Coil for use in induction experiments, c 1837.
© Science Museum / Science & Society Picture Library
This coil is said to have been used by the American physicist and pioneer of electromagnetism Joseph Henry (1797-1878) in his work on induction. Henry discovered electromagnetic induction, the use of magnets to produce electric current, in 1830. However, Michael Faraday independently discovered it himself, and was the first to publish his work in 1831. Henry went on to discover self-induction in 1832, and its unit of measurement is named after him. A coil has a self-inductance of 1 henry (H) if the back emf in it is 1 volt when the current through it is changing at 1 ampere per second. In 1846 Henry became the first director of the Smithsonian Institution.