Joseph Henry (1797-1878), American physicist. Henry improved the design of the electromagnet, using a soft iron core wrapped in many turns of wire. He also designed the first reciprocating electric motor. He discovered the phenomenon of electromagnetic induction around the same time as Michael Faraday, but Faraday published his results first. Henry, however, is credited with discovering the phenomenon of self-induction, and the unit of inductance is named after him. He also introduced the electric relay, which made long- distance telegraphy possible. Henry was the first director of the Smithsonian Institute.