i8s THE POPULAR SCIENCE MONTHLY. 



Faraday obtained no answer to his questions, but the solution of 

 them is directly related to his theories. If electric waves crossing 

 space exist, the independence of the forces that produce them is 

 demonstrated. We know that the forces do not traverse vacua 

 instantaneously, for we can follow their propagation each instant 

 from one point to another. Faraday's problems can, however, be 

 solved by very simple experiments. If they had occurred to him, 

 his theory would have triumphed at once. The relation of light 

 and electricity would have been so clear that it could not have 

 escaped even a less perspicacious eye than his own. 



But so simple and speedy a way was not yet open to science. 

 The first experiments brought no solution, and the current view 

 was inconsistent with Faraday's ideas. In affirming that electric 

 forces could exist independent of corresponding fluids, he contra- 

 dicted the theory generally received at the time. A fundamental 

 discussion of either hypothesis promised to be only a barren spec- 

 ulation. How much, then, should we admire the man who had 

 the sagacity to co-ordinate these two hypotheses, apparently so 

 distantly separated, so that they should eventually support one 

 another, and a theory come out of them to which it should be im- 

 possible to deny probability ! This man was Clerk Maxwell, 

 whose Mathematical Theory of Light was published in 1865. We 

 can not study the theory without feeling that mathematical for- 

 mulas have a life of their own, and that they appear sometimes 

 more intelligent than we ourselves, and even than the master who 

 established them, giving out more than he looked for in them. 

 Direction was given to Maxwell's researches by the fact that 

 magnetic forces are produced from electricity in motion, and elec- 

 tric forces from magnetism in motion, but the effects were not 

 appreciable except at great velocities. The idea of velocity, 

 therefore, enters into the relation between electricity and mag- 

 netism, and the constant determining this relation, which is 

 always found in it, is a velocity of enormous value. The velocity 

 of electricity had been determined by delicate researches, and 

 found equal to that of light. A disciple of Faraday could not 

 fail to explain this coincidence by supposing that the same ether 

 carried the electric forces and light. Hence the most important 

 optical constant already existed in the electrical formulas. Max- 

 well labored to confirm this connection between the two orders of 

 phenomena. He extended the electrical formulas so as to make 

 them express, along with all the known phenomena, an entire 

 class of hypothetical facts electrical undulations. He figured 

 them as transversal waves, the length of which might have any 

 value, but which propagated themselves through the ether at a 

 constant velocity, that of light. It was then possible for Maxwell 

 to demonstrate that there really exist in nature undulations pos- 



