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 contradicted the theory generally received at the time. A fundamental discussion of either hypothesis promised to be only a barren speculation. 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 impossible 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 formulas 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 electric 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 magnetism, 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. Maxwell 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-
