_James Clerk Maxwell, born November 13, 1831, attended Edinburgh University 1847-1850. Entering Cambridge, he graduated second wrangler in 1854. He then taught for four years in Marischal College, Aberdeen, and in 1860 was called to King’s College, London, where he remained for the following eight years. He early revealed his mathematical genius and before he was nineteen had the honor of reading several pages before the Royal Society of Edinburgh. He developed by mathematics the theory that electricity was a condition of stress or strain in the ether, a wave moving in the same medium as light and traveling at the same rate of speed. The theory was substantiated by the experiments of Hertz, a pupil of Helmholtz, who in 1887 proved the existence of the waves which now bear his name. Maxwell died at Cambridge, November 5, 1879._ THE MAXWELL AND HERTZ THEORY OF ELECTRICITY AND LIGHT[36] It was at the moment when the experiments of Fresnel were forcing the scientific world to admit that light consists of the vibrations of a highly attenuated fluid filling interplanetary spaces that the researches of Ampère were making known the laws of the mutual action of currents and were so enunciating the fundamental principles of electro-dynamics. It needed but one step to the supposition that that same fluid, the ether, which is the medium of luminous phenomena, is at the same time the vehicle of electrical action. In imagination Ampère made this stride; but the illustrious physicist could not foresee that the seducing hypothesis with which he was toying, a mere dream for him, was ere long to take a precise form and become one of the vital concerns of exact science. A dream it remained for many years, till one day, after electrical measurements had become extremely exact, some physicist, turning over the numerical data, much as a resting pedestrian might idly turn over a stone, brought to light an odd coincidence. It was that the factor of transformation between the system of electro-statical units and the system of electro-dynamical units was equal to the velocity of light. Soon the observations directed to this strange coincidence became so exact that no sane head could longer hold it a mere coincidence. No longer could it be doubted that some occult affinity existed between optical and electrical phenomena. Perhaps, however, we might be wondering to this day what this affinity could be were it not for the genius of Clerk Maxwell. DISPLACEMENT CURRENTS