ABSTRACT
Lorentz's most important idea was the theory of electrons. After he put forward the theory, it became the point of departure for all future theories of electromagnetism and, one may say, of physical theories in general. The central problem, for him, was to give an electromagnetic theory of moving bodies which both accounted for the Fresnel drag coefficient and for the failure of experiments to yield a measurement of the 'ether wind'. Lorentz's aim was to find a transformation from the time of the ether system to the moving system which would put the equations of the moving system into the same form as those for the resting system. Lorentz had created a new theory out of three old theories namely Maxwell's electromagnetic theory, Fresnel's ether theory and the old particle theories of charge. He showed that the new theory could account for a key fact of the optics of moving bodies, namely Fresnel's dragging coefficient.
