Joseph Henry

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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, 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.


  • 1826 Professor of mathematics and natural philosophy at The Albany Academy, New York.
  • 1832 Professor at Princeton.
  • 1835 Invented the electromechanical relay.
  • 1846 First secretary of the Smithsonian Institution until 1878
  • 1848 Edited Ephraim G. Squier and Edwin H. Davis' Ancient Monuments of the Mississippi Valley, the Institution's first publication.
  • 1852 Appointed to the Lighthouse Board
  • 1871 Appointed chairman of the Lighthouse Board
  • A United States Liberty Ship was named in his honor



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