Place: United States of America
Subject: biography, physics
US physicist who carried out early experiments in electromagnetic induction.
Henry was born in Albany, New York, on 17 December 1797, the son of a labourer. He had little schooling, working his way through Albany Academy to study medicine and then, from 1825, engineering. He worked at the academy as a teacher, and in 1826 was made professor of mathematics and physics. He moved to New Jersey College (later Princeton) in 1832 as professor of natural philosophy, in which post he lectured in most of the sciences. He was the Smithsonian Institution's first director, from 1846, and first president of the National Academy of Sciences, from 1868, a position he held until his death, in Washington, on 13 May 1878.
Many of Henry's early experiments were with electromagnetism. By 1830 he had made powerful electromagnets by using many turns of fine insulated wire wound on iron cores. In that year he anticipated Michael Faraday's discovery of electromagnetic induction (although Faraday published first), and two years later he discovered self-induction. He also built a practical electric motor and in 1835 developed the relay (later to be much used in electric telegraphy). In astronomy Henry studied sunspots and solar radiation, and his meteorological studies at the Smithsonian led to the founding of the US Weather Bureau. The unit of inductance was named the henry in 1893.
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