A New Understanding of the First Electromagnetic Machine: Joseph Henry's Vibrating Motor

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In 1831, Joseph Henry invented a battery-powered rocking-beam motor that he later described as the first electromagnetic machine. He repeatedly modified the design over his career, but only one version of a motor actually constructed by Henry is known to exist in a collection of Henry instruments at Princeton University. The authors found that the Princeton motor cannot have operated in the form that was displayed as early as 1884. They also found evidence in several historical documents and in the instrument itself that the field magnet shown with the motor is a mistake. Instead of a single horizontal bar magnet, the motor was designed to use two elliptical magnets. Littman and Stern presume the error was made by whoever assembled the first public display. They modeled the dynamics of Henry's vibrating motor and compared our results to the operation of a replica motor. Modeling provides insight into how the motor is able to vibrate indefinitely even in the presence of energy loss due to friction.


  • Henry, Joseph 1797-1878
  • College of New Jersey (Princeton, N.J.)
  • Princeton University


Smithsonian History Bibliography



Contained within

American Journal of Physics Vol. 79, No. 172 (Journal)

Contact information

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




  • Magnetic induction
  • Inventors
  • Inventions
  • Motors
  • Electromagnets
  • Electric machinery
  • Electric motors
  • Electromagnetism

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