Joule, James Prescott 1818-89
English natural philosopher

Born in Salford, Greater Manchester, he was educated by private tutors, notably the chemist John Dalton, and became famous for his experiments on heat. The 'Joule effect' (1840) asserted that the heat produced in a wire by an electric current was proportional to the resistance and to the square of the current, and in a series of notable researches (1843-78) he showed experimentally that heat is a form of energy, determined quantitatively the amount of mechanical (and later electrical) energy to be expended in the propagation of heat energy and established the mechanical equivalent of heat. Between 1853 and 1862 he collaborated with Lord Kelvin on the 'porous plug' experiments showing that when a gas expands without doing external work its temperature falls (the Joule-Thomson effect), and he was also the first to describe the phenomenon of magnetostriction. Recognition came with the award of the Royal Society's Royal (1852) and Copley (1870) medals. During the 1850s his ideas were recast in terms of the principle of the conservation of energy. The joule, a unit of work or energy, is named after him.

Bibliography: D S Cardwell, James Joule (1989)