"I have yet another motive to undertake these inquiries. In the memoirs in which M. Hertz treats bodies in motion, he admits that the ether they contain moves with them. Now, optical phenomena have long since demonstrated that it is not always so. I therefore wished to know the laws that govern the electrical motions in bodies that traverse the ether without entraining it; and it seemed to me difficult to attain this end without having as guide a theoretical idea. The views of James Clerk Maxwell [namely, on the application of mechanical principles to the field and charges as a 'connected mechanical system'] can serve as foundation of the desired theory." Hendrik Lorentz