Unit of Inductance Named the "Henry"

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  • In August 1893, an International Congress of Electricians meets in Chicago during the World's Columbian Exposition. Scientists and engineers at the congress adopt names and definitions for eight units of electrical measure: the ohm, the ampere, the volt, the coulomb, the farad, the joule, the watt, and the henry.
  • The motion to adopt the henry, the only unit named after an American, is introduced by the leader of the French delegation, physicist Éleuthère Élie Nicolas Mascart. Joseph Henry had been the first Smithsonian Secretary and a world-renowned physicist known for his research in electromagnetism and induction. The henry is defined as "the induction in a circuit when the electro-motive force induced in this circuit is one international volt, while the inducing current varies at the rate of one ampère per second."


  • Henry, Joseph 1797-1878
  • International Electrical Congress


Chronology of Smithsonian History


  • Annual Report of the Board of Regents of the Smithsonian Institution...to July, 1893 (Washington, [1895]), p. 10.
  • T.C. Mendenhall, "The Henry, "Annual Report of the Board of Regents of the Smithsonian Institution...to July, 1894 (Washington, 1896), pp. 141, 143, 152.
  • Mascart, Éleuthère Élie Nicolas, Dictionary of Scientific Biography, Vol. 9. New York: Charles Scribner's Sons, 1974, p. 155.
  • Report of the Action of the International Electrical Congress held in Chicago August, 1893, in the Matter of Units of Electrical Measure, pp. 1-4, Box 27, Joseph Henry Collection, Record Unit 7001, Smithsonian Institution Archives.

Contact information

Institutional History Division, Smithsonian Institution Archives, 600 Maryland Avenue, SW, Washington, D.C. 20024-2520, SIHistory@si.edu


August 1893


  • Magnetic induction
  • Electricity
  • Electromagnets
  • Units
  • Physics
  • Electromagnetic Induction

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