Henry, Joseph

SUBJECT AREA: Electricity, Telecommunications

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b. 17 December 1797 Albany, New York, USA

d. 13 May 1878 Washington, DC, USA

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American scientist after whom the unit of inductance is named.

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Sent to stay with relatives at the age of 6 because of the illness of his father, when the latter died in 1811 Henry was apprenticed to a silversmith and then turned to the stage. Whilst he was ill himself, a book on science fired his interest and he began studying at Albany Academy, working as a tutor to finance his studies. Initially intending to pursue medicine, he then spent some time as a surveyor before becoming Professor of Mathematics and Natural Philosophy at Albany Academy in 1826. There he became interested in the improvement of electromagnets and discovered that the use of an increased number of turns of wire round the core greatly increased their power; by 1831 he was able to supply to Yale a magnet capable of lifting almost a ton weight. During this time he also discovered the principles of magnetic induction and self-inductance. In the same year he made, but did not patent, a cable telegraph system capable of working over a distance of 1 mile (1.6 km). It was at this time, too, that he found that adiabatic expansion of gases led to their sudden cooling, thus paving the way for the development of refrigerators. For this he was recommended for, but never received, the Copley Medal of the Royal Society. Five years later he became Professor of Natural Philosophy at New Jersey College (later Princeton University), where he deduced the laws governing the operation of transformers and observed that changes in magnetic flux induced electric currents in conductors. Later he also observed that spark discharges caused electrical effects at a distance. He therefore came close to the discovery of radio waves. In 1836 he was granted a year's leave of absence and travelled to Europe, where he was able to meet Michael Faraday. It was with his help that in 1844 Samuel Morse set up the first patented electric telegraph, but, sadly, the latter seems to have reaped all the credit and financial rewards. In 1846 he became the first secretary of the Washington Smithsonian Institute and did much to develop government support for scientific research. As a result of his efforts some 500 telegraph stations across the country were equipped with meteorological equipment to supply weather information by telegraph to a central location, a facility that eventually became the US National Weather Bureau. From 1852 he was a member of the Lighthouse Board, contributing to improvements in lighting and sound warning systems and becoming its chairman in 1871. During the Civil War he was a technical advisor to President Lincoln. He was a founder of the National Academy of Science and served as its President for eleven years.

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Principal Honours and Distinctions

President, American Association for the Advancement of Science 1849. President, National Academy of Science 1893–1904. In 1893, to honour his work on induction, the International Congress of Electricians adopted the henry as the unit of inductance.

Bibliography

1824. "On the chemical and mechanical effects of steam". 1825. "The production of cold by the rarefaction of air".

1832, "On the production of currents \& sparks of electricity \& magnetism", American

Journal of Science 22:403.

"Theory of the so-called imponderables", Proceedings of the American Association for the Advancement of Science 6:84.

Further Reading

Smithsonian Institution, 1886, Joseph Henry, Scientific Writings, Washington DC.

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