Joule, James Prescott

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Joule, James Prescott

(jo͞ol, joul), 1818–89, English physicist. His scientific researches began in his youth when he invented an electromagnetic engine. Joule made valuable contributions to the fields of heat, electricity, and thermodynamics. His work established the mechanical theory of heatheat,
nonmechanical energy in transit, associated with differences in temperature between a system and its surroundings or between parts of the same system. Measures of Heat
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, and he was the first to determine the relationship between heat energy and mechanical energy (the mechanical equivalent of heat). Joule discovered the first law of thermodynamicsthermodynamics,
branch of science concerned with the nature of heat and its conversion to mechanical, electric, and chemical energy. Historically, it grew out of efforts to construct more efficient heat engines—devices for extracting useful work from expanding hot gases.
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, which is a form of the law of conservation of energy (see conservation lawsconservation laws,
in physics, basic laws that together determine which processes can or cannot occur in nature; each law maintains that the total value of the quantity governed by that law, e.g., mass or energy, remains unchanged during physical processes.
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). He was one of the great experimental scientists of the 19th cent. The mechanical unit of work is named for him.
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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Joule, James Prescott


Born Dec. 24, 1818, in Salford, Lancashire; died Oct. 11, 1889, in Sale, Cheshire. English physicist; member of the London Royal Society (beginning in 1850). Owner of a brewery near Manchester.

Joule made important contributions to the study of electromagnetism and thermal phenomena, to the establishment of low-temperature physics, and to the justification of the law of conservation of energy. He established (in 1841; published in 1843) that the amount of heat dissipated in a metal conductor carrying an electric current is proportional to the electrical resistance of the conductor and to the square of the current.

In 1843-50 Joule proved by experiments that heat can be produced by mechanical work and defined the mechanical equivalent of heat; this work furnished an experimental foundation for the law of conservation of energy. In 1851, regarding heat as the motion of particles, he determined theoretically the heat capacity of some gases. Working with W. Thomson (Lord Kelvin), Joule found by experiment that the temperature of a gas changes upon slow, stationary adiabatic flow through a porous barrier (the Joule-Thomson effect). He also discovered the phenomenon of magnetic saturation, which occurs during the magnetization of ferromagnetic materials.


The Scientific Papers, vols. 1-2. London, 1884-87.
In Russian translation:
“Nekotorye zamechaniia o teplote i o stroenii uprugikh zhidkostei.” In Osnovateli kineticheskoi teorii materii. Moscow-Leningrad, 1937.


Wood, A. Joule and the Study of Energy. London, 1925.
The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.