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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/texts/XML/archimedes/it/volta_nuoMemLetTerz_922_it_1795.xml Fri Dec 07 17:05:22 2012 +0100 @@ -0,0 +1,2215 @@ +<?xml version="1.0" encoding="UTF-8"?> +<archimedes> + <info> + <author>Volta, Alessandro</author> + <title>Nuova Memoria sull'Elettricita Animale - Lettera Terza</title> + <date>1795</date> + <place>Como</place> + <translator/> + <lang>it</lang> + <cvs_file>volta_nuoMemLetTerz_922_it_1795.xml</cvs_file> + <cvs_version/> + <locator>922.xml</locator> + <echodir>/permanent/volta_collected_papers/volta_nuoMemLetTerz_922_it_1795</echodir> + </info> + <text> + <front> + <section> + <pb/> + <p id="N10018" type="head"> + <s id="N1001A"> + LETTERA TERZA + <lb/> + DEL SIG. CAV. + <lb/> + DON ALESSANDRO VOLTA + <lb/> + P. PROFESSORE, EC. + <lb/> + AL SIG. AB. + <lb/> + ANTON MARIA VASSALLI + <lb/> + PROFESSORE DI FISICA A TORINO, EC. + <lb/> + SULL’ELETTRICITÀ ANIMALE. + </s> + </p> + <p id="N1002A" type="main"> + <s id="N1002C"> + <emph type="italics"/>Como, 27 Ottobre 1795. <emph.end type="italics"/> + </s> + </p> + </section> + <section type="editorcomment"> + <p id="N10036" type="head"> + <s id="N10038"> + FONTI. + </s> + </p> + <p id="N1003A" type="main"> + <s id="N1003C"> + STAMPATE. + <lb/> + Br. Ann. T. XI. 1796. pg. 84. + <lb/> + Ant. Coll. T. II. P. I. pg. 230. + </s> + </p> + <p id="N10042" type="main"> + <s id="N10044"> + MANOSCRITTE. + <lb/> + Copia presso Ac. Sc. Torino. (B. XI.8). + <lb/> + Cart. Volt.: J 27; J 32; J 49; L 14; + <lb/> + L 15. + </s> + </p> + <p id="N1004C" type="main"> + <s id="N1004E"> + OSSERVAZIONI. + <lb/> + TITOLO: Da Br. Ann. + <lb/> + DATA: dalla copia presso Acc. Sc. Tor. + <lb/> + in Br. Ann. trovasi 24 ottobre 1795. + </s> + </p> + <p id="N10056" type="main"> + <s id="N10058"> + J 27 contiene un abbozzo della Scala dei poteri elettromotori analoga a quella con-<lb/> + tenuta in questo numero. + </s> + <lb/> + <s id="N1005D"> + J 32. Prime minute più ristrette da cui togliesi una nota. + </s> + <lb/> + <s id="N10060"> + L. 14. Vari fogli che nel loro assieme formano quasi tutta la lettera. + </s> + <lb/> + <s id="N10063"> + L. 15. Vari fogli che contengono le note. + </s> + <lb/> + <s id="N10066"> + Un brano di questa lettera leggesi nel « Manuale della letteratura italiana » compi-<lb/> + lato dai professori A. D’Ancona ed O. Bacci (Firenze, 1897, Barbera), Vol. IV, pag. 562. + </s> + </p> + <pb/> + <p id="N1006B" type="main"> + <s id="N1006D"> + [Empty Page] + </s> + </p> + </section> + <section> + <pb/> + <p id="N10071" type="head"> + <s id="N10073"> + LETTERA TERZA. + </s> + </p> + </section> + </front> + <body> + <chap> + <p id="N10077" type="main"> + <s id="N10079"> + <emph type="italics"/>da Como li 27 8bre 1795. <emph.end type="italics"/> + </s> + </p> + <p id="N10081" type="main"> + <s id="N10083"> + Dopo le due lunghe lettere da me scrittevi, illustre Accademico e Collega, + <lb/> + ha già un anno e mezzo, e inserite ne’ Giornali del nostro comune amico Dr. BRU-<lb/> + GNATELLI, sul soggetto della pretesa <emph type="italics"/>Elettricità animale<emph.end type="italics"/>, propria cioè degli or-<lb/> + gani, in cui si suppone una carica o sbilancio qualsiasi di fluido elettrico, quale + <lb/> + elettricità organica ideata dal valente Fisico e Professore di Anatomia Dr. GAL-<lb/> + VANI dietro le bellissime sue sperienze e scoperte invero mirabili ammisi io + <lb/> + pure per qualche tempo, ma presto cominciai a rivocare in dubbio, e finalmente . + <lb/> + dovetti con dispiacere riconoscere e dichiarare per insussistente [l]: dopo che + <lb/> + dalla maggior parte de’ Fisici, massime oltramontani, erasi adottata la mia opi-<lb/> + nione, esposta nelle mentovate lettere e in altre memorie e scritti antecedenti, + <lb/> + che riconosce bensì nelle sperienze di cui si tratta, una vera elettricità [2], + <lb/> + ma elettricità meramente artificiale ed estrinseca, mossa cioè da conduttori + <lb/> + acconciamente applicati; risvegliossi di nuovo qui in Italia, e crebbe più che + <lb/> + mai il fermento delle contrarie opinioni in occasione che si pubblicarono + <lb/> + nell’autunno scorso con un opuscolo del Dr. EUSEBIO VALLI delle nuove interes-<lb/> + santi sperienze in soccorso del primo ormai abbandonato sistema. + </s> + <s id="N100A9"> + Invero tali + <lb/> + sperienze non solo comparvero favorevoli e consentanee all’ipotesi di un’elet-<lb/> + tricità propria e attiva degli organi animali, di una vera carica o sbilancio + <lb/> + di fluido elettrico tra nervi e muscoli dipendenti, o tra l’interno e l’esterno + <lb/> + di essi muscoli, la qual carica o sbilancio producasi naturalmente per le forze + <lb/> + della vita, e manifestisi anche negli animali trucidati, e ne’ membri recisi, + <lb/> + finchè vi dura un certo grado di vitalità; non solo, dico, parvero tali sperienze + <lb/> + favorire grandemente siffatta ipotesi, altronde bella e seducente, proposta dal + <lb/> + prefato illustre Professor Bolognese adottata e difesa contro le forti mie obbie-<lb/> + zioni da ALDINI suo nipote e collega, e da altri seguaci non pochi; ma sembra-<lb/> + rono dimostrarla evidentemente, e porla fuori d’ogni dubbio; e sì ne imposero + <lb/> + a molti, e tiraronli di nuovo agli stendardi Galvaniani quando già soscritto + <lb/> + aveano, o stavano per soscrivere alla mia sentenza affatto diversa. + </s> + </p> + <p id="N100C3" type="main"> + <s id="N100C5"> + Questa, che sostenni già con molti argomenti e prove sperimentali, e che + <lb/> + <pb pagenum="290"/> + sostengo ancora, riduce tutto ad un giuoco de’ conduttori in conveniente + <lb/> + modo applicati, alla virtù cioè che loro attribuisco, o dirò meglio di cui ho sco-<lb/> + perto esser essi dotati, d’impellere e smuovere, ove si affrontino o combacino + <lb/> + alcuni di classe o di specie diversa, il fluido elettrico: dal che poi viene che se + <lb/> + concorrano tre, o più, tutti diversi a compiere il circolo conduttore, se p. e. + <lb/> + a due metalli, argento e ferro, piombo ed ottone, argento e zinco ecc. sia in-<lb/> + terposto uno o più conduttori non metallici, della classe cioè da me chiamata + <lb/> + de’ <emph type="italics"/>conduttori umidi<emph.end type="italics"/>, perchè o fluidi in tutta la massa, o contenenti qualche + <lb/> + umore, fra i quali i corpi animali e tutte le loro parti fresche e succose; se, dico, + <lb/> + un conduttore di questa 2<emph type="sup"/>a<emph.end type="sup"/> classe trovisi di mezzo e a contatto di due di + <lb/> + quella 1<emph type="sup"/>a<emph.end type="sup"/>, di due metalli diversi, ne viene che si determini una corrente continua + <lb/> + di fluido elettrico, secondo che l’azione su di esso in virtù di tali combaciamenti + <lb/> + prevale da una parte o dall’altra + <note n="a"> + <p id="N100F9" type="main"> + <s id="N100FC"> + Ciò basta per mostrare quanto sia diversa dalla pretesa elettricità animale, dalle + <lb/> + idee di GALVANI e suoi seguaci, quell’elettricità che sostengo io; la quale non suppone alcuna + <lb/> + carica o sbilancio, e conseguente scarica degli organi animali, e neppure carica o scarica pro-<lb/> + priamente detta de’ conduttori applicati, ma una circolazione, ossia corrente continua di + <lb/> + fluido elettrico, cagionata e mantenuta da una forza arcana, che risulta dal combaciamento + <lb/> + di conduttori diversi fra loro; i quali in simili circostanze sono qualche cosa più che semplici + <lb/> + deferenti, facendola da veri <emph type="italics"/>eccitatori<emph.end type="italics"/> o <emph type="italics"/>motori<emph.end type="italics"/>. + </s> + </p> + </note> + . + </s> + </p> + <p id="N10119" type="main"> + <s id="N1011B"> + Tale mia spiegazione venendo confermata da innumerabili sperienze va-<lb/> + riate in molte maniere, come ho fatto vedere in diversi scritti, e bastando solo + <lb/> + a render ragione di tanti fenomeni e apparenti anomalie in ogni altra guisa + <lb/> + inesplicabili, ho dovuto indurne che la pretesa elettricità animale, propria e + <lb/> + attiva degli organi, non ha fondamento, molto meno prove decisive che la + <lb/> + dimostrino: che conseguentemente gli organi animali in simili sperienze vo-<lb/> + gliono risguardarsi come puramente <emph type="italics"/>passivi<emph.end type="italics"/>, come semplici <emph type="italics"/>elettroscopj<emph.end type="italics"/> di un + <lb/> + genere particolare; e che debbono invece aversi per <emph type="italics"/>attivi<emph.end type="italics"/> i Conduttori appli-<lb/> + cati al mutuo combaciamento, purchè diversi; e tanto appunto più attivi ed + <lb/> + efficaci quanto più differiscono tra loro sotto certi rapporti. + </s> + </p> + <p id="N10141" type="main"> + <s id="N10143"> + Così ho conchiuso sono già tre anni circa [3], e così sostengo ancora, torno + <lb/> + a ripetere, a fronte delle nuove mentovate sperienze del Dr. VALLI, ed altre + <lb/> + di simil fatta; le quali con tutta l’apparenza favorevole alla teoria di GALVANI, + <lb/> + per cui furono avidamente abbracciate da’ suoi partigiani, che ne menarono + <lb/> + gran rumore; vedremo che esaminate in tutte le loro circostanze e aggiunti, + <lb/> + moltiplicate e variate come si conviene, comprovano anzi evidentemente l’opi-<lb/> + nione mia, e non lasciano a quell’altra più alcun appiglio o risorsa. + </s> + </p> + <p id="N10151" type="main"> + <s id="N10153"> + Io non so se tra quelli che stanno ancora per l’elettricità animale vera e + <lb/> + propria nel senso sopra spiegato, vi troviate ancor voi, mio caro professore, + <lb/> + a cui è piaciuto sempre di ampliare, forse anche troppo, l’impero dell’elettri-<lb/> + <pb pagenum="291"/> + cismo, e sottomettere alla sua influenza il più gran numero possibile di feno-<lb/> + meni naturali, e in particolare alcuni dell’economia vegetabile ed animale, + <lb/> + e che anzi prevenuto vi mostraste in alcune operette dalle idee di un’elettri-<lb/> + cità spontanea negli animali, e molto vi studiaste di comprovarla con esperienze + <lb/> + varie, alcune delle quali veramente curiose, e ciò molto innanzi che fosser note + <lb/> + quelle affatto sorprendenti di GALVANI: non so bene qual impressione vi abbian + <lb/> + fatta dapprima tali sperienze del Prof.<emph type="sup"/>re<emph.end type="sup"/> Bolognese; in seguito le mie molto + <lb/> + più estese e variate, dalle quali ho tratto conseguenze ben diverse e in nulla + <lb/> + favorevoli alla supposta elettricità animale, e finalmente le nuove di VALLI + <lb/> + ed altre analoghe, con cui si è preteso di ristabilirla inconcussamente. + </s> + <s id="N10176"> + So che + <lb/> + queste ultime ne hanno imposto a molti, come già dissi; i quali veggendo + <lb/> + ottenersi in qualche modo le convulsioni nelle rane di fresco preparate e sensi-<lb/> + bilissime, anche senza l’intervento di alcun conduttore metallico o carbone, + <lb/> + ciò ch’io avea pronunciato non succedere mai [4], perchè non m’era fino allora + <lb/> + riuscito (e infatti non riesce che difficilmente) non cercarono dippiù per darla + <lb/> + vinta ai sostenitori dell’elettricita animale in senso proprio, della pretesa ca-<lb/> + rica cioè o sbilancio di fluido elettrico tra nervi e rispettivi muscoli, o tra l’in-<lb/> + terno e l’esterno di essi muscoli. + </s> + <s id="N10188"> + Eppure in niun modo vien provata da tali + <lb/> + sperienze siffatta elettricità animale, come mi propongo di far vedere: esse + <lb/> + mostrano soltanto, che sono io andato troppo innanzi asserendo, che non si + <lb/> + potrebbe mai coll’applicazione di soli conduttori umidi, ossia di 2<emph type="sup"/>a<emph.end type="sup"/> classe, + <lb/> + senza l’intervento cioè di alcun metallo o conduttore di 1<emph type="sup"/>a<emph.end type="sup"/> classe, eccitare le + <lb/> + convulsioni nelle rane comunque preparate e facilissime a risentirsi. + </s> + <s id="N101A0"> + Ecco in + <lb/> + che debbo ritrattarmi, ossia correggere le espressioni troppo generali da me + <lb/> + avanzate: non già riguardo alla proposizione capitale, che ho sostenuta, e + <lb/> + che sostengo ancora, cioè che la mossa al fluido elettrico vien data, non già + <lb/> + dagli organi animali in cui trovisi esso fluido, come suppongono i Galvaniani, + <lb/> + in uno stato di carica o di sbilancio; bensì da una forza che risulta dal comba-<lb/> + ciamento di conduttori dissimili che entrano nel circolo: che insomma ella è + <lb/> + anche in tali sperienze, in cui non s’adoprano metalli, un’elettricità artificiale + <lb/> + eccitata da causa estrinseca, ossia movente esterno, e in niun modo da prin-<lb/> + cipio o forza interna degli organi animali, de’ nervi e muscoli. + </s> + </p> + <p id="N101B4" type="main"> + <s id="N101B6"> + Per venire ora più davvicino a codeste sperienze, non mi fa stupore che + <lb/> + abbian sorpreso e tirato molti, che prima ne dubitavano, a credere alla supposta + <lb/> + elettricità animale, e a dichiararsi apertamente per essa; tutti quelli cioè, che + <lb/> + non sono andati più innanzi, e non han fatto il dovuto riflesso alle circostanze. + </s> + <lb/> + <s id="N101BF"> + Senza questo dovettero restare sedotti (e chi poteva non esserlo a prima + <lb/> + giunta?) dal vedere eccitarsi delle contrazioni più o meno forti in tutti i mu-<lb/> + scoli delle gambe posteriori di una rana compitamente preparata, con ripie-<lb/> + gare semplicemente una di esse gambe, e addurla al contatto de’ nervi ischia-<lb/> + tici ossia crurali, oppur de’ muscoli del dorso. + </s> + </p> + <pb pagenum="292"/> + <p id="N101CB" type="main"> + <s id="N101CD"> + Codesta è l’esperienza principale, con cui crede VALLI, e credono i Galva-<lb/> + niani tutti vecchj e nuovi, di aver vinta la causa contro di me, e fino di avermi + <lb/> + ridotto al silenzio. + </s> + <s id="N101D3"> + Altre sperienze consimili son quelle di tenere sospesa pe’ + <lb/> + piedi la rana con una mano, e con un dito dell’altra o colla lingua toccare i + <lb/> + nervi crurali pendenti, o la porzione di spina, che ad essi si è lasciata attaccata; + <lb/> + di tener in egual modo sospesa la rana per una gamba, far passare detta spina, + <lb/> + o buona parte del tronco, se tutto o quasi tutto è rimasto attaccato [5] (come + <lb/> + io pratico perloppiù di lasciarvelo, troncandone la sola testa), nell’acqua di + <lb/> + un catino, e portare l’altra sua gamba al contatto dell’acqua medesima; nel-<lb/> + l’uno e nell’altro de’ quali modi succede pure qualche volta di eccitare le con-<lb/> + vulsioni; come succede in quell’altra maniera descritta già nell’operetta ano-<lb/> + nima (intitolata <emph type="italics"/>Dell’uso e dell’attività dell’Arco conduttore nelle contrazioni dei + <lb/> + muscoli<emph.end type="italics"/> [6]), di cui ebbi occasione di parlare nelle note alla 2<emph type="sup"/>a<emph.end type="sup"/> delle lettere che + <lb/> + vi scrissi nella primavera dell’anno scorso; la qual maniera consiste in fare + <lb/> + che i nervi pendenti, o il pezzetto di spina attaccato vadano a toccare le coscie. + </s> + </p> + <p id="N101F9" type="main"> + <s id="N101FB"> + Queste e simili sperienze, ove non interviene alcun conduttore metallico, + <lb/> + ossia di quelli che io chiamato avea <emph type="italics"/>eccitatori<emph.end type="italics"/> o <emph type="italics"/>motori<emph.end type="italics"/>; ove una parte dell’ani-<lb/> + male medesimo fa tutto l’arco conduttore, o se non lo fa tutto, il resto per com-<lb/> + pire il circolo è fatto da altri deferenti umidi; tali sperienze, gridano i Galva-<lb/> + niani, sono decisive, perentorie: qui l’elettricità non può ripetersi che dagli + <lb/> + organi animali, ne’ quali cioè trovisi il fluido elettrico in istato di carica o di + <lb/> + disequilibrio, sbilanciato, come pare, tra i nervi e i muscoli in cui quelli s’im-<lb/> + piantano, o tra l’interno e l’esterno de’ muscoli medesimi, come ebbe per più + <lb/> + probabile l’istesso GALVANI. + </s> + <s id="N10219"> + E voi, che ne dite, amico? + </s> + <s id="N1021B"> + La date così subito loro + <lb/> + vinta? + </s> + <s id="N1021F"> + O restate ancora perplesso per le tante altre sperienze da me prodotte, + <lb/> + nelle quali è pur manifesto che l’elettricità è meramente artificiale, che il fluido + <lb/> + elettrico è mosso da causa estrinseca, per un’azione cioè che risulta dal comba-<lb/> + ciamento di conduttori dissimili? + </s> + <s id="N10227"> + Oppure per far la pace e conciliare le une colle + <lb/> + altre sperienze, adottate voi ambidue i principj, e tenete (come opinai anch’io + <lb/> + una volta, ma per poco tempo [7]) che quando l’uno e quando l’altro sia la causa + <lb/> + delle convulsioni eccitate? + </s> + <s id="N1022F"> + Può infatti credersi, che i metalli di specie diversa + <lb/> + abbiano realmente nel combaciamento loro CO’ conduttori umidi la virtù di + <lb/> + muovere il fluido elettrico, e che ad una tal’azione, alla corrente elettrica + <lb/> + quindi eccitata, troppo debole per potersi manifestare co’ segni de’ comuni + <lb/> + elettrometri, ma pure più che sufficiente ad irritare i muscoli volontarj, o piut-<lb/> + tosto i rispettivi nervi, ed altri molto sensibili, per cui passi raccolta, a siffatta + <lb/> + corrente abbastanza attiva si risentano le rane anche preparate da lungo tempo, + <lb/> + e già molto debilitate, anche le non intieramente preparate, anche senza averne + <lb/> + denudati i nervi, e fino i semplici muscoli staccati di esse, o di qualunque ani-<lb/> + male, e così pure si risentano i nervi del gusto, della visione ec., come ho sco-<lb/> + perto; anzi non può credersi altrimenti in tante e tante sperienze, nelle quali + <lb/> + <pb pagenum="293"/> + con questo mezzo solamente de’ metalli diversi ottener si possono gli accennati + <lb/> + effetti; e può credersi nell’istesso tempo, o sospettarsi almeno, che anche tal-<lb/> + volta proceda il moto del fluido elettrico da una vera carica o sbilancio negli + <lb/> + organi animali, come presumono i Galvaniani, quando cioè si eccitano le con-<lb/> + vulsioni o con un sol pezzo di metallo, o con due, ma della stessa specie, e fino + <lb/> + senza alcun metallo, con un arco cioè di soli conduttori umidi, ossia di 2<emph type="sup"/>a<emph.end type="sup"/> classe, + <lb/> + come le novelle sperienze ci mostrano che pur succede talvolta. + </s> + <s id="N1025C"> + Quando però + <lb/> + si ammetta una tal carica o tensione del fluido elettrico negli organi, dovrà + <lb/> + dirsi che sia sommamente debole, e abbia luogo solo per pochissimo tempo, + <lb/> + osservandosi che non si eccitano d’ordinario se non convulsioni deboli, e diffi-<lb/> + cilmente, e solo nelle rane preparate di tutto punto e di fresco, e dotate di + <lb/> + somma vitalità. + </s> + <s id="N10268"> + Ma infine se basta, come farò vedere e toccar con mano, a + <lb/> + spiegare anche queste poche sperienze ambigue il solo principio dell’azione + <lb/> + de’ conduttori dissimili, principio dimostrato da tante altre prove sperimentali + <lb/> + chiare e parlanti, e senza paragone più numerose, a che ricorrere ad un altro + <lb/> + principio supposto, e non provato, di un’elettricità’ cioè propria e attiva degli + <lb/> + organi animali? + </s> + <s id="N10274"> + Perchè introdurre due principj affatto diversi per fenomeni + <lb/> + dell’istesso genere, e del tutto simili? [8] + </s> + </p> + <p id="N10278" type="main"> + <s id="N1027A"> + Dietro queste riflessioni osservando più attentamente, ed analizzando + <lb/> + quelle sperienze, in cui mi riusciva di eccitare le convulsioni nella rana con due + <lb/> + armature dell’istesso metallo, e fino con un arco di un sol pezzo senz’altra ar-<lb/> + matura, venni a scoprire che anche picciole accidentali differenze tra dette + <lb/> + armature, o tra i due capi dell’arco metallico, nella tempera cioè, nel poli-<lb/> + mento ecc. bastavano a dar mossa al fluido elettrico, e ad indurre una corrente + <lb/> + del medesimo valevole a scuotere la rana compitamente e di fresco preparata: + <lb/> + la qual cosa, ch’io avea verificata con moltissime prove sperimentali, fece il + <lb/> + soggetto della 1<emph type="sup"/>a<emph.end type="sup"/> delle lettere già mentovate scrittevi l'anno scorso. + </s> + <s id="N10292"> + Così poi + <lb/> + quando alcuni mesi dopo fu richiamata la mia attenzione alle nuove sperienze + <lb/> + del VALLI, in cui non entra metallo di sorta, ripetendo e analizzando anche + <lb/> + queste con variarle in più maniere, non tardai molto a riconoscere, che qui + <lb/> + pure la diversità de’ conduttori combaciantisi è necessaria; e che tutto il giuoco + <lb/> + dipende da questa diversità: e di tale ulteriore scoperta e spiegazione ne feci + <lb/> + parte in lettera fin dal principio del passato inverno al Cav.<emph type="sup"/>re<emph.end type="sup"/> BANKS Presi-<lb/> + dente della Società Reale di Londra, e ad altri miei Corrispondenti; per nulla + <lb/> + dire dei molti e nazionali e forastieri, a cui ho mostrate in tutto il corrente + <lb/> + anno le sperienze, e che trovandole decisive hanno senza più esitare sottoscritto + <lb/> + alla mia opinione. + </s> + </p> + <p id="N102AE" type="main"> + <s id="N102B0"> + Non dubito pertanto, che non siate per soscrivervi ancor voi, Collega ama-<lb/> + tissimo, qualunque sia stato fino ad ora il vostro sentimento, sol che pesiate + <lb/> + bene le ragioni, e più le sperienze, che con maggior ampiezza di quello ho fatto + <lb/> + con altri vado ad esporvi, e vi piaccia di ripeterle voi medesimo. + </s> + </p> + <pb pagenum="294"/> + <p id="N102BA" type="main"> + <s id="N102BC"> + Quest’ultimo oso dire è necessario: non basta leggere o sentire da altri le + <lb/> + descrizioni, bisogna vedere le sperienze, farle, rifarle, cambiando forma e ma-<lb/> + niera, come ho praticato io, per ritrarne una perfetta convinzione [9]. + </s> + </p> + <p id="N102C2" type="main"> + <s id="N102C4"> + Non sarà inutile prima di tutto, ch’io mi trattenga un poco a farvi più + <lb/> + da proposito osservare quello, che di passaggio ho già toccato, cioè che non + <lb/> + sempre, e a mala pena, anche nelle rane preparate di tutto punto, e solo per + <lb/> + poco tempo riescono le vantate sperienze delle convulsioni eccitatevi senza + <lb/> + l’intervento di alcun metallo, come avrete diggià voi medesimo provato; + <lb/> + laddove coll’applicazione di due conduttori metallici assai diversi, ed anche di + <lb/> + un solo metallo interposto però a due conduttori non metallici molto pure di-<lb/> + versi fra loro (che è un secondo mezzo da me scoperto poco meno efficace del + <lb/> + primo [10]) non si manca mai di ottenere le convulsioni incomparabilmente più + <lb/> + forti, e per assai più lungo tempo, e sì anche nelle rane intiere, o preparate + <lb/> + per metà, cioè sviscerate soltanto. + </s> + <s id="N102DA"> + Son dunque ben poco efficaci tutti que’ mezzi + <lb/> + in cui non si adoprano gli eccitatori metallici, se è assolutamente necessario + <lb/> + per ottener qualche cosa, che la rana sia preparata nella miglior maniera possi-<lb/> + bile, in guisa cioè che le gambe tengano al tronco per i soli nervi ischiatici, e + <lb/> + preparata così di fresco, e piene le sue membra di vitalità; e se non sempre si + <lb/> + ottengono le convulsioni neppure con tale perfetta preparazione, e le altre fa-<lb/> + vorevoli circostanze, anzi solo rarissime volte nella maggior parte de’ sopra + <lb/> + descritti modi. + </s> + </p> + <p id="N102EA" type="main"> + <s id="N102EC"> + Più spesso è vero, e per più lungo tempo si ottengono nella maniera de-<lb/> + scritta per la prima, che è di ripiegare una delle gambe della rana, e addurla + <lb/> + al contatto o de’ detti nervi ischiatici, pe’ quali restano esse gambe attaccate + <lb/> + al tronco, o di una parte qualunque carnosa del tronco medesimo; non però + <lb/> + sempre neppure nelle rane più vivaci, e ne’ primi momenti dopo la dissezione, + <lb/> + che sono i più favorevoli: non sempre, dico, si ottengono le convulsioni neppure + <lb/> + adoperando in questa maniera: e se si osserveranno le circostanze, nelle quali + <lb/> + suol succedere, e quelle in cui non succede mai, o quasi mai l’esperienza, si + <lb/> + verranno facilmente a scoprire le condizioni richieste al riuscimento; e queste + <lb/> + condizioni ci faran conoscere finalmente la causa vera di tali fenomeni, il prin-<lb/> + cipio generale da cui dipendono. + </s> + </p> + <p id="N10302" type="main"> + <s id="N10304"> + Queste condizioni sono dunque: + </s> + </p> + <p id="N10306" type="main"> + <s id="N10308"> + 1° Che il corpo della rana trucidata, scorticata, e finita di preparare, + <lb/> + non sia già deterso e netto, come sarebbe lavato nell’acqua, ma anzi sporco, + <lb/> + imbrattato in parte almeno di sangue, o di altro umore più o men viscido e + <lb/> + tegnente: la qual circostanza, delle membra cioè lorde di sangue si accenna di + <lb/> + passaggio dall’istesso Dr. VALLI. + </s> + <s id="N10312"> + In difetto giova intridere a bella posta quella + <lb/> + parte della gamba, de’ nervi, o del tronco, ove ha da succedere in appresso + <lb/> + il combaciamento ossia mutuo contatto, con scialiva, come ha notato l’anzi-<lb/> + <pb pagenum="295"/> + detto autore, con acqua salata + <note n="b"> + <p id="N10320" type="main"> + <s id="N10323"> + Anche nelle sperienze oppostemi nell’operetta sopracitata <emph type="italics"/>Dell’uso e dell’attività + <lb/> + dell’Arco conduttore<emph.end type="italics"/> ec., delle quali ho reso conto nella nota 4 della lettera 2<emph type="sup"/>a<emph.end type="sup"/>, accenna l'Au-<lb/> + tore anonimo, che succede molto più facilmente di veder eccitate le convulsioni nell’atto che + <lb/> + il picciol troncone di spina pendente dai nervi ischiatici si porta a toccare le nude coscie, + <lb/> + ore siano state queste per qualche tempo in un bagno di acqua salata e se ne trovino inzup-<lb/> + pate. + </s> + <s id="N1033C"> + Or dunque non mi attengo più alla spiegazione ch’ivi ho cercato di dare, ricorrendo + <lb/> + cioè ad un’irritazione meccanica per via di urto o pressione qualsiasi, spiegazione di cui non + <lb/> + mi trovava neppur allora soddisfatto pienamente, e colla quale non si può render ragione al-<lb/> + cuna del come e perchè l’acqua salata ed altri liquori contribuiscano tanto alla riuscita di + <lb/> + tali sperienze; ma riduco sì queste che le altre analoghe ad un’azione sopra il fluido elet-<lb/> + trico che esercitino anche i conduttori non metallici, sebbene incomparabilmente più debole, + <lb/> + in virtù del mutuo combaciamento, ove siano pure codesti conduttori ed eccitatori a para-<lb/> + gon de’ metalli imperfettissimi, tra loro diversi: come verrò spiegando. + </s> + </p> + </note> + , con orina, con muco, con diversi succhi ecc., + <lb/> + o meglio con sapone stemperato in poca acqua, o assai meglio ancora con li-<lb/> + quori acidi od alcalini concentrati, come ho trovato io nel moltiplicare e va-<lb/> + riare in mille modi codeste, sperienze, e come vi sarà facile di verificare. + </s> + </p> + <p id="N10355" type="main"> + <s id="N10357"> + 2° Che il contatto de’ nudi nervi ischiatici, e de’ nudi muscoli del tronco + <lb/> + si faccia, non da qualsivoglia parte della gamba, ma dal tendine in cui termina + <lb/> + il muscolo grosso della gamba, ossia il gastrocnemio, il qual tendine o ligamento + <lb/> + passando sopra l’articolazione del piede si prolunga fino alle dita [11], e compare + <lb/> + scoperto per tutto quel tratto. + </s> + <s id="N10361"> + È cosa veramente curiosa il vedere come addu-<lb/> + cendo al contatto de’ muscoli dorsali anche intrisi di sangue o di altro umore + <lb/> + viscido o salino, i muscoli delle coscie, niente di ordinario succede; e niente pure + <lb/> + facendo a quelli combaciare l’istesso muscolo gastrocnemio al disopra della + <lb/> + sua metà, cioè per tutta quella parte ch’esso si mostra puramente carnoso, + <lb/> + e che all’incontro facendolo toccare al disotto, cioè per la parte in cui il muscolo + <lb/> + medesimo degenera in sostanza tendinosa, e presenta una superficie bianchiccia + <lb/> + di un lucido di perla, nascono le convulsioni. + </s> + <s id="N10371"> + Convien dunque imprimere sopra + <lb/> + i muscoli del tronco, o sopra i nervi ischiatici l’estremità di detto muscolo + <lb/> + gastrocnemio, o l’articolazione del piede, o il resto ove compar fuori il gran + <lb/> + tendine, cioè portare al detto combaciamento qualche punto di quel lungo + <lb/> + tratto bianco, e non altrimenti, se ottener si vogliono le convulsioni: le quali + <lb/> + neppure con ciò si ottengono sempre, anzi non mai, o quasi mai, se anche l’altra + <lb/> + condizione non vi si ritrova, cioè dell’umor viscido o salino interposto. + </s> + </p> + <p id="N1037F" type="main"> + <s id="N10381"> + In prova di che, se lavisi ben bene la rana preparata con acqua netta, + <lb/> + non servirà più a nulla neppure il contatto fatto sopra i muscoli dorsali colle + <lb/> + parti tendinose bianche della gamba. + </s> + <s id="N10387"> + Che se pure succeda alcune volte di ecci-<lb/> + tare così delle convulsioni anche dopo tal lavatura, si può credere, che tuttor + <lb/> + vi sia dell’umore eterogeneo aderente: infatti quando dopo aver lavata la + <lb/> + <pb pagenum="296"/> + rana una sol volta, e per poco tempo, mi è succeduto per accidente di poter + <lb/> + ancora eccitarvi le convulsioni nel modo indicato, non le ottenni più dopo una + <lb/> + seconda lavatura più accurata, in cui venni stropicciando bene le parti, massime + <lb/> + il dorso, e i contorni delle ferite. + </s> + </p> + <p id="N10398" type="main"> + <s id="N1039A"> + Vi vogliono dunque ambedue le condizioni, e dell’umore eterogeneo in-<lb/> + terposto, e dell’eterogeneità, dirò così, delle parti animali che si affacciano, che + <lb/> + non siano cioè quest’e troppo simili, come muscolo e muscolo, massime d’eguale + <lb/> + struttura e consistenza, ma differiscano anzi notabilmente; e la differenza che + <lb/> + trovo più conducente è quella appunto tra tendine e muscolo o tra tendine e + <lb/> + nervo (quella tra muscolo e nervo non lo è tanto); siccome la differenza, che + <lb/> + fa meglio tra questi conduttori animali, e il terzo che dee trovarsi ad essi in-<lb/> + terposto nel venire al contatto, e compiersi il circolo, è che questo terzo corpo + <lb/> + preso di mezzo sia un umore viscido o salino, o meglio sapone stemperato, + <lb/> + o meglio ancora alcali reso appena liquido, come già ho indicato. + </s> + </p> + <p id="N103AE" type="main"> + <s id="N103B0"> + Or queste circostanze e condizioni richieste all’uopo di destare le convul-<lb/> + sioni nelle rane puntualmente preparate senza l’intervento di alcun metallo, + <lb/> + o conduttore della 1<emph type="sup"/>a<emph.end type="sup"/> classe, bastano già a mostrare, che non procede dunque + <lb/> + la corrente del fluido elettrico eccitatrice di tali convulsioni da alcuna scarica + <lb/> + o mossa data al fluido dagli organi animali; giacchè per qual ragione succede-<lb/> + rebbe siffatta scarica soltanto portando al contatto dei muscoli del tronco, + <lb/> + o dei nervi ischiatici le parti tendinose della gamba, e in niun modo facendovi + <lb/> + toccare nella stessa foggia le parti muscolari ossia le carnose e molli dell’istessa + <lb/> + gamba, o delle coscie, quando il circolo conduttore sarebbe in questo caso com-<lb/> + pito egualmente, ed egualmente atto, anzi meglio, per essere più corto, e per + <lb/> + essere quelle parti appunto perchè più molli e succose, più deferenti che il + <lb/> + duro tendine, e men umido? + </s> + <s id="N103CE"> + E per qual ragione ancora non succederebbe, fa-<lb/> + cendosi il contatto immediato di qualsisia parte della gamba coi muscoli dor-<lb/> + sali, senza l’interposizione di un terzo corpo deferente diverso dall’una e dal-<lb/> + l’altra sostanza animale, e diverso dall’umor acqueo, senza l’interposizione, + <lb/> + dico, di un umor glutinoso e salino? + </s> + <s id="N103D8"> + E non dovrebbe anzi succedere assai + <lb/> + meglio coll’applicazione immediata della gamba ai muscoli dorsali, che frap-<lb/> + ponendosi tal terzo corpo, il quale ben lungi dal rendere più facile e spiccia + <lb/> + la via conduttrice già alquanto resistente per essere le istesse sostanze e umori + <lb/> + animali deferenti non del tutto perfetti, non può che renderla vieppiù resistente, + <lb/> + sendo esso pure che si trammezza un conduttore imperfetto? + </s> + <s id="N103E4"> + Or come dunque + <lb/> + moltiplicando i conduttori imperfetti, formando l’arco di tre di questi invece + <lb/> + di due, si faciliterebbe la supposta scarica e tragitto del fluido elettrico? + </s> + <s id="N103EA"> + Come + <lb/> + anzi in questo modo solamente avrebbe luogo essa scarica e tragitto, tale al-<lb/> + meno da convellere la rana, e non nell’altro modo, del contatto cioè immediato + <lb/> + della gamba, che pur dovrebbe essere più adatto? + </s> + </p> + <p id="N103F2" type="main"> + <s id="N103F4"> + Se ciò, come vedesi, è un paradosso inesplicabile stando alle idee che ab-<lb/> + <pb pagenum="297"/> + biamo delle cariche elettriche, e de’ conduttori considerati semplicemente come + <lb/> + tali, ossia come corpi permeabili al fluido elettrico, e non altro; se, dico, non + <lb/> + possono conciliarsi in alcun modo con queste idee, anzi si contraddicono mani-<lb/> + festamente gli enunciati fenomeni, convien dunque ricorrere ad altri principj, + <lb/> + e abbandonata tal supposizione di carica o sbilancio qualsiasi di fluido elet-<lb/> + trico ne’ nervi e muscoli della nostra rana preparata, considerare i conduttori, + <lb/> + di cui si tratta, sotto un altro aspetto, riguardarli cioè al dippiù come <emph type="italics"/>eccita-<lb/> + tori<emph.end type="italics"/> o <emph type="italics"/>motori<emph.end type="italics"/>, val a dire dotati della maravigliosa virtù di concitare il fluido + <lb/> + elettrico, impellerlo, smuoverlo, tosto che vengano al contatto, e si combacino + <lb/> + alcuni tra di loro di diversa specie, come appunto nelle sperienze testè descritte. + </s> + <lb/> + <s id="N1041A"> + Volgete e rivolgete la cosa in tutti gli aspetti, quest’è l’unica maniera di spie-<lb/> + gare tali sperienze, ed infinite altre, che si riducono al medesimo principio, + <lb/> + come farò vedere. + </s> + </p> + <p id="N10420" type="main"> + <s id="N10422"> + Ma che? saranno anche i conduttori non metallici, i conduttori liquidi, + <lb/> + o contenenti in qualsisia modo umore, che chiamo conduttori di 2<emph type="sup"/>a<emph.end type="sup"/> classe, + <lb/> + saranno anch'essi combinati fra loro soli, eccitatori, come lo sono i metalli con-<lb/> + duttori di 1<emph type="sup"/>a<emph.end type="sup"/> classe combinati assieme a quelli di 2<emph type="sup"/>a<emph.end type="sup"/>? + </s> + <s id="N1043C"> + Godranno anche tali con-<lb/> + duttori di 2<emph type="sup"/>a<emph.end type="sup"/> classe dell’istessa virtù? + </s> + <s id="N10446"> + Sì certo; ma in grado molto inferiore, + <lb/> + cedendo per tal riguardo ai conduttori metallici, come cedono loro anche ri-<lb/> + spetto a tal facoltà conduttrice. + </s> + <s id="N1044C"> + Io ebbi queste idee fin dal principio, e le + <lb/> + spiegai ad alcuni amici e corrispondenti, fra’ quali al sig. Abate TOMMASELLI + <lb/> + di Verona, e al Dr. VAN MARUM celebre Fisico Olandese in alcune lettere scritte + <lb/> + nell’estate del 1792; dall’una o dall’altra delle quali vi ricopierò qualche squarcio + <lb/> + a pie’ di pagina, acciò vediate s’io non inclinava a credere, e tenea quasi per + <lb/> + fermo, che anche nel combaciamento de’ conduttori umidi, ossia di 2<emph type="sup"/>a<emph.end type="sup"/> classe, + <lb/> + sol che fosser diversi fra loro, veniva dato impulso al fluido elettrico, non altri-<lb/> + menti che nel combaciamento de’ metalli, o conduttori di 1<emph type="sup"/>a<emph.end type="sup"/> classe coi detti + <lb/> + umidi + <note n="c"> + <p id="N1046D" type="main"> + <s id="N10470"> + Nella lettera all’Ab. TOMMASELLI io mi spiegava ne’ seguenti termini: « Son dunque + <lb/> + « i metalli non solo conduttori perfetti, ma <emph type="italics"/>motori<emph.end type="italics"/> dell’elettricità; non solo prestano essi la + <lb/> + « via facilissima al passaggio del fluido elettrico, che trovandosi già sbilanciato tenda a por-<lb/> + « tarsi dal luogo in cui sovrabbonda a quello che rispettivamente ne scarseggia; ma van pro-<lb/> + « ducendo essi stessi e promovendo un tal quale sbilancio, con estrarre di esso fluido od in-<lb/> + « tradurne dove pur trovasi in giusta dose ripartito; e ciò col solo stare applicati a qualsiasi + <lb/> + « altro conduttore, non altrimenti che avviene collo stropicciamento degli idioelettrici; e + <lb/> + « siccome tal metallo prevale sopra tal altro nel tirare il fluido o nel rilasciarlo; così avviene + <lb/> + « che due armature di diverso metallo, applicate come si è detto, se comunichino fra loro lo + <lb/> + « mettano in un perpetuo giro... Ella è questa una nuova virtù de’ metalli da nessuno ancora + <lb/> + « sospettata, che le mie sperienze mi hanno condotto ad iscoprire ». + </s> + <s id="N1048D"> + Or fate attenzione a quello, + <lb/> + ce immediatamente soggiungo: « Nè però io penso, che sia essa propria soltanto de’ metalli, + <lb/> + « ma bene di <emph type="italics"/>tutti i conduttori<emph.end type="italics"/>; e tengo debba stabilirsi per legge generale, che il semplice con-<lb/> + « tatto o combaciamento di conduttori di diversa superficie, e di qualità soprattutto diversa, + <lb/> + « basta a turbare in qualche modo l’equilibrio del fluido elettrico, e a smuoverlo, senza cioè + <lb/> + « che siavi bisogno di stropicciamento alcuno: il quale stropicciamento, siccome pure il per-<lb/> + « cuotere, ed anche il sol premere, non per altro riescono tanto più efficaci, che perchè dan + <lb/> + «luogo a miglior combaciamento delle superficie, adducendo un più gran numero di punti + <lb/> + « a un più perfetto contatto ». + </s> + <lb/> + <s id="N104A8"> + Ciò che qui viene da ultimo semplicemente indicato riguardo all’essere verosimilmente + <lb/> + l’istesso principio, l’istessa virtù cioè che si dispiega pel combaciamento di corpi diversi, la + <lb/> + causa tanto dell’elettricità conosciuta, che s’induce a forza di stropicciare un contro l’altro + <lb/> + due idioelettrici, od un idioelettrico e un conduttore, quanto di quella ultimamente sco-<lb/> + pertasi e meno apparente, mossa da’ semplici contatti di soli conduttori, l’ho poi spie-<lb/> + gato con qualche maggiore ampiezza nella lunga lettera al Dr. VAN MARUM, e cercherò di + <lb/> + porlo vieppiù in chiaro un’altra volta. + </s> + </p> + </note> + . + </s> + <s id="N104B9"> + Senza abbandonare del tutto tali idee mi spiegai in seguito qualche + <lb/> + <pb pagenum="298"/> + volta diversamente, non tanto perchè credessi che nulla realmente fosse l’azione + <lb/> + sul fluido elettrico de’ conduttori di 2<emph type="sup"/>a<emph.end type="sup"/> classe combaciantisi fra loro, comunque + <lb/> + diversi, e che in niun modo godessero della virtù eccitatrice; quanto perchè + <lb/> + stimai si meschina tal loro virtù ed azione, sì picciola e languida la corrente + <lb/> + elettrica che si potrebbe con essi soli indurre, da non riuscir valevole ad ecci-<lb/> + tare le contrazioni nella rana neppure la più vivace e meglio preparata. + </s> + <s id="N104D0"> + Non + <lb/> + debbonsi dunque intendere a rigore alcune espressioni, e come dove nella 2<emph type="sup"/>a<emph.end type="sup"/> + <lb/> + delle lettere scrittevi l’anno scorso ho avanzato: « che l’arco conduttore for-<lb/> + « mato da una o più persone, da cuoi, panni, cartoni, o corpi bagnati quali essi + <lb/> + « sieno, da deferenti insomma non metallici, nulla più essendo atto a prestare + <lb/> + « che l’officio appunto di conduttore, non può determinare alcuna corrente + <lb/> + « di esso fluido, che invada i nervi e muscoli dell’animale, e ne gli irriti e scuota ». + </s> + <lb/> + <s id="N104E5"> + Non debbe dico intendersi quello che ivi si avanza a tutto rigore, cioè che nulla + <lb/> + affatto sia l’azione nel mutuo combaciamento di tali conduttori di 2<emph type="sup"/>a<emph.end type="sup"/> classe + <lb/> + anche i più diversi; ma bene esser quella un’azione così da poco, che può quasi + <lb/> + aversi per nulla. + </s> + <s id="N104F3"> + Che se pure volli dire che fosse nulla del tutto, e pensai un mo-<lb/> + mento così; troppo m’allontanai, come si vede, dalle idee che ebbi per lungo + <lb/> + tempo; e alle quali fui tosto richiamato dalle sperienze qui innanzi descritte + <lb/> + del VALLI, ed altre di questo genere da me intraprese: nè picciola fu la compia-<lb/> + cenza in vedere così verificate le antiche mie congetture, colle quali generaliz-<lb/> + zando il principio, che pel semplice combaciamento di conduttori diversi si + <lb/> + toglie dal riposo il fluido elettrico, si concita e smuove, non altrimenti che per + <lb/> + la confricazione, tantochè se il circolo conduttore è compito si determina + <lb/> + ad una corrente continua, io attribuiva qualche poco di cotesta virtù eccita-<lb/> + trice anche ai conduttori non metallici, qualunque fossero, purchè s’incontras-<lb/> + sero dissimili nel combaciamento. + </s> + <s id="N10509"> + Dico <emph type="italics"/>qualche poco<emph.end type="italics"/> di virtù, avendola sempre + <lb/> + creduta, e credendola tuttora di molto inferiore a quella che manifestasi nel + <lb/> + combaciamento di uno di tai conduttori non metallici, o di 2<emph type="sup"/>a<emph.end type="sup"/> classe, con due + <lb/> + metallici, o di 1<emph type="sup"/>a<emph.end type="sup"/> classe fra loro pure diversi. + </s> + </p> + <pb pagenum="299"/> + <p id="N10525" type="main"> + <s id="N10527"> + Ad ogni modo non può più dirsi essere tanto debole, che l’effetto ne sia + <lb/> + sempre insensibile, conforme stimai in addietro, ora che impariamo da nuove + <lb/> + sperienze, come in alcuni casi, nelle circostanze cioè e condizioni sopra spie-<lb/> + gate, si eccita tal corrente elettrica, che giunge a destare delle convulsioni in + <lb/> + una rana perfettamente e di fresco preparata: a produrre il qual effetto per + <lb/> + altro ci vuole pochissimo, un nulla quasi; come si può provare colle scariche + <lb/> + elettriche comuni, segnatamente delle boccie di Leyden, bastando le più de-<lb/> + boli, incapaci non che a dar la menoma scintilla, ma a movere alcun poco il + <lb/> + più delicato elettrometro [12], quello di BENNET a listerelle di foglia d’oro da + <lb/> + voi perfezionato. + </s> + </p> + <p id="N1053B" type="main"> + <s id="N1053D"> + Ci vuole ancor poco assai, sebben ci voglia quattro o cinque volte dippiù, + <lb/> + a scuotere la rana non del tutto preparata, ma scorticata e sventrata in guisa + <lb/> + che compaiano i nervi ischiatici, senza però recidere le parti di dietro su cui + <lb/> + riposano; tanto poco ci vuole, che basta ancora per eccitare le convulsioni in + <lb/> + cotesta rana, che diremo mezza preparata, la carica di una boccia che non + <lb/> + move, o move appena un elettrometro sensibilissimo [13]; e similmente basta + <lb/> + la corrente elettrica eccitata e indotta dal semplice accozzamento di tre con-<lb/> + duttori diversi, de’ quali uno o due siano metallici, ossia di 1<emph type="sup"/>a<emph.end type="sup"/> classe; ove + <lb/> + cioè od un conduttore umido, un conduttore di 2<emph type="sup"/>a<emph.end type="sup"/> classe trovisi interposto a + <lb/> + due di 1<emph type="sup"/>a<emph.end type="sup"/> molto diversi tra loro; od al rovescio uno di 1<emph type="sup"/>a<emph.end type="sup"/> classe trovisi frap-<lb/> + posto a due di 2<emph type="sup"/>a<emph.end type="sup"/> molto pure diversi, (intorno alla quale seconda maniera, + <lb/> + accennata qui soltanto, mi riservo a trattenervi un’altra volta più a lungo). + </s> + </p> + <p id="N10573" type="main"> + <s id="N10575"> + Dico <emph type="italics"/>molto diversi<emph.end type="italics"/>, perchè, se qualunque anche picciola diversità, sia dei + <lb/> + due conduttori di 1<emph type="sup"/>a<emph.end type="sup"/> classe, sia dei due di 2<emph type="sup"/>a<emph.end type="sup"/>, interpolati rispettivamente da + <lb/> + uno dell’altra classe, può in alcune circostanze bastare all’uopo; se quella de-<lb/> + bolissima corrente di fluido elettrico, che s’induce in virtù di siffatti accozza-<lb/> + menti può eccitare le convulsioni nelle gambe della rana compitamente prepa-<lb/> + rata, in guisa cioè che pe’ soli nervi crurali debba passare tutta ristretta tal + <lb/> + corrente; non è già valevole ad eccitarle nella rana sol mezzo preparata, in cui + <lb/> + minor parte di essa corrente passa pe’ detti nervi, più larga via presentandole + <lb/> + le annesse parti, egualmente, se non più ancora, umide e deferenti: conviene + <lb/> + quindi in tal caso per ottenere l’effetto, che sia non così debole e meschina la + <lb/> + corrente elettrica, ma alquanto più copiosa o più forte (sebbene non ancor tanto + <lb/> + da darne segno i comuni elettrometri anche più sensibili), quale si eccita sol-<lb/> + tanto ove o i due conduttori di 1<emph type="sup"/>a<emph.end type="sup"/> classe interpolati da uno di 2<emph type="sup"/>a<emph.end type="sup"/>, o i due di 2<emph type="sup"/>a<emph.end type="sup"/> + <lb/> + interpolati da uno di 1<emph type="sup"/>a<emph.end type="sup"/>, come si è indicato, siano un dall’altro assai diversi. + </s> + </p> + <p id="N105BB" type="main"> + <s id="N105BD"> + Ma coll’accozzamento di tre conduttori tutti della 2<emph type="sup"/>a<emph.end type="sup"/> classe, o conduttori + <lb/> + umidi, escluso cioè dal circolo ogni metallo, miniera, pirite, carbone, ogni con-<lb/> + duttore insomma di 1<emph type="sup"/>a<emph.end type="sup"/> classe, con quei soli di 2<emph type="sup"/>a<emph.end type="sup"/> quanto si voglia diversi, in-<lb/> + trecciati e applicati in qualunque modo, non ho potuto mai ottenere la più + <lb/> + piccola convulsione o sbattimento nella rana preparata soltanto a metà; + <lb/> + <pb pagenum="300"/> + molto meno è possibile ottenerle in una rana, che non sia neppure sventrata (nel + <lb/> + qual caso vi vuole una forza elettrica otto o dieci volte ancora maggiore, come + <lb/> + ho trovato colle scariche de’ conduttori della macchina, delle boccie ecc. [14]), + <lb/> + molto meno in un membro, o muscolo staccato dalla medesima, o da altro + <lb/> + animale, se tal membro o muscolo non è preparato in maniera, che il nervo + <lb/> + inserviente al moto sia snudato, e ne penda fuori tutto libero intorno, ecc,; + <lb/> + laddove le ottengo facilmente in cotali membri e muscoli spogliati appena degli + <lb/> + integumenti, senza cioè scoprire e mettere a nudo alcun nervo, e fino nelle + <lb/> + rane, anguille, ecc., intiere e intatte, ottengo, dico, delle forti contrazioni mu-<lb/> + scolari, e moto violento de’ membri impiegando due metalli molto diversi [15], + <lb/> + e. g. argento e piombo, o meglio argento e foglio stagnato, o meglio ancora + <lb/> + argento e zinco, ed applicandoli o immediatamente uno ad una parte, l’altro + <lb/> + all’altra di quel tal’animale, di quel tal membro o muscolo, o coll’interposizione + <lb/> + d’altri conduttori umidi ossia di 2<emph type="sup"/>a<emph.end type="sup"/> classe; ed anche con un solo metallo o con-<lb/> + duttore di 1<emph type="sup"/>a<emph.end type="sup"/> classe ottengo gli stessi moti, segnatamente col zinco interponen-<lb/> + dolo a due conduttori di 2<emph type="sup"/>a<emph.end type="sup"/> classe molto diversi, come all’acqua da una parte + <lb/> + o ad un corpo qualunque imbevuto d’umor acquoso, e dall’altra a un forte + <lb/> + liquor acido od alcalino. + </s> + <s id="N10612"> + Ma di quest’ultima maniera, in cui interviene un solo + <lb/> + conduttore di 1<emph type="sup"/>a<emph.end type="sup"/> classe, ho già detto che mi riservo a parlare più lungamente + <lb/> + un’altra volta. + </s> + <s id="N1061E"> + Qui consideriamo le combinazioni, in cui non ne entra nessuno + <lb/> + di detta 1<emph type="sup"/>a<emph.end type="sup"/> classe nel circolo de’ conduttori, e conchiudiamo dal fin qui detto, + <lb/> + che se l’azione sul fluido elettrico nell’accozzamento di tre tutti della 2<emph type="sup"/>a<emph.end type="sup"/> classe, + <lb/> + comunque diversi tra loro, non può dirsi che sia sempre senza effetto sen-<lb/> + sibile, è però debolissima, e incomparabilmente meno efficace di quella che ri-<lb/> + sulta per l’intreccio di due di una classe, ed uno dell’altra diversi molto tra + <lb/> + loro. + </s> + </p> + <p id="N10638" type="main"> + <s id="N1063A"> + Ed ecco così generalizzato il principio, che in ogni combaciamento di con-<lb/> + duttori diversi nasce un’azione, che dà mossa più o meno al fluido elettrico, + <lb/> + tantochè ove compiasi il circolo da tre appunto quali essi sieno, purchè diversi, + <lb/> + una qualche corrente, o mediocre, o debole, o debolissima di esso fluido viene + <lb/> + sempre incitata. + </s> + <s id="N10644"> + Inerendo al quale principio, o legge generale da me scoperta, + <lb/> + e che tutto concorre a stabilire, invece di restringerci a dire, come per lo pas-<lb/> + sato, che il fluido elettrico è messo in corrente ogniqualvolta due conduttori + <lb/> + metallici diversi comunicando fra loro o immediatamente o per altri metalli, + <lb/> + combaciano e prendon di mezzo uno o più conduttori umidi, ossia della 2<emph type="sup"/>a<emph.end type="sup"/> classe, + <lb/> + continui; diremo semplicemente e in generale : ogniqualvolta uno o più condut-<lb/> + tori continui di questa 2<emph type="sup"/>a<emph.end type="sup"/> classe s’interpongono a due diversi e tra loro, e col + <lb/> + corpo che combaciano; lasciando fuori il termine <emph type="italics"/>metallici<emph.end type="italics"/>, che pone una certa + <lb/> + limitazione non troppo giusta, oppure cambiando le parole <emph type="italics"/>conduttori metal-<lb/> + lici diversi<emph.end type="italics"/> in <emph type="italics"/>conduttori diversi, massime metallici<emph.end type="italics"/>, o di 1<emph type="sup"/>a<emph.end type="sup"/> classe; col quale <emph type="italics"/>mas-<lb/> + sime<emph.end type="italics"/> e si conserva la prerogativa, che fin nelle prime Memorie ho attribuita + <lb/> + <pb/> + <pb/> + <pb pagenum="301"/> + a tali conduttori di 1<emph type="sup"/>a<emph.end type="sup"/> classe, di essere cioè eccitatori, o motori che dir si voglia, + <lb/> + per eccellenza; e l’istessa virtù in grado molto inferiore si concede pur anche + <lb/> + a quelli di 2<emph type="sup"/>a<emph.end type="sup"/> classe, come fu già mio pensiero, e come viene finalmente dimo-<lb/> + strato, che la possiedono diffatti, ma appunto debole assai, dalle sperienze + <lb/> + sopra addotte; intorno alle quali mi propongo di trattenervi ancora in un’altra + <lb/> + lettera [16], che seguirà dappresso la presente. + </s> + </p> + <p id="N1069F" type="main"> + <s id="N106A1"> + Scrivo da Como, e nell’ozio delle vacanze, che stanno per terminare; onde difficil-<lb/> + mente potrò spedire l’altra lettera prima di restituirmi a Pavia, che sarà verso S. Martino. + </s> + <lb/> + <s id="N106A6"> + Aspetto con desiderio sue righe, che mi spieghino il sentimento suo sopra la materia in + <lb/> + questione, e mi diano altre nuove letterarie, e in particolare delle sue studiose ricerche. + </s> + </p> + <p id="N106AA" type="main"> + <s id="N106AC"> + Io ho continuato ad occuparmi molto intorno ai vapori elastici, e sono stato condotto + <lb/> + ad alcuni bei ritrovati consentanei molto alla teoria di DE LUC: p. e. che la quantità del va-<lb/> + pore è la stessa in uno spazio vuoto o pieno d’aria, rara o densa, e dipende unicamente dal + <lb/> + grado di calore; onde cade affatto la teoria della dissoluzione de’ vapori nell’aria; che la forza + <lb/> + del vapore, ossia la pressione che esso equilibra, cresce in una progressione geometrica cre-<lb/> + scendo il calore in una progressione aritmetica: che tal progressione geometrica è come 1, 2, + <lb/> + 4 ecc. crescendo il calore di 16 in 16 gradi circa; cosicchè essendo la pressione del vapor acqueo + <lb/> + eguale a 13 pollici di mercurio alla temperatura di 64 gradi Reaumur, divenendo eguale a + <lb/> + 28 pollici a gr. 80, cioè crescendo di 15 poll., cresce poi di 30 poll. e arriva a 58 alla tempera-<lb/> + tura di 96 gradi ecc. : che questa stessa progressione in ragion dupla di 16 in 16 gradi ha luogo + <lb/> + come pel vapor acqueo, così per ogni altro vapore elastico, dello sp. di vino, dell’etere ecc. + <lb/> + la differenza stando solo nel grado di calore richiesto a produrre il vapore di tal densità e + <lb/> + forza elastica, che equilibri una data pressione, p. e. quella di 28 poll. di mercurio (giugnendo + <lb/> + al qual termine circa bolle il liquido ne’ vasi aperti, come si sa). + </s> + <s id="N106C8"> + Or dunque essendo la tempe-<lb/> + ratura richiesta all’indicata forza del vapore, 80 gradi per quello dell’acqua, 65 per quello + <lb/> + dell’alcool, e 31 per quello dell’etere vitriolico, diminuirà egualmente in tutti essa forza o + <lb/> + pressione di poll. 15, e ridurrassi quindi a 13, ove scemi la rispettiva temperatura di 16 gr., + <lb/> + cioè riducasi a 64 gr. il vapor acqueo, a 49 quello dell’alcool, a 15 quello dell’etere; e simil-<lb/> + mente crescerà in tutti di 30 poll., arrivando a 58, se invece s’innalzi la rispettiva tempera-<lb/> + tura di 16 gr. portandola pel vapor acqueo a 96, per quello dell’alcool a 81, per quello del-<lb/> + l’etere a 47 ecc. + </s> + <s id="N106D8"> + Per tali sperienze sopra i vapori ho immaginati e costrutti varj apparati, che + <lb/> + meritano d’essere descritti; e lo farò pubblicando alcune Memorie su questa materia bellis-<lb/> + sima e importantissima, ohe ho già abbozzato. ma che non SO quando potrò terminare. + </s> + </p> + <p id="N106DE" type="main"> + <s id="N106E0"> + Sono colla maggior stima + </s> + </p> + </chap> + </body> + <back> + <section type="editorcomment"> + <pb/> + <p id="N106E6" type="main"> + <s id="N106E8"> + <emph type="italics"/>NOTE DELLA COMMlSSIONE <emph.end type="italics"/> + <lb/> + ED AGGIUNTE TRATTE DAI MANOSCRITTI DI A. VOLTA + </s> + </p> + <p id="N106F2" type="main"> + <s id="N106F4"> + [1] <emph type="italics"/>In Cart. Volt. J 32 a questo punto ha la seguente nota:<emph.end type="italics"/> + </s> + </p> + <p id="N106FC" type="main"> + <s id="N106FE"> + Passano due anni, che mi sono spiegato decisamente su di ciò, rifon-<lb/> + dendo tutta l’azione ne’ conduttori metallici diversi posti a combaciamento + <lb/> + di altro od altri conduttori non metallici, della Classe cioè de’ Conduttori, che + <lb/> + ho chiamato <emph type="italics"/>conduttori umidi<emph.end type="italics"/>, perchè o fluidi, o totalmente contenenti qualche + <lb/> + umore, fra i quali i corpi animali, e tutte le loro parti fresche e succose. + </s> + <s id="N1070E"> + Da quel + <lb/> + tempo mi sono sempre più confermato in tal opinione di un’elettricita mossa + <lb/> + estrinsecamente: il che ho mostrato in più maniere, ed è pur evidente in mol-<lb/> + tissimi casi, nella massima parte cioè delle sperienze di questo genere. + </s> + <s id="N10716"> + Che se + <lb/> + in qualche altro caso, e sperienza può sembrare che gli organi animali, anzi + <lb/> + chè i conduttori applicati siano i moventi del fluido elettrico, che in quelli + <lb/> + esista veramente una carica o sbilancio di esso fluido, e che questi facciano + <lb/> + semplicemente l’officio di scaricatori, se, dico, può sembrare talvolta che i moti + <lb/> + muscolari, le convulsioni eccitate procedano da una vera e propria elettricità + <lb/> + animale; non dobbiam così facilmente lasciarci sedurre da simili apparenze; e + <lb/> + ammettere, così per poco quest’altro principio dell’elettricità propria e attiva + <lb/> + degli organi; quando v’è maniera di spiegare anche queste poche sperienze + <lb/> + col solo principio che spiega tutte le altre, dell’azione cioè de’ conduttori di-<lb/> + versi applicati al mutuo combaciamento: principio stabilito già, e dimostrato + <lb/> + da me con tante prove. + </s> + <s id="N1072E"> + Potendosi spiegare così, non dirò già la maggior parte + <lb/> + delle sperienze, ma tutte affatto, l’altro principio o causa supposta diviene su-<lb/> + perflua; e quindi sommamente improbabile, e tanto più inammissibile, quanto + <note n="1'" type="editorcomment"> + <p id="N10738" type="main"> + <s id="N1073B"> + <emph type="italics"/>Così nel Manoscritto.<emph.end type="italics"/> + </s> + </p> + </note> + <lb/> + che nell’applicazione di tal principio e di qualunque teoria fabbricatavi sopra + <lb/> + alle particolari sperienze, incontransi moltissime difficoltà, e anomalie inespli-<lb/> + cabili, quali certo non s’incontrano nell’applicazione del principio da me stabi-<lb/> + lito, trovando tutte le sperienze, anche quelle. . . . + <note n="1'" type="editorcomment"> + <p id="N10752" type="main"> + <s id="N10755"> + <emph type="italics"/>Così nel Manoscritto. <emph.end type="italics"/> + </s> + </p> + </note> + . . . . . . una facile e chiara + <lb/> + spiegazione, come si vedrà. + </s> + </p> + <pb pagenum="303"/> + <p id="N10764" type="main"> + <s id="N10766"> + [2] <emph type="italics"/>In Br. Ann., T. XI. pag. 85 e Ant. Coll., T. II, P. I, pq. 230, si legge la nota + <lb/> + seguente : <emph.end type="italics"/> + </s> + </p> + <p id="N10770" type="main"> + <s id="N10772"> + Non vi è dubbio che il fluido messo in moto in tali sperienze non sia il + <lb/> + vero e genuino fluido elettrico, lo stesso cioè che si sbilancia, si accumula, si + <lb/> + scarica ec. nelle sperienze dell’elettricità comune; e non SO come si siano imma-<lb/> + ginato alcuni esser quello un altro fluido, o affatto diverso, o analogo soltanto + <lb/> + al fluido elettrico, ma non identico; un fluido animale specifico, d’indole in + <lb/> + certo modo elettrica, oppur anche il vero fluido elettrico, ma diversamente + <lb/> + modificato, spogliato più o meno delle sue native proprietà e doti, e rivestito + <lb/> + di altre, <emph type="italics"/>animalizzato<emph.end type="italics"/> in certo qual modo, cui han dato nome di fluido <emph type="italics"/>elet-<lb/> + trico-animale. <emph.end type="italics"/> + </s> + <s id="N10790"> + Vane idee, precarie e inutili supposizioni! Che serve involger + <lb/> + le cose in una nube di termini e di idee vaghe e confuse, da cui in vece di ri-<lb/> + schiararsi si oscurano vieppiù? + </s> + <s id="N10796"> + Riteniamo il fluido elettrico qual è, e attri-<lb/> + buiamo pure con sicurezza ad esso gli effetti, di cui si tratta. + </s> + <s id="N1079A"> + Sì: egli è il fluido + <lb/> + elettrico comune e genuino, che messo in corrente per un’azione (mirabile + <lb/> + in vero e nuovamente scoperta) de’ conduttori eterogenei applicati a mutuo + <lb/> + combaciamento, stimola i nervi, cui invade e attraversa, ed eccita per mezzo + <lb/> + di essi le contrazioni de’ muscoli dipendenti; non altrimenti che quando ven-<lb/> + gono gli stessi nervi percorsi dal fluido elettrico lanciato dai conduttori della + <lb/> + macchina ordinaria, da boccie di Leyden cariche, ec.. + </s> + <s id="N107A8"> + Gli effetti sopra i detti + <lb/> + nervi e muscoli sono nell’una e nell’altra maniera similissimi: ed è già questo + <lb/> + un grande argomento onde presumere la somiglianza della causa. + </s> + <s id="N107AE"> + Osservando + <lb/> + poi che. sono gli stessi i coibenti, i buoni, e i cattivi deferenti, tanto dell’elettri-<lb/> + cità comune, quanto del fluido messo in corrente nelle sperienze in questione, + <lb/> + qual dubbio può restar più che sia questo lo stesso stessissimo fluido elettrico? + </s> + </p> + <p id="N107B6" type="main"> + <s id="N107B8"> + Le obbiezioni tratte dal non osservarsi nè scintilla, nè alcun altro de’ con-<lb/> + sueti segni elettrici, non sono di alcun peso. + </s> + <s id="N107BC"> + Questi non si osservano neppure + <lb/> + nelle scariche dei conduttori elettrizzati debolissimamente, e delle boccie di + <lb/> + Leyden pochissimo caricate, tanto cioè che non arrivano a 1/4 o a 1/10 di grado + <lb/> + del più sensibile Elettrometro a boccetta; eppure sono scariche di vero fluido + <lb/> + elettrico, che realmente passa e trascorre pe’ conduttori, che da un capo al-<lb/> + l’altro lo trasmettono; fra i quali se trovinsi compresi i nervi sensibilissimi + <lb/> + di un animale, e disposti in guisa, che tutta o gran parte della corrente debba + <lb/> + passare ristretta per essi, può questa, ancorchè debole a tal segno, eccitarli + <lb/> + sensibilmente, e cagionare il sapore nella lingua, il lampo nell’occhio, e soprat-<lb/> + tutto le contrazioni nei muscoli dipendenti; come ho mostrato con varie spe-<lb/> + rienze, applicando appunto l’elettricità artificiale comune. + </s> + <s id="N107D2"> + Questa prodigiosa + <lb/> + eccitabilità de’ nervi allo stimolo elettrico, specialmente di quegli inservienti + <lb/> + a’ moti volontarj, fa che la rana preparata alla maniera di GALVANI ci pre-<lb/> + senti una specie di <emph type="italics"/>Elettroscopio vivente<emph.end type="italics"/>, che supera di molto in sensibilità; i + <lb/> + più fini Elettrometri a fogliette d’oro, ec.. + </s> + <s id="N107E2"> + Or dunque basta supporre che la + <lb/> + <pb pagenum="304"/> + corrente elettrica, mossa dai semplici combaciamenti de’ conduttori fra loro + <lb/> + diversi, è anch’essa molto debole (supposizione naturalissima), debole cioè + <lb/> + quanto quella prodotta dall’anzidetta scarica della boccia di Leyden, che ap-<lb/> + pena può dirsi carica, per intendere come similmente valga soltanto ad ecci-<lb/> + tare sensazioni e moti muscolari ne’ divisati <emph type="italics"/>Elettroscopj viventi<emph.end type="italics"/> oltremodo + <lb/> + sensibili, e non giunga mai a dare nè scintilla, nè altro degli ordinarj segni + <lb/> + elettrici. + </s> + </p> + <p id="N107FB" type="main"> + <s id="N107FD"> + [3] <emph type="italics"/>In Br. Ann., T. XI, pag. 90, e in Cart. Volt. L 15 (in due minute successive) tro-<lb/> + vasi la seguente nota che è un'amplificazione di quella precedentemente riportata da J 32 alla + <lb/> + nota<emph.end type="italics"/> [1]: + </s> + </p> + <p id="N10809" type="main"> + <s id="N1080B"> + Da quel tempo mi sono sempre più confermato in tal opinione di un’elet-<lb/> + tricità propriamente artificiale, voglio dire mossa da causa estrinseca: il che + <lb/> + ho mostrato in più maniere, singolarmente colle sperienze del sapore, che ho + <lb/> + scoperto eccitarsi sulla lingua coll’artificio de’ metalli; e questo sapore acido + <lb/> + od alcalino, secondo che dei due metalli, argento e. g. e zinco, ch’entrano + <lb/> + con essa lingua nel circolo conduttore, questo o quello è rivolto contro il di + <lb/> + lei apice. + </s> + <s id="N10819"> + Ma che più? + </s> + <s id="N1081B"> + L’azione de’ conduttori in virtù del semplice loro comba-<lb/> + ciamento, quando sieno diversi di specie, tal azione che determina una corrente + <lb/> + elettrica in giro (seppure il circolo conduttore sia compito), è manifesta, e si + <lb/> + tocca con mano nella massima parte delle sperienze, di cui si tratta; in quelle + <lb/> + singolarmente in cui il combaciamento coi conduttori umidi, o di 2<emph type="sup"/>a<emph.end type="sup"/> classe si + <lb/> + fa alle opposte parti da due metalli, ossia conduttore di 1<emph type="sup"/>a<emph.end type="sup"/> classe, molto diversi + <lb/> + uno dall’altro, come argento od oro da una parte, ferro, o meglio piombo o + <lb/> + stagno, o assai meglio ancora, zinco dall’altra: nei quali incontri ho io ben anche + <lb/> + scoperto qual è la direzione della corrente elettrica da tali combaciamenti ecci-<lb/> + tata, cioè dallo stagno o zinco per la via del conduttore o conduttori umidi + <lb/> + interposti all’oro, o all’argento; e in generale sempre dal metallo superiore al-<lb/> + l’inferiore attraversando detti conduttori umidi o di 2<emph type="sup"/>a<emph.end type="sup"/> classe; e con forza + <lb/> + tanto maggiore, quanto più distano fra loro i due metalli o corpi di 1<emph type="sup"/>a<emph.end type="sup"/> classe; + <lb/> + nell’ordine in cui sono posti nella seguente colonna o scala, che dietro a queste + <lb/> + sperienze io avea già sbozzata al principio del 1793 (Vegg. le due lettere + <lb/> + precedenti e le altre mie Memorie e lettere dirette a diversi, e pubblicate ne’ + <lb/> + Giornali), e che differisce poco da quell’altra scala o serie, che ci ha data il + <lb/> + Dr. PFAFF anch’esso nel 1793, ristretta per allora a pochi metalli, indi più + <lb/> + estesa, compresivi cioè varj semimetalli, piriti e miniere, verso la fine del 1794 + <lb/> + (Vegg. <emph type="italics"/><foreign lang="de">Journal der Physik</foreign><emph.end type="italics"/> di GREN, Vol. VIII, a. 1794). + </s> + </p> + </section> + <section type="editorcomment"> + <pb pagenum="305"/> + <p id="N10867" type="head"> + <s id="N10869"> + TAVOLA. + </s> + </p> + <p id="N1086B" type="main"> + <s id="N1086D"> + <emph type="italics"/>De’ conduttori della prima Classe, che posseggono un diverso potere di spingere + <lb/> + il fluido elettrico e cacciarlo avanti ne’ conduttori umidi, ossia di seconda + <lb/> + Classe.<emph.end type="italics"/> + </s> + </p> + <p id="N10879" type="main"> + <s id="N1087B"> + Zinco. + <lb/> + ................ + <lb/> + ................ + <lb/> + ................ + <lb/> + Alcuni di que’ fogli stagnati, che si chiamano impropriamente <emph type="italics"/>carta d’argento<emph.end type="italics"/>. + <lb/> + <app><rdg loc="inline">................</rdg><rdg loc="supralinear">................ </rdg></app>Stagnole diverse + <lb/> + Piombo. + <lb/> + Alcune qualità di Stagno in lastre, o in verghe. + <lb/> + Regolo d’Antimonio. + <lb/> + Altre qualità di stagno. + <lb/> + Alcune qualità di Ferro. + <lb/> + Regolo di Bismuto. + <lb/> + Altre qualità di Ferro. + <lb/> + Bronzi varj. + <lb/> + Ottone, Oricalco, ec. + <lb/> + Rame. + <lb/> + Regolo di Cobalto. + <lb/> + Ferro piritoso non cristallizzato. + <lb/> + Galena, tessulare, ossia pirite di piombo. + <lb/> + Platina. + <lb/> + . . . . . . . . . . . . . . . . + <lb/> + Mercurio + <note n="2'" type="editorcomment"> + <p id="N108B9" type="main"> + <s id="N108BC"> + <emph type="italics"/>Nella II Lettera all’Aldini il V. nota essere incorso in errore dovendosi il Mercurio + <lb/> + porre vicino al Piombo ed allo Stagno. V. N° XX (B) di questo Volume. <emph.end type="italics"/> + </s> + </p> + </note> + . + <lb/> + Pirite di Ferro cubica. + <lb/> + Pirite arsenicale cristallizzata. + <lb/> + Oro. + <lb/> + Argento. + <lb/> + Miniera di Manganese grigia radiata. + <lb/> + Rame piritoso. + <lb/> + Piombaggine. + <lb/> + Alcuni pezzi di Carbone di legna. + </s> + </p> + <pb pagenum="306"/> + <p id="N108DB" type="main"> + <s id="N108DD"> + Riguardo a questa tavola conviene ch’io faccia osservare due cose. + </s> + <s id="N108DF"> + La + <lb/> + prima, che le linee punteggiate interposte ad alcuni dei nominati corpi dino-<lb/>tano altrettanti gradi di distanza, ossia di differenza in ordine alla virtù, di + <lb/> + cui si tratta. + </s> + <s id="N108E7"> + All’incontro dove si succedono immediatamente i corpi specifi-<lb/> + cati, la differenza è di un grado solamente, ossia picciola; anzi talvolta così + <lb/> + picciola, che dalle sperienze da me fatte a questo oggetto mi rimane ancora + <lb/> + qualche dubbio, se sian posti tutti giustamente nel luogo, che loro compete, + <lb/> + e qualcheduno non debba confondersi affatto, o scambiarsi col vicino: dipen-<lb/> + dendo fors’anche da circostanze accidentali, che di due collocati immediata-<lb/> + mente vicini nella tavola, ora il superiore prevalga all’inferiore, or l’inferiore + <lb/> + al superiore, secondo che si variano le sperienze. + </s> + <s id="N108F7"> + Se però la differenza è poco + <lb/> + marcata, talora incerta, e forse anche variabile tra due corpi vicinissimi, ossia + <lb/> + distanti di un sol grado nella quì esposta tavola (la quale vorrebbe essere + <lb/> + con ulteriori sperienze rettificata ed estesa ancora), ella è marcatissima, nè + <lb/> + soggiace ad incertezza od equivoco tra quelli, che distano di molti gradi, + <lb/> + come l’argento dal ferro, e questo dai fogli stagnati o dallo zinco; e notabile + <lb/> + sì anche, nè punto equivoca, ove la distanza notata dalla Tavola giunga a 3, + <lb/> + 4 o più gradi, come tra il regolo di Antimonio e quello di Bismuto; tra il Ferro + <lb/> + e il Rame; la Platina e l’Argento ec. + </s> + </p> + <p id="N10909" type="main"> + <s id="N1090B"> + La seconda cosa che merita osservazione si è, che non i soli metalli, ma + <lb/> + molte miniere, e le piriti singolarmente, ancorchè contengano assai più solfo, + <lb/> + il quale è pur materia coibente, che sostanza metallica; riescono non ostante + <lb/> + conduttori e motori tanto buoni presso a poco quanto i metalli puri: all’opposto + <lb/> + altre miniere ricche, e alcune ricchissime di metallo, ma calciforme, ossia <emph type="italics"/>ossi-<lb/> + dato<emph.end type="italics"/>, si mostrano assai cattivi conduttori. + </s> + <s id="N1091D"> + È osservabile ancora, che le anzi-<lb/> + dette piriti, o <emph type="italics"/>solfuri metallici<emph.end type="italics"/>, godendo in un colla virtù conduttrice quasi al-<lb/> + l’istesso grado dei metalli (come dicemmo) anche della facoltà motrice, tengono + <lb/> + in ordine a questa dei posti vicini all’argento e all’oro: ai quali pure stanno + <lb/> + vicini, cioè uno o due gradi sotto, la piombaggine e il carbone. + </s> + <s id="N1092D"> + Tutti questi + <lb/> + corpi però io li pongo in una sol classe, che chiamo de' <emph type="italics"/>Conduttori metallici<emph.end type="italics"/>, + <lb/> + o 1<emph type="sup"/>a<emph.end type="sup"/> classe. + </s> + </p> + <p id="N1093F" type="main"> + <s id="N10941"> + Or dunque, ritornando al proposito, ogni qualvolta due di tai conduttori + <lb/> + e insiem motori di 1<emph type="sup"/>a<emph.end type="sup"/> classe, diversi di specie, combaciando un di quà l’altro + <lb/> + di là de’ conduttori umidi o di 2<emph type="sup"/>a<emph.end type="sup"/> classe continui, comunicano anche fra loro, o + <lb/> + immediatamente, o per mezzo d’altri anch’essi di 1<emph type="sup"/>a<emph.end type="sup"/> classe, e compiesi così + <lb/> + il circolo; ogniqualvolta, dico, han luogo queste condizioni, il fluido elettrico + <lb/> + viene smosso e tratto in giro nella direzione, che va da quello di detta 1<emph type="sup"/>a<emph.end type="sup"/> classe, + <lb/> + che è superiore nella disegnata tavola, all’altro inferiore, attraversando il + <lb/> + conduttore, o conduttori di 2<emph type="sup"/>a<emph.end type="sup"/> classe interposti, rifluendo indi in quel primo, + <lb/> + e proseguendo una tal circolazione, finchè non s’interrompe il circolo in alcun + <lb/> + luogo: la qual corrente è tanto più forte, quanto i due conduttori di 1<emph type="sup"/>a<emph.end type="sup"/> classe + <lb/> + <pb pagenum="307"/> + sono più diversi, ossia distano più gradi un dall’altro nella tavola o scala sovra-<lb/> + esposta. + </s> + <s id="N10980"> + Tutto ciò ho io dimostrato con tali e tante sperienze, che non lasciano + <lb/> + più alcun dubbio. + </s> + <s id="N10984"> + Debbe dunque ammettersi che in moltissimi casi ove com-<lb/> + piesi un circolo o catena di conduttori diversi di specie, anzi in tutti i casi, + <lb/> + in cui intervengono nel modo suaccennato due della 1<emph type="sup"/>a<emph.end type="sup"/> classe appunto diversi, + <lb/> + eccitasi in virtù de' loro combaciamenti co’ conduttori di 2<emph type="sup"/>a<emph.end type="sup"/> classe interposti, + <lb/> + una corrente elettrica; la direzione e la forza della quale viene determinata + <lb/> + da quella delle due azioni, che si dispiegano ne' detti respettivi combaciamenti, + <lb/> + che prevale. + </s> + <s id="N1099E"> + Or se in qualche altro caso e sperienza, in cui o non s’adoprino + <lb/> + conduttori metallici, o metalli simili, può sembrare che gli organi animali, + <lb/> + anzichè i conduttori applicati, siano i moventi del fluido elettrico; che in quegli + <lb/> + esista veramente una carica o sbilancio di esso fluido, e che questi facciano + <lb/> + semplicemente l’officio di scaricatori; se, dico, può sembrare talvolta che le + <lb/> + convulsioni muscolari procedano da una vera e propria elettricità animale, + <lb/> + quale se la figurano i Galvaniani; non dobbiamo così facilmente lasciarci se-<lb/> + durre da simili apparenze, e ammettere così per poco quest’altro principio + <lb/> + dell’elettricità propria ed attiva degli organi, quando vi sia pur maniera di + <lb/> + spiegare anche codeste poche sperienze col solo principio, che spiega tutte + <lb/> + le altre, dell'azione cioè de’ conduttori diversi applicati a mutuo combacia-<lb/> + mento: principio già stabilito e dimostrato con tante altre prove. + </s> + <s id="N109B6"> + Se pertanto + <lb/> + io farò vedere, che possono diffatti spiegarsi così, non che la maggior parte + <lb/> + delle sperienze, ma tutte affatto; l’altro principio della supposta elettricità + <lb/> + propria e attiva degli organi diverrà superfluo, e quindi sommamente impro-<lb/> + babile. + </s> + <s id="N109C0"> + Dessa poi è tanto più inammissibile, quantochè nell’applicazione di tal + <lb/> + principio, e di qualunque teoria fabbricatavi sopra, alle particolari esperienze, + <lb/> + incontransi ad ogni passo nuove difficoltà e anomalie inesplicabili, come han + <lb/> + dovuto già provare i sostenitori suoi, obbligati ad immaginare ogni sorta di + <lb/> + ripieghi, e a moltiplicare ipotesi, per dare una tal quale spiegazione, e conci-<lb/> + liare in qualche maniera tanti fenomeni disparati e ripugnanti; i quali all’in-<lb/> + contro non sono più tali, nè presentano anomalie, tostochè si riducano al prin-<lb/> + cipio da me stabilito, in cui trovano una facile e chiara spiegazione, come si + <lb/> + vedrà. + </s> + </p> + <p id="N109D2" type="main"> + <s id="N109D4"> + [4] <emph type="italics"/>In Br. Am., T. XI, pag. 96 e Cart. Volt. L 15 trovasi la seguente nota:<emph.end type="italics"/> + </s> + </p> + <p id="N109DC" type="main"> + <s id="N109DE"> + Così ho avanzato con troppa franchezza nella 2<emph type="sup"/>a<emph.end type="sup"/> delle Lettere scritte l’anno + <lb/> + scorso « Che fuori dei metalli, delle miniere, e del carbone di legna, il quale per + <lb/> + « la virtù di cui si tratta, non meno che per quella di esser eccellente conduttore, + <lb/> + « va posto in compagnia de' metalli, niun’altro conduttore è atto, applicandolo + <lb/> + « in qualità di armatura, a produrre nè il sapor elettrico sulla lingua, nè la cor-<lb/> + « ruscazione nell’occhio, nè il bruciore, nè movimento alcuno ne’ muscoli della + <lb/> + « rana la più vivace, e meglio preparata ». + </s> + <s id="N109F2"> + Tuttociò va bene, a riserva dell’ul-<lb/> + <pb pagenum="308"/> + tima riga, in cui ho oltrepassato il vero dicendo, che non si possano in alcun + <lb/> + modo eccitare, senza l’intervento dei conduttori metallici o di 1<emph type="sup"/>a<emph.end type="sup"/> classe, i moti + <lb/> + convulsivi de’ muscoli nelle rane comunque vivaci e preparate nella miglior + <lb/> + maniera. + </s> + <s id="N10A05"> + Ho dunque detto troppo in quello, e in altri passi; come dove torno + <lb/> + a dichiarare: « Che nulla mai e poi mai può ottenersi senza di quelli (i condut-<lb/> + « tori metallici), cioè coi soli deferenti umidi, nelle rane anche più vivaci e + <lb/> + « meglio preparate »; e dove replico ancora infine dell’ultima nota « Che non + <lb/> + « succedono mai le convulsioni facendo comunicare i nervi della rana CO’ suoi + <lb/> + « muscoli mediante arco conduttore, che non sia metallico ». + </s> + <s id="N10A11"> + Or si vedrà come + <lb/> + debbano tali espressioni correggersi o modificarsi. + </s> + </p> + <p id="N10A15" type="main"> + <s id="N10A17"> + [5] <emph type="italics"/>In Br. Ann., T. XI, pag. 99 trovasi la seguente nota:<emph.end type="italics"/> + </s> + </p> + <p id="N10A1F" type="main"> + <s id="N10A21"> + Nella preparazione della rana alla maniera di GALVANI si pratica comune-<lb/> + mente di lasciar attaccato ai nervi ischiatici soltanto un pezzetto di spina dor-<lb/> + sale, cioè tre o quattro vertebre al più: ma io soglio lasciar tutto il tronco + <lb/> + colle zampe davanti, recisa unicamente la testa; e ciò mi è di vantaggio e di + <lb/> + comodo in molte sperienze. + </s> + <s id="N10A2B"> + Truovo del resto spediente di finir di trucidare + <lb/> + la rana col passarle uno stecco tutt’al lungo della spinal midolla: con che + <lb/> + convellendosi furiosamente, e stendendo ella le gambe posteriori, in pochi + <lb/> + istanti e dopo brevi palpitazioni muore affatto; cioè si rilasciano le sue membra + <lb/> + e diventano naturalmente immobili, restando solo eccitabili per lungo tempo + <lb/> + ancora agli stimoli meccanici, e molto più agli elettrici. + </s> + <s id="N10A37"> + In tale stato i moti + <lb/> + che vi si destano cogli artifizj dei conduttori ec., non possono essere equivoci, + <lb/> + o confondersi con i moti volontarj; come allorchè la rana, per averle conservata + <lb/> + illesa la midolla spinale, vive ancora, tuttochè decapitata; o almeno tiene ri-<lb/> + piegate e attratte le gambe, e fa resistenza a chi gliele stenda, le ritira di nuovo + <lb/> + con forza, spesso le vibra calcitrando ec. + </s> + </p> + <p id="N10A43" type="main"> + <s id="N10A45"> + [6] <emph type="italics"/>In Br. Ann., T. XI, pag. 100 trovasi in più: « Modena 1794 ».<emph.end type="italics"/> + </s> + </p> + <p id="N10A4D" type="main"> + <s id="N10A4F"> + [7] <emph type="italics"/>In Br. Ann., T. XI, pag. 101 e in Cart. Volt. L 15 si trova la seguente<emph.end type="italics"/> nota: + </s> + </p> + <p id="N10A57" type="main"> + <s id="N10A59"> + Ecco ciò ch’io scrivea in una lettera all’Ab. TOMMASELLI di Verona in ago-<lb/> + sto del 1792 + <note n="7'" type="editorcomment"> + <p id="N10A61" type="main"> + <s id="N10A64"> + <emph type="italics"/>Vedi N° VII di questo Volume. <emph.end type="italics"/> + </s> + </p> + </note> + : « Ho ottenuto molti nuovi fenomeni; tali però, che estendendo + <lb/> + « apparentemente gli effetti di siffatta elettricità animale, ne ristringono assai + <lb/> + « l’influenza, e distruggono in gran parte le spiegazioni del Dott. GALVANI, + <lb/> + « e mostrano qualmente i moti muscolari, che si eccitano coll’artificio delle + <lb/> + « armature metalliche, sono d’ordinario effetti d’un’elettricità appunto arti-<lb/> + « ficiale estrinseca: non sempre però, come si potrebbe essere tentato di cre-<lb/> + « dere; giacchè ho pur dimostrato,.... che anche per sola forza organica viene + <lb/> + « squilibrato e mosso il fluido elettrico tra nervi e muscoli, o tra l’interno e + <lb/> + <pb pagenum="309"/> + « l’esterno di questi; onde sussiste ferma e stabile la grande scoperta di GAL-<lb/> + « VANI di una vera e propria <emph type="italics"/>elettricità animale<emph.end type="italics"/>, comunque debbasi a più pochi + <lb/> + « fenomeni limitare ». +</s> + <s id="N10A8C"> + E poco dopo: « Ma lasciando le spiegazioni, e conside-<lb/> + « rando il puro fatto del trasporto di fluido elettrico dall’una all’altra parte + <lb/> + « dell’animale occasionato da due armature di diverso metallo applicatevi, + <lb/> + « torno a dire, che quando siffatta circostanza è necessaria, cioè che siano ap-<lb/> + « punto armature diverse, perchè eccitinsi i moti muscolari, di maniera che, + <lb/> + « ove siano quelle eguali, questi moti più non succedano; non può dirsi a ra-<lb/> + « gione che ivi giuochi alcuna vera <emph type="italics"/>elettricità animale<emph.end type="italics"/>, potendosi o dovendosi + <lb/> + « quegli effetti attribuire propriamente ad <emph type="italics"/>elettricità artificiale<emph.end type="italics"/>, eccitata di pre-<lb/> + « sente col nuovo indicato mezzo. +</s> + </p> + <p id="N10AAA" type="main"> + <s id="N10AAC"> + « Ma in caso diverso, cioè quando snudato ed isolato il nervo alla maniera + <lb/> + « del Dott. GALVANI, si tocca sì questo, che il muscolo in cui s’impianta, con due + <lb/> + « capi del medesimo metallo, oppure armati essendo tanto il muscolo, quanto + <lb/> + « il nervo coll’istesso metallo, e nella stessa stessissima foggia, si eccitano + <lb/> + « nulladimeno le convulsioni; oh! allora sì, che possiamo con sicurezza asserire + <lb/> + « esser causa di cotai fenomeni una <emph type="italics"/>vera e propria elettricità animale<emph.end type="italics"/>. + </s> + <s id="N10ABE"> + E invero + <lb/> + « d’onde mai può venire la mossa al fluido elettrico, non essendovi ragione + <lb/> + « per cui venga in virtù delle armature, che sono affatto simili; se non procede + <lb/> + « originariamente dalle parti organiche medesime, cui stanno quelle applicate, + <lb/> + « in grazia di trovarsi esso fluido sbilanciato tra coteste parti, cioè tra nervo e + <lb/> + « muscolo, o tra l’interno e l’esterno del muscolo, in cui penetra e si dirama + <lb/> + « esso nervo? + </s> + <s id="N10ACC"> + Un tale stato però di naturale elettricità, ossia sbilancio di fluido + <lb/> + « negli organi, dura poco dopo la morte dell’animale, e la sua dissezione; e + <lb/> + « quindi cessa in pochi minuti di convellersi la rana tentata così: laddove ten-<lb/> + « tata nell’altra maniera, cioè coll’artificio delle armature dissimili, continua + <lb/> + « l’animaletto a sgambettare per ore ed ore, e sì anche applicandole ambedue + <lb/> + « all’esterna faccia de’ muscoli, senza snudare alcun nervo ». + </s> + </p> + <p id="N10AD8" type="main"> + <s id="N10ADA"> + Non diversamente mi spiegai in un’altra lunga lettera scritta verso il + <lb/> + tempo medesimo ad un celebre Fisico Ollandese il Dott. VAN MARUM, la quale + <lb/> + deve essere stata pubblicata negli Atti della Società di Harlem, o in qualche + <lb/> + giornale; e nella Memoria mandata in quel torno alla Società R. di Londra, + <lb/> + per ordine di cui venne inserita nel Volume delle Transazioni Filosofiche per + <lb/> + l’anno 1793. + </s> + <s id="N10AE6"> + Trascriverò quì uno squarcio anche di questa. <foreign lang="fr"><quote>Enfin puisqu’avec + <lb/> + des armures de differents métaux, appliquées soit aux nerfs seuls, soit aux seuls + <lb/> + muscles, on vient à bout d’exciter les contractions dans ceux-ci, et le mou-<lb/> + vement des membres, on doit conclure que s’il y a des cas (ce qui pourroit + <lb/> + bien encore paroître douteux) où la prétendüe decharge entre nerf et muscle + <lb/> + est cause des mouvements musculaires dont il s’agit; il y a bien aussi des + <lb/> + circonstances, et plus fréquentes, où l’on obtient les mêmes mouvements + <lb/> + par un tout autre jeu, une toute autre circulation du fluide électrique. + </quote></foreign></s> + </p> + <pb pagenum="310"/> + <p id="N10AFB" type="main"> + <foreign lang="fr"> + <s id="N10AFF"> + « Oui: c’est un tout autre jeu de ce fluide (dont on trouble plûtôt l’équi-<lb/> + « libre que de le retablir) en ce qu’il coule d’une partie à l’autre..... non pas + <lb/> + « en conséquence d’un excès ou défaut respectif; mais par une action propre + <lb/> + « de ces mêmes métaux, lorsque ceux-ci sont de differente espèce. + </s> + <s id="N10B07"> + C’est ainsi que + <lb/> + « j’ai découvert une nouvelle loi, qui n’est pas tant une loi d’électricité ani-<lb/> + « male, qu’une loi d’électricité commune, à laquelle on doit attribuer la plûpart + <lb/> + « des phénomenes, qui paroissoient, d’après les expériences de Mr. GALVANI + <lb/> + « et plusieurs autres que j’avois faites moi-même à la suite de celles-là, appar-<lb/> + « tenir à une véritable électricité animale spontanée, et qui n’en sont pas: ce + <lb/> + « sont reellément des effets d’une <emph type="italics"/>électricité artificielle<emph.end type="italics"/> très-foible, qui s’excite + <lb/> + « d’une manière, dont on ne s’étoit pas douté, savoir par la simple application + <lb/> + « de deux armures de differents métaux, comme j’ai indiqué, et j’expliquerai + <lb/> + « mieux dans la suite. + </s> + </foreign> + </p> + <p id="N10B21" type="main"> + <foreign lang="fr"> + <s id="N10B25"> + « Je dois dire ici, qu’à la découverte de cette loi nouvelle, de cette électri-<lb/> + « cité artificielle jusqu’à présent inconnue, je me défiai d’abord de tout ce qui + <lb/> + « m’avoit paru demontrer une électricité animale naturelle dans le sens propre; + <lb/> + « et que j’étois sur le point de revenir de cette idée. + </s> + <s id="N10B2D"> + Mais, repassant avec un + <lb/> + « examen reflechi tous les phénomenes, et repetant les expériences sous ce + <lb/> + « nouveau point de vüe, je trouvai enfin que quelques unes soutiennent encore + <lb/> + « cet examen, celles par ex. où l’on n’a pas besoin des armures différentes, + <lb/> + « ni même d’armure quelconque, un simple fil métallique étant suffisant, ou + <lb/> + « tout autre corps qui puisse faire office d’arc conducteur entre le nerf dé-<lb/> + « pouillé et un des muscles dependants, pour exciter dans ces derniers les con-<lb/> + « vulsions; et qu’ainsi l’électricité animale naturelle et proprement organique + <lb/> + « subsiste, et ne peut pas être renversée entierement. + </s> + <s id="N10B3F"> + Les phénomenes qui l’éta-<lb/> + « blissent, quoique beaucoup plus limités, ne laissent pas que d’être demons-<lb/> + « tratifs, comme je viens d’indiquer, et je ferai voir plus amplement dans la + <lb/> + « suite ». + </s> + </foreign> + </p> + <p id="N10B47" type="main"> + <s id="N10B49"> + Ma in seguito fui anzi costretto di abbandonare del tutto una tal idea: + <lb/> + e come già avea trovato, che nella maggior parte dei casi dovevansi le convul-<lb/> + sioni eccitate a quella specie di elettricità artificiale, che movono colla lor ap-<lb/> + plicazione e combaciamento i conduttori dissimili, massime metallici, piut-<lb/> + tosto che alla supposta elettricità animale; cominciai ben presto a sospettare, + <lb/> + che anche negli altri casi assai rari, nelle pochissime sperienze cioè, in cui senza + <lb/> + l’intervento de’ metalli diversi succedono pure le convulsioni, e lascian luogo + <lb/> + a crederle cagionate da una vera e propria elettricità animale (con che mi com-<lb/> + piaceva pure di mantener salva, almeno in parte, la teoria di GALVANI), po-<lb/> + tessero similmente procedere gli effetti da elettricità estrinseca, da una mossa + <lb/> + cioè data al fluido mercè l’incontro e combaciamento di conduttori in qualche + <lb/> + modo diversi nell’arco di comunicazione: e un tal sospetto andò pur troppo + <lb/> + verificandosi, a misura che mi avanzai con più sottili ricerche ed esperienze + <lb/> + <pb pagenum="311"/> + in mille modi variate, a danno della povera elettricità animale, che non ha più + <lb/> + onde sostenersi: come in parte ho già fatto vedere ne’ scritti posteriori al 1792, + <lb/> + segnatamente nelle altre due Lettere all’Ab. VASSALLI del 1794, e finirò di mo-<lb/> + strare in questa e nelle seguenti. + </s> + </p> + <p id="N10B6E" type="main"> + <s id="N10B70"> + [8] <emph type="italics"/>In Br. Ann., T. XI, pag. 107 trovasi la seguente nota: « Vegg. la nota 3 », che è quella + <lb/> + di cui alla nota<emph.end type="italics"/> [3]. + </s> + </p> + <p id="N10B7A" type="main"> + <s id="N10B7C"> + [9] <emph type="italics"/>In Br. Ann., T. XI, pag. 108 trovasi la seguente nota: <emph.end type="italics"/> + </s> + </p> + <p id="N10B84" type="main"> + <s id="N10B86"> + Finchè si leggono soltanto le Memorie di chi sostiene, e di chi nega l’Elet-<lb/> + tricità Animale in questione; essendo per avventura in maggior numero gli + <lb/> + Scritti in favore, massime dopo la pubblicazione delle sperienze, in cui si ecci-<lb/> + tano le convulsioni nella rana facendo far arco conduttore ad una delle sue + <lb/> + gambe senza adoperar metalli, nè altro corpo estraneo all’animale; e mostrando + <lb/> + al di più cotesti Scritti una cert’aria di trionfo; è facile restarne preso ed abba-<lb/> + gliato: tanto maggiormente, che più bella e plausibile, più feconda di applica-<lb/> + zioni comparendo l’ipotesi di tal elettricità propria degli organi animali, più + <lb/> + volentieri si lascia il facile lettore tirare ad essa. + </s> + <s id="N10B98"> + A vincere codesta propensione, + <lb/> + a toglier d’inganno i prevenuti o sedotti, non basta il racconto e la descrizione + <lb/> + anche minuta di altre sperienze in molto maggior numero, che depongono in + <lb/> + contrario, quali sono le mie, e che spiegano in tal senso contrario quelle stesse + <lb/> + credute favorevoli all’elettricità animale in questione: bisogna per convin-<lb/> + cerli ch’essi medesimi vedano e tocchino con mano codeste sperienze, che vor-<lb/> + rebbero non credere se potessero, e che la loro fantasia sfigura quanto può, + <lb/> + finchè vengono soltanto narrate. + </s> + <s id="N10BA8"> + Ma se avviene così, descrivendole cioè so-<lb/> + lamente, che si tolga a tali sperienze molto dell’impressione, che dovrebbero + <lb/> + fare; succede poi, allorchè son poste sott’occhio, che convincano a dirittura: + <lb/> + come è seguito a molti, a cui ho avuto occasione in quest’anno di mostrarle. + </s> + </p> + <p id="N10BB0" type="main"> + <s id="N10BB2"> + [10] <emph type="italics"/>In Br. Ann., T. XI, pag. 110 trovansi in più le parole:<emph.end type="italics"/> « come farò vedere in pro-<lb/> + gresso » <emph type="italics"/>In Cart. Volt. L 14 trovansi le parole:<emph.end type="italics"/> « come spiegherò in seguito » + </s> + </p> + <p id="N10BC2" type="main"> + <s id="N10BC4"> + [11] <emph type="italics"/>In Br. Ann., T. XI, pag. 113 trovansi le parole:<emph.end type="italics"/> « alle estreme dita e salti all’oc-<lb/> + chio pel suo colore bianco e di un lucido argenteo o piuttosto di perla ». + </s> + </p> + <p id="N10BCE" type="main"> + <s id="N10BD0"> + [12] <emph type="italics"/>In Br. Ann., T. XI, pag. 121 trovasi l’annotazione:<emph.end type="italics"/> « Vegg. la prima memoria, + <lb/> + pag. 77 », cioè: <emph type="italics"/>Seconda memoria, sull’Elettricità animale, N. III<emph.end type="italics"/>, § 43. + </s> + </p> + <p id="N10BE0" type="main"> + <s id="N10BE2"> + [13] <emph type="italics"/>In Br. Ann., T. XI, pag. 122:<emph.end type="italics"/> « Vegg. le mie prime Memorie pubblicate ». + </s> + </p> + <p id="N10BEA" type="main"> + <s id="N10BEC"> + [14] <emph type="italics"/>In Br. Ann., T. XI, pag. 124 trovasi la nota:<emph.end type="italics"/> « Vegg. le prime Memorie ». + </s> + </p> + <p id="N10BF4" type="main"> + <s id="N10BF6"> + [15] <emph type="italics"/>In Br. Ann., T. XI, pag. 124 trovasi la nota:<emph.end type="italics"/> « Vegg. le prime Memorie ». + </s> + </p> + <p id="N10BFE" type="main"> + <s id="N10C00"> + [16]<emph type="italics"/> Qui termina la 3<emph type="sup"/>a<emph.end type="sup"/> lettera stampata in Br. Ann. ed in Ant. Coll.<emph.end type="italics"/> + </s> + </p> + </section> + </back> + </text> +</archimedes>