Joseph Henry

Joseph Henry (1797-1878), American physicist, who did his most important work in electromagnetism. He was born in Albany, New York, and educated at Albany Academy. He was appointed professor of mathematics and natural philosophy at Albany Academy in 1826 and professor of natural philosophy at Princeton University in 1832. The foremost American physicist of his day, he discovered the principle of electromagnetic induction before the British physicist Michael Faraday announced his discovery of electromagnetically induced currents, but Faraday published his findings first and is credited with the discovery. The discovery of the phenomenon of self-inductance, which Henry announced in 1832, is, however, attributed to him, and the unit of inductance is named the henry in his honor.

Henry experimented with and improved the electromagnet, which had been invented in 1823 by the Briton William Sturgeon. By 1829 he had developed electromagnets of great lifting power and efficiency and essentially of the same form used later in dynamos and motors. He also developed electromagnets that were capable of magnetizing iron at a distance from the source of current, and in 1831 he constructed the first practical electromagnetic telegraph. Henry also devised and constructed one of the first electric motors. In 1842 he recognized the oscillatory nature of an electric discharge.

In 1846 Henry was elected secretary and director of the newly formed Smithsonian Institution, and he served in those positions until his death. Under his direction, the institution stimulated activity in many fields of science. He organized meteorological studies at the Smithsonian and was the first to use the telegraph to transmit weather reports, to indicate daily atmospheric conditions on a map, and to make weather forecasts from meteorological data. The meteorological work of the Smithsonian led to the creation of the U.S. Weather Bureau. Henry was a founder of the American Association for the Advancement of Science and president (1868-78) of the National Academy of Sciences.