There is a single discovery of Faraday that stands out sharply amidst all his other discoveries, great as they were, and is so important in its far-reaching results that it alone would have stamped him as a philosophical investigator of the highest merits, had he never done anything else. This was his discovery of the means for developing electricity directly from magnetism. It was made on the 29th of August, 1831, and should be regarded as inspired by the great discovery made by Oersted in 1820, of the relations existing between the voltaic pile and electro-magnetism. It was in the same year that Ampere had conducted that memorable investigation as to the mutual attractions and repulsions between circuits through which electric currents are flowing, which resulted in a theory of electro-magnetism, and finally led to the production of the electro-magnet itself. Ampere had shown that a coil of wire, or helix, through which an electric current is passing, acted practically as a magnet, and Arago had magnetized an iron bar by placing it within such a helix. In common with the other scientific men of his time, Faraday believed that since the flow of an electric current invariably produced magnetism, so magnetism should, in its turn, be capable of producing electricity. Many investigators before Faraday's time had endeavored to solve this problem, but it was reserved to Faraday alone to be successful. Since success in this investigation resulted from some experiments he made while endeavoring to obtain inductive action on a quiescent circuit from a neighboring circuit through which an electric current was flowing, we will first briefly examine this experiment. All his experiments in this direction were at first unsuccessful. He passed an electric current through a circuit, which was located close to another circuit containing a galvanometer,--a device for showing the presence of an electric current and measuring its strength,--but failed to obtain any result. He looked for such results only when the current had been fully established in the active circuit. Undismayed by failure, he reasoned that probably effects were present, but that they were too small to be observed owing to the feeble inducing current employed. He therefore increased the strength of the current in the active wire; but still with no results.