Page:Popular Science Monthly Volume 76.djvu/120

116 this hypothesis, that light consisted of a motion of the nature of waves, obtained the victory over the old notion that light consisted of small particles shot out from the luminous object with great rapidity. The laws of the propagation of these waves were thoroughly described by Fresnel, but what the properties of the substance in which they were propagated, and called the ether, might be, was long a matter of difficulty. Green had shown that an elastic solid of a certain sort would possess many of the properties of the ether, but this mechanical theory was insufficient in certain ways. It was the conjecture of Faraday that the actions of electrified and magnetic bodies upon each other, so thoroughly investigated by him, were transmitted to each other by means of the ether, and it was the genius of Maxwell and his wonderful scientific imagination, that enabled him to erect this conjecture into a remarkably perfect theory. By means of the hypothesis that electrical and magnetic actions are subject to the laws of mechanics, Maxwell was able to apply to electric currents the equations of Lagrange for dealing with the motion of the most general mechanical systems of bodies. In this way Maxwell explained the laws of the induction of currents, the difficulty of starting or stopping a current corresponding to the inertia of a heavy body. Presently by the aid of an auxiliary assumption the properties of the ether were described, and the remarkable result found that electrical and magnetic effects would be propagated with the velocity of light. From this it was a short step to declare light waves to be electromagnetic waves. Such waves were not known at the time of Maxwell's paper in 1865, and his theory waited long for acceptance. In 1888, however, Heinrich Hertz, guided by his great master Helmholtz into acceptance of Maxwell's theory, succeeded, in a most brilliant series of experiments, in producing the very waves predicted by Maxwell, and in showing that they traveled with the velocity of light. These are the waves made use of by Marconi for transmitting intelligence, and conquering the sea in peace and in war. But this is not all, for Maxwell, in his description of the manner in which the ether transmitted the electromagnetic waves, assumed that it was subject to certain stresses, so that a surface receiving a beam of light would experience a certain pressure, the amount of which he calculated. This result awaited verification until 1900, when the Russian physicist Lebedew, and in 1903 still more exactly the Americans Nichols and Hull, now president and professor, respectively, at Dartmouth College, gave it a magnificent verification. Thus by faith Maxwell subdued kingdoms, obtained promises, out of weakness was made strong, turned to flight the armies of the aliens of ignorance.

An interesting conclusion that may be drawn from the history of scientific endeavor is that there is an accepted time for each discovery, that is, that a certain stage of human progress the discovery is