During the 19th century three branches of physics are firmly established\: mechanics describes the motion of bodies, thermodynamics explains heat phenomena, and electrodynamics deals with electricity, magnetism, and light. These three disciplines also have their secure place in industrial practice.
Towards the end of the century, most physicists are convinced that physics has thus reached completion. But the problems situated at the borderlines between the three main branches become the starting point for Einstein's revolution.