles ſubiſſent, pro-<lb/>cédent ſeulement de quelque changement <lb/>de l’atmoſphére de Mars, ſemblable à ce-<lb/>lui de la nôtre, cauſé en partie par la dif-<lb/>férente conſtitution de l’air en Eté & </s> <s xml:id="echoid-s4497" xml:space="preserve">en <lb/>Hyver, & </s> <s xml:id="echoid-s4498" xml:space="preserve">en partie par la différente quan-<lb/>tité de pluye, & </s> <s xml:id="echoid-s4499" xml:space="preserve">de beau tems en diffé-<lb/>rens endroits du même Climat. </s> <s xml:id="echoid-s4500" xml:space="preserve">C’eſt ainſi <lb/>que depuis le 17. </s> <s xml:id="echoid-s4501" xml:space="preserve">Mai juſqu’au mois de No-<lb/>vembre 1719. </s> <s xml:id="echoid-s4502" xml:space="preserve">le Pole, qui eſt à notre é-<lb/>gard le Méridional, ſe trouvant éclairé par <lb/>le Soleil, & </s> <s xml:id="echoid-s4503" xml:space="preserve">par conſéquent l’Eté y régnant, <lb/>& </s> <s xml:id="echoid-s4504" xml:space="preserve">l’Atmoſphére y étant rareſiée autant qu’el-<lb/>le l’a pu être, la lumiere éclatante de cette <lb/>Zone déliée a pu ſrapper notre vûe, dans <lb/>le tems que celle du Pole oppoſé, qui avoit <lb/>paru aux Obſervateurs en 1704 & </s> <s xml:id="echoid-s4505" xml:space="preserve">1717. </s> <s xml:id="echoid-s4506" xml:space="preserve">a- <pb o="332" file="0356" n="357" rhead="DE LA PHILOSOPHIE"/> vec le même éclat que la derniére, ſe dé-<lb/>roboit alors à nos yeux à la faveur des <lb/>nuages & </s> <s xml:id="echoid-s4507" xml:space="preserve">des vapeurs congelées, qui y <lb/>changeoient l’Atmoſphére, & </s> <s xml:id="echoid-s4508" xml:space="preserve">la rendoient <lb/>moins tranſparente. </s> <s xml:id="echoid-s4509" xml:space="preserve">La différence de la <lb/>clarté de cette Zone, dont une moitié con-<lb/>ſerva conſtamment le même degré de lu-<lb/>miére, & </s> <s xml:id="echoid-s4510" xml:space="preserve">dont l’autre au contraire diminua, <lb/>diſparut, puis reparut, ne reſſemble pas <lb/>mal à la différence dú tems qu’il fait aux <lb/>Andes du Pérou, où il ne pleut jamais, & </s> <s xml:id="echoid-s4511" xml:space="preserve"><lb/>à Borneo où il pleut preſque tous les jours. <lb/></s> <s xml:id="echoid-s4512" xml:space="preserve">Il ſe peut qu’il y ait encore d’autres raiſons <lb/>qui puiſſent produire cet effet; </s> <s xml:id="echoid-s4513" xml:space="preserve">mais il eſt <lb/>toujours conſtant que cette diverſité d’ap-<lb/>parences vient de la diverſe conſtitution <lb/>de l’Atmoſphére.</s> <s xml:id="echoid-s4514" xml:space="preserve"/> </p> </div> <div xml:id="echoid-div180" type="section" level="1" n="40"> <head xml:id="echoid-head65" xml:space="preserve"><emph style="sc">Jupiter.</emph></head> <p> <s xml:id="echoid-s4515" xml:space="preserve">Jupiter la plus grande de toutes les Pla-<lb/>netes de notre Syſtême, parcourt en 4331 <lb/>jours, ou 12 ans, en comptant rondement, <lb/>une Orbite, dont le demi-diametre, en ſa <lb/>moyenne quantité, ou la diſtance moyen-<lb/>ne du Soleil, eſt de 156. </s> <s xml:id="echoid-s4516" xml:space="preserve">millions de lieues. <lb/></s> <s xml:id="echoid-s4517" xml:space="preserve">Son diametre eſt dix fois plus grand que <pb o="333" file="0357" n="358" rhead="DE NEUTON."/> celui de la Terre. </s> <s xml:id="echoid-s4518" xml:space="preserve">La peſanteur des corps <lb/>qui tendent vers le centre de cette Planete, <lb/>ou l’eſpace qu’ils parcourent en tombant di-<lb/>rectement ſur elle, ſe peut calculer.</s> <s xml:id="echoid-s4519" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4520" xml:space="preserve">Pour cet effet, l’on cherche premiére-<lb/> <anchor type="note" xlink:label="note-0357-01a" xlink:href="note-0357-01"/> ment le tems périodique d’un Satellite <lb/>qui raſeroit la ſurface de Jupiter, ce qui <lb/>ſe trouve par cette règle: </s> <s xml:id="echoid-s4521" xml:space="preserve">Comme le cube <lb/>de 25 {1/3} de demi-diametres de Jupiter, (qui <lb/>font la diſtance du quatrième Satellite), eſt <lb/>au quarré de ſon tems périodique, qui eſt <lb/>de 16 {2/3} de jours; </s> <s xml:id="echoid-s4522" xml:space="preserve">ainſi le cube d’un ſeul ſémi-<lb/>diametre de Jupiter eſt au quarré du tems <lb/>périodique qu’on cherche. </s> <s xml:id="echoid-s4523" xml:space="preserve">On trouve par-<lb/>là qu’un tel Satellite acheveroit ſa période <lb/>autour de Jupiter, près de ſa ſurface, en <lb/>193 à 194 minutes.</s> <s xml:id="echoid-s4524" xml:space="preserve"/> </p> <div xml:id="echoid-div180" type="float" level="2" n="1"> <note position="right" xlink:label="note-0357-01" xlink:href="note-0357-01a" xml:space="preserve">Maniére <lb/>de calcu-<lb/>ler la pe-<lb/>ſanteur <lb/>des <lb/>corps <lb/>quitom-<lb/>bent ſur <lb/>la ſurfa-<lb/>ce de Ju-<lb/>piter.</note> </div> <p> <s xml:id="echoid-s4525" xml:space="preserve">Comme toutes ſortes de peſanteurs ſont <lb/>en raiſon directe des rayons des cercles que <lb/>décrivent les corps peſants, ſans tomber, <lb/>& </s> <s xml:id="echoid-s4526" xml:space="preserve">en raiſon inverſe des quarrés des tems <lb/>périodiques, on détermine la quantité de la <lb/>peſanteur de ces corps ſur Jupiter de cette <lb/>maniére: </s> <s xml:id="echoid-s4527" xml:space="preserve">Comme 1 ſémi-diametre de la Ter-<lb/>re eſt à 10 {1/2} des mêmes ſémi-diametres, qui <pb o="334" file="0358" n="359" rhead="DE LA PHILOSOPHIE"/> ſont la meſure de celui de Jupiter; </s> <s xml:id="echoid-s4528" xml:space="preserve">ainſi <lb/>15 {1/12} de pieds de chûte ſur la Terre, pendant <lb/>la premiére ſeconde, ſont à 158 {3/8} de pieds de <lb/>chûte ſur Jupiter pendant la premiére ſe-<lb/>conde, ſi les tems périodiques des Satelli-<lb/>tes aux ſurfaces de Jupiter & </s> <s xml:id="echoid-s4529" xml:space="preserve">de la Terre <lb/>ſont égaux. </s> <s xml:id="echoid-s4530" xml:space="preserve">Mais ayant trouvé ci-deſſus <lb/>que le tems périodique d’un Satellite de la <lb/>Terre, auprès de ſa ſurſace, eſt de 84 {2/5} de <lb/>minutes, il en faut venir à cette derniére rè-<lb/>gle: </s> <s xml:id="echoid-s4531" xml:space="preserve">Comme le quarré de 193 {1/2} de minutes <lb/>eſt au quarré de 84 {2/5} de minutes; </s> <s xml:id="echoid-s4532" xml:space="preserve">ainſi 158@ <lb/>de pieds de chûte, (ſi les deux périodes ſont <lb/>égales) ſont à 30 pieds de chûte véritable <lb/>ſur Jupiter. </s> <s xml:id="echoid-s4533" xml:space="preserve">Le pendule à ſecondes ſera <lb/>donc en Jupiter de 7 pieds & </s> <s xml:id="echoid-s4534" xml:space="preserve">{1/2}.</s> <s xml:id="echoid-s4535" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4536" xml:space="preserve">Ccs mêmes conſidérations nous font auſſi <lb/>voir que le diametre polaire, ou l’axe de <lb/>rotation de Jupiter, eſt plus petit que ce-<lb/>lui de ſon équateur, & </s> <s xml:id="echoid-s4537" xml:space="preserve">que cette différen-<lb/>ce doit être bien plus ſenſible ſur la ſurface <lb/>de Jupiter, que ſur celle de la Terre. </s> <s xml:id="echoid-s4538" xml:space="preserve">La ré-<lb/>volution journaliére de Jupiter eſt de 9 heu-<lb/>res 56 minutes; </s> <s xml:id="echoid-s4539" xml:space="preserve">& </s> <s xml:id="echoid-s4540" xml:space="preserve">la révolution du plus bas <lb/>Satellite, qui pourroit être autour de lui, <lb/>ayant été trouvée de 194 minutes, qui n’eſt <pb o="335" file="0359" n="360" rhead="DE NEUTON."/> quaſi que le tiers de ſa révolution journa-<lb/>liére, ſa peſanteur reſtante, c’eſt-à-dire, <lb/>diminuée par les forces centrifuges ſous l’é-<lb/>quinoxiale de Jupiter, ſera à la peſanteur <lb/>primitive (en ſuppoſant la figure de Jupiter <lb/>exactement ſphérique) comme 8 ſont à 9. </s> <s xml:id="echoid-s4541" xml:space="preserve">C’eſt <lb/>ce qui donne la proportion du petit axe au <lb/>grand, à peu de choſe prè<unsure/>s, comme 17 ſont à <lb/>18, en dreſſant le calcul ſelon les principes de <lb/>Mrs. </s> <s xml:id="echoid-s4542" xml:space="preserve">Huygens & </s> <s xml:id="echoid-s4543" xml:space="preserve">Herman, & </s> <s xml:id="echoid-s4544" xml:space="preserve">comme 7 à 8, <lb/>en ſuivant ceux de Neuton, fondés ſur la <lb/>gravitation mutuelle de toutes les parties in-<lb/>térieures de la Planete. </s> <s xml:id="echoid-s4545" xml:space="preserve">Le ſentiment de <lb/>Neuton ſemble être appuyé par les Obſer-<lb/>vations de Mr. </s> <s xml:id="echoid-s4546" xml:space="preserve">Caſſini, le Pere, rapportées <lb/>à la fin de la XIX. </s> <s xml:id="echoid-s4547" xml:space="preserve">Propoſition du III. </s> <s xml:id="echoid-s4548" xml:space="preserve">Li-<lb/>vre de ſa Philoſophie, où il eſt dit, que <lb/>le diametre de Jupiter d’Orient en Occi-<lb/>dent eſt viſiblement plus grand que celui <lb/>du Sud au Nord.</s> <s xml:id="echoid-s4549" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4550" xml:space="preserve">Les bandes obſcures de Jupiter, cou-<lb/>chées le long de ſon diſque, & </s> <s xml:id="echoid-s4551" xml:space="preserve">toujours pa-<lb/>rallèles, à-peu-près, à ſon équateur, ſont <lb/>repréſentées par les deux Figures ſuivantes.</s> <s xml:id="echoid-s4552" xml:space="preserve"/> </p> <pb o="336" file="0360" n="361" rhead="DE LA PHILOSOPHIE"/> <figure> <image file="0360-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0360-01"/> </figure> <p> <s xml:id="echoid-s4553" xml:space="preserve">Cet équateur ne fait avec l’orbite de Ju-<lb/>piter qu’une obliquité de 2. </s> <s xml:id="echoid-s4554" xml:space="preserve">deg. </s> <s xml:id="echoid-s4555" xml:space="preserve">55. </s> <s xml:id="echoid-s4556" xml:space="preserve">min. <lb/></s> <s xml:id="echoid-s4557" xml:space="preserve">au lieu que la nôtre eſt de 23. </s> <s xml:id="echoid-s4558" xml:space="preserve">deg. </s> <s xml:id="echoid-s4559" xml:space="preserve">& </s> <s xml:id="echoid-s4560" xml:space="preserve">demi. </s> <s xml:id="echoid-s4561" xml:space="preserve"><lb/>Ces bandes ſemblent n’être que des exha-<lb/>laiſons, qui, en s’élevant & </s> <s xml:id="echoid-s4562" xml:space="preserve">ſe joignant en-<lb/>ſemble, prennent une figure circulaire. </s> <s xml:id="echoid-s4563" xml:space="preserve">Il <lb/>eſt vrai qu’elles ne ſe produiſent jamais <lb/>toutes entiéres à la fois, témoin ſur-<lb/>tout cette bande Méridionale, qui renaît <lb/>quaſi de ſix en ſix ans, & </s> <s xml:id="echoid-s4564" xml:space="preserve">qui nous ramene <lb/>toujours une tache noire, ſituée à ſon <lb/>bord Septentrional, comme cela eſt arrivé <lb/>aux années 1665. </s> <s xml:id="echoid-s4565" xml:space="preserve">1677. </s> <s xml:id="echoid-s4566" xml:space="preserve">1713. </s> <s xml:id="echoid-s4567" xml:space="preserve">au mois <lb/>de Septembre, & </s> <s xml:id="echoid-s4568" xml:space="preserve">aux années 1672. </s> <s xml:id="echoid-s4569" xml:space="preserve">& </s> <s xml:id="echoid-s4570" xml:space="preserve"><lb/>1708. </s> <s xml:id="echoid-s4571" xml:space="preserve">au mois d’Avril. </s> <s xml:id="echoid-s4572" xml:space="preserve">En comparant les <lb/>anciennes Obſervations avec celles qui ont <lb/>été faites en dernier lieu, on remarque que <lb/>ces bandes, qui avoient d’abord paru ſubir <pb o="337" file="0361" n="362" rhead="DE NEUTON."/> des changemens tout-à-fait bizarres, & </s> <s xml:id="echoid-s4573" xml:space="preserve">ne <lb/>ſuivre aucune règle, ne laiſſent pas d’avoir <lb/>des retours aſſez réguliers, qui nous met-<lb/>tront peut-être un jour en état de prédire <lb/>leurs apparences avec la même certitude <lb/>qu’on peut calculer les Eclipſes.</s> <s xml:id="echoid-s4574" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4575" xml:space="preserve">La bande dont nous venons de parler, <lb/> <anchor type="note" xlink:label="note-0361-01a" xlink:href="note-0361-01"/> accompagnée de la tache noire, ſe préſente <lb/>ordinairement, quand Jupiter eſt aux der-<lb/>niers degrés de la Vierge & </s> <s xml:id="echoid-s4576" xml:space="preserve">des Poiſſons, <lb/>vers le tems qu’il a été en oppoſition avec <lb/>cet aſtre. </s> <s xml:id="echoid-s4577" xml:space="preserve">Ce qu’il y a de plus particulier, <lb/>c’eſt que ces apparences ſuivent plutôt le <lb/>vrai mouvement de Jupiter que le moyen; <lb/></s> <s xml:id="echoid-s4578" xml:space="preserve">car on voit bien que depuis l’oppoſition de <lb/>cette Planete avec le Soleil au Signe des <lb/>Poiſſons juſqu’à celle qui ſe fait au Signe de <lb/>la Vierge, il ſe paſſe 6 ans & </s> <s xml:id="echoid-s4579" xml:space="preserve">demi, & </s> <s xml:id="echoid-s4580" xml:space="preserve">5 <lb/>ſeulement & </s> <s xml:id="echoid-s4581" xml:space="preserve">demi de celle ci au retour de <lb/>la premiére, le tout faiſant enſemble 12 <lb/>années, pendant leſquelles s’acheve la révo-<lb/>lution de Jupiter. </s> <s xml:id="echoid-s4582" xml:space="preserve">Ceci fait voir que, ſi l’on <lb/>pouvoit marquer tous les changemens qui <lb/>ſurviennent à ces bandes, & </s> <s xml:id="echoid-s4583" xml:space="preserve">qui ſont ſans <lb/>doute affectés à certains Signes du Zodia-<lb/>que, auſſi-bien que le Phénomêne de la ta- <pb o="338" file="0362" n="363" rhead="DE LA PHILOSOPHIE"/> che noire, on auroit lieu d’eſpérer, quo <lb/>l’ordre de leur retour ſe pourroit prédire, <lb/>comme celui de cette tache.</s> <s xml:id="echoid-s4584" xml:space="preserve"/> </p> <div xml:id="echoid-div181" type="float" level="2" n="2"> <note position="right" xlink:label="note-0361-01" xlink:href="note-0361-01a" xml:space="preserve">Remar-<lb/>que ſur <lb/>la tache <lb/>noire de <lb/>Jupiter.</note> </div> <p> <s xml:id="echoid-s4585" xml:space="preserve">C’eſt principalement à cette même tache <lb/>que nous ſommes redevables de la con-<lb/>noiſſance que nous avons de la révolution <lb/>journaliére de Jupiter, dont la vîteſſe nous <lb/>ſurprendroit, ſans doute, par rapport à la <lb/>grandeur de ſon corps, ſi Mr. </s> <s xml:id="echoid-s4586" xml:space="preserve">de Mai-<lb/>ran n’en avoit pas démontré la poſſibilité, <lb/>dans un ſavant Mémoire inſéré dans ceux <lb/>de l’Académie de l’Année 1729. </s> <s xml:id="echoid-s4587" xml:space="preserve">où il dé-<lb/>montre que la différence qu’il y a entre <lb/>le poids de la partie inférieure d’une Pla-<lb/>nete, qui eſt tournée vers le Soleil, & </s> <s xml:id="echoid-s4588" xml:space="preserve">ce-<lb/>lui de la ſupérieure qui ne l’eſt pas, eſt ca-<lb/>pable de produire ſa rotation d’Occident en <lb/>Orient.</s> <s xml:id="echoid-s4589" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4590" xml:space="preserve">Cetre tache eſt auſſi connue aux Aſtro-<lb/>nomes, que la ſituation d’une célèbre Vil-<lb/>le aux Géographes; </s> <s xml:id="echoid-s4591" xml:space="preserve">& </s> <s xml:id="echoid-s4592" xml:space="preserve">on en a déterminé <lb/>la Latitude Méridionale ſur la ſurface de Ju-<lb/>piter d’environ 16. </s> <s xml:id="echoid-s4593" xml:space="preserve">degrés, commel’on déter-<lb/>mine celle de quelque Place remarquable ſur <lb/>la Terre. </s> <s xml:id="echoid-s4594" xml:space="preserve">Il eſt vrai qu’en obſervant ſes ré- <pb o="339" file="0363" n="364" rhead="DE NEUTON."/> volutions au milieu de ſon parallèle expoſé <lb/>vers nous, on a trouvé qu’elles n’étoient pas <lb/>tout-à-fait les mêmes, & </s> <s xml:id="echoid-s4595" xml:space="preserve">qu’elles différoient <lb/>de quelques ſecondes, quoiqu’il ſoit très na-<lb/>turel de les ſuppoſer toujours égales entr’el-<lb/>les, comme ſont celles de la Terre; </s> <s xml:id="echoid-s4596" xml:space="preserve">mais <lb/>cela n’eſt pas de conſéquence, & </s> <s xml:id="echoid-s4597" xml:space="preserve">dans une <lb/>recherche de cette nature, bien loin de blâ-<lb/>mer les Aſtronomes, on doit admirer leur <lb/>ſagacité, & </s> <s xml:id="echoid-s4598" xml:space="preserve">leur ſavoir bon gré de ne diffé-<lb/>rer entr’eux qu’en ſecondes.</s> <s xml:id="echoid-s4599" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4600" xml:space="preserve">Les Statellites de Jupiter, & </s> <s xml:id="echoid-s4601" xml:space="preserve">ſur-tout le <lb/> <anchor type="note" xlink:label="note-0363-01a" xlink:href="note-0363-01"/> quatrième, étant tournés vers nous, ont des <lb/>taches obſcures, qui les font paroître quelque-<lb/>fois bien plus petits qu’ils ne ſont ordinaire-<lb/>ment; </s> <s xml:id="echoid-s4602" xml:space="preserve">ce qui fait que le quatrième diſparoît <lb/>quelquefois entiérement, lorſqu’il eſt bien <lb/>éloigné du corps & </s> <s xml:id="echoid-s4603" xml:space="preserve">de l’ombre de Jupiter. <lb/></s> <s xml:id="echoid-s4604" xml:space="preserve">Mais on n’a point encore déterminé, ſi <lb/>ces taches naiſſent ſubitement, ou ſi c’eſt <lb/>le tournoyement des Satellites autour d’eux-<lb/>mêmes, qui nous montre ces taches dans <lb/>un terns, & </s> <s xml:id="echoid-s4605" xml:space="preserve">nous les cache dans un autre; </s> <s xml:id="echoid-s4606" xml:space="preserve"><lb/>quoiqu’il y ait bien à parier pour ce tour-<lb/>noyement, à cauſe des circonſtances pé-<lb/>riodiques qu’on prétend avoir obſervées <pb o="340" file="0364" n="365" rhead="DE LA PHILOSOPHIE"/> dans le quatrième Satellite. </s> <s xml:id="echoid-s4607" xml:space="preserve">Il ſe pourroit <lb/>auſſi, que les ombres memes des Satellites <lb/>fiſſent entr’eux de petites Eclipſes, dont <lb/>on ne pourroit s’appercevoir que par la di-<lb/>minution de leur éclat; </s> <s xml:id="echoid-s4608" xml:space="preserve">mais c’eſt ce qui <lb/>n’a point encore été examiné.</s> <s xml:id="echoid-s4609" xml:space="preserve"/> </p> <div xml:id="echoid-div182" type="float" level="2" n="3"> <note position="right" xlink:label="note-0363-01" xlink:href="note-0363-01a" xml:space="preserve">Pour-<lb/>quoi les <lb/>Satelli-<lb/>tes de <lb/>Jupiter <lb/>ſem-<lb/>blent <lb/>quel-<lb/>quefois <lb/>moins <lb/>grands.</note> </div> </div> <div xml:id="echoid-div184" type="section" level="1" n="41"> <head xml:id="echoid-head66" xml:space="preserve"><emph style="sc">Saturne.</emph></head> <p> <s xml:id="echoid-s4610" xml:space="preserve">Saturne parcourt ſon orbe autour du So-<lb/>leil en 29 ans & </s> <s xml:id="echoid-s4611" xml:space="preserve">demi. </s> <s xml:id="echoid-s4612" xml:space="preserve">Si, en comptant <lb/>rondement, la diſtance moyenne de la <lb/>Terre au Soleil eſt, comme nous l’avons dit <lb/>par-tout ailleurs, de trente millions de nos <lb/>lieues, il s’enſuit par la même raiſon, que <lb/>la diſtance médiocre de Saturne à cet Aſtre <lb/>eſt de 285. </s> <s xml:id="echoid-s4613" xml:space="preserve">à 286. </s> <s xml:id="echoid-s4614" xml:space="preserve">millions des mêmes <lb/>lieues. </s> <s xml:id="echoid-s4615" xml:space="preserve">C’eſt la derniére Planete, & </s> <s xml:id="echoid-s4616" xml:space="preserve">la plus <lb/>éloignée du Soleil qui nous ſoit connue; </s> <s xml:id="echoid-s4617" xml:space="preserve">du <lb/>moins n’a-t-on point encore découvert au-<lb/>delà aucun corps dans de Ciel, qui ait une or-<lb/>bite conſtante, & </s> <s xml:id="echoid-s4618" xml:space="preserve">qui tourne circulaire-<lb/>ment. </s> <s xml:id="echoid-s4619" xml:space="preserve">Il eſt vrai que les Cometes font <lb/>leurs cours dans des Régions bien plus éloi-<lb/>gnées que ne fait Saturne; </s> <s xml:id="echoid-s4620" xml:space="preserve">mais comme <lb/>leur excentricité eſt beaucoup plus grande <lb/>que celles des Planetes ordinaires, elles ne <pb o="341" file="0365" n="366" rhead="DE NEUTON."/> font point partie du Syſtême planétaire que <lb/>nous conſidérons dans ce Chapitre. </s> <s xml:id="echoid-s4621" xml:space="preserve">Car <lb/>quand même on en ſuppoſeroit quelqu’une <lb/>qui feroit réguliérement ſa révolution autour <lb/>du Soleil, par exemple, à 600. </s> <s xml:id="echoid-s4622" xml:space="preserve">millions de <lb/>lieues de diſtance du Centre univerſel de <lb/>notre Syſtême, de quoi lui ſerviroit la lu-<lb/>miére & </s> <s xml:id="echoid-s4623" xml:space="preserve">la chaleur de cet Aſtre, dans une <lb/>diſtance où il ne paroîtroit pas plus grand <lb/>que ne nous paroiſſent Jupiter & </s> <s xml:id="echoid-s4624" xml:space="preserve">Venus? <lb/></s> <s xml:id="echoid-s4625" xml:space="preserve">J’ai ſuppoſé 600 millions de lieues de diſ-<lb/>tance moyenne de ce prétendu corps au <lb/>Soleil, parce que ſi cette diſtance étoit <lb/>moindre, les Planetes ſe tireroient & </s> <s xml:id="echoid-s4626" xml:space="preserve">s’em-<lb/>barraſſeroient trop par leurs gravitations <lb/>réciproques.</s> <s xml:id="echoid-s4627" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4628" xml:space="preserve">Le diametre de Saturne eſt près de 10. </s> <s xml:id="echoid-s4629" xml:space="preserve">fois <lb/> <anchor type="note" xlink:label="note-0365-01a" xlink:href="note-0365-01"/> plus grand que celui de la Terre. </s> <s xml:id="echoid-s4630" xml:space="preserve">Par ce moyen <lb/>on peut calculer la proportion de la peſan-<lb/>teur ſur Saturne à celle que nous éprou-<lb/>vons ſur notre Terre. </s> <s xml:id="echoid-s4631" xml:space="preserve">Son dernier Satelli-<lb/>te étant éloigné de lui de 53 à 54. </s> <s xml:id="echoid-s4632" xml:space="preserve">de ſes ſé-<lb/>mi-diametres, c’eſt-à-dire, le rayon de ſon <lb/>orbite étant 53 ou 54. </s> <s xml:id="echoid-s4633" xml:space="preserve">fois plus grand que <lb/>le ſémi-diametre de Saturne, ſa révolution <lb/>doit ſe faire en 79. </s> <s xml:id="echoid-s4634" xml:space="preserve">jours 22, heures, qui <pb o="342" file="0366" n="367" rhead="DE LA PHIL OSOPHIE"/> font 1918. </s> <s xml:id="echoid-s4635" xml:space="preserve">heures. </s> <s xml:id="echoid-s4636" xml:space="preserve">Je dis donc que com-<lb/>me 157464, cube de 54 ſémi-diame-<lb/>tres de Saturne, eſt à l’unité, ou au cube <lb/>d’un ſeul ſémi-diametre du même Satur-<lb/>ne, ainſi 3678724, quarré de 1918. </s> <s xml:id="echoid-s4637" xml:space="preserve">heu-<lb/>res, eſt à 23 {2/5}, à-peu-près; </s> <s xml:id="echoid-s4638" xml:space="preserve">d’où tirant la <lb/>racine quarrée, l’on trouve pourle tems pé-<lb/>riodique de cette révolution 4 heures & </s> <s xml:id="echoid-s4639" xml:space="preserve">{5/6}, <lb/>ou 4 heures 50 minutes. </s> <s xml:id="echoid-s4640" xml:space="preserve">Donc un corps <lb/>qui feroit le tour de la ſurface de Saturne, <lb/>ſans baiſſer jamais par ſa peſanteur, le fe-<lb/>roit, comme nous venons de voir, en 4 <lb/>heures 50 minutes.</s> <s xml:id="echoid-s4641" xml:space="preserve"/> </p> <div xml:id="echoid-div184" type="float" level="2" n="1"> <note position="right" xlink:label="note-0365-01" xlink:href="note-0365-01a" xml:space="preserve">Calcul <lb/>de la pe-<lb/>ſanteur <lb/>des <lb/>corpsqui <lb/>tombent <lb/>ſur la ſur-<lb/>face de <lb/>Saturne.</note> </div> <p> <s xml:id="echoid-s4642" xml:space="preserve">Pour trouver, à-préſent, de combien de <lb/>pieds les corps peſants tombent ſur Saturne <lb/>pendant la premiére ſeconde de tems, je <lb/>dis que, comme 1. </s> <s xml:id="echoid-s4643" xml:space="preserve">ſémi-diametre de la Ter-<lb/>re, diviſé par le quarré de 84. </s> <s xml:id="echoid-s4644" xml:space="preserve">min. </s> <s xml:id="echoid-s4645" xml:space="preserve">& </s> <s xml:id="echoid-s4646" xml:space="preserve">{2/5}, <lb/>que nous avons trouvées page 320, eſt à <lb/>9 {1/2} ſémi-diametres de la Terre, ou à un <lb/>ſeul ſémi-diametre de Saturne, diviſé par <lb/>le quarré de 290. </s> <s xml:id="echoid-s4647" xml:space="preserve">minutes, que nous ve-<lb/>nons de trouver; </s> <s xml:id="echoid-s4648" xml:space="preserve">ainſi 15. </s> <s xml:id="echoid-s4649" xml:space="preserve">pieds parcourus <lb/>par la chûte d’une ſeconde de tems vers la <lb/>Terre, ſont à 12. </s> <s xml:id="echoid-s4650" xml:space="preserve">pieds de chûte vers Sa-<lb/>turne pendant la premiére ſeconde, &</s> <s xml:id="echoid-s4651" xml:space="preserve"> <pb o="343" file="0367" n="368" rhead="DE NEUTON."/> quelque peu davantage. </s> <s xml:id="echoid-s4652" xml:space="preserve">Mais cette peſan-<lb/>teur des corps vers le centre de Saturne <lb/>ſouffre une diminution conſidérable par leur <lb/>gravitation, en ſens contraire, vers la cavité <lb/>de ſon anneau, comme nous l’allons mon-<lb/>trer dans la ſuite.</s> <s xml:id="echoid-s4653" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4654" xml:space="preserve">Les Figures ſuivantes nous repréſentent <lb/>les différentes configurations de Satur-<lb/>ne: </s> <s xml:id="echoid-s4655" xml:space="preserve">1. </s> <s xml:id="echoid-s4656" xml:space="preserve">Sa phaſe ronde avec une ſeu-<lb/>le bande obſcure au milieu, cauſée par <lb/>l’ombre de l’anneau, & </s> <s xml:id="echoid-s4657" xml:space="preserve">par ſa partie ob-<lb/>ſcure, qui ne reçoit point de rayons du So-<lb/>leil: </s> <s xml:id="echoid-s4658" xml:space="preserve">2. </s> <s xml:id="echoid-s4659" xml:space="preserve">Cette même phaſe ronde avec d’autres <lb/>bandes encore, telles qu’on les a vues en <lb/>1715: </s> <s xml:id="echoid-s4660" xml:space="preserve">3. </s> <s xml:id="echoid-s4661" xml:space="preserve">La phaſe de ſon anneau, qui <lb/>ſe perd de vûe, & </s> <s xml:id="echoid-s4662" xml:space="preserve">qui reparoît après avoir <lb/>été quelque tems inviſible; </s> <s xml:id="echoid-s4663" xml:space="preserve">& </s> <s xml:id="echoid-s4664" xml:space="preserve">4. </s> <s xml:id="echoid-s4665" xml:space="preserve">Cet anneau <lb/>dans ſa plus grande largeur, avec des ban-<lb/>des qui environnent le diſque de Saturne, <lb/>comme cela s’eſt vu en 1696.</s> <s xml:id="echoid-s4666" xml:space="preserve"/> </p> <pb o="344" file="0368" n="369" rhead="DE LA PHILOSOPHIE"/> <figure> <image file="0368-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0368-01"/> </figure> <p> <s xml:id="echoid-s4667" xml:space="preserve">Le diametre extérieur de l’anneau de Sa-<lb/>turne, pris d’un bout à l’autre, eſt au diametre <lb/>de cette Planete, comme 9 ſont à 4, ſelon la <lb/>meſure de Mr. </s> <s xml:id="echoid-s4668" xml:space="preserve">Huygens, ou comme 11 <lb/>ſont à 5, ſelon celle de Mr. </s> <s xml:id="echoid-s4669" xml:space="preserve">Caſſini. </s> <s xml:id="echoid-s4670" xml:space="preserve">Le dia-<lb/>metre intérieur, compris entre les deux ca-<lb/>vités oppoſées, eſt à celui de Saturne com-<lb/>me 6 {1/2} ſont à 4; </s> <s xml:id="echoid-s4671" xml:space="preserve">car depuis le corps de Saturne <lb/>juſqu’à la cavité de ſon anneau, il y a au-<lb/>tant d’eſpace, que depuis cette cavité juſ-<lb/>qu’à ſa circonférence extérieure. </s> <s xml:id="echoid-s4672" xml:space="preserve">Si Sa-<lb/>turne lui-même a 30000 lieues de diame-<lb/>tre, il y aura depuis ſa ſurface, juſqu’à <lb/>la cavité en queſtion, 9375 lieues, & </s> <s xml:id="echoid-s4673" xml:space="preserve">de-<lb/>là juſqu’au bout, auſſi 9375, au lieu deſ-<lb/>quelles on en compte ordinairement 8000. <lb/></s> <s xml:id="echoid-s4674" xml:space="preserve">de largeur.</s> <s xml:id="echoid-s4675" xml:space="preserve"/> </p> <pb o="345" file="0369" n="370" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s4676" xml:space="preserve">La quatrième Figure nous repréſente <lb/>cet anneau dans ſa plus grande ouverture, <lb/>lorſque ſa largeur de B, en C, ou de D en <lb/>F, nous paroît la moitié de ſa longueur A, <lb/>E. </s> <s xml:id="echoid-s4677" xml:space="preserve">C’eſt par cette proportion de longueur <lb/>& </s> <s xml:id="echoid-s4678" xml:space="preserve">de largeur que l’on a calculé l’angle que <lb/>fait cet anneau avec l’orbite de ſa Planete, <lb/>ſavoir de 30 à 31 degrés. </s> <s xml:id="echoid-s4679" xml:space="preserve">Il eſt à remar-<lb/>quer qu’au milieu de ſa largeur apparen-<lb/>te, on obſerve une ligne obſcure, <lb/>telle qu’on la voit marquée par la ligne <lb/>pointillée. </s> <s xml:id="echoid-s4680" xml:space="preserve">La couleur de ſa partie intérieu-<lb/>re, qui eſt plus près du corps de la Plane-<lb/>te, paroît plus vive & </s> <s xml:id="echoid-s4681" xml:space="preserve">plus lumineuſe, que <lb/>celle de ſa partie extérieure, & </s> <s xml:id="echoid-s4682" xml:space="preserve">la ligne <lb/>noire, dont nous venons de parler, en fait <lb/>la ſéparation. </s> <s xml:id="echoid-s4683" xml:space="preserve">Ainſi toutes les fois que cet <lb/>anneau diſparoît, c’eſt ſa partie extérieure <lb/>qui ſe perd la premiére; </s> <s xml:id="echoid-s4684" xml:space="preserve">car l’autre ne diſ-<lb/>paroît que quelques jours après.</s> <s xml:id="echoid-s4685" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4686" xml:space="preserve">Dans les années 1714 & </s> <s xml:id="echoid-s4687" xml:space="preserve">1715, où l’on <lb/>a vu cet anneau diſparoître & </s> <s xml:id="echoid-s4688" xml:space="preserve">reparoître <lb/>deux fois, on a obſervé que ſa partie O-<lb/>rientale ſe perdoit de vûe un jour ou deux <lb/>plutôt que ſa partie Occidentale, & </s> <s xml:id="echoid-s4689" xml:space="preserve">que cette <pb o="346" file="0370" n="371" rhead="DE LA PHIL OSOPHIE"/> même partie Occidentale ſe découvroit au <lb/>contraire un jour ou deux plutôt que ſa par-<lb/>tie Orientale. </s> <s xml:id="echoid-s4690" xml:space="preserve">En 1671. </s> <s xml:id="echoid-s4691" xml:space="preserve">Mr. </s> <s xml:id="echoid-s4692" xml:space="preserve">Caſſini, le Pere, <lb/>avoit déja obſervé quelque choſe de ſembla-<lb/>ble; </s> <s xml:id="echoid-s4693" xml:space="preserve">ce qui lui fit juger avec raiſon que les <lb/>parties de cet anneau, qui ſont du même cô-<lb/>té, par exemple, A, B, & </s> <s xml:id="echoid-s4694" xml:space="preserve">D, E, de la <lb/>troiſième Figure, ne ſont pas dans le même <lb/>plan, & </s> <s xml:id="echoid-s4695" xml:space="preserve">que par conſéquent il eſt plus <lb/>mince ou plus pointu par ſes extrémités A <lb/>& </s> <s xml:id="echoid-s4696" xml:space="preserve">E, que vers la cavité intérieure B, C, <lb/>ou D, F.</s> <s xml:id="echoid-s4697" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4698" xml:space="preserve">Il y a deux cauſes différentes, qui nous <lb/> <anchor type="note" xlink:label="note-0370-01a" xlink:href="note-0370-01"/> font perdre cet anneau de vûe. </s> <s xml:id="echoid-s4699" xml:space="preserve">La pre-<lb/>miére eſt que ſon plan venant à paſ-<lb/>ſer par le centre du Soleil, ſes deux côtés <lb/>ne reçoivent ſes rayons que fort oblique-<lb/>ment de part & </s> <s xml:id="echoid-s4700" xml:space="preserve">d’autre; </s> <s xml:id="echoid-s4701" xml:space="preserve">ce qui fait que ſa <lb/>lumiére devient trop foible pour frapper <lb/>nos yeux. </s> <s xml:id="echoid-s4702" xml:space="preserve">Cela arrive lorſque Saturne, à <lb/>l’égard du Soleil, eſt au 19 degré 45 min. <lb/></s> <s xml:id="echoid-s4703" xml:space="preserve">des Poiſſons ou de la Vierge. </s> <s xml:id="echoid-s4704" xml:space="preserve">Quand il <lb/>n’y a point d’autre cauſe qui produit la <lb/>phaſe ronde de Saturne, que celle-là, el-<lb/>elle ne dure guères au delà d’un mois, com-<lb/>me on le prouve par les Obſervations des an- <pb o="347" file="0371" n="372" rhead="DE NEUTON."/> nées 1685 & </s> <s xml:id="echoid-s4705" xml:space="preserve">1701. </s> <s xml:id="echoid-s4706" xml:space="preserve">Vers la fin de la cette <lb/>phaſe, on s’apperçoit plus clairement de <lb/>l’ombre de l’anneau ſur le corps de Saturne, <lb/>qui paroît un peu au-deſſus ou au-deſl<unsure/>ous du <lb/>milieu de ſon diſque, comme cela ſe voit Fig. </s> <s xml:id="echoid-s4707" xml:space="preserve">1.</s> <s xml:id="echoid-s4708" xml:space="preserve"/> </p> <div xml:id="echoid-div185" type="float" level="2" n="2"> <note position="left" xlink:label="note-0370-01" xlink:href="note-0370-01a" xml:space="preserve">Raiſons <lb/>de la <lb/>diſpari-<lb/>tion de <lb/>l’an-<lb/>neau de <lb/>Saturne.</note> </div> <p> <s xml:id="echoid-s4709" xml:space="preserve">La ſeconde cauſe qui nous rend l’anneau <lb/>inviſible, eſt la coïncidence de ſa partie <lb/>éclairée avec le rayon viſuel, qui paſſe <lb/>du côté de celle qui ne l’eſt pas. </s> <s xml:id="echoid-s4710" xml:space="preserve">Cette <lb/>apparence a des termes moins limités que <lb/>celle dont il a été parlé ci-devant; </s> <s xml:id="echoid-s4711" xml:space="preserve">cependant <lb/>on eſt toujours aſſûré de la voir deux fois, <lb/>quand Saturne, apperçu du Soleil au 19 de-<lb/>gré 45 min. </s> <s xml:id="echoid-s4712" xml:space="preserve">des Poiſſons ou de la Vierge, <lb/>eſt retrograde par rapport à nous. </s> <s xml:id="echoid-s4713" xml:space="preserve">Sa La-<lb/>titude étant obſervée de la Terre, ne <lb/>peut différer chaque fois que de fort peu de <lb/>choſe; </s> <s xml:id="echoid-s4714" xml:space="preserve">mais ce peu de choſe ne laiſſe pas <lb/>d’être aſſez ſenſible, pour avancer ou pro-<lb/>roger ces termes. </s> <s xml:id="echoid-s4715" xml:space="preserve">En 1671, il y eut plus <lb/>de ſix mois entre les deux diſparitions des <lb/>anſes, à compter depuis la fin du mois de <lb/>Mai juſqu’au 8 de Décembre. </s> <s xml:id="echoid-s4716" xml:space="preserve">Le lieu de <lb/>Saturne, etant vu du Soleil, ſe trouvoit la <lb/>premiére fois au 13 degré des Poiſſons, & </s> <s xml:id="echoid-s4717" xml:space="preserve"><lb/>la ſeconde au commencement du vingtième.</s> <s xml:id="echoid-s4718" xml:space="preserve"> <pb o="348" file="0372" n="373" rhead="DE LA PHIL OSOPHIE"/> En 1714. </s> <s xml:id="echoid-s4719" xml:space="preserve">le 12 Octobre, jour auquel les anſes <lb/>diſparurent, Saturne ſe voyoit du Soleil au <lb/>commencement du 17<emph style="super">e</emph> degré de la Vierge, <lb/>& </s> <s xml:id="echoid-s4720" xml:space="preserve">le 22<emph style="super">e</emph>. </s> <s xml:id="echoid-s4721" xml:space="preserve">de Mars. </s> <s xml:id="echoid-s4722" xml:space="preserve">En 1715. </s> <s xml:id="echoid-s4723" xml:space="preserve">jour moyen de <lb/>la ſeconde diſparition, il étoit déja à 21 de-<lb/>grés & </s> <s xml:id="echoid-s4724" xml:space="preserve">demi du même Signe à l’égard du <lb/>Soleil; </s> <s xml:id="echoid-s4725" xml:space="preserve">mais le tems qui s’écoula entre ces <lb/>deux diſparitions, n’eſt que de 5 mois & </s> <s xml:id="echoid-s4726" xml:space="preserve"><lb/>quelques jours. </s> <s xml:id="echoid-s4727" xml:space="preserve">Ainſi les phaſes rondes <lb/>vers le commencement de Juillet 1744, & </s> <s xml:id="echoid-s4728" xml:space="preserve"><lb/>au mois de Mars 1760. </s> <s xml:id="echoid-s4729" xml:space="preserve">ne ſe redoubleront <lb/>point; </s> <s xml:id="echoid-s4730" xml:space="preserve">& </s> <s xml:id="echoid-s4731" xml:space="preserve">il faudra par conſéquent laiſſer à <lb/>la Poſtérité l’obſervation du retour de ce <lb/>Phénomêne.</s> <s xml:id="echoid-s4732" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4733" xml:space="preserve">Bien des gens ſont curieux de ſavoir ſi <lb/>cet anneau eſt un corps continu ou ſolide, <lb/>ou ſi ce ne ſont que des Satellites, qui ſont <lb/>ſi près les uns des autres, que notre vûe ne <lb/>peutles diſtinguer. </s> <s xml:id="echoid-s4734" xml:space="preserve">La derniére de ces deux <lb/>conjectures me paroît plus vraiſemblable. <lb/></s> <s xml:id="echoid-s4735" xml:space="preserve">Car ſi l’on m’objecte que le mouvement de <lb/>tous ces Satellites, dans une orbite commu-<lb/>ne, ne pourroit ſe faire, ſans qu’ils ſe cho-<lb/>quaſſent les uns les autres, s’il y avoit tant <lb/>ſoit peu d’excentricité; </s> <s xml:id="echoid-s4736" xml:space="preserve">il me ſuffira de répon-<lb/>dre que ce mouvement n’eſt point du tout <pb o="349" file="0373" n="374" rhead="DE NEUTON."/> excentrique. </s> <s xml:id="echoid-s4737" xml:space="preserve">Si l’on dit auſſi que les Satel-<lb/>lites ſupérieurs ne pourroient pas achever <lb/>leurs périodes en même tems que les infé-<lb/>rieurs, parce que la peſanteur, ou la force <lb/>centripète de leur mouvement circulaire, <lb/>diminue en raiſon quarrée de leur éloigne-<lb/>ment du centre de Saturne: </s> <s xml:id="echoid-s4738" xml:space="preserve">je réponds <lb/>encore, qu’à la vérité cette différence <lb/>de leurs periodes eſt telle que l’on pré-<lb/>tend; </s> <s xml:id="echoid-s4739" xml:space="preserve">mais que la reſſemblance exacte de <lb/>tous les Satellites d’un même ordre nous <lb/>ſait regarder cet aſſemblage de Satellites <lb/>ſéparez comme un corps continu.</s> <s xml:id="echoid-s4740" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4741" xml:space="preserve">Il reſte pourtant encore une petite dif-<lb/>ficulté à lever. </s> <s xml:id="echoid-s4742" xml:space="preserve">Cette orbite, dira-t-on, <lb/>loin de pouvoir être exactement circulaire, <lb/>eſt elliptique, ſon grand axe étant tou-<lb/>jours perpendiculaire à une ligne tirée du <lb/>centre du Soleil à celui de Saturne; </s> <s xml:id="echoid-s4743" xml:space="preserve">parce <lb/>que tous les Satellites ne ſont que des Lu-<lb/>nes, qui pour cette raiſon doivent obéïr aux <lb/>mêmes loix de la gravitation que la nôtre. <lb/></s> <s xml:id="echoid-s4744" xml:space="preserve">Or comme l’orbite de la Lune doit un peu <lb/>s’applatir dans les conjonctions, de même que <lb/>dans les oppoſitions, & </s> <s xml:id="echoid-s4745" xml:space="preserve">avoir plus de cour-<lb/>bure aux quadratures, ainſi que nous l’avons <pb o="350" file="0374" n="375" rhead="DE LA PHIL OSOPHIE"/> prouvé au Chapitre XXII. </s> <s xml:id="echoid-s4746" xml:space="preserve">il s’enſuit néceſ-<lb/>ſairement que le même changement arrivera <lb/>dans celle des autres Satellites. </s> <s xml:id="echoid-s4747" xml:space="preserve">La choſe <lb/>dépend donc uniquement de la différence <lb/>de la gravitation de Saturne ſur le Soleil, <lb/>& </s> <s xml:id="echoid-s4748" xml:space="preserve">de celle de ſes Satellites ſur lui-même; <lb/></s> <s xml:id="echoid-s4749" xml:space="preserve">& </s> <s xml:id="echoid-s4750" xml:space="preserve">c’eſt de cette différence que nous don-<lb/>nerons la meſure au Chap. </s> <s xml:id="echoid-s4751" xml:space="preserve">XXV.</s> <s xml:id="echoid-s4752" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4753" xml:space="preserve">Les bandes de Saturne, dont le parallè-<lb/>liſme avec ſon anneau fait voir, que ce qui <lb/>les cauſe eſt élevé au-deſſus de la ſurſace <lb/>de cette Planete à une aſſez grande diſ-<lb/>tance, pour que leur courbure ne ſoit que <lb/>peu ou point ſenſible, prouvent indubita-<lb/>blement, que Saturne eſt environné d’une <lb/>Atmoſphére beaucoup plus vaſte que la <lb/>nôtre. </s> <s xml:id="echoid-s4754" xml:space="preserve">Mais en ſuppoſant, comme ci-<lb/>deſſus, que cet anneau n’eſt compoſé, que <lb/>d’une infinité de Satellites, il ne ſera pas <lb/>néceſſaire de l’étendre juſque-là. </s> <s xml:id="echoid-s4755" xml:space="preserve">Cepen-<lb/>dant quelque vaſte que ſoit cette At-<lb/>moſphére, il ſaut qu’elle ſoit incompara-<lb/>blement plus tranſparente que la nôtre, <lb/>puiſque les Fixes que l’on voit quelque-<lb/>fois entre les anſes & </s> <s xml:id="echoid-s4756" xml:space="preserve">le corps de Saturne, <lb/>n’y ſouffrent jamais ni réfraction, ni chan- <pb o="351" file="0375" n="376" rhead="DE NEUTON."/> gement de figure, comme dans les autres <lb/>Atmoſphéres.</s> <s xml:id="echoid-s4757" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4758" xml:space="preserve">C’eſt une choſe fort remarquable, que <lb/>parmi les 5 Satellites de Saturne, il y en a <lb/>quatre, qui font leurs révolutions dans le <lb/>plan même de ſon anneau, & </s> <s xml:id="echoid-s4759" xml:space="preserve">que le cinquiè-<lb/>me eſt le ſeul, qui ſuive une route particu-<lb/>liére. </s> <s xml:id="echoid-s4760" xml:space="preserve">Ce dernier n’a que 15 à 16 degrés <lb/>d’inclinaiſon de ſon orbite à celle de Satur-<lb/>ne, au lieu que les 4 autres circulent <lb/>dans un plan incliné à celui de leur Planete <lb/>principale de 30 deg. </s> <s xml:id="echoid-s4761" xml:space="preserve">ou davantage. </s> <s xml:id="echoid-s4762" xml:space="preserve">Auſſi <lb/>ſes nœuds ſont-ils un peu différens de ceux <lb/>des autres. </s> <s xml:id="echoid-s4763" xml:space="preserve">Ceux-ci ont les mêmes nœuds, <lb/>que l’anneau, ſavoir au 19 degré 45 min. <lb/></s> <s xml:id="echoid-s4764" xml:space="preserve">des Poiſſons & </s> <s xml:id="echoid-s4765" xml:space="preserve">de la Vierge; </s> <s xml:id="echoid-s4766" xml:space="preserve">mais le der-<lb/>nier coupe l’orbite de Saturne environ <lb/>quinze degrés plutôt, ſavoir au quatriè-<lb/>me, ou au cinquième degré des mêmes Si-<lb/>gnes.</s> <s xml:id="echoid-s4767" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4768" xml:space="preserve">Avant que de quitter Saturne, il faut <lb/> <anchor type="note" xlink:label="note-0375-01a" xlink:href="note-0375-01"/> remarquer une autre particularité de ſon <lb/>mouvement qu’on n’a point encore ob-<lb/>ſervée à l’égard des autres Planetes. </s> <s xml:id="echoid-s4769" xml:space="preserve">Tou-<lb/>tes les plus anciennes Obſervations étant <pb o="352" file="0376" n="377" rhead="DE LA PHILOSOPHIE"/> comparées entr’elles, ainſi qu’avec les mo-<lb/>dernes, nous donnent ſon moyen mouve-<lb/>ment annuel de 12 degrés 13 minutes, & </s> <s xml:id="echoid-s4770" xml:space="preserve"><lb/>33 à 36 ſecondes, au plus. </s> <s xml:id="echoid-s4771" xml:space="preserve">Mais les <lb/>modernes ſeules, comparées les unes <lb/>avec les autres, donnent ce même mou-<lb/>vement diminué de quelques ſecondes, <lb/>ſavoir de 12 degrés 13 min. </s> <s xml:id="echoid-s4772" xml:space="preserve">& </s> <s xml:id="echoid-s4773" xml:space="preserve">20 à 29 ſe-<lb/>condes par an. </s> <s xml:id="echoid-s4774" xml:space="preserve">On a encore obſervé d’au-<lb/>tres petites inégalitez dans le mouvement <lb/>de Saturne depuis Tycho-Brahé; </s> <s xml:id="echoid-s4775" xml:space="preserve">mais <lb/>qui ne laiſſent pas de s’accorder toutes à <lb/>nous faire voir, que ſon moyen mouve-<lb/>ment eſt moins prompt à préſent, que du <lb/>tems des Chaldéens & </s> <s xml:id="echoid-s4776" xml:space="preserve">des Egyptiens. </s> <s xml:id="echoid-s4777" xml:space="preserve">Mr. <lb/></s> <s xml:id="echoid-s4778" xml:space="preserve">Caſſini a prouvé cela inconteſtablement, en <lb/>comparant les obſervations modernes, ainſi <lb/>que celles de Ptolomée, avec une ob-<lb/>ſervation fort ancienne faite le 1. </s> <s xml:id="echoid-s4779" xml:space="preserve">Mars <lb/>de l’année 4485 de la Période Julienne, <lb/>dans un Mémoire préſenté à l’Académie le <lb/>10. </s> <s xml:id="echoid-s4780" xml:space="preserve">Janvier 1728.</s> <s xml:id="echoid-s4781" xml:space="preserve"/> </p> <div xml:id="echoid-div186" type="float" level="2" n="3"> <note position="right" xlink:label="note-0375-01" xlink:href="note-0375-01a" xml:space="preserve">Ralen-<lb/>tiſſe-<lb/>ment du <lb/>mouve-<lb/>ment de <lb/>Saturne.</note> </div> <p> <s xml:id="echoid-s4782" xml:space="preserve">Quoique Neuton ait prouvé que, lorſ-<lb/>que Jupiter eſt le plus près de Saturne <lb/>qu’il eſt poſſible, il dérange ſenſiblement le <lb/>mouvement de cette Planete, néanmoins le <pb o="353" file="0377" n="378" rhead="DE NEUTON."/> ralentiſſement du mouvement de celui-ci <lb/>eſt trop ſenſible, & </s> <s xml:id="echoid-s4783" xml:space="preserve">d’une nature trop dif-<lb/>férente de ce qu’elle devroit être, pour en <lb/>accuſer ſeulement Jupiter. </s> <s xml:id="echoid-s4784" xml:space="preserve">En effet, s’il n’y <lb/>avoit pas d’autres corps qui y contribuaſſent, <lb/>comment ſe pourroit-il faire que, dans les <lb/>plus grandes proximités de ces Planetes, le <lb/>mouvement de Saturne fût tantôt accéléré, <lb/>& </s> <s xml:id="echoid-s4785" xml:space="preserve">tantôt retardé, comme le démontrent les <lb/>obſervations rapportées par Mr. </s> <s xml:id="echoid-s4786" xml:space="preserve">Caſſini?</s> <s xml:id="echoid-s4787" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4788" xml:space="preserve">Je crois donc que le ralentiſſement <lb/>du mouvement qu’éprouve Saturne beau-<lb/>coup plus ſenſiblement que toutes les <lb/>autres Planetes, eſt cauſé par l’attraction <lb/>de pluſieurs Cometes, qui font leurs traver-<lb/>ſes dans les immenſes Régions de l’Univers <lb/>au-delà de lui. </s> <s xml:id="echoid-s4789" xml:space="preserve">Leur nombre & </s> <s xml:id="echoid-s4790" xml:space="preserve">leur gran-<lb/>deur ſont aſſez conſidérables pour pouvoir <lb/>être ſenſible à l’égard de la peſanteur de Sa-<lb/>turne ſur le Soleil, qui n’eſt que la 9ome. <lb/></s> <s xml:id="echoid-s4791" xml:space="preserve">partie de l’attraction de la Terre vers le <lb/>centre de notre Syſtême. </s> <s xml:id="echoid-s4792" xml:space="preserve">Auſſi les in-<lb/>égalités de ce ralentiſſement s’expliquent-<lb/>elles bien plus commodément par les diffé-<lb/>rentes proximités des Cometes, que par <pb o="354" file="0378" n="379" rhead="DE LA PHILOSOPHIE"/> toute autre cauſe; </s> <s xml:id="echoid-s4793" xml:space="preserve">& </s> <s xml:id="echoid-s4794" xml:space="preserve">ſi les Planetes infé-<lb/>rieures ſe ſentent moins que Saturne de <lb/>leur approchement, c’eſt parce que la force <lb/>attractive du Soleil eſt bien plus forte que <lb/>celle des Cometes dans les Régions infé-<lb/>rieures, que dans celle de Saturne, comme <lb/>nous l’avons déja dit.</s> <s xml:id="echoid-s4795" xml:space="preserve"/> </p> <figure> <image file="0378-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0378-01"/> </figure> <pb file="0379" n="380"/> </div> <div xml:id="echoid-div188" type="section" level="1" n="42"> <head xml:id="echoid-head67" xml:space="preserve">CHAP. VINGT-QUATRE.</head> <head xml:id="echoid-head68" style="it" xml:space="preserve">De la Lumiére Zodiacale, des Cometes, <lb/>& des Fixes.</head> <head xml:id="echoid-head69" style="it" xml:space="preserve">De la Lumiére Zodiacale.</head> <p> <s xml:id="echoid-s4796" xml:space="preserve">LA principale raiſon qui nous engage <lb/>à faire ici mention de la Lumiére Zo-<lb/>diacale, eſt que certaines Hypothèſes, <lb/>par leſquelles on explique ce Phénomê-<lb/>ne, ſemblent contraires aux Démonſtra-<lb/>tions de Neuton ſur le mouvement des <lb/>corps dans des milieux réſiſtans; </s> <s xml:id="echoid-s4797" xml:space="preserve">& </s> <s xml:id="echoid-s4798" xml:space="preserve">c’eſt <lb/>ce qu’il faut tâcher d’éclaircir.</s> <s xml:id="echoid-s4799" xml:space="preserve"/> </p> <pb o="356" file="0380" n="381" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s4800" xml:space="preserve">La lumiére zodiacale eſt une clarté ſem-<lb/>blable à celle de la Voye Lactée, & </s> <s xml:id="echoid-s4801" xml:space="preserve">quelque-<lb/>fois meme plus claire, qui s’étend preſque <lb/>le long du Zodiaque à 50, 60, 70, 80, <lb/>90, & </s> <s xml:id="echoid-s4802" xml:space="preserve">quelquefois à 100 degrés & </s> <s xml:id="echoid-s4803" xml:space="preserve">davan-<lb/>tage du lieu du Soleil, de part & </s> <s xml:id="echoid-s4804" xml:space="preserve">d’au-<lb/>tre. </s> <s xml:id="echoid-s4805" xml:space="preserve">Ainſi ſes pointes & </s> <s xml:id="echoid-s4806" xml:space="preserve">une grande par-<lb/>tie de ſon arc lumineux, quand elle n’eſt <lb/>pas enveloppée, ou mélée de notre cré-<lb/>puſcule, paroiſſent avoir un mouvement <lb/>annuel & </s> <s xml:id="echoid-s4807" xml:space="preserve">journalier autour de la Terre, pa-<lb/>reil à celui que le Vulgaire attribue au <lb/>Soleil. </s> <s xml:id="echoid-s4808" xml:space="preserve">Selon les ſavantes remarques de Mr. <lb/></s> <s xml:id="echoid-s4809" xml:space="preserve">de Mairan, tirées des Obſervation de Mrs. </s> <s xml:id="echoid-s4810" xml:space="preserve"><lb/>Caſſini, Eimmart, Kirch & </s> <s xml:id="echoid-s4811" xml:space="preserve">d’autres, c’eſt <lb/>ſur la fin de l’Hyver, & </s> <s xml:id="echoid-s4812" xml:space="preserve">au commencement <lb/>du Printems, que le ſoir eſt plus propre <lb/>dans nos Climats pour bien obſerver cette <lb/>Lumiére; </s> <s xml:id="echoid-s4813" xml:space="preserve">& </s> <s xml:id="echoid-s4814" xml:space="preserve">le matin vers la fin de l’Eté <lb/>& </s> <s xml:id="echoid-s4815" xml:space="preserve">le commencement de l’Automne. </s> <s xml:id="echoid-s4816" xml:space="preserve">Cette <lb/>différence eſt un effet de la différente po-<lb/>ſition de l’Ecliptique ſur l’Horizon, qui <lb/>fait tomber la pointe de la lumiére en <lb/>queſtion, quelquefois plus haut, quelque-<lb/>fois plus bas.</s> <s xml:id="echoid-s4817" xml:space="preserve"/> </p> <pb o="357" file="0381" n="382" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s4818" xml:space="preserve">L’angle de ſa pointe, où les deux côtés <lb/>ſe réuniſſent, eſt fort inégal. </s> <s xml:id="echoid-s4819" xml:space="preserve">On l’a vu <lb/>quelquefois de 20 degrés, & </s> <s xml:id="echoid-s4820" xml:space="preserve">quelquefois <lb/>de huit ſeulement. </s> <s xml:id="echoid-s4821" xml:space="preserve">Mr. </s> <s xml:id="echoid-s4822" xml:space="preserve">de Mairan rappor-<lb/>te encore des obſervations de Mr. </s> <s xml:id="echoid-s4823" xml:space="preserve">Caſſini, <lb/>qui l’avoit trouvée d’une figure irré-<lb/>guliére, & </s> <s xml:id="echoid-s4824" xml:space="preserve">courbée comme une faucille; </s> <s xml:id="echoid-s4825" xml:space="preserve">il <lb/>en rapporte auſſi de Mr. </s> <s xml:id="echoid-s4826" xml:space="preserve">Fatio de Duilliers, <lb/>où les deux côtés ont eu des points qu’on <lb/>appelle en Géométrie points de rebrouſſe-<lb/>ment, ou d’inflexion contraire, ſembla-<lb/>bles à ceux de deux conchoïdes ſur une <lb/>même aſymptote.</s> <s xml:id="echoid-s4827" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4828" xml:space="preserve">Une connoiſſance des plus eſſentiel-<lb/>les de ce Phénomêne, dont nous ſom-<lb/>mes redevables à la grande ſagacité <lb/>de Mr. </s> <s xml:id="echoid-s4829" xml:space="preserve">de Mairan, eſt que la ſection <lb/>du milieu de cette lumiére, ou de <lb/>la matiére qui la réfléchit vers nous, eſt <lb/>la même que le plan de l’équateur du So-<lb/>leil, ayant tous deux les mémes nœuds a-<lb/>vec notre Ecliptique, & </s> <s xml:id="echoid-s4830" xml:space="preserve">faiſant avec elle <lb/>un angle de 7 degrés & </s> <s xml:id="echoid-s4831" xml:space="preserve">demi. </s> <s xml:id="echoid-s4832" xml:space="preserve">Cela <lb/>prouve fort vraiſemblablement, que cette <lb/>matiére appartient naturellement au Soleil;</s> <s xml:id="echoid-s4833" xml:space="preserve"> <pb o="358" file="0382" n="383" rhead="DE LA PHILOSOPHIE"/> auſſi n’eſt-ce pas ſans raiſon, qu’on lui a <lb/>donné le nom d’Atmoſphére Solaire, quoi-<lb/>qu’il ne faille pas la confondre avec celle <lb/>qui l’environne de plus près, & </s> <s xml:id="echoid-s4834" xml:space="preserve">dans la-<lb/>quelle nagent les taches Solaires, qui font <lb/>avec elle leur révolution périodique en 25 <lb/>jours & </s> <s xml:id="echoid-s4835" xml:space="preserve">demi.</s> <s xml:id="echoid-s4836" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4837" xml:space="preserve">La Figure de cette Atmoſphére ex-<lb/>térieure eſt une Sphéroïde fort platte, <lb/>dont le grand diametre eſt ſouvent 5, <lb/>ou 8 à 9 fois plus grand, que celui <lb/>qu’on imagine d’un Pole à l’autre. </s> <s xml:id="echoid-s4838" xml:space="preserve">Son é-<lb/>tendue eſt en différens tems ſi inégale, <lb/>que ſa pointe ſupérieure eſt quelquefois <lb/>bien au-deſſous de l’orbite de la Terre, & </s> <s xml:id="echoid-s4839" xml:space="preserve"><lb/>va quelquefois bien au - delà. </s> <s xml:id="echoid-s4840" xml:space="preserve">C’eſt ce <lb/>qui a porté, Mr. </s> <s xml:id="echoid-s4841" xml:space="preserve">de Mairan à croire, que <lb/>cette Sphéroïde étoit fort excentrique, & </s> <s xml:id="echoid-s4842" xml:space="preserve"><lb/>que ſes apſides avoient un mouvement bien <lb/>plus prompt, & </s> <s xml:id="echoid-s4843" xml:space="preserve">peut-être moins régulier, <lb/>que celles des orbites planétaires. </s> <s xml:id="echoid-s4844" xml:space="preserve">Il fau-<lb/>droit donc que l’aphélie de cette Sphéroï-<lb/>de s’étendît juſqu’entre les orbites de Mars <lb/>& </s> <s xml:id="echoid-s4845" xml:space="preserve">de la Terre, & </s> <s xml:id="echoid-s4846" xml:space="preserve">que ſon périhélie ſe ter-<lb/>minât au-deſſus de l’orbite de Vénus, ſans <lb/>atteindre celle de la Terre.</s> <s xml:id="echoid-s4847" xml:space="preserve"/> </p> <pb o="359" file="0383" n="384" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s4848" xml:space="preserve">Sur cela on auroit raiſon de demander <lb/>comment il ſe peut faire, que la Terre & </s> <s xml:id="echoid-s4849" xml:space="preserve"><lb/>la Lune, qui entrent toutes deux dans cet-<lb/>te Atmoſphére Solaire, ne ſentent pas la <lb/>réſiſtance d’une matiére, qui doit néceſſai-<lb/>rement avoir quelque denſité? </s> <s xml:id="echoid-s4850" xml:space="preserve">Pourquoi la <lb/>vîteſſe de leur mouvement ne ſe ralentit <lb/>point? </s> <s xml:id="echoid-s4851" xml:space="preserve">Et pourquoi enfin l’orbite de la <lb/>Terre ne devient pas plus petite de ſiècle <lb/>en ſiècle, comme cela devroit arriver in-<lb/>failliblement, ſi ce mouvement ſe faiſoit <lb/>dans un milieu réſiſtant?</s> <s xml:id="echoid-s4852" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4853" xml:space="preserve">C’eſt une vérité inconteſtable, & </s> <s xml:id="echoid-s4854" xml:space="preserve">dé-<lb/>montrée par Neuton dans la IV. </s> <s xml:id="echoid-s4855" xml:space="preserve">Section <lb/>du Livre II. </s> <s xml:id="echoid-s4856" xml:space="preserve">de ſa Philoſophie, que la den-<lb/>ſité du milieu étant poſée en raiſon inverſe <lb/>des diſtances du centre du mouvement, & </s> <s xml:id="echoid-s4857" xml:space="preserve"><lb/>la peſanteur en double raiſon inverſe de ces <lb/>mêmes diſtances, le mouvement circulaire <lb/>doit ſe changer en celui de ſpirale; </s> <s xml:id="echoid-s4858" xml:space="preserve">& </s> <s xml:id="echoid-s4859" xml:space="preserve">que <lb/>cette ſpirale eſt préciſément celle que <lb/>Deſcartes & </s> <s xml:id="echoid-s4860" xml:space="preserve">le R. </s> <s xml:id="echoid-s4861" xml:space="preserve">P. </s> <s xml:id="echoid-s4862" xml:space="preserve">Merſène ont connue <lb/>les premiers; </s> <s xml:id="echoid-s4863" xml:space="preserve">je veux dire, celle qui coupe <lb/>tous les rayons partans d’un ſeul centre, <lb/>ſous un angle toujours égal. </s> <s xml:id="echoid-s4864" xml:space="preserve">Donc, ſi l’At- <pb o="360" file="0384" n="385" rhead="DE LA PHILOSOPHIE"/> moſphére Solaire enveloppe la Terre & </s> <s xml:id="echoid-s4865" xml:space="preserve">la <lb/>Lune, les années doivent toujours devenir <lb/>plus courtes, parce que l’Orbite devient <lb/>plus étroite: </s> <s xml:id="echoid-s4866" xml:space="preserve">la vîteſſe de mouvement an-<lb/>nuel & </s> <s xml:id="echoid-s4867" xml:space="preserve">journalier diminuera toujours: </s> <s xml:id="echoid-s4868" xml:space="preserve">le <lb/>diametre apparent du Soleil nous paroîtra <lb/>toujours plus grand; </s> <s xml:id="echoid-s4869" xml:space="preserve">& </s> <s xml:id="echoid-s4870" xml:space="preserve">la chaleur augmentera <lb/>à la fin juſqu’à faire périr tout ce qu’il y a <lb/>de vivant ſur la Terre.</s> <s xml:id="echoid-s4871" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4872" xml:space="preserve">Voici la maniére, dont je crois pouvoir <lb/>réſoudre cette difficulté. </s> <s xml:id="echoid-s4873" xml:space="preserve">Toutes les par-<lb/>ties les plus petites de cette Atmoſphére <lb/>ſont autant de petites Planetes, qui tour-<lb/>nent autour du Soleil, à peu près de la même <lb/>maniére & </s> <s xml:id="echoid-s4874" xml:space="preserve">dans le même ſens, que les gran-<lb/>des qu’on a connues juſqu’ici ſous ce nom. <lb/></s> <s xml:id="echoid-s4875" xml:space="preserve">Cela fait qu’elles ont elles-mêmes par-tout <lb/>des vîteſſes fort peu différentes de celles de <lb/>la Terre dans les mêmes diſtances du Soleil.</s> <s xml:id="echoid-s4876" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4877" xml:space="preserve">On voit bien qu’un amas de particules, <lb/>qui tournent avec la même rapidité qu’un <lb/>corps d’une grandeur conſidérable, qui en <lb/>eſt environné, ne peut faire aucune réſiſ-<lb/>tance au mouvement que ce corps fait <lb/>dans le même ſens. </s> <s xml:id="echoid-s4878" xml:space="preserve">On voit auſſi que, ſi <pb o="361" file="0385" n="386" rhead="DE NEUTON."/> les vîteſſes de cet aſſemblage de petites Pla-<lb/>netes réſiſtent quelquefois un peu à une <lb/>plus grande qui ſe trouve parmi elles, les <lb/>vîteſſes du côté oppoſé, qui doivent être <lb/>plus grandes, lui font bien-tôt regagner, <lb/>ce qu’elle en avoit perdu auparavant.</s> <s xml:id="echoid-s4879" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4880" xml:space="preserve">C’eſt particuliérement au célèbre Fatio <lb/>de Duilliers que nous avons l’obligation de <lb/>cette idée. </s> <s xml:id="echoid-s4881" xml:space="preserve">Quoique ce grand Géométre <lb/>n’ait pas prévu l’inconvénient, qui naîtroit <lb/>de la réſiſtance de cette matiére par rap-<lb/>port au mouvement de la Terre, de la Lu-<lb/>ne, de Vénus & </s> <s xml:id="echoid-s4882" xml:space="preserve">de Mercure; </s> <s xml:id="echoid-s4883" xml:space="preserve">il eſt cepen-<lb/>dant le premier, qui nous ait averti, que <lb/>cette lumiére pourroit bien être un amas <lb/>ſphéroïde de petites Planetes, comme la <lb/>Voye Lactée n’eſt qu’un nombre infini de <lb/>Fixes ſi petites, qu’on ne peut les apper-<lb/>cevoir.</s> <s xml:id="echoid-s4884" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4885" xml:space="preserve">Mais, quoi, dira-t-on, vous avez <lb/> <anchor type="note" xlink:label="note-0385-01a" xlink:href="note-0385-01"/> détruit au Chapitre XVI. </s> <s xml:id="echoid-s4886" xml:space="preserve">les Tourbillons <lb/>de Deſcartes, & </s> <s xml:id="echoid-s4887" xml:space="preserve">maintenant vous en <lb/>établiſſez un autre entiérement contraire à <lb/>vos principes? </s> <s xml:id="echoid-s4888" xml:space="preserve">Cette Atmoſphére, qui, ſe- <pb o="362" file="0386" n="387" rhead="DE LA PHILOSOPHIE"/> lon vous, doit tourner inceſſamment autour <lb/>du Soleil, & </s> <s xml:id="echoid-s4889" xml:space="preserve">dont le mouvement s’étend <lb/>juſqu’au-delà de l’orbite de la Terre, n’eſt-<lb/>elle pas un nouveau Tourbillon, par lequel <lb/>vous prétendez remplacer celui que vous <lb/>vous êtes tant efforcé d’anéantir en faveur <lb/>de la Philoſophie de Neuton? </s> <s xml:id="echoid-s4890" xml:space="preserve">Et, tourbillon <lb/>pour tourbillon, pourquoi ne pas adopter <lb/>plutôt celui de Deſcartes?</s> <s xml:id="echoid-s4891" xml:space="preserve"/> </p> <div xml:id="echoid-div188" type="float" level="2" n="1"> <note position="right" xlink:label="note-0385-01" xlink:href="note-0385-01a" xml:space="preserve">Premié-<lb/>re Ob-<lb/>jection <lb/>contre <lb/>le ſenti-<lb/>ment de <lb/>Mr. de <lb/>Duil-<lb/>liers.</note> </div> <p> <s xml:id="echoid-s4892" xml:space="preserve">A cela je réponds, que les Tourbil-<lb/>lons de Deſcartes ſont bien différens du <lb/>mouvement circulaire ou elliptique des pe-<lb/>tites Planetes de cette Atmoſphére, au quel <lb/>je conſens qu’on donne, ſi l’on veut, le <lb/>nom de Tourbillon, pourvû que l’on m’ac-<lb/>corde que celui-ci ne reſſemble point à ceux <lb/>de Deſcartes. </s> <s xml:id="echoid-s4893" xml:space="preserve">Il n’eſt pas néceſſaire de ré-<lb/>péter tous les inconvéniens des Tourbil-<lb/>lons que nous avons examinés dans les <lb/>Chapitres précédens; </s> <s xml:id="echoid-s4894" xml:space="preserve">nous nous contente-<lb/>rons de parler d’une ſeule choſe en quoi ils <lb/>différent de celui dont il s’agit. </s> <s xml:id="echoid-s4895" xml:space="preserve">En effet, <lb/>pour que les Tourbillons de Deſcartes ayent <lb/>aſſez de force pour emporter les Plane-<lb/>tes, qui y nagent, il eſt néceſſaire qu’el-<lb/>les n’ayent jamais ni plus, ni moins de <pb o="363" file="0387" n="388" rhead="DE NEUTON."/> matiére, que la partie du Tourbillon qui <lb/>les met en mouvement, ce qui eſt contrai-<lb/>re à l’expérience. </s> <s xml:id="echoid-s4896" xml:space="preserve">Car leur mouvement <lb/>dans leurs aphélies eſt plus lent, que dans <lb/>leurs périhélies, & </s> <s xml:id="echoid-s4897" xml:space="preserve">cependant la quantité <lb/>de matiére, qu’elles contiennent, eſt tou-<lb/>jours égale. </s> <s xml:id="echoid-s4898" xml:space="preserve">Ce qui les fait tourner, n’eſt <lb/>donc point une force qui leur eſt imprimée <lb/>par une matiére étrangere, autrement cet-<lb/>te même matiére étant plus vaſte dans <lb/>leurs aphélies, & </s> <s xml:id="echoid-s4899" xml:space="preserve">plus reſſerrée dans leurs <lb/>périhélies, produiroit un effet tout-à-fait <lb/>contraire. </s> <s xml:id="echoid-s4900" xml:space="preserve">Mais notre Tourbillon ne doit <lb/>pas ſe prendre pour un premier reſſort du <lb/>mouvement planétaire, puiſque nous conſi-<lb/>dérons la peſanteur ou l’attraction vers le <lb/>Soleil, comme ſa cauſe véritable & </s> <s xml:id="echoid-s4901" xml:space="preserve">primiti-<lb/>ve. </s> <s xml:id="echoid-s4902" xml:space="preserve">En effet, nous ne le poſons que pour <lb/>ne pas retarder le mouvement de la Terre <lb/>& </s> <s xml:id="echoid-s4903" xml:space="preserve">des Planetes inférieures, ce qui eſt bien <lb/>différent de leur imprimer du mouvement, <lb/>comme devroient faire ceux de Deſcartes.</s> <s xml:id="echoid-s4904" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4905" xml:space="preserve">On pourroit faire une objection bien plus <lb/> <anchor type="note" xlink:label="note-0387-01a" xlink:href="note-0387-01"/> réelle ſur la nature du mouvement circulai-<lb/>re ou curviligne, cauſé par quelque corps <lb/>central vers lequel tous les autres ſont atti- <pb o="364" file="0388" n="389" rhead="DE LA PHILOSOPHIE"/> rés. </s> <s xml:id="echoid-s4906" xml:space="preserve">On ne doute point que le centre des <lb/>forces ne doive toujours être dans le même <lb/>plan où ſe fait le mouvement; </s> <s xml:id="echoid-s4907" xml:space="preserve">car c’eſt <lb/>une ſuite néceſſaire des Démonſtrations, <lb/>par leſquelles nous avons prouvé au Chap. <lb/></s> <s xml:id="echoid-s4908" xml:space="preserve">XIX. </s> <s xml:id="echoid-s4909" xml:space="preserve">l’égalité des aires décrites en tems é-<lb/>gaux. </s> <s xml:id="echoid-s4910" xml:space="preserve">Comment donc, dira-t on, ſe peut-il <lb/>faire que deux corps ou pluſieurs, dont la <lb/>circulation ſe commence dans des plans dif-<lb/>férens, mais à égale diſtance du Soleil, ne <lb/>ſe choquent pas quelque part, avant que d’a-<lb/>chever ſeulement leur premiére révolution; </s> <s xml:id="echoid-s4911" xml:space="preserve"><lb/>puiſqu’il eſt impoſſible que deux plans circu-<lb/>laires différens & </s> <s xml:id="echoid-s4912" xml:space="preserve">qui ont pourtant le même <lb/>centre, ne ſe coupent pas en deux points de <lb/>leurs périphéries? </s> <s xml:id="echoid-s4913" xml:space="preserve">Néanmoins nous ne voyons <lb/>pas que cela arrive à la matiére qui produit <lb/>la lumiére zodiacale, puiſqu’un choc com-<lb/>me celui-là, la réduiroit bien-tôt en une <lb/>ſeule maſſe, & </s> <s xml:id="echoid-s4914" xml:space="preserve">en feroit une nouvelle Plane <lb/>te, ſelon les théorêmes du mouvement cauſé <lb/>par la percuſſion, démontré ſi clairement <lb/>par Mrs. </s> <s xml:id="echoid-s4915" xml:space="preserve">Mariotte, Huygens & </s> <s xml:id="echoid-s4916" xml:space="preserve">Herman. </s> <s xml:id="echoid-s4917" xml:space="preserve"><lb/>Quoique certains petillements de cette lu-<lb/>miére, obſervés par Mrs. </s> <s xml:id="echoid-s4918" xml:space="preserve">Caſſini & </s> <s xml:id="echoid-s4919" xml:space="preserve">de <lb/>Duilliers, prouvent aſſez viſiblement que <lb/>le choc des corpuſcules qui compoſent cet- <pb o="365" file="0389" n="390" rhead="DE NEUTON."/> te matiére, eſt quelque choſe de fort com-<lb/>mun, cela ne l’empêche pas de ſubſiſter tou-<lb/>jours, & </s> <s xml:id="echoid-s4920" xml:space="preserve">d’avoir ſes viciſſitudes de diminu-<lb/>tion & </s> <s xml:id="echoid-s4921" xml:space="preserve">d’accroiſſement. </s> <s xml:id="echoid-s4922" xml:space="preserve">Mais un choc dans <lb/>l’interſection de deux, ou de pluſieurs Plans, <lb/>tel que celui dont nous venons de parler <lb/>ligne 7 & </s> <s xml:id="echoid-s4923" xml:space="preserve">ſuiv. </s> <s xml:id="echoid-s4924" xml:space="preserve">p. </s> <s xml:id="echoid-s4925" xml:space="preserve">364, n’a jamais été re-<lb/>marqué, & </s> <s xml:id="echoid-s4926" xml:space="preserve">ne le ſera certainement jamais.</s> <s xml:id="echoid-s4927" xml:space="preserve"/> </p> <div xml:id="echoid-div189" type="float" level="2" n="2"> <note position="right" xlink:label="note-0387-01" xlink:href="note-0387-01a" xml:space="preserve">Secon-<lb/>de Ob-<lb/>jection.</note> </div> <p> <s xml:id="echoid-s4928" xml:space="preserve">Pour réſoudre cette difficulté, il faut <lb/>voir ce qui arriveroit, s’il y avoit une ſe-<lb/>conde Terre de la même figure & </s> <s xml:id="echoid-s4929" xml:space="preserve">de la mê-<lb/>me grandeur que la nôtre, & </s> <s xml:id="echoid-s4930" xml:space="preserve">ſi ces deux <lb/>Terres ſe touchoient tellement aux deux <lb/>Poles de leur orbite commune, que le Pole <lb/>Méridional de l’une fût appliqué immédia-<lb/>tement au Pole Septentrional de l’autre. </s> <s xml:id="echoid-s4931" xml:space="preserve">Il <lb/>eſt clair que le centre de l’une ou de l’autre <lb/>décriroit une orbite particuliére, dont le <lb/>plan non-ſeulement ne paſſeroit pas par le <lb/>centre du Soleil; </s> <s xml:id="echoid-s4932" xml:space="preserve">mais en ſeroit même éloi-<lb/>gné du demi-diametre de chacune des deux.</s> <s xml:id="echoid-s4933" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4934" xml:space="preserve">Je dis plus. </s> <s xml:id="echoid-s4935" xml:space="preserve">Si au lieu de ces deux Ter-<lb/>res j’en ſuppoſe quatre, ſix, huit, ou da-<lb/>vantage, il en faudra néceſſairement reve-<lb/>nir au même raiſonnement; </s> <s xml:id="echoid-s4936" xml:space="preserve">& </s> <s xml:id="echoid-s4937" xml:space="preserve">la multipli- <pb o="366" file="0390" n="391" rhead="DE LA PHILOSOPHIE"/> cation de ces corps de part & </s> <s xml:id="echoid-s4938" xml:space="preserve">d’autre ne <lb/>produira que la multiplication des centres <lb/>particuliers des orbites particuliéres. </s> <s xml:id="echoid-s4939" xml:space="preserve">Mais <lb/>le centre commun de gravité de toutes ces <lb/>Terres jointes enſemble, ſitué au point du <lb/>contact des deux Poles du milieu, décrira <lb/>pareillement une orbite qui tiendra le mi-<lb/>lieu de toutes les autres, & </s> <s xml:id="echoid-s4940" xml:space="preserve">paſſera imman-<lb/>quablement par le centre du Soleil.</s> <s xml:id="echoid-s4941" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4942" xml:space="preserve">Pour revenir aux petits corpuſcules qui <lb/>compoſent cette Atmoſphére, figurons-<lb/>nous que tous ceux qui ſont à la même diſ-<lb/>tance du Soleil ſe touchent; </s> <s xml:id="echoid-s4943" xml:space="preserve">il n’y a pas <lb/>de doute qu’ils ne s’accompagnaſſent éter-<lb/>nellement, comme feroit une rangée de <lb/>pluſieurs Terres, qui auroient toutes des ré-<lb/>volutions égales autour du Soleil. </s> <s xml:id="echoid-s4944" xml:space="preserve">Il eſt vrai <lb/>qu’un autre ordre ſupérieur ou inférieur de <lb/>ces corpuſcules feroit une révolution par-<lb/>ticuliére dans un tems périodique différent <lb/>de celui de la précédente; </s> <s xml:id="echoid-s4945" xml:space="preserve">mais ce ſeroit <lb/>toujours de compagnie, & </s> <s xml:id="echoid-s4946" xml:space="preserve">ſans que les cor-<lb/>puſcules d’une même rangée ſe quittaſſent <lb/>jamais. </s> <s xml:id="echoid-s4947" xml:space="preserve">Il importe peu que des rangées diffé-<lb/>rentes ſupérieures & </s> <s xml:id="echoid-s4948" xml:space="preserve">inférieures ſe tou-<lb/>chent, ou ne ſe touchent pas, pourvû qu’il <pb o="367" file="0391" n="392" rhead="DE NEUTON."/> n’y ait ni inégalité, ni friction, qui puiſſe <lb/>en retarder le mouvement.</s> <s xml:id="echoid-s4949" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4950" xml:space="preserve">Voici encore une objection qu’on pour-<lb/> <anchor type="note" xlink:label="note-0391-01a" xlink:href="note-0391-01"/> roit faire contre le mouvement de l’Atmoſ-<lb/>phére Solaire, tel que nous l’imaginons. <lb/></s> <s xml:id="echoid-s4951" xml:space="preserve">Le tems périodique des taches du Soleil & </s> <s xml:id="echoid-s4952" xml:space="preserve"><lb/>par conſéquent de la partie la plus baſſe de <lb/>cette Atmoſphére, avec laquelle ces taches <lb/>font viſiblement leur révolution, eſt de 25 <lb/>jours & </s> <s xml:id="echoid-s4953" xml:space="preserve">demi, que l’on compte depuis qu’u-<lb/>ne partie de cette Atmoſphére a été ſous <lb/>une Fixe quelconque, juſqu’à ſon retour <lb/>ſous la même Fixe.</s> <s xml:id="echoid-s4954" xml:space="preserve"/> </p> <div xml:id="echoid-div190" type="float" level="2" n="3"> <note position="right" xlink:label="note-0391-01" xlink:href="note-0391-01a" xml:space="preserve">Troiſiè-<lb/>me Ob-<lb/>jection.</note> </div> <p> <s xml:id="echoid-s4955" xml:space="preserve">Comparons maintenant le tems périodi-<lb/>que du ſédiment de l’Atmoſphére Solaire a-<lb/>vec celui qu’employent ſes parties ſituées à <lb/>une élévation égale à celle de la Terre. <lb/></s> <s xml:id="echoid-s4956" xml:space="preserve">Pour cet effet nous commencerons par éta-<lb/>blir que toutes les Planetes, tant grandes <lb/>que petites, font leurs révolutions dans la <lb/>même Région du Ciel en tems égaux; </s> <s xml:id="echoid-s4957" xml:space="preserve">car <lb/>il n’y a perſonne qui puiſſe le nier, ſans <lb/>contredire l’expérience même, qui prouve <lb/>que la diſproportion des maſſes de Jupiter, <lb/>de Mars & </s> <s xml:id="echoid-s4958" xml:space="preserve">de Mercure, ne dérange rien <lb/>à la proportion de leurs tems périodiques.</s> <s xml:id="echoid-s4959" xml:space="preserve"/> </p> <pb o="368" file="0392" n="393" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s4960" xml:space="preserve">Les corpuſcules planétaires de cette At-<lb/>moſphére étant à une diſtance égale à celle <lb/>de notre Terre feront donc leur révolution <lb/>en une année; </s> <s xml:id="echoid-s4961" xml:space="preserve">mais pour bien expliquer la <lb/>choſe il faut avoir recours à cette Règle de <lb/>Kepler: </s> <s xml:id="echoid-s4962" xml:space="preserve">Comme le cube de 213 ſémi-dia-<lb/>metres du Soleil, qui font la diſtance <lb/>moyenne de la Terre à cet Aſtre, eſt au <lb/>quarré de 525949 minutes, ou d’une an-<lb/>née, de même le cube d’un ſeul ſémi-dia-<lb/>metre du Soleil eſt au quarré de 169 à 170 <lb/>minutes. </s> <s xml:id="echoid-s4963" xml:space="preserve">Le ſond ou le ſédiment de l’At-<lb/>moſphére Solaire devroit donc tourner en <lb/>169 ou 170 minutes; </s> <s xml:id="echoid-s4964" xml:space="preserve">mais l’expérience <lb/>nous apprend qu’il fait ſa révolution en 25 <lb/>jours & </s> <s xml:id="echoid-s4965" xml:space="preserve">demi, comme on l’a vu ci-deſſus, <lb/>ce qui fait une diſproportion trop ſenſible.</s> <s xml:id="echoid-s4966" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4967" xml:space="preserve">Pour faire voir que cette objection a plus <lb/>de brillant que de ſolide, il nous ſuffira de <lb/>dire que l’Atmoſphére Solaire eſt ſéparée en <lb/>deux parties différentes par un vuide aſſez <lb/>grand, pour que la partie ſupérieure n’ait <lb/>aucune communication avec l’inférieure. <lb/></s> <s xml:id="echoid-s4968" xml:space="preserve">Or comme cette ſéparation fait que l’At-<lb/>moſphére inférieure peut ſuivre le mouve- <pb o="369" file="0393" n="394" rhead="DE NEUTON."/> ment du Soleil autour de ſon axe, & </s> <s xml:id="echoid-s4969" xml:space="preserve">avoir <lb/>le même tems périodique, elle nous met <lb/>en droit de ſoutenir que la partie ſupérieure, <lb/>pour ne pas tomber ſur l’inférieure, a be-<lb/>ſoin d’un mouvement planétaire, dont les <lb/>forces centrifuges contrebalancent les cen-<lb/>tripètes. </s> <s xml:id="echoid-s4970" xml:space="preserve">On ne peut donc s’empêcher de <lb/>nous accorder que cette Atmoſphére ſupé-<lb/>rieure doit avoir différens degrés de vîteſſe <lb/>dans ſes différentes parties, autrement les <lb/>plus baſſes tomberoient toujours vers le So-<lb/>leil, & </s> <s xml:id="echoid-s4971" xml:space="preserve">les plus hautes pourroient s’élever <lb/>même au-delà de Saturne.</s> <s xml:id="echoid-s4972" xml:space="preserve"/> </p> </div> <div xml:id="echoid-div192" type="section" level="1" n="43"> <head xml:id="echoid-head70" xml:space="preserve"><emph style="sc">Des</emph> <emph style="sc">Cometes.</emph></head> <p> <s xml:id="echoid-s4973" xml:space="preserve">Neuton eſt le premier qui nous ait donné <lb/>la véritable idée du mouvement des Come-<lb/>tes. </s> <s xml:id="echoid-s4974" xml:space="preserve">Cependant Mr. </s> <s xml:id="echoid-s4975" xml:space="preserve">Caſſini, le Pere, a-<lb/>voit deja trouvé avant lui le moyen de pré-<lb/>dire leur ſituation apparente, lorſqu’elles <lb/>ne ſont pas trop près du Soleil. </s> <s xml:id="echoid-s4976" xml:space="preserve">Car, quoi-<lb/>qu’il ſût très-bien que leur mouvement eſt <lb/>curviligne, il ne laiſſa pas d’en ſuppoſer la <lb/>courbure ſi peu ſenſible, qu’on pouvoit la <lb/>regarder comme une ligne droite; </s> <s xml:id="echoid-s4977" xml:space="preserve">& </s> <s xml:id="echoid-s4978" xml:space="preserve">à l’ai-<lb/>de de cette ſuppoſition il parvint à un cal- <pb o="370" file="0394" n="395" rhead="DE LA PHILOSOPHIE"/> cul qui ne différe que peu ou point de celui <lb/>de Neuton, puiſque plus des ſegmens égaux <lb/>d’une Parabole s’éloignent de ſon ſommet, <lb/>plus ils approchent d’une ligne droite.</s> <s xml:id="echoid-s4979" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4980" xml:space="preserve">Quand Neuton a inventé l’Hypothèſe du <lb/>mouvement parabolique des Cometes, pour <lb/>en rendre le calcul plus Géométrique & </s> <s xml:id="echoid-s4981" xml:space="preserve"><lb/>moins embarraſſant, il n’a pas cru pour ce-<lb/>la que les courbes de leurs trajets ſoient de <lb/>véritables Paraboles. </s> <s xml:id="echoid-s4982" xml:space="preserve">Au contraire, dans <lb/>la XLII. </s> <s xml:id="echoid-s4983" xml:space="preserve">Propoſition du III. </s> <s xml:id="echoid-s4984" xml:space="preserve">Livre de ſa Phi-<lb/>loſophie il nous enſeigne le moyen de <lb/>trouver par approximation les grands axes <lb/>de leurs orbites elliptiques, avec cette reſ-<lb/>triction néanmoins que ces orbites ſont <lb/>d’une figure ſi oblongue que nous ne ſau-<lb/>rions les voir toutes entiéres. </s> <s xml:id="echoid-s4985" xml:space="preserve">Nous ne <lb/>voyons donc les Cometes que lorſqu’elles <lb/>ſont près de leurs périhélies, parce que <lb/>tout le reſte de leur cours ſe fait dans des <lb/>Régions ſi éloignées, que notre vûe ne peut <lb/>porter juſque-là. </s> <s xml:id="echoid-s4986" xml:space="preserve">Ce que nous voyons <lb/>d’une orbite Cométique n’eſt ſouvent pas <lb/>la centième partie de ce que nous n’en <lb/>voyons point. </s> <s xml:id="echoid-s4987" xml:space="preserve">Car comme les Cometes ne <lb/>commencent à paroître ordinairement que <pb o="371" file="0395" n="396" rhead="DE NEUTON."/> quand elles ſont à une diſtance du Soleil plus <lb/>petite que celle de Jupiter, & </s> <s xml:id="echoid-s4988" xml:space="preserve">plus grande que <lb/>celle de Mars; </s> <s xml:id="echoid-s4989" xml:space="preserve">lorſqu’elles paſſent dans les <lb/>Régions ſupérieures & </s> <s xml:id="echoid-s4990" xml:space="preserve">qu’elles ſe trouvent <lb/>à une diſtance du Soleil égale à celle de Ju-<lb/>piter, leur lumiére eſt ſi foible qu’à peine <lb/>peut-elle être apperçue.</s> <s xml:id="echoid-s4991" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4992" xml:space="preserve">Comme la Parabole n’eſt qu’une Ellipſe, <lb/>dont le centre eſt infiniment éloigné de ſon <lb/>foyer, on s’en ſert, ſuivant les règles de <lb/>Neuton, au lieu de l’Ellipſe, quand on ne ſait <lb/>pas préciſément la meſure des deux axes, <lb/>pourvû que le grand axe excéde du moins <lb/>20 fois le petit. </s> <s xml:id="echoid-s4993" xml:space="preserve">Autrement ce ſeroit non-<lb/>ſeulement une faute conſidérable de pro-<lb/>longer le mouvement parabolique au-delà <lb/>des diſtances où les Cometes ſont viſibles; <lb/></s> <s xml:id="echoid-s4994" xml:space="preserve">mais l’on ſe priveroit encore par-là de l’eſ-<lb/>pérance de les revoir jamais.</s> <s xml:id="echoid-s4995" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s4996" xml:space="preserve">Ainſi le mouvement des Cometes autour <lb/>du Soleil reſſemble tellement à celui des <lb/>Planetes ordinaires, que quoique les pre-<lb/>miéres approchent beaucoup plus près de <lb/>cet Aſtre que les autres, elles ne ſont pas <lb/>expoſées à tomber ſur lui, lorſque la cour- <pb o="372" file="0396" n="397" rhead="DE LA PHILOSOPHIE"/> be de leur mouvement devient perpendicu-<lb/>laire à ſa diſtance. </s> <s xml:id="echoid-s4997" xml:space="preserve">Car la force centripète <lb/> <anchor type="note" xlink:label="note-0396-01a" xlink:href="note-0396-01"/> étant plus petite que la troiſième propor-<lb/>tionnelle à la diſtance du Soleil & </s> <s xml:id="echoid-s4998" xml:space="preserve">à la vî-<lb/>teſſe du périhélie, la Planete ou la Comete <lb/>n’eſt pas plutôt parvenue à ſa plus grande <lb/>proximité du Soleil, qu’elle commence à <lb/>s’en éloigner.</s> <s xml:id="echoid-s4999" xml:space="preserve"/> </p> <div xml:id="echoid-div192" type="float" level="2" n="1"> <note position="left" xlink:label="note-0396-01" xlink:href="note-0396-01a" xml:space="preserve">Pour <lb/>quoi les <lb/>Come-<lb/>tes & les <lb/>Planetes <lb/>ne tom-<lb/>bent <lb/>point <lb/>ſur le <lb/>Soleil <lb/>dans <lb/>leurs pé-<lb/>rihélies.</note> </div> <p> <s xml:id="echoid-s5000" xml:space="preserve">L’Atmoſphére, la durée, la queue & </s> <s xml:id="echoid-s5001" xml:space="preserve">le <lb/>retour d’une Comete eſt ce qu’il y a de plus <lb/>remarquable.</s> <s xml:id="echoid-s5002" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5003" xml:space="preserve">L’Atmoſphére d’une Comete différe de <lb/>celle d’une Planete ordinaire en ce que ſon <lb/>noyau eſt beaucoup plus petit. </s> <s xml:id="echoid-s5004" xml:space="preserve">Il y en a <lb/>qui ont 15 fois plus de diametre que les <lb/>corps des Cometes. </s> <s xml:id="echoid-s5005" xml:space="preserve">Auſſi une même At-<lb/>moſphére n’eſt-elle pas toujours d’une égale <lb/>extenſion, vû qu’elle diminue & </s> <s xml:id="echoid-s5006" xml:space="preserve">s’aggran-<lb/>dit par repriſes.</s> <s xml:id="echoid-s5007" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5008" xml:space="preserve">On ne ſait pas bien encore ſi ces diminu-<lb/>tions & </s> <s xml:id="echoid-s5009" xml:space="preserve">ces accroiſſemens ſe font réguliére-<lb/>ment aux mêmes diſtances du Soleil & </s> <s xml:id="echoid-s5010" xml:space="preserve">du <lb/>périhélie. </s> <s xml:id="echoid-s5011" xml:space="preserve">Car ſelon les Obſervations d’He-<lb/>velius, alleguées par Neuton, ces Atmoſphé-<lb/>res diminuent à meſure qu’elles approchent <pb o="373" file="0397" n="398" rhead="DE NEUTON."/> du Soleil, & </s> <s xml:id="echoid-s5012" xml:space="preserve">augmentent à meſure qu’el-<lb/>les s’en éloignent. </s> <s xml:id="echoid-s5013" xml:space="preserve">Au contraire Mr. <lb/></s> <s xml:id="echoid-s5014" xml:space="preserve">de Mairan aſſûre, qu’elles groſſiſſent à <lb/>l’approche du Soleil par les parties de l’Atmo-<lb/>ſphére Solaire qu’elles emportent avec elles <lb/>en paſſant. </s> <s xml:id="echoid-s5015" xml:space="preserve">L’un & </s> <s xml:id="echoid-s5016" xml:space="preserve">l’autre de ces ſentimens <lb/>paroiſſent fondés ſur ce que les Atmoſphé-<lb/>res des Cometes peuvent diminuer juſqu’á <lb/>la rencontre de celle du Soleil, dans la-<lb/>quelle elles puiſent de nouvelles matiéres. </s> <s xml:id="echoid-s5017" xml:space="preserve"><lb/>De plus ces Atmoſphéres contenant un air <lb/>ſemblable au nôtre, elles doivent toujours <lb/>occuper plus d’eſpace en deſcendant vers <lb/>le Soleil qu’en remontant; </s> <s xml:id="echoid-s5018" xml:space="preserve">parce que cet <lb/>air ſe rarefie extrêmement lorſqu’elles deſ-<lb/>cendent, & </s> <s xml:id="echoid-s5019" xml:space="preserve">ſe condenſe de même, lorſ-<lb/>qu’elles remontent.</s> <s xml:id="echoid-s5020" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5021" xml:space="preserve">La durée des Cometes ſe prouve, ſelon <lb/>le raiſonnement de Neuton, par les degrés <lb/>de chaleur exceſſifs qu’elles ſubiſſent dans <lb/>leurs périhélies. </s> <s xml:id="echoid-s5022" xml:space="preserve">Ce Philoſophe a calculé <lb/>que la Comete de l’année 1680, qui paſſa <lb/>au-deſſus de la ſurface du Soleil juſqu’à un <lb/>ſixième de ſon diametre, dut ſentir une <lb/>chaleur 2000 fois plus grande que celle d’un <lb/>fer rouge. </s> <s xml:id="echoid-s5023" xml:space="preserve">D’où il a conclu que ce corps <pb o="374" file="0398" n="399" rhead="DE LA PHILOSOPHIE"/> devoit être bien compacte & </s> <s xml:id="echoid-s5024" xml:space="preserve">auſſi ancien que <lb/>le monde, puiſqu’il fut ſi près du Soleil & </s> <s xml:id="echoid-s5025" xml:space="preserve"><lb/>qu’il réſiſta ſi long-tems à ſes rayons, ſans <lb/>s’évaporer.</s> <s xml:id="echoid-s5026" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5027" xml:space="preserve">Comme le ſentiment de Neuton eſt une <lb/>eſpèce de Paradoxe pour ceux qui ne ſont <lb/>pas bien au fait de ces matiéres, il eſt bon <lb/>de voir ſurquoi il eſt appuyé. </s> <s xml:id="echoid-s5028" xml:space="preserve">La ligne <lb/>compriſe entre le centre du Soleil & </s> <s xml:id="echoid-s5029" xml:space="preserve">la <lb/>Comete en queſtion dans ſon périhélie, é-<lb/>toit au rayon de l’orbite de la Terre comme <lb/>600 ſont à 100000. </s> <s xml:id="echoid-s5030" xml:space="preserve">La chaleur qui ſe fait <lb/>ſentir à la Terre fut donc alors à celle <lb/>de la Comete comme 360000 ſont à <lb/>10000000000, ou comme 1 eſt à 28000. <lb/></s> <s xml:id="echoid-s5031" xml:space="preserve">Or comme la plus grande chaleur de l’Eté <lb/>n’eſt à celle de l’eau bouillante que comme <lb/>1 eſt à 3 {1/2}; </s> <s xml:id="echoid-s5032" xml:space="preserve">& </s> <s xml:id="echoid-s5033" xml:space="preserve">que cette derniére eſt encore <lb/>quatre fois moindre que celle d’un fer rou-<lb/>ge, il a trouvé que cette chaleur eſt à celle <lb/>de la Comete comme 14 ſont à 28000, ou <lb/>comme 1 eſt à 2000.</s> <s xml:id="echoid-s5034" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5035" xml:space="preserve">Si une balle de fer rougie au feu perd ſa <lb/>chaleur en une heure, & </s> <s xml:id="echoid-s5036" xml:space="preserve">que le tems qu’il <lb/>faut pour refroidir des Sphéres échauffées <pb o="375" file="0399" n="400" rhead="DE NEUTON."/> ſoit comme leurs diametres & </s> <s xml:id="echoid-s5037" xml:space="preserve">leurs degrés <lb/>de chaleur, il faudra 108 millions d’années <lb/>pour refroidir le corps de cette Comete, <lb/>s’il eſt égal à notre Terre.</s> <s xml:id="echoid-s5038" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5039" xml:space="preserve">Cette réflexion nous découvre & </s> <s xml:id="echoid-s5040" xml:space="preserve">nous <lb/> <anchor type="note" xlink:label="note-0399-01a" xlink:href="note-0399-01"/> fait également admirer la ſageſſe du Créa-<lb/>teur. </s> <s xml:id="echoid-s5041" xml:space="preserve">Rien ne pourroit ſubſiſter dans les <lb/>Cometes, ſi elles n’avoient pas une chaleur <lb/>ſuffiſante pour la conſervation de leur ma-<lb/>tiére. </s> <s xml:id="echoid-s5042" xml:space="preserve">La Nature, afin de leur en donner <lb/>autant qu’elles en avoient beſoin, même <lb/>dans les Régions les plus reculées, où un <lb/>mouvement circulaire, ou peu excentrique, <lb/>les auroit privés de la chaleur du Soleil, a <lb/>augmenté ſi conſidérablement leurs excen-<lb/>tricités, que l’embraſement qu’elles ſouffrent <lb/>pendant très-peu de tems, fait qu’elles jouïſ-<lb/>ſent d’une chaleur tempérée pendant le <lb/>reſte de leur révolution. </s> <s xml:id="echoid-s5043" xml:space="preserve">Mais ſi d’un autre <lb/>côté il y a des Créatures animées dans les <lb/>Cometes, comme Mr. </s> <s xml:id="echoid-s5044" xml:space="preserve">Huygens a prouvé <lb/>qu’il y en a dans les Planetes, il faut abſo-<lb/>lument qu’elles ſe retirent dans les cavités <lb/>intérieures de ces Cometes, pour ſe garantir <lb/>de cet incendie général qui ſe fait à leurs <lb/>ſurfaces extérieures.</s> <s xml:id="echoid-s5045" xml:space="preserve"/> </p> <div xml:id="echoid-div193" type="float" level="2" n="2"> <note position="right" xlink:label="note-0399-01" xlink:href="note-0399-01a" xml:space="preserve">Pour-<lb/>quoi les <lb/>Orbites <lb/>des Co-<lb/>metes <lb/>ſont ſi <lb/>excen-<lb/>triques.</note> </div> <pb o="376" file="0400" n="401" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s5046" xml:space="preserve">A conſidérer la figure irréguliére de quel-<lb/>ques Cometes, on juge qu’elles ne tour-<lb/>nent point autour de leur axe; </s> <s xml:id="echoid-s5047" xml:space="preserve">parce qu’el-<lb/>les ne ſauroient avoir cette rotation ſans a-<lb/>voir en même tems une figure ſphérique, <lb/>ou ſphéroïde, & </s> <s xml:id="echoid-s5048" xml:space="preserve">un ſeul noyau enfermé <lb/>dans leur atmoſphére. </s> <s xml:id="echoid-s5049" xml:space="preserve">Mais on en a vu <lb/>quelques-unes, qui n’étoient ni exactement <lb/>ſphériques, ni ſphéroïdes: </s> <s xml:id="echoid-s5050" xml:space="preserve">d’autres qui pa-<lb/>roiſſoient un amas de pluſieurs noyaux de <lb/>figures & </s> <s xml:id="echoid-s5051" xml:space="preserve">de grandeurs différentes; </s> <s xml:id="echoid-s5052" xml:space="preserve">ce qui <lb/>ne convient nullement à un mouvement <lb/>journalier, & </s> <s xml:id="echoid-s5053" xml:space="preserve">rend la poſition de leur axe <lb/>extrêmement variable. </s> <s xml:id="echoid-s5054" xml:space="preserve">Outre cela leurs <lb/>queues, qui ſont très-inégales, & </s> <s xml:id="echoid-s5055" xml:space="preserve">qui chan-<lb/>gent preſqu’à tous momens, devoient ou <lb/>retarder ſenſiblement, ou arrêter tout-à-<lb/>fait le tournoyement dont eſt queſtion, ce <lb/>qu’on n’a point encore remarqué.</s> <s xml:id="echoid-s5056" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5057" xml:space="preserve">Mais ſi les Cometes ne tournent point au-<lb/>tour d’elles-mêmes, il faut qu’avant & </s> <s xml:id="echoid-s5058" xml:space="preserve">a-<lb/>près leur embraſement la même partie ſoit <lb/>preſque toujours expoſée au Soleil; </s> <s xml:id="echoid-s5059" xml:space="preserve">& </s> <s xml:id="echoid-s5060" xml:space="preserve">qu’il <lb/>n’y ait par conſéquent qu’une moitié de <lb/>leurs Sphéres qui ſoit habitable, puiſqu’elle <pb o="377" file="0401" n="402" rhead="DE NEUTON."/> voit toujours le Soleil, & </s> <s xml:id="echoid-s5061" xml:space="preserve">que l’autre eſt <lb/>enſévelie dans une nuit de pluſieurs années, <lb/>ou de pluſieurs ſiècles; </s> <s xml:id="echoid-s5062" xml:space="preserve">ce qui n’empêche <lb/>pourtant pas que cet hémiſphére n’ait autant <lb/>de chaleur que celui qui eſt éclairé. </s> <s xml:id="echoid-s5063" xml:space="preserve">Pour ex-<lb/>pliquer cette eſpèce de Paradoxe nous ajou-<lb/>terons à ce qui a été dit page 375, que la <lb/>chaleur qu’elles peuvent recevoir du Soleil <lb/>dans leurs aphélies n’eſt pas la 10000 me. <lb/></s> <s xml:id="echoid-s5064" xml:space="preserve">partie de celle qui ſe ſent aux Poles de la <lb/>Terre, & </s> <s xml:id="echoid-s5065" xml:space="preserve">que celle qui reſte après qu’elles <lb/>ont paſſé leurs périhélies doit être égale par <lb/>toute leur ſurface.</s> <s xml:id="echoid-s5066" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5067" xml:space="preserve">La fumée qui ſort des Cometes, & </s> <s xml:id="echoid-s5068" xml:space="preserve">qui <lb/>ſe diſperſe dans les Régions du Ciel qu’elles <lb/>traverſent, compoſe leurs queues. </s> <s xml:id="echoid-s5069" xml:space="preserve">Elles com-<lb/>mencent à ſe former un peu avant que les <lb/>Cometes arrivent à leurs périhélies, & </s> <s xml:id="echoid-s5070" xml:space="preserve">dès <lb/>que la chaleur du Soleil eſt aſſez forte pour <lb/>enflammer les matiéres combuſtibles de <lb/>leurs ſurfaces, & </s> <s xml:id="echoid-s5071" xml:space="preserve">pour que la fumée faſſe <lb/>brêche à leurs atmoſphéres. </s> <s xml:id="echoid-s5072" xml:space="preserve">Il eſt pour-<lb/>tant vrai que cet incendie commence un <lb/>peu avant qu’on en voye la fumée; </s> <s xml:id="echoid-s5073" xml:space="preserve">mais <lb/>nous ne conſidérons ici que le moment où <pb o="378" file="0402" n="403" rhead="DE LA PHILOSOPHIE"/> nous commençons à appercevoir leurs <lb/>queues.</s> <s xml:id="echoid-s5074" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5075" xml:space="preserve">Elles ne ſont jamais plus longues que <lb/>quand les Cometes ſortent de leurs périhé-<lb/>lies, après quoi elles diminuent toujours, <lb/>lors même qu’elles s’approchent de la Ter-<lb/>re. </s> <s xml:id="echoid-s5076" xml:space="preserve">C’eſt par ces degrés d’augmentation & </s> <s xml:id="echoid-s5077" xml:space="preserve"><lb/>de diminution que le ſavant Neuton a connu <lb/>que les queues des Cometes n’étoient que <lb/>des fumées. </s> <s xml:id="echoid-s5078" xml:space="preserve">Cela ſe confirme encore par <lb/>leur direction qui s’étend toujours vers les <lb/>parties oppoſées au Soleil. </s> <s xml:id="echoid-s5079" xml:space="preserve">On ne ſauroit <lb/>donner une comparaiſon plus ſenſible de la <lb/>choſe, que celle qu’en a donné ce Philoſo-<lb/>phe, quoiqu’elle ait beſoin d’être un peu <lb/>plus circonſtanciée.</s> <s xml:id="echoid-s5080" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5081" xml:space="preserve">Figurons-nous donc une torche allumée <lb/>dont le lumignon ſoit renverſé, & </s> <s xml:id="echoid-s5082" xml:space="preserve">qui par <lb/>un mouvement projectile tourne autour de la <lb/>Terre; </s> <s xml:id="echoid-s5083" xml:space="preserve">toute ſa fumée montera en haut, & </s> <s xml:id="echoid-s5084" xml:space="preserve"><lb/>tendra à s’éloigner du centre de la Terre <lb/>malgré ce renverſement. </s> <s xml:id="echoid-s5085" xml:space="preserve">De plus cette <lb/>fumée ſe courbera tellement vers les Ré-<lb/>gions contraires à la direction du mouve-<lb/>ment de la torche, que la partie ſupérieure <pb o="379" file="0403" n="404" rhead="DE NEUTON."/> ſemblera ſe mouvoir moins vîte que l’infé-<lb/>rieure. </s> <s xml:id="echoid-s5086" xml:space="preserve">Et ce qu’il y a encore de plus re-<lb/>marquable, c’eſt que la fumée paroîtra plus <lb/>large en haut qu’en bas, comme on le voit <lb/>par celle qui au ſortir des cheminées occupe <lb/>toujours plus d’eſpace qu’elle n’en occupoit <lb/>auparavant. </s> <s xml:id="echoid-s5087" xml:space="preserve">Tout cela quadre parfaite-<lb/>ment avec les Phénomênes de ces queues. <lb/></s> <s xml:id="echoid-s5088" xml:space="preserve">La partie embraſée d’une Comete, qui eſt <lb/>tournée vers le Soleil, pouſſe ſa fumée à l’op-<lb/>poſite de cet Aſtre.</s> <s xml:id="echoid-s5089" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5090" xml:space="preserve">Cette fumée a toujours quelque courbu-<lb/>re à ſon extrémité, qui eſt d’autant plus <lb/>reclinée, c’eſt-à-dire, panchée en arrié, <lb/>re, que la queue eſt plus longue; </s> <s xml:id="echoid-s5091" xml:space="preserve">& </s> <s xml:id="echoid-s5092" xml:space="preserve">la <lb/>même extrémité ſe trouve auſſi plus large <lb/>que celle qui adhére au corps de la Come-<lb/>te. </s> <s xml:id="echoid-s5093" xml:space="preserve">Cette comparaiſon eſt ſi juſte qu’el-<lb/>le ne laiſſe aucun lieu de douter que la <lb/>queue des Cometes ne ſoit une véritable <lb/>fumée que cauſe leur embraſement à l’ap-<lb/>proche du Soleil.</s> <s xml:id="echoid-s5094" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5095" xml:space="preserve">Voici une autre cauſe que Mr. </s> <s xml:id="echoid-s5096" xml:space="preserve">de Mai-<lb/>ran aſſigne fort ingénieuſement à la queue <lb/>des Cometes, & </s> <s xml:id="echoid-s5097" xml:space="preserve">que nous allons tâcher de <pb o="380" file="0404" n="405" rhead="DE LA PHILOSOPHIE"/> concilier, autant qu’il eſt poſſible, avec celle <lb/>que Neuton vient de nous fournir. </s> <s xml:id="echoid-s5098" xml:space="preserve">Il re-<lb/>marque que les Cometes en paſſant par <lb/>l’Atmoſphére Solaire en ramaſſent non-ſeu-<lb/>lement des parties qui font corps avec elles, <lb/>eomme il a été dit page 373; </s> <s xml:id="echoid-s5099" xml:space="preserve">mais encore <lb/>d’autres qui ne peuvent d’abord ſuivre la <lb/>Comete, & </s> <s xml:id="echoid-s5100" xml:space="preserve">s’en détachent pour former <lb/>derriére elle une eſpèce de Cone. </s> <s xml:id="echoid-s5101" xml:space="preserve">Cette fi-<lb/>gure, ſelon ce grand Philoſophe, pouſſée <lb/>par la matiére céleſte, prend une route con-<lb/>traire à celle de la Comete, comme la che-<lb/>velure d’une tête, que l’on porteroit contre <lb/>le vent, prendroit une direction contraire à <lb/>cette tête.</s> <s xml:id="echoid-s5102" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5103" xml:space="preserve">Cette comparaiſon n’eſt bonne que pour <lb/>les queues naiſſantes des Cometes, qui n’ont <lb/>pas encore atteint leurs périhélies. </s> <s xml:id="echoid-s5104" xml:space="preserve">Car les <lb/>amas coniques de l’Atmoſphére Solaire que <lb/>les Cometes traînent après elles & </s> <s xml:id="echoid-s5105" xml:space="preserve">le com-<lb/>mencement de leurs fumées étant deux <lb/>cauſes différentes, qui ne laiſſent pas de <lb/>produire les mêmes apparences, les uns & </s> <s xml:id="echoid-s5106" xml:space="preserve"><lb/>les autres doivent faire les mêmes effets ſur <lb/>notre vûe. </s> <s xml:id="echoid-s5107" xml:space="preserve">Mais au-delà de leurs périhélies <lb/>la matiére céleſte dirige vers le Soleil celle <pb o="381" file="0405" n="406" rhead="DE NEUTON."/> qui s’accroche aux Cometes. </s> <s xml:id="echoid-s5108" xml:space="preserve">Ainſi l’on ne <lb/>doit pas s’étonner ſi leurs fumées s’obſer-<lb/>vent beaucoup plus facilement que ce petit <lb/>amas de matiére qu’elles emportent avec <lb/>elles.</s> <s xml:id="echoid-s5109" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5110" xml:space="preserve">La révolution périodique des Cometes <lb/>fait aujourd’hui le principal objet de l’at-<lb/>tention de pluſieurs Philoſophes. </s> <s xml:id="echoid-s5111" xml:space="preserve">Le re-<lb/>tour de celle qui parut en 1682 pourroit ſe <lb/>prédire, ſelon Neuton, pour l’année 1757, <lb/>ou 1758. </s> <s xml:id="echoid-s5112" xml:space="preserve">Il y a tout lieu de croire que c’eſt <lb/>la même qui fut vue en 1607; </s> <s xml:id="echoid-s5113" xml:space="preserve">car il ſe <lb/>trouve ſi peu de différence entre la vîteſ-<lb/>ſe, les nœuds & </s> <s xml:id="echoid-s5114" xml:space="preserve">l’inclinaiſon de l’une & </s> <s xml:id="echoid-s5115" xml:space="preserve"><lb/>de l’autre, qu’on peut la regarder comme <lb/>un pur effet de l’attraction des Planetes & </s> <s xml:id="echoid-s5116" xml:space="preserve"><lb/>des autres Cometes.</s> <s xml:id="echoid-s5117" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5118" xml:space="preserve">Mr. </s> <s xml:id="echoid-s5119" xml:space="preserve">Caſſini a trouvé que preſque tous ces <lb/>Corps paſſagers ont une route différente de <lb/>celle des Planetes. </s> <s xml:id="echoid-s5120" xml:space="preserve">On a ignoré juſqu’ici <lb/>de quelle conſéquence ſont ce nouveau Zo-<lb/>diaque & </s> <s xml:id="echoid-s5121" xml:space="preserve">ce retour périodique des Come-<lb/>tes, pour la conſervation du Genre Humain. <lb/></s> <s xml:id="echoid-s5122" xml:space="preserve">Imaginez-vous, par exemple, que ce ſont des <lb/>Corps fortuits, qui ſe trouvent par hazard <pb o="382" file="0406" n="407" rhead="DE LA PHILOSOPHIE"/> dans notre Ecliptique; </s> <s xml:id="echoid-s5123" xml:space="preserve">quel deſaſtre ne ſeroit-<lb/>ce pas pour notre Terre, ſi malheureuſement <lb/>elle venoit à ſe trouver au même point? <lb/></s> <s xml:id="echoid-s5124" xml:space="preserve">L’idée de deux bombes qui créveroient en <lb/>ſe choquant en l’air, eſt infiniment au-deſ-<lb/>ſous de celle qu’on en doit avoir. </s> <s xml:id="echoid-s5125" xml:space="preserve">Heu-<lb/>reuſement pour nous, on a découvert que <lb/>la plûpart des Cometes dans les nœuds de <lb/>leurs orbites ſont bien moins éloignées du <lb/>Soleil, que ne ſont notre Terre, Venus & </s> <s xml:id="echoid-s5126" xml:space="preserve"><lb/>Mercure. </s> <s xml:id="echoid-s5127" xml:space="preserve">C’eſt ce qui fait toute notre ſû-<lb/>reté, & </s> <s xml:id="echoid-s5128" xml:space="preserve">qui nous fait connoître combien <lb/>nous avons de graces à rendre à Dieu pour <lb/>un ſi grand bienfait.</s> <s xml:id="echoid-s5129" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5130" xml:space="preserve">Les Cometes par leurs retours inopinés <lb/>produiſent quelquefois des Phénoménes <lb/>tout-à-fait ſurprenans, quand on en ignore <lb/>la cauſe. </s> <s xml:id="echoid-s5131" xml:space="preserve">Telle eſt, ſelon Whiſton, l’é-<lb/>clipſe extraordinaire de Soleil dont parle <lb/>Hérodote, & </s> <s xml:id="echoid-s5132" xml:space="preserve">qui arriva au Printems de <lb/>l’année 4334 de la Période Julienne, lorſ-<lb/>que Xerxès partit de Sardes, Capitale de <lb/>la Lydie, où il avoit paſſé l’Hyver. </s> <s xml:id="echoid-s5133" xml:space="preserve">Telle <lb/>eſt auſſi ſelon Wolff, celle de Lune, qui ar-<lb/>riva dans le XV me. </s> <s xml:id="echoid-s5134" xml:space="preserve">Siècle, puiſque ce célèbre <lb/>Mathématicien dans ſes Elémens de Phyſi- <pb o="383" file="0407" n="408" rhead="DE NEUTON."/> que dit, après George Phranza, que ce Phé-<lb/>nomêne n’a pu arriver naturellement, la <lb/>Lune étant alors dans une de ſes quadratu-<lb/>res. </s> <s xml:id="echoid-s5135" xml:space="preserve">Enfin, il en eſt de même de celui dont <lb/>Grégoire Abulpharache, Auteur Arabe, <lb/>fait mention dans ſon Hiſtoire des Dynaſ-<lb/>ties Orientales, où il marque, que ſous <lb/>l’Empereur Héraclius le Soleil parut par <lb/>tout le Monde, pendant trois jours, rouge <lb/>comme du ſang; </s> <s xml:id="echoid-s5136" xml:space="preserve">ce qui toutefois a pu ar-<lb/>river par l’interpoſition de la queue d’une <lb/>Comete.</s> <s xml:id="echoid-s5137" xml:space="preserve"/> </p> </div> <div xml:id="echoid-div195" type="section" level="1" n="44"> <head xml:id="echoid-head71" xml:space="preserve"><emph style="sc">Des fixes.</emph></head> <p> <s xml:id="echoid-s5138" xml:space="preserve">Comme le Syſtême de Neuton paroît ſe <lb/> <anchor type="note" xlink:label="note-0407-01a" xlink:href="note-0407-01"/> contredire à l’égard des Fixes, qui, ſelon lui, <lb/>ſe tirent les unes les autres, & </s> <s xml:id="echoid-s5139" xml:space="preserve">demeurent <lb/>pourtant immobiles, il faut commencer par <lb/>éclaircir ſon ſentiment, & </s> <s xml:id="echoid-s5140" xml:space="preserve">faire voir qu’il <lb/>n’implique aucune contradiction.</s> <s xml:id="echoid-s5141" xml:space="preserve"/> </p> <div xml:id="echoid-div195" type="float" level="2" n="1"> <note position="right" xlink:label="note-0407-01" xlink:href="note-0407-01a" xml:space="preserve">Contra-<lb/>diction <lb/>appa-<lb/>rente du <lb/>Syſtême <lb/>de Neu-<lb/>ton à l’é-<lb/>gard des <lb/>Fixes.</note> </div> <p> <s xml:id="echoid-s5142" xml:space="preserve">La diſtance qu’il y a d’une Fixe à l’autre <lb/>eſt ſi immenſe, que leur chûte ne feroit pas <lb/>ſeulement une lieue en un an. </s> <s xml:id="echoid-s5143" xml:space="preserve">C’eſt ce qu’on <lb/>va voir par le calcul ſuivant. </s> <s xml:id="echoid-s5144" xml:space="preserve">I°. </s> <s xml:id="echoid-s5145" xml:space="preserve">Selon nos <lb/>ſupputations pages 280 & </s> <s xml:id="echoid-s5146" xml:space="preserve">281. </s> <s xml:id="echoid-s5147" xml:space="preserve">les corps pe <pb o="384" file="0408" n="409" rhead="DE LA PHILOSOPHIE"/> ſants, en comptant rondement, tombent ſur <lb/>la ſurface du Soleil de 1260000 pieds, tout <lb/>au moins, pendant la premiére minute. </s> <s xml:id="echoid-s5148" xml:space="preserve">2°. <lb/></s> <s xml:id="echoid-s5149" xml:space="preserve">Selon Huygens les Fixes les plus proches du <lb/>Soleil en ſont éloignées de 28000 ſémi-dia-<lb/>metres de l’orbite de la Terre, ou environ, <lb/>c’eſt-à-dire, de plus de 5600000 ſémi-<lb/>diametres Solaires, dont le quarré eſt <lb/>31360000000000. </s> <s xml:id="echoid-s5150" xml:space="preserve">Donc la Fixe la plus <lb/>proche de cet Aſtre s’avance vers lui de <lb/>{1260000/31360000000000} d’un pied, pendant la premiére <lb/>minute. </s> <s xml:id="echoid-s5151" xml:space="preserve">Mais ſi au lieu de cette fraction <lb/>l’on compte {1/25000000} d’un pied, l’on trou-<lb/>vera pour la premiére année 11000 pieds, <lb/>à peu de choſe près, eu égard à la ſomme <lb/>totale.</s> <s xml:id="echoid-s5152" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5153" xml:space="preserve">Neuton a démontrè dans la XII. </s> <s xml:id="echoid-s5154" xml:space="preserve">Propo-<lb/>ſition du III. </s> <s xml:id="echoid-s5155" xml:space="preserve">Livre de ſa Philoſophie, que <lb/>le centre commun de gravité de notre Syſ-<lb/>tême Planétaire ſeroit eloigné de celui du <lb/>Soleil même, d’un de ſes ſémi-diametres, <lb/>c’eſt-à-dire, de 4000000000 pieds, ou à <lb/>peu près, ſi toutes les Planetes étoient d’un <lb/>côté & </s> <s xml:id="echoid-s5156" xml:space="preserve">cet aſtre de l’autre. </s> <s xml:id="echoid-s5157" xml:space="preserve">Quelle diſpro-<lb/>portion donc entre le dérangement du So- <pb o="385" file="0409" n="410" rhead="DE NEUTON."/> leil, cauſé par les Planetes qui l’environ-<lb/>nent, & </s> <s xml:id="echoid-s5158" xml:space="preserve">celui qui vient de l’attraction de <lb/>la Fixe qui en eſt plus près; </s> <s xml:id="echoid-s5159" xml:space="preserve">j’entends, <lb/>entre 11000 & </s> <s xml:id="echoid-s5160" xml:space="preserve">4000000000 pieds?</s> <s xml:id="echoid-s5161" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5162" xml:space="preserve">Or comme le Soleil ſe trouve tantôt <lb/>d’un côté du centre univerſel de ſon pro-<lb/>pre Syſtême, tantôt de l’autre, & </s> <s xml:id="echoid-s5163" xml:space="preserve">que la <lb/>même choſe arrive à chaque Fixe à l’égard <lb/>des Planetes inconnues qui l’environnent, <lb/>l’on voit clairement que ces corps lumineux <lb/>s’attirent réciproquement par des forces <lb/>beaucoup plus foibles que celles qui les éloi-<lb/>gnent quelquefois les uns des autres. </s> <s xml:id="echoid-s5164" xml:space="preserve">Ces <lb/>viciſſitudes d’approchement & </s> <s xml:id="echoid-s5165" xml:space="preserve">d’éloigne-<lb/>ment ſont donc ce qui retient toujours les <lb/>Fixes dans leur aſſiette naturelle, ſans <lb/>qu’elles puiſſent jamais tomber les unes ſur <lb/>les autres.</s> <s xml:id="echoid-s5166" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5167" xml:space="preserve">Comme quelques Fixes, qui, ſelon les ob-<lb/>ſervations de Montanaro, ont diſparu de-<lb/>puis quelques années, n’ont pas empêché <lb/>celles qui ſont reſtées, d’être ſtables, il <lb/>faut voir quelles peuvent être les cauſes de <lb/>leur diſparition. </s> <s xml:id="echoid-s5168" xml:space="preserve">Le célèbre Wolff en ſpé-<lb/>cifie trois dans ſa Phyſique. </s> <s xml:id="echoid-s5169" xml:space="preserve">1°. </s> <s xml:id="echoid-s5170" xml:space="preserve">Elles peu- <pb o="386" file="0410" n="411" rhead="DE LA PHILOSOPHIE"/> vent, ſelon lui, acquérir du mouvement <lb/>& </s> <s xml:id="echoid-s5171" xml:space="preserve">par-là ſe dérober à nôtre vûe: </s> <s xml:id="echoid-s5172" xml:space="preserve">2°. </s> <s xml:id="echoid-s5173" xml:space="preserve">En <lb/>retombant dans le Chaos elles peuvent cré-<lb/>ver & </s> <s xml:id="echoid-s5174" xml:space="preserve">s’évaporer entiérement; </s> <s xml:id="echoid-s5175" xml:space="preserve">Et 30. </s> <s xml:id="echoid-s5176" xml:space="preserve">elles <lb/>peuvent ou perdre tout-à-fait leur lumiére, <lb/>ou en perdre du moins aſſez pour nous de-<lb/>venir inviſibles.</s> <s xml:id="echoid-s5177" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5178" xml:space="preserve">La premiére de ces cauſes paroît d’autant <lb/>moins vraiſemblable, que l’attraction de <lb/>la Fixe, qui diſparoîtroit, deviendroit plus <lb/>forte & </s> <s xml:id="echoid-s5179" xml:space="preserve">précipiteroit, les unes ſur les au-<lb/>tres, toutes celles qui l’environneroient. <lb/></s> <s xml:id="echoid-s5180" xml:space="preserve">La ſeconde n’eſt pas plus recevable, vû <lb/>que cette prétendue diſſolution changeroit <lb/>la gravitation réciproque des Etoiles les <lb/>plus voiſines de celle qui s’évanouïroit, & </s> <s xml:id="echoid-s5181" xml:space="preserve"><lb/>qu’elles n’auroient plus rien qui les tien-<lb/>droit en équilibre. </s> <s xml:id="echoid-s5182" xml:space="preserve">Ainſi nous adopterons <lb/>la troiſième, parce qu’en ſuppoſant la ſta-<lb/>bilité de la Fixe, elle conſerve toute ſa <lb/>force attractive.</s> <s xml:id="echoid-s5183" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5184" xml:space="preserve">Il faut faire le même jugement des re-<lb/>tours périodiques d’apparition & </s> <s xml:id="echoid-s5185" xml:space="preserve">de diſpa-<lb/>rition des Etoiles, qu’on a obſervées dans <lb/>les Conſtellations de la Baleine, du Cigne <pb o="387" file="0411" n="412" rhead="DE NEUTON."/> & </s> <s xml:id="echoid-s5186" xml:space="preserve">de l’Hydre. </s> <s xml:id="echoid-s5187" xml:space="preserve">Car quoique la partie qui <lb/>nous regarde ſoit plus ou moins lumineuſe, <lb/>& </s> <s xml:id="echoid-s5188" xml:space="preserve">que nous les perdions quelquefois tout-<lb/>à-fait de vûe, elles ne quittent pas pour <lb/>cela leurs places, & </s> <s xml:id="echoid-s5189" xml:space="preserve">leur attraction ne laiſſe <lb/>pas de tenir l’Univers en équilibre.</s> <s xml:id="echoid-s5190" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5191" xml:space="preserve">Il s’enſuit de tout ce raiſonnement, que <lb/>la gravitation réciproque de deux Fixes ne <lb/>diminue pas préciſément en raiſon inverſe <lb/>des quarrés des diſtances, ſur-tout aux en-<lb/>virons du centre commun de leur peſan-<lb/>teur. </s> <s xml:id="echoid-s5192" xml:space="preserve">Il s’enſuit auſſi que la loi de la gra-<lb/>vitation peut varier, comme on le peut <lb/>voir ſur la fin du Chapitre VII. </s> <s xml:id="echoid-s5193" xml:space="preserve">où il eſt parlé <lb/>des différentes ſortes d’attraction. </s> <s xml:id="echoid-s5194" xml:space="preserve">L’action <lb/>de l’Aiman ſur le Fer en raiſon inverſe des <lb/>cubes de ſes diſtances, & </s> <s xml:id="echoid-s5195" xml:space="preserve">celle des corps <lb/>tranſparens ſur les rayons, ou les atomes de <lb/>la lumiére, nous prouvent la réalité auſſi-<lb/>bien que la poſſibilité de la choſe.</s> <s xml:id="echoid-s5196" xml:space="preserve"/> </p> <pb o="388" file="0412" n="413"/> <figure> <image file="0412-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0412-01"/> </figure> </div> <div xml:id="echoid-div197" type="section" level="1" n="45"> <head xml:id="echoid-head72" xml:space="preserve">CHAPITRE VINGT-CINQ</head> <head xml:id="echoid-head73" style="it" xml:space="preserve">Des ſecondes inégalités du mouvement des <lb/>Satellites, & des Phénomênes qui <lb/>en dépendent.</head> <p> <s xml:id="echoid-s5197" xml:space="preserve">APrès avoir rapporté au Chapitre XXI. <lb/></s> <s xml:id="echoid-s5198" xml:space="preserve">diverſes particularités du mouvement <lb/>de la Lune, pour établir la néceſſité de l’at-<lb/>traction, il nous reſte à faire voir dans ce-<lb/>lui-ci que la Théorie de ces inégalités, cau-<lb/>ſées par ce méchaniſme, eſt entiérement <lb/>conforme aux Obſervations.</s> <s xml:id="echoid-s5199" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5200" xml:space="preserve">Neuton aſſigne trois cauſes à ces ſortes <pb o="389" file="0413" n="414" rhead="DE NEUTON."/> d’irrégularités. </s> <s xml:id="echoid-s5201" xml:space="preserve">Il prétend: </s> <s xml:id="echoid-s5202" xml:space="preserve">1°. </s> <s xml:id="echoid-s5203" xml:space="preserve">Que la for-<lb/>ce qui tire la Lune vers la Terre, eſt moin-<lb/>dre que celle qui tire ces deux Planetes <lb/>vers le Soleil: </s> <s xml:id="echoid-s5204" xml:space="preserve">2°<unsure/>. </s> <s xml:id="echoid-s5205" xml:space="preserve">Qu’en conſidérant les <lb/>orbites comme exactement circulaires, la <lb/>force qui tire la Terre vers le Soleil eſt tou-<lb/>jours égale, au lieu que celle qui tire la Lu-<lb/>ne vers cet Aſtre eſt plus grande dans ſa <lb/>Conjonction que dans ſon Oppoſition; </s> <s xml:id="echoid-s5206" xml:space="preserve">Ec <lb/>3°. </s> <s xml:id="echoid-s5207" xml:space="preserve">Que les lignes d’attraction, qui tendent <lb/>vers le Soleil ſe reſſerrent à meſure qu’elles <lb/>en approchent, & </s> <s xml:id="echoid-s5208" xml:space="preserve">augmentent toujours la <lb/>gravitation de la Lune vers la Terre, ſur-<lb/>tout lorſque cette Planete eſt dans ſes Qua-<lb/>dratures.</s> <s xml:id="echoid-s5209" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5210" xml:space="preserve">Si l’on ſuppoſe, par exemple, que la <lb/>Lune ſoit en Conjonction avec le Soleil, <lb/>on verra que, par ſa ſeule gravitation vers <lb/>la Terre, elle décrira en 10 heures 20 <lb/>min. </s> <s xml:id="echoid-s5211" xml:space="preserve">un petit are de 100 parties, dont 1000 <lb/>compoſent le rayon de ſon orbite, & </s> <s xml:id="echoid-s5212" xml:space="preserve">336000 <lb/>font ſa diſtance du Soleil. </s> <s xml:id="echoid-s5213" xml:space="preserve">Or ſi pendant <lb/>ce tems-là la Lune parcourt 100 parties de <lb/>ſon rayon, il faut que (ſuivant la règle du <lb/>mouvement circulaire dont nous avons fait <lb/>mention page 372 lignes 3 & </s> <s xml:id="echoid-s5214" xml:space="preserve">4) comme 1000 <pb o="390" file="0414" n="415" rhead="DE LA PHILOSOPHIE"/> parties de ce dit rayon ſont à 100 (corde <lb/>qui différe très-peu de l’arc en queſtion,) <lb/>de même le nombre de 100 ſoit à 10, chûte <lb/>(uniforme) de la Lune vers la Terre. </s> <s xml:id="echoid-s5215" xml:space="preserve">Mais ſi <lb/>l’on veut déterminer les chûtes de la Terre <lb/>& </s> <s xml:id="echoid-s5216" xml:space="preserve">de la Lune vers le Soleil, il faut ſe con-<lb/>former aux règles données pages 268 & </s> <s xml:id="echoid-s5217" xml:space="preserve">269, <lb/>en diſant par cette opération abregée: </s> <s xml:id="echoid-s5218" xml:space="preserve">1°. <lb/></s> <s xml:id="echoid-s5219" xml:space="preserve">Comme 1. </s> <s xml:id="echoid-s5220" xml:space="preserve">(diſtance de la Lune à la Terre) <lb/>diviſé par le quarré d’un mois périodique, eſt <lb/>à 337 diviſés par le quarré d’une année, ainſi <lb/>10 (chûte de la Lune vers la Terre) ſont à <lb/>19, chûte de la Terre vers le Soleil; </s> <s xml:id="echoid-s5221" xml:space="preserve">2°. </s> <s xml:id="echoid-s5222" xml:space="preserve">Com-<lb/>me le quarré de 336000 eſt au quarré de <lb/>337000, ainſi 19 (chûte de la Terre vers le <lb/>Soleil) ſont à 19 {19/168}, chûte de la Lune vers <lb/>cet Aſtre. </s> <s xml:id="echoid-s5223" xml:space="preserve">Il y a donc {19/168} d’une ſeule par-<lb/>tie du rayon de la Lune, qu’il faut ôter de <lb/>10 parties du même rayon, pour trouver ſa <lb/>véritable chûte vers la Terre, qui ſera ſeu-<lb/>lement de 9 {149/168}, au lieu qu’elle ſeroit de 10, <lb/>ſans l’action particuliére du Soleil ſur ce Sa-<lb/>tellite. </s> <s xml:id="echoid-s5224" xml:space="preserve">Par la même raiſon, la diſtance de <lb/>la Lune à la Terre, qui étoit de 1000 par-<lb/>ties, ſe trouvera de 1000 {19/168}; </s> <s xml:id="echoid-s5225" xml:space="preserve">ce qui con-<lb/>tribuera encore plus à la dimunition de ſa <lb/>peſanteur.</s> <s xml:id="echoid-s5226" xml:space="preserve"/> </p> <pb o="391" file="0415" n="416" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s5227" xml:space="preserve">Tandis que la Lune eſt encore ſi peu é-<lb/>loignée de ſa Conjonction, la force qui la <lb/>pouſſe vers la ligne des Syzygies n’a rien <lb/>de conſidérable; </s> <s xml:id="echoid-s5228" xml:space="preserve">mais elle augmente à me-<lb/>ſure que cette Planete approche de ſon <lb/>Quartier. </s> <s xml:id="echoid-s5229" xml:space="preserve">Lorsqu’au contraire elle y eſt <lb/>parvenue, cette ſeconde force, qui agit en <lb/>même ſens que ſa peſanteur vers la Terre, <lb/>la pouſſe toujours vers notre Globe, juſ-<lb/>qu’à ce qu’étant dans ſon Oppoſition elle <lb/>ne s’en trouve plus éloignée que de 1000 <lb/>parties.</s> <s xml:id="echoid-s5230" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5231" xml:space="preserve">Par le mêlange de ces deux forces, l’éloi-<lb/>gnement de la Lune à la Terre, dans ſes <lb/>Quadratures, ſera de 1023 à 1024 parties, <lb/>en continuant le calcul que nous avons é-<lb/>bauché ci-deſſus, & </s> <s xml:id="echoid-s5232" xml:space="preserve">en ſe ſouvenant de <lb/>l’obliquité naiſſante de la configuration de <lb/>ce Satellite avec le Soleil. </s> <s xml:id="echoid-s5233" xml:space="preserve">Au reſte nous <lb/>n’admettons point encore ici d’excentrici-<lb/>té, autrement l’orbite ſeroit toujours ova-<lb/>le, quoique de largeur & </s> <s xml:id="echoid-s5234" xml:space="preserve">de figure diffé-<lb/>rentes, ſelon la capacité de l’angle compris <lb/>entre les deux lignes des apſides & </s> <s xml:id="echoid-s5235" xml:space="preserve">des <lb/>conjonctions. </s> <s xml:id="echoid-s5236" xml:space="preserve">Car en ſuppoſant cet angle <lb/>Zero, l’excentricité devient plus grande <pb o="392" file="0416" n="417" rhead="DE LA PHILOSOPHIE"/> que s’il étoit de 90 degrés, puisque le <lb/>grand axe au premier cas eſt de 2000 & </s> <s xml:id="echoid-s5237" xml:space="preserve"><lb/>au ſecond de 2047. </s> <s xml:id="echoid-s5238" xml:space="preserve">Il eſt vrai que nos di-<lb/>menſions ne ſont pas les mêmes que celles <lb/>de Neuton; </s> <s xml:id="echoid-s5239" xml:space="preserve">mais comme ce grand Hom-<lb/>me reconnoît, ſur la fin de ſa Préface, que <lb/>ſa Théorie Lunaire a ſes imperfections, <lb/>nous avons cru qu’il ſuffiſoit de nous atta-<lb/>cher à ſes Principes, ſans nous aſſujettir <lb/>à ſes meſures.</s> <s xml:id="echoid-s5240" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5241" xml:space="preserve">Quant aux Satellites qui compoſent l’an-<lb/>neau de Saturne, on trouvera, par un pa-<lb/>reil calcul, que le grand axe de leur Or-<lb/>bite eſt au petit comme 1000 ſont à <lb/>1000 {1/94}, & </s> <s xml:id="echoid-s5242" xml:space="preserve">que par conſéquent cette même <lb/>Orbite eſt 2250 fois moins ovale que celle <lb/>de la Lune.</s> <s xml:id="echoid-s5243" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5244" xml:space="preserve">Mais pour raſſûrer ceux qui pour-<lb/>roient douter que notre calcul ſoit con-<lb/>forme aux Obſervations, revenons aux <lb/>excentricités, que nous n’avons fait <lb/>qu’indiquer ci-devant, & </s> <s xml:id="echoid-s5245" xml:space="preserve">faiſons voir, par <lb/>une nouvelle ſupputation, qu’elles s’accor-<lb/>dent avec les diametres apparens & </s> <s xml:id="echoid-s5246" xml:space="preserve">les <lb/>mouvemens horaires de la Lune.</s> <s xml:id="echoid-s5247" xml:space="preserve"/> </p> <pb o="393" file="0417" n="418" rhead="DE NEUTON."/> <p> <s xml:id="echoid-s5248" xml:space="preserve">Lorsque les Apſides tombent dans les <lb/>Syzygies, la plus grande excentricité de <lb/>l’Orbite étant, ſelon les plus fameux Aſtro-<lb/>nomes, à la diſtance médiocre de la Lune <lb/>comme 67 ſont à 1000, on conçoit bien <lb/>que l’Apogée eſt éloigné de 1067 de la <lb/>Terre, & </s> <s xml:id="echoid-s5249" xml:space="preserve">le Périgée de 933. </s> <s xml:id="echoid-s5250" xml:space="preserve">Par la même <lb/>raiſon, quand les apſides ſont aux quadratu-<lb/>res, l’excentricité en queſtion n’étant que <lb/>de 44, & </s> <s xml:id="echoid-s5251" xml:space="preserve">la diſtance médiocre de 1024, <lb/>celle de l’Apogée à la Terre doit être de <lb/>1068, & </s> <s xml:id="echoid-s5252" xml:space="preserve">celle du Périgée de 980.</s> <s xml:id="echoid-s5253" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5254" xml:space="preserve">Or le diametre apparent de la Lune dans <lb/>ſon Apogée eſt, (à compter rondement) de <lb/>29 min. </s> <s xml:id="echoid-s5255" xml:space="preserve">40 ſec. </s> <s xml:id="echoid-s5256" xml:space="preserve">& </s> <s xml:id="echoid-s5257" xml:space="preserve">ne varie jamais qu’entre <lb/>1067 & </s> <s xml:id="echoid-s5258" xml:space="preserve">1068. </s> <s xml:id="echoid-s5259" xml:space="preserve">Au contraire il varie tou-<lb/>jours dans ſon Périgée depuis 34 min. </s> <s xml:id="echoid-s5260" xml:space="preserve">juſ-<lb/>qu’à 32 {1/2}, c’eſt à-dire en raiſon inverſe de <lb/>933 à 980. </s> <s xml:id="echoid-s5261" xml:space="preserve">Donc les diſtances de l’Apogée <lb/>& </s> <s xml:id="echoid-s5262" xml:space="preserve">du Périgée ſont préciſément, ſuivant no-<lb/>tre calcul, en raiſon inverſe des diametres <lb/>apparens, qu’on a trouvés juſqu’ici par les <lb/>Obſervations.</s> <s xml:id="echoid-s5263" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5264" xml:space="preserve">Le mouvement horaire ne prouve pas <pb o="394" file="0418" n="419" rhead="DE LA PHILOSOPHIE"/> moins l’exactitude de ces rapports. </s> <s xml:id="echoid-s5265" xml:space="preserve">Car <lb/>tant que les aires décrites ſont égales, ces <lb/>mouvemens ſont par-tout en raiſon inverſe <lb/>des quarrés des diſtances. </s> <s xml:id="echoid-s5266" xml:space="preserve">Ainſi comme le <lb/>quarré de 933 eſt à 29 min. </s> <s xml:id="echoid-s5267" xml:space="preserve">20 ſec. </s> <s xml:id="echoid-s5268" xml:space="preserve">(horai-<lb/>re de l’Apogée) de même le quarré de 1067 <lb/>eſt, ſelon les Obſervations, à 38 minutes, <lb/>horaire du Périgée dans les Syzygies. </s> <s xml:id="echoid-s5269" xml:space="preserve">Et <lb/>ſi le quarré de 980 donne 29 min. </s> <s xml:id="echoid-s5270" xml:space="preserve">20 ſec.</s> <s xml:id="echoid-s5271" xml:space="preserve">, <lb/>celui de 1067 en donnera, conformément <lb/>aux Obſervations, 35 d’horaire du Périgée <lb/>dans les Quadratures.</s> <s xml:id="echoid-s5272" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5273" xml:space="preserve">On voit auſſi que, par les mêmes loix de <lb/>la gravitation vers le Soleil, la Lune qui <lb/>n’eſt pas dans l’Ecliptique, s’en doit appro-<lb/>cher juſqu’aux Syzygies; </s> <s xml:id="echoid-s5274" xml:space="preserve">parce que, ſelon <lb/>l’angle de ſon orbite avec la nôtre, ſa Lati-<lb/>tude devient toujours moindre qu’elle ne <lb/>devroit être. </s> <s xml:id="echoid-s5275" xml:space="preserve">Cet angle diminue donc à <lb/>chaque inſtant, & </s> <s xml:id="echoid-s5276" xml:space="preserve">au lieu que dans les <lb/>Quadratures, près des nœuds, il étoit de 5 <lb/>degrés 18 min. </s> <s xml:id="echoid-s5277" xml:space="preserve">il n’eſt que de 5 degrés dans <lb/>les Conjonctions comme dans les Oppo-<lb/>ſitions; </s> <s xml:id="echoid-s5278" xml:space="preserve">ce qui rend la ſurface de l’orbite <lb/>curviligne. </s> <s xml:id="echoid-s5279" xml:space="preserve">Si au contraire les nœuds ſe <lb/>trouvent dans les Syzygies, l’action du So- <pb o="395" file="0419" n="420" rhead="DE NEUTON."/> leil ne diminue point les Latitudes, l’angle <lb/>en queſtion demeure toujours le même, & </s> <s xml:id="echoid-s5280" xml:space="preserve"><lb/>l’orbite devient une ſurface plane. </s> <s xml:id="echoid-s5281" xml:space="preserve">Quant <lb/>à leur mouvement, il eſt alors d’une extrê-<lb/>me lenteur, parce que l’action du Soleil, <lb/>qui eſt, pendant un tems aſſez conſidérable, <lb/>preſque parallèle à la diſtance de la Lune <lb/>& </s> <s xml:id="echoid-s5282" xml:space="preserve">de la Terre, ne ſe ralentit guère; </s> <s xml:id="echoid-s5283" xml:space="preserve">mais <lb/>il n’en eſt pas de même des Quadratures, <lb/>où ils rétrogradent conſidérablement. </s> <s xml:id="echoid-s5284" xml:space="preserve">Car <lb/>la Lune les rencontre chaque mois environ <lb/>trois heures plutôt, ſur-tout au milieu de <lb/>ſon Croiſſant auſſi-bien que de ſon Decours, <lb/>où la différence de ſa gravitation & </s> <s xml:id="echoid-s5285" xml:space="preserve">de cel-<lb/>le de la Terre vers le Soleil augmente & </s> <s xml:id="echoid-s5286" xml:space="preserve"><lb/>diminue plus vîte que par-tout ailleurs.</s> <s xml:id="echoid-s5287" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5288" xml:space="preserve">La préceſſion des Equinoxes eſt encore <lb/> <anchor type="note" xlink:label="note-0419-01a" xlink:href="note-0419-01"/> auſſi-bien que la rétrogradation des nœuds <lb/>un effet de ces inégalités, quoique beau-<lb/>coup plus lente, parce que la quantité de la <lb/>matiére terreſtre, qui eſt ſous l’Equateur, <lb/>différe très-peu de celle des Méridiens, & </s> <s xml:id="echoid-s5289" xml:space="preserve"><lb/>que ce petit excédant, ſous l’Equinoxiale, <lb/>tient la place d’un Satellite, ou d’un anneau <lb/>tel que celui de Saturne.</s> <s xml:id="echoid-s5290" xml:space="preserve"/> </p> <div xml:id="echoid-div197" type="float" level="2" n="1"> <note position="right" xlink:label="note-0419-01" xlink:href="note-0419-01a" xml:space="preserve">Mouve-<lb/>ment <lb/>des Po-<lb/>les de la <lb/>Terre, <lb/>p. 295.</note> </div> <pb o="396" file="0420" n="421" rhead="DE LA PHILOSOPHIE"/> <p> <s xml:id="echoid-s5291" xml:space="preserve">Ii y a quelques autres cauſes qui rendent <lb/>le mouvement des Satellites un peu irrégu-<lb/>lier, mais dont l’effet n’eſt guére conſidé-<lb/>rable que par rapport à eux. </s> <s xml:id="echoid-s5292" xml:space="preserve">On a remar-<lb/>qué que l’Apogée du premier & </s> <s xml:id="echoid-s5293" xml:space="preserve">du quatriè-<lb/>me Satellites de Jupiter eſt conſtamment le <lb/>même que celui de cette Planete, & </s> <s xml:id="echoid-s5294" xml:space="preserve">que <lb/>ce n’eſt qu’après pluſieurs révolutions de <lb/>celle-ci que l’orbite du troiſième ſe retrou-<lb/>ve à la même inclinaiſon. </s> <s xml:id="echoid-s5295" xml:space="preserve">Auſſi les nœuds <lb/>de ces quatre petites Etoiles n’ont-ils point <lb/>varié, du moins depuis plus de cent ans <lb/>qu’il y a qu’on les obſerve. </s> <s xml:id="echoid-s5296" xml:space="preserve">En un mot, <lb/>toutes ces inégalités n’approchent pas de <lb/>celles de la Lune, ſans parler de ſa rota-<lb/>tion, qui différe conſidérablement de celle <lb/>qu’on a cru appercevoir dans les autres Sa-<lb/>tellites.</s> <s xml:id="echoid-s5297" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5298" xml:space="preserve">Après avoir parcouru tous ces différens <lb/>mouvemens, nous ne pouvons guère nous <lb/>diſpenſer d’en indiquer la cauſe. </s> <s xml:id="echoid-s5299" xml:space="preserve">Elle n’eſt <lb/>pas ſi obſcure que bien des gens pourroient <lb/>ſe l’imaginer. </s> <s xml:id="echoid-s5300" xml:space="preserve">La voici en peu de mots: <lb/></s> <s xml:id="echoid-s5301" xml:space="preserve">le nombre & </s> <s xml:id="echoid-s5302" xml:space="preserve">la proximité des Satellites <lb/>font que leur attraction réciproque l’em-<lb/>porte beaucoup ſur l’action du Soleil. </s> <s xml:id="echoid-s5303" xml:space="preserve">Par- <pb o="397" file="0421" n="422" rhead="DE NEUTON."/> là il eſt aiſé de juger que l’anneau de Satur-<lb/>ne doit extrêmement déranger les Satelli-<lb/>tes qui font leurs revolutions autour de lui, <lb/>ſur-tout les plus petits & </s> <s xml:id="echoid-s5304" xml:space="preserve">les plus excentri-<lb/>ques. </s> <s xml:id="echoid-s5305" xml:space="preserve">On conçoit pareillement que l’attrac-<lb/>tion de cet anneau doit retarder conſidéra-<lb/>blement la chûte des corps ſur la ſurface de <lb/>Saturne. </s> <s xml:id="echoid-s5306" xml:space="preserve">Enfin, l’exemple du flux & </s> <s xml:id="echoid-s5307" xml:space="preserve">du re-<lb/>flux de la Mer ne nous permet pas de dou-<lb/>ter de cette vérité. </s> <s xml:id="echoid-s5308" xml:space="preserve">Car il s’enſuit de tout ce <lb/>qui a été dit au Chapitre XVIII.</s> <s xml:id="echoid-s5309" xml:space="preserve">, que la <lb/>peſanteur du centre de la Terre vers la Lu-<lb/>ne eſt toujours la même; </s> <s xml:id="echoid-s5310" xml:space="preserve">au lieu que les <lb/>eaux qui ſe trouvent entre ce centre & </s> <s xml:id="echoid-s5311" xml:space="preserve"><lb/>cette Planete, y ſont attirées avec plus de <lb/>vîteſſe, que lorſque le tournoyement jour-<lb/>nalier de la Terre les a fait paſſer au point <lb/>diamétralement oppoſé.</s> <s xml:id="echoid-s5312" xml:space="preserve"/> </p> <p> <s xml:id="echoid-s5313" xml:space="preserve">Voilà ce que nous avions à dire des princi-<lb/>paux effets de l’Attraction Neutonienne, telle <lb/>que ce fameux Mathématicien l’a imaginée, <lb/>en la regardant comme la cauſe unique de la <lb/>réfraction de la Lumiére, & </s> <s xml:id="echoid-s5314" xml:space="preserve">comme le premier <lb/>reſſort du Méchaniſme de l’Univers. </s> <s xml:id="echoid-s5315" xml:space="preserve">Il eſt <lb/>vrai qu’en qualité de Philoſophe, il lui aſ- <pb o="398" file="0422" n="423" rhead="DE LA PHILOSOPHIE"/> ſigne un empire bien plus vaſte dans la Na-<lb/>ture, en réduiſant ſous ſes loix toutes les <lb/>opérations de la chaleur, le mêlange des <lb/>Mixtes, leur décompoſition, & </s> <s xml:id="echoid-s5316" xml:space="preserve">l’électri-<lb/>cité qu’on remarque dans l’ambre, le dia-<lb/>mant, la cire d’Eſpagne & </s> <s xml:id="echoid-s5317" xml:space="preserve">autres corps de <lb/>cette nature; </s> <s xml:id="echoid-s5318" xml:space="preserve">mais nous n’entrerons point <lb/>dans ce détail, parce qu’il nous meneroit <lb/>trop loin, & </s> <s xml:id="echoid-s5319" xml:space="preserve">qu’il n’a aucun rapport à la <lb/>Géométrie, que nous n’avons point perdu <lb/>de vûe dans tout cet Ouvrage. </s> <s xml:id="echoid-s5320" xml:space="preserve">Nous <lb/>le finirons donc ſans parler de la dou-<lb/>ble réfraction du Cryſtal d’Iſlande, de la <lb/>diminution de la denſité & </s> <s xml:id="echoid-s5321" xml:space="preserve">de l’élaſticité de <lb/>l’air, de la ténacité des milieux viſqueux, <lb/>dans leſquels peut ſe mouvoir un corps <lb/>quelconque, ni de pluſieurs autres matiéres <lb/>ſemblables. </s> <s xml:id="echoid-s5322" xml:space="preserve">C’eſt par la même raiſon, que <lb/>nous n’avons touché que legérement cer-<lb/>taines choſes, comme la préceſſion des E-<lb/>quinoxes & </s> <s xml:id="echoid-s5323" xml:space="preserve">le retour périodique des Ma-<lb/>rées; </s> <s xml:id="echoid-s5324" xml:space="preserve">Phénomênes où il faut qu’il y ait en-<lb/>core quelqu’autre cauſe mixte, qui a été <lb/>inconnue juſqu’ici. </s> <s xml:id="echoid-s5325" xml:space="preserve">Car ſi l’on ignore ce <lb/>qui fait l’égalité du mouvement des points <lb/>Equinoxiaux de Jupiter & </s> <s xml:id="echoid-s5326" xml:space="preserve">des nœuds de ſes <pb o="399" file="0423" n="424" rhead="DE NEUTON."/> Satellites, l’on ne ſait pas plus pourquoi le <lb/>flux & </s> <s xml:id="echoid-s5327" xml:space="preserve">le reflux de la Mer ſuivent plutôt <lb/>le moyen que le vrai mouvement de la <lb/>Lune. </s> <s xml:id="echoid-s5328" xml:space="preserve">Du moins faut-il convenir, que la <lb/>concurrence des actions du Soleil & </s> <s xml:id="echoid-s5329" xml:space="preserve">d’un <lb/>Satellite ſur la Planete principale dans les <lb/>Sizygies, ou leur différence dans les Qua-<lb/>dratures, ne ſauroit rendre raiſon de ces <lb/>deux expériences.</s> <s xml:id="echoid-s5330" xml:space="preserve"/> </p> <figure> <image file="0423-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0423-01"/> </figure> <pb file="0424" n="425" rhead="ERRATA."/> <p> <s xml:id="echoid-s5331" xml:space="preserve">Le Lecteur eſt prié de corriger les en-<lb/>droits marqués ci-deſſous, ſans quoi il ne <lb/>pourroit pas quelquefois trouver le ſens de <lb/>l’Auteur.</s> <s xml:id="echoid-s5332" xml:space="preserve"/> </p> <note position="right" xml:space="preserve"> <lb/>Page. # Ligne. # Faute. # Correction. <lb/>4 # 6 # un fauſſe # une fauſſe <lb/>23 # 5 # le Nature, # la Nature, <lb/>29 # 6 # yon, # point de virgule. <lb/>46 # 2 # A, B, C. # A, B. <lb/>53 # 1 # B, A, C. # B & C. <lb/>73 # dern. # huit # quatre <lb/>74 # 2 # quatre # huit <lb/>78 # 20 # à deux # à huit <lb/>79 # 8 # deux pieds # huit pieds; <lb/>105 # 15 # Or qu’elle # Or quelle <lb/>128 # dern. # La rayon # Le rayon <lb/>148 # 3 # de courbes # de droites infiniment \\ petites <lb/>182 # # Dans la Planche \\ au-deſſus de Si, {3/4} \\ & au-deſſus de La, {1/3} # {3/5} \\ {2/3} <lb/>192 # 4 # récipent # récipient <lb/>198 # 15 # ſe meuvent & agiſſent # ſe mouvoient & agiſ-ſoient <lb/>237 # 10 # qu’el # qu’elle <lb/>246 # 4 # S, B, A. S, H, B. # S, B, A. S, C, B. <lb/>259 # 5 # dans Jupiter # dans les Satellites de \\ Jupiter <lb/>267 # 23 # la Soleil # le Soleil <lb/>269 # 1 # elliplique # elliptique <lb/>281 # 11 # 27 # 24 <lb/>289 # 1 # 27 # 24 <lb/>289 # 3 # plus denſe # Après denſe ajoutez une \\ virgule & ces mots: & \\ que le diametre du \\ Soleil ſurpaſſe ſeu- \\ lement 97 fois & de- \\ mi celui de la Terre. <lb/>289 # 6 # 413 # 350 <lb/>295 # dern. # Chap. ſuivant. # Chap. XXV. <lb/></note> <pb file="0425" n="426"/> <pb file="0426" n="427"/> <pb file="0427" n="428"/> <pb file="0428" n="429"/> </div></text> </echo>