The first to make what is known as an electro-magnet was an Englishman named Sturgeon, who used a bar of soft iron bent in a horseshoe form (as had long been common in making permanent steel magnets), and, after varnishing the iron for insulation, a single coil of copper wire was wrapped about it, through which the current from a battery was passed. There were thus two ways of producing visible motion by means of an electric current: that of Oersted’s simple experiment, in which a suspended magnetic needle was deflected by a current, and that made possible by the production, at will, of an electro-magnet. The application of both of these ideas to the construction of an electric telegraph was quickly attempted, and two different systems of telegraphy grew out of them. One, depending on Oersted’s experiment, was developed in England first and afterwards in Europe; the other, that involving the use of signals produced by an electric magnet, was developed in America, and was generally known as the American method. It has long ago superseded the first method in actual practice. Its possibility depended on perfecting the electro-magnet and especially on an understanding of the principles on which that perfecting depended. For the complete and satisfactory solution of this problem we are indebted to the most famous student of electricity America has produced during the century, Joseph Henry. In 1829, while a teacher in the academy at Albany, New York, Henry exhibited an electro-magnet of enormously greater power than any before made, involving all of the essential features of the magnet of to-day. The wire was insulated by silk wrapping, and many coils were placed upon the iron core, the intensity of magnetization being thus multiplied. Henry studied, also, the best form and arrangement of the battery under varying conditions of the conductor. An electro-magnetic telegraph had been declared impossible in 1825, by Barlow, an Englishman, who pointed out the apparently fatal fact that the resistance offered to the current was proportional to the length of the conducting wire and that the strength of the current would be thus so much reduced for even short distances as to become too feeble to be detected. Henry showed that what is known as an “intensity battery” would overcome this difficulty, discovering experimentally and independently the beautifully simple law showing the relation of current to electro-motive force which Ohm had announced in 1827. He also invented the principle of the relay, by which the action of a very feeble current controls the operation of a more powerful local system. It will thus be seen that the essential features of the so-called American system of telegraphy are to be credited to Henry, who had a working line in his laboratory as early as 1832.