Joseph Henry

Joseph Henry was an American physicist and inventor who served as the first secretary of the Smithsonian Institution. Born in Albany, New York, on 17 December 1797 to Scottish immigrant parents, he became an apprentice watchmaker and silversmith at the age of thirteen and came close to becoming a professional actor before turning to science. In 1826 he was appointed professor of mathematics and natural philosophy at The Albany Academy. While building electromagnets he discovered the phenomenon of self-inductance, and he found mutual inductance independently of Michael Faraday, who was first to publish it. He developed the electromagnet into a practical device, invented a precursor of the electric doorbell in 1831 and the electric relay in 1835, and his work on the relay was the basis of the practical electrical telegraph. He served as president of the National Academy of Sciences from 1868 to 1878, and the SI unit of inductance, the henry, is named in his honour.