Joseph Henry Demonstrates Primitive "Relay" Telegraph

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Using a self-made electromagnet, Joseph Henry arranges a small intensity magnet, which works well at low power over great distances, to control a much larger quantity magnet supporting a load of weights. By breaking the intensity circuit, he also de-energizes the quantity circuit, causing the weights to crash to the floor. Students who witnessed such demonstrations by Henry at the College of New Jersey, later recalled that Henry described the arrangement as a means to control mechanical effects at long range, such as the ringing of distant church bells. In other words, Henry had demonstrated that an electromagnetic telegraph was possible. In 1846, Joseph Henry would become Secretary of the Smithsonian Institution.


Henry, Joseph 1797-1878


Chronology of Smithsonian History


  • Summary adapted from "Joseph Henry: Inventor of the Telegraph?" by David Hochfelder at
  • Moyer, Albert. Joseph Henry: The Rise of an American Scientist. Washington, D.C.: Smithsonian Institution Press, 1997, pp. 143-44.

Contact information

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




  • Electric apparatus and appliances
  • Magnetic induction
  • Telegraph
  • Scientific apparatus and instruments
  • Inventions
  • Electromagnets
  • Experiments
  • Discoveries in science
  • Electromagnetic Induction
  • Electromagnetic telegraph

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