JOULE, JAMES PRESCOTT (1818–1889)

James Joule was born in Salford, near Manchester, England, on December 24, 1818. He was the second son of a wealthy brewery owner and was educated at home by private tutors. For three years he was fortunate enough to have the eminent British chemist, John Dalton as his chemistry teacher. He never attended a university; as a consequence, while he was bright enough to learn a great deal of physics on his own, he remained, like Michael Faraday, unskilled in advanced mathematics.

Joule had the means to devote his time to what became the passion of his life — obtaining highly accurate experimental results in physics, for which he displayed a precocious aptitude. His genius showed itself in his ability to devise new methods, whenever needed, to improve on the accuracy of his quantitative results.

Joule had no real profession except as an amateur scientist, and no job except for some involvement in running the family brewery. Since his father was ill and forced to retire in 1833, his son had to become more involved in the affairs of the brewery from 1833 to 1854, when the brewery was sold by his family. While Joule was working at the brewery, he carried out his experiments before 9:00 a.m., when the factory opened, and after 6:00 p.m., when it closed. Because his father built a laboratory for him in his home, in 1854 he had the time and means to devote himself completely to physics research. Later in life, he suffered severe financial misfortune, but the Royal Society and Queen Victoria in 1878 each provided a £200 subsidy for Joule to continue his important researches.

In 1847 Joule married Amelia Grimes, and they had two children who survived them. Another son was born on June 8, 1854, but died later that month. This was followed by an even greater tragedy—within a few months Joule's wife also passed away. Joule never remarried, but spent the rest of his life with his two children in a variety of residences near Manchester.

Joule died in Sale, Cheshire, England, on October 11, 1889. He always remained a modest, unassuming man, and a sincerely religious one (even though he was in the habit of falling asleep during sermons). Two years before his death he said to his brother, "I have done two or three little things, but nothing to make a fuss about." Those "two or three little things" were so important for the advancement of science that Joule was elected in 1850 as a fellow of the Royal Society of London, received the Copley Medal (its highest award) in 1866, and was elected president of the British Association for the Advancement of Science in 1872 and again in 1887. Joule is memorialized by a tablet in Westminster Abbey, and constantly comes to the attention of physicists whenever they use the unit of energy now officially called the joule (J).

JOULE'S CONTRIBUTIONS TO THE PHYSICS OF ENERGY

Joule's interest in the conservation of energy developed as a consequence of some work he did in his teens on electric motors. In 1841 he proposed, on the basis of his experiments, that the rate at which heat Q is generated by a constant electric current i passing through a wire of electrical resistance R is: now called Joule's Law.

From 1841 to 1847 Joule worked steadily on measuring the heat produced by electrical processes (Joule's Law), mechanical processes (rotating paddles churning water or mercury), and frictional processes (the rubbing of materials together, as Count Rumford had done in 1798). In each case he compared the amount of energy entering the system with the heat produced. He proved his mettle as a physicist by spending endless days ferreting out the causes of errors in his experiments and then modifying his experimental set-up to eliminate them. In this way he produced a remarkably precise and accurate value for the constant that relates the energy entering the system (in joules) with the heat produced (in calories). This constant is now called Joule's Equivalent, or the mechanical equivalent of heat.

In 1847 Joule published a paper that contained an overwhelming amount of experimental data. All his results averaged out to a value of 4.15 J/cal (in modern units), with a spread about this mean of only five percent. The best modern value of Joule's Equivalent is 4.184 J/cal, and so his results were accurate to better than one percent. This was truly amazing, for the heat measurements Joule performed were the most difficult in all of physics at that time.

At the British Association meeting at Oxford in June 1847, at which Joule presented his results, his audience's reaction was much more subdued and uninterested than he had expected. Joule fully believed that his paper would have passed unnoticed had not the 23-year-old William Thomson (later Lord Kelvin) asked a number of penetrating questions. These awakened his colleagues to the significance of Joule's work as a proof of the conservation-of-energy principle (now commonly called the first law of thermodynamics) under a variety of experimental conditions and involving many different types of energy.

This event marked the turning point in Joule's career. From 1847 on, when Joule spoke, scientists listened. His research results were one of the two major contributions to the establishment of the first law of thermodynamics, the other being that of the German physician Julius Robert Mayer. Mayer's work, although historically important for its insights into the conservation-of-energy principle, was however tainted by errors in physics and an unacceptable reliance on philosophical arguments.

In addition to his work on the conservation of energy, Joule made a number of other important contributions to physics. In 1846 he discovered the phenomenon of magnetostriction, in which an iron rod was found to change its length slightly when magnetized. In 1852, together with William Thomson, he showed that when a gas is allowed to expand into a vacuum, its temperature drops slightly. This "Joule-Thomson effect" is still very useful in the production of low temperatures.

Joule believed that nature was ultimately simple, and strove to find the simple relationships (like Joule's law in electricity), which he was convinced must exist between important physical quantities. His phenomenal success in finding such relationships in the laboratory made a crucial contribution to the understanding of energy and its conservation in all physical, chemical and biological processes.

Joseph F. Mulligan

BIBLIOGRAPHY

Cardwell, D. S. L. (1971). From Watt to Clausius. Ithaca, New York: Cornell University Press.

Cardwell, D. S. L. (1989). James Joule: A Biography. Manchester, England: Manchester University Press.

Crowther, J. G. (1936). "James Prescott Joule." In Men of Science. New York: W.W. Norton.

Joule, J. P. (1963). The Scientific Papers of James Prescott Joule, 2 vols. London: Dawson's.

Rosenfeld, L. (1973). "Joule, James Prescott." In Dictionary of Scientific Biography, ed. Charles Coulston Gillispie, Vol. 7, pp. 180–182. New York: Scribner.

Steffens, H. J. (1979). James Prescott Joule and the Development of the Concept of Energy. New York: Science History Publications.

Wood, A. (1925). Joule and the Study of Energy. London: G. Bell and Sons, Ltd.