Joseph Henry

By Emeka Obi

Joseph Henry was born in 1797 in Albany, New York, to poor Scottish immigrants, and seemed headed for the stage — as a boy he was stagestruck, until a chance encounter with a book on natural philosophy turned him toward science. He became a schoolteacher, then a professor at the Albany Academy, where in the late 1820s he took up the electromagnet — then a feeble toy that could lift a few ounces — and made it a giant. By winding many turns of insulated wire tightly around an iron core (he insulated the wire with his wife's silk, lacquering each layer), he built magnets that lifted hundreds of pounds, then a ton. He demonstrated them publicly, horseshoes of iron lifting anvils, and the age of the practical electromagnet began.

In 1831 — the same year Faraday discovered induction across the Atlantic — Henry discovered it independently, and went further into application. He built a small electromagnetic motor with a rocking beam, one of the first, and then the device that made the telegraph possible: the relay. A faint current arriving down a long wire was too weak to click a sounder — but Henry showed it could energize an electromagnet that closed a second circuit, a local battery driving the sounder. Weak signal in, strong action out: amplification by relay, the principle that would let telegraph lines span continents. Samuel Morse visited Henry, studied his work, and built the American telegraph system on Henry's electromagnets and relays; Henry, characteristically, never patented the relay and never sued.

In 1846 Henry became the first secretary of the Smithsonian Institution, which he ran for thirty-two years, building American science almost single-handedly — the weather service began as his telegraphic network of observers. The unit of inductance, the henry, bears his name. He died in Washington in 1878. He was the great enabler standing just behind the famous names: without his magnets, no Morse telegraph; without his relay, no long-distance wires at all. At the Albany Academy he built his magnets in a converted classroom, winding silk-insulated wire with his own hands while teaching full days; at Princeton, where he moved in 1832, he strung a mile of wire around the campus and rang a bell by electromagnet — the first electric telegraph in miniature, years before Morse's line. As Smithsonian secretary he built the institution's museum, library, and research program, and organized 600 volunteer weather observers reporting by telegraph — the ancestor of the National Weather Service. He corresponded with every great physicist of the age and asked for nothing. The henry, the unit of inductance, was named for him by international agreement in 1893: the quiet man's name, stamped on every coil.

Impact on civilization

The electromagnet is one of the most-used devices in civilization: it clicks in every relay, clamps in every crane, drives every electric motor, focuses every particle accelerator, and lifts scrap in every junkyard on earth. Henry made it practical — from ounces to tons — and in doing so gave the nineteenth century its working electrical muscle. The relay was the subtler revolution: it solved the fundamental problem of long-distance signaling, that signals die with distance, by letting a dying current summon a fresh one. That principle — regeneration, amplification — underlies the telegraph networks that first wired continents, the telephone exchanges that followed, and in spirit every repeater and amplifier in modern communications. Henry published freely and patented nothing, so his name is less known than Morse's; but the telegraph system, the electrical age's first network, was built from his parts. His decision to publish rather than patent set a standard for American science: the Smithsonian's mission of 'the increase and diffusion of knowledge' was Henry's creed made institutional. Generosity, systematized.