THE IDENTITY OF LIGHT AND ELECTRICITY. 181 



that could enter upon, the study of the phenomena without pre- 

 conceived opinions, and was capable of starting from what it ob- 

 served, and not from what it had heard, read, or learned. 



Faraday followed that course. He had heard that, in electri- 

 fying a body, something new was introduced into it ; but he saw 

 that the changes were external, and not within. He was told that 

 the forces traversed space, but he remarked that the nature of the 

 matter that filled the space had great influence on them. He had 

 read that electricities existed, and that we only had to consider 

 their properties ; and yet he observed every day the effects of the 

 forces without ever seeing the electricities themselves : in this 

 way he reversed the proposition. The electric and magnetic 

 forces became to him the only tangible reality, while electricity 

 and magnetism fell to the rank of objects the existence of which is 

 contestable. Considering these lines of forces, as he called them, 

 independently of their cause, he regarded them under the form of 

 states of space, tension, whorls, and currents, without occupying 

 himself with what they might really be. He was satisfied with 

 having established their existence, with observing their influence 

 upon each other, their attractions for material bodies, and their 

 propagation by the transmission of the excitation from one point 

 of space to another. If it was objected that there could be no 

 other state than absolute rest in empty space, he could answer : 

 " Is space, then, empty ? Does not the transmission of light force 

 us to regard it as filled with matter ? Can not the ether, which 

 transmits the luminous waves, suffer modifications which we per- 

 ceive under the form of electrical and magnetic actions ? Is there 

 not a relation between these modifications and these vibrations ? 

 Are not the luminous waves a kind of scintillation of these lines 

 of force ? " Such were the inductions and hypotheses which Fara- 

 day conceived. They were as yet only mental views ; he applied 

 himself earnestly to demonstrate them scientifically ; and the re- 

 lations of light, electricity, and magnetism became the favorite 

 object of his studies. 



The relation he found was not the one he sought. He con- 

 tinued his researches till age put an end to his labors. One of 

 his principal questions was whether the transmission of electri- 

 cal and magnetic forces is instantaneous. Is the magnetic field 

 constituted at once to the limits of space whenever the current 

 excites an electro-magnet ? Or does the action first reach the 

 nearer points and gradually propagate itself to the more remote 

 ones ? And is the sudden modification of the electric condition 

 of a body felt simultaneously in identical variations, in all points 

 of space, or is there a retardation augmented as the distance in- 

 creases ? In the latter case, the effect of the variation would be 

 transmitted as a wave through space. Do such waves exist ? 



