Joseph Henry (December 17, 1797 – May 13, 1878) was an American scientist who served as the first Secretary of the
Smithsonian Institution. He was the secretary for the
National Institute for the Promotion of Science, a precursor of the Smithsonian Institution. He was highly regarded during his lifetime. While building electromagnets, Henry discovered the
electromagnetic phenomenon of self-
inductance. He also discovered mutual inductance independently of
Michael Faraday, (1791-1867), though Faraday was the first to make the discovery and publish his results. Henry developed the
electromagnet into a practical device. He invented a precursor to the electric
doorbell (specifically a bell that could be rung at a distance via an electric wire, 1831) and electric
relay (1835). The
SI unit of
inductance, the
henry, is named in his honor. Henry's work on the electromagnetic relay was the basis of the practical
electrical telegraph, invented by
Samuel F. B. Morse and
Sir Charles Wheatstone, separately.