Joule, James Prescott (1818-1889) English Physicist (Scientist)

One of the leading experimentalists of his time, James Prescott Joule’s main contributions to science were the discovery of the first law of thermodynamics, the law of the conservation of energy, and his findings concerning the mechanical equivalent of heat. Joule also collaborated with Baron William Thomson Kelvin to develop the Joule-Thomson effect, which stated that the temperature of an expanding gas cooled if the gas did not perform external work.

The second of five children, Joule grew up in a wealthy brewing family. Born on December 24, 1818, in Salford, near Manchester, England, to Benjamin and Alice Prescott Joule, Joule was a shy and frail child. He and a brother were tutored at home, and from 1834 to 1837 the brothers learned mathematics and science from chemist john dalton, known for his work on atomic theory. Joule developed an interest in physics at an early age and set up a laboratory near the brewery to conduct experiments.

James Prescott Joule discovered the first law of thermodynamics.

James Prescott Joule discovered the first law of thermodynamics.

Though Joule did not receive a formal education or a college degree, he made significant discoveries, most before reaching the age of 30. At the age of 19, Joule began independent research under the guidance of William Sturgeon, an amateur scientist. Joule was influenced by Sturgeon’s interest in electromagnetic theories. At about the same time, Joule began to investigate the problems of heat, particularly the heat developed by an electric current. He found that the heat produced in a wire by an electric current was connected to the current and resistance of the wire. Joule announced his findings in 1840 in a paper entitled On the Production of Heat by Voltaic Electricity.

From 1837 to 1847, Joule studied the mechanical equivalent of heat and other forms of energy and established the principle of conservation of energy. He systematically studied the thermal effects caused by the production and passage of current in an electric current, and in 1843 Joule determined the amount of mechanical work needed to produce a given amount of heat; his discovery was guided by precise experiments in which he measured the degree of heat produced by rotating paddle wheels, powered by an electromagnetic engine, in water. Joule presented his observations in 1849 to the Royal Society in On the Mechanical Equivalent of Heat. A year earlier Joule had also written a paper on the kinetic theory of gases. The paper included the first estimation of the speed of gas molecules.

Joule worked with Thomson from 1852 to 1859 on experiments in thermodynamics. Their most significant discovery was that an expanding gas’s temperature cooled under certain conditions. This became known as the Joule-Thomson effect and provided the basis for the development of a large refrigeration industry in the 19th century.

In 1850 Joule was elected to the Royal Society and enjoyed broad recognition and a strong reputation. He continued to carry out experimental investigations, but his findings failed to match the accomplishments of his early years. Joule married Amelia Grimes of Liverpool in 1847; she died in 1854, leaving him to raise their two children. Though Joule never received an academic appointment, his work on thermodynamics and the mechanical equivalent of heat were widely accepted and helped advance the sciences. The joule, a unit of energy, was named in his honor. Joule died on October 11, 1889, in Sale, Cheshire, after a lengthy bout with a degenerative brain disease.

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