James Prescott Joule
James Prescott Joule (24 December 1818 – 11 October 1889) was an English physicist and brewer whose careful experiments in the 1840s showed that a fixed amount of mechanical work always produces the same quantity of heat, establishing the mechanical equivalent of heat and helping found the law of conservation of energy; the SI unit of energy, the joule, is named after him.
Major contributions
- Discovered in 1840–1841 that the heat produced by an electric current is proportional to the resistance times the square of the current (Joule's first law, P = I²R; see Ohm's Law)
- Measured the mechanical equivalent of heat in a series of experiments from 1843 to 1850, most famously with falling weights driving a paddle wheel in water, obtaining a value close to the modern 4.186 J per calorie (see First Law)
- Showed in 1845 that a gas expanding freely into a vacuum shows no measurable temperature change, supporting the view that internal energy of an ideal gas depends on temperature only (see Internal Energy)
- With William Thomson, discovered the Joule–Thomson effect (1852–1862), the temperature change of a real gas forced through a porous plug or valve
Named concepts
| Concept | Statement | Codex page |
|---|---|---|
| Joule (unit) | SI unit of energy, work and heat | View entry |
| Joule's first law | Heating power P = I²R | View entry |
| Joule–Thomson effect | Throttling cools or heats real gases | View entry |
Career
Joule was born in Salford, near Manchester, into a wealthy brewing family, and was educated at home, including lessons from the chemist John Dalton. He managed the family brewery and pursued science privately, without a university post; his skill at precise temperature measurement owed something to brewing practice. His early papers met scepticism, partly because the measured temperature differences were tiny and partly because he was an outsider to the scientific establishment.
His work gained acceptance after the 1847 British Association meeting in Oxford, where William Thomson took notice; the two then collaborated for over a decade. Joule was elected a Fellow of the Royal Society in 1850, received its Royal Medal in 1852 and the Copley Medal in 1870. His fortune declined in later life, and he received a civil-list pension from 1878. The British Association adopted the joule as a unit of energy in 1882.
Key publications
- Joule, J.P. (1841). “On the Heat Evolved by Metallic Conductors of Electricity.” Philosophical Magazine, 19, 260–277.
- Joule, J.P. (1850). “On the Mechanical Equivalent of Heat.” Philosophical Transactions of the Royal Society, 140, 61–82.
- Joule, J.P., Thomson, W. (1853). “On the Thermal Effects of Fluids in Motion.” Philosophical Transactions of the Royal Society, 143, 357–365.
Nobel Prize
Joule died in 1889, before the Nobel Prizes were established in 1901.
Historical context
Energy conservation emerged from several people working independently in the 1840s: Julius Robert Mayer (1842), Joule (1843 onwards), Ludvig Colding and Hermann von Helmholtz (1847). Mayer's claim to priority led to a bitter dispute with Joule's supporters, notably Tait, while John Tyndall championed Mayer. Historians now credit Mayer with the earlier statement of the principle and Joule with its decisive experimental demonstration (see First Law). Joule's work, together with Kelvin's and Clausius's, ended the caloric theory of heat (see Heat).
Sources
- Joule, J.P. (1850). Philosophical Transactions of the Royal Society, 140, 61–82.
- Cardwell, D.S.L. (1989). James Joule: A Biography. Manchester University Press.
- Joule, J.P. (1841). Philosophical Magazine, 19, 260–277.