Joseph Henry

Joseph Henry was born December 17, 1797, and built his name winding electromagnets in the 1820s and early '30s. While doing that work he discovered self-inductance, the property that makes a coil resist changes in its own current, and independently found mutual inductance around the same time Faraday did — though Faraday published first. Henry turned the electromagnet from curiosity into tool, invented a bell that rang at a distance via electric wire in 1831, and in 1835 built the electric relay, the switch that made long-distance telegraphy possible for Morse and Wheatstone. In 1846 he became…