JOULE, JAMES PRESCOTT (1818-89), English physi cist, was born on Dec. 24, 1818, at Salford, near Manchester. He owned a large brewery but devoted himself to scientific research. From the first he appreciated the importance of accurate measure ment, and all through his life the attainment of exact quantitative data was one of his chief considerations. In 1840 Joule gave a quantitative statement of the law according to which heat is pro duced in a conductor by the passage of an electric current. He continued to study the relations between electrical, mechanical and chemical effects and was led to the discovery of the first law of thermodynamics. He determined the mechanical equivalent of heat in four ways. He found that to raise one pound of water 1°F (heat unit), 772 foot-pounds of mechanical work were required. In the C.G.S. system the mechanical equivalent, often called Joule's equivalent, is 4.184X ergs per gram-degree Centigrade
(see Brit. Assoc. Report, 1845). In 1849 he presented to the Royal Society a memoir which, together with a history of the subject, contained details and results of a long series of determina tions. In addition, numerous other researches stand to Joule's credit—the work done in compressing gases and the thermal changes they undergo when forced under pressure through small apertures (with Lord Kelvin), known as the Joule-Thomson por ous plug experiment the change of volume on solution, the change of temperature produced by the longitudinal extension and com pression of solids, etc. Joule died at Sale on Oct. I I, 1889.
His scientific papers were collected and published by the Physical Society of London: the first volume appeared in