The great importance which electricity has attained in many departments of human activity is so constantly evident that we have difficulty in realizing how short is the time which has been occupied in its development. The latter half of the nineteenth century must ever remain memorable, not only for the great advances in nearly all the useful arts, but for the peculiarly rapid electric progress, and the profound effect which it has had upon the lives and business of the people. In the preceding century we find no evidences of the application of electricity to any useful purpose. Few of the more important principles of the science were then known. Franklin’s invention of the lightning-rod was not intended to utilize electric force, but to guard life and property from the perils of the thunder-storm. The numerous instructive experiments in frictional electricity, the first-known form of electric manifestation except lightning, made clear certain principles, such as conduction and insulation, and served to distinguish the two opposite electric conditions known as positive and negative. Franklin’s kite experiment confirmed the long-suspected identity of lightning and electric sparks. It was not, however, until the discovery by Alexander Volta, in 1799, of his pile, or battery, that electricity could take its place as an agent of practical value. Volta, when he made this great discovery, was following the work of Galvani, begun in 1786. But Galvani in his experiments mistook the effect for the cause, and so missed making the unique demonstration that two different metals immersed in a solution could set up an electric current. Volta, a professor in the University of Pavia and a foreign member of the Royal Society of England, communicated his discovery to the president of the society in March, 1800, and brought to the notice of the world the first means for obtaining a steady flow of electricity. Before this event electric energy had been known to the experimenter in pretty effects of attraction and repulsion of light objects, in fitful flashes of insignificant power, or, as it appeared in nature, in the fearful bursts of energy during a thunder-storm, uncontrolled and erratic. The analogous and closely related phenomena of magnetism had already found an important application in the navigator’s compass.