James Prescott Joule

English physicist

• Born: December 24, 1818; Salford, England
• Died: October 11, 1889; Sale, England

James Prescott Joule was a nineteenth-century physicist who studied heat and energy. His work as a brewer inspired him to study the nature of heat and led to his discovery of the first law of thermodynamics. The international unit used to measure energy is named the joule in his honor.

Primary field: Physics

Specialty: Thermodynamics

Early Life

James Prescott Joule was born on December 24, 1818 in Salford, England to Benjamin and Alice Prescott Joule. His father owned and operated the Joule Brewery. It was attached to the family’s house, and the Joule children grew up surrounded by the family business. Joule was tutored at home until he was sixteen. In 1834, Joule and his brother were sent to study under chemist John Dalton at the Manchester Literary and Philosophical Society. Dalton was famous for his pioneering work on atomic structure, which would later influence Joule’s work.

Although Dalton suffered a stroke that took him out of teaching two years after the Joule brothers came, Joule continued to be interested in science and research, particularly electricity. Frustrated with the lack of precise measurements available for electrical research, he invented his own standard unit of the amount of electricity needed to break up nine grains of water in one hour (a grain is a unit measuring the presence of minerals in water). Joule believed that electrical research had to be measured by the same units by all scientists, so that experiments carried out in different places and under different conditions could be directly compared.

Joule began his investigations into electricity at an early age, and continued them even after he and his brother Benjamin were required to take over the family business from their ailing father. Joule constructed his own scientific apparatus at home, and one of his early machines was featured in the Annals of Electricity magazine when he was only nineteen. Joule was among the growing ranks of scientists who imagined electricity could replace steam as a source of energy.

Joule continued to work in the brewery until it was sold in 1854. His wife, Amelia Grimes, also died that year, leaving him two children. After the brewery was sold, Joule began devoting all his time to scientific research.

Life’s Work

Joule began his scientific career early and enthusiastically; the Royal Society lists him as the author of ninety-seven papers. However, living outside of London, with very little formal training, he was considered a mere dabbler instead of a serious scientist. Joule had to work harder than his peers to make his theories known.

Joule’s early work focused on electromagnetism. He built his own instruments and invented his own unit of measurement after becoming frustrated by the lack of precision in other scientists’ work. In his earliest experiments, he determined the upper limit to the strength of electromagnets, or iron shot with electricity. His methods allowed him to create the strongest electromagnet yet built.

In 1840, Joule began focusing his work on the heat and energy involved in magnets and early batteries. At the time, the prevailing theory of heat transfer was the caloric theory, developed in part by French scientist Antoine Lavoisier in the late eighteenth century. Caloric theory stated that heat is made of a fluid or gas that repels itself, spreading from hotter to cooler areas. This theory postulated that heat could not be created or destroyed, only manipulated by machines.

Batteries in Joule’s time were mainly voltaic or galvanic cells—simple constructions of two different metals, usually zinc and copper, suspended in two different salt solutions of each metal. The solutions and metals were connected by a salt bridge, either a glass tube filled with a gelled salt solution or paper soaked in the solution. Joule discovered that the heat generated by these primitive batteries was equal to the heat produced in the cell of the battery. In other words, he found that his batteries were indeed creating heat in a chemical process and transferring the heat throughout the battery. This did not agree with caloric theory, but Joule’s lack of prominence among his scientific peers made convincing them an uphill battle.

Joule was convinced that there was a connection between heat and mechanical motion, or force. Against the beliefs of his scientific peers, he posited that heat was not a substance, but the effect of motion. In one of his most famous papers, read before the British Association at Cork in 1843, he described the results of his experiments with magnets and water. The paper, “The Caloric Effects of Magneto-Electricity and the Mechanical Value of Heat,” eventually gained acceptance as the experiments were repeated by other scientists across Europe. One of Joule’s experiments involved submerging an electromagnet in water and letting it spin. Joule found that the friction caused by the spinning magnet caused the water to heat up. Other experiments involved forcing water through narrow tubes, or churning it with a paddle wheel. He measured the energy it took to heat one pound of water with friction by one degree Fahrenheit and then equated it to the amount of energy needed to lift 838 pounds by one foot. This number was recalculated and measured more precisely many years later, until the frictional energy needed to heat one pound of water was determined to be the equivalent of 772.55 foot-pounds.

Although it was rejected at first, Joule’s work eventually came to the attention of several important scientific figures, which led to his collaboration with prominent scientists such as Lord Kelvin of Ireland and British chemist Michael Faraday. Joule even helped Kelvin in the development of his temperature scale. However, it was his work with heat and electricity that led scientists to develop the first law of thermodynamics.

Joule died in 1889 in Sale, England. He was seventy years old. Over the course of his career, he earned the respect and admiration of the scientific community. He twice served as president of the British Association for the Advancement of Science and was awarded honorary degrees from Trinity College Dublin, the University of Oxford, and the University of Edinburgh.

Impact

Once Joule’s work gained prominence, many scientists were inspired to develop it further. Several scientists are credited with forming the first law of thermodynamics, but all based their investigations on experiments similar to Joule’s.

Joule was later honored by having a unit of energy measurement named for him, the joule. The unit refers to the amount of energy expended by applying one newton of force across one meter.

One reason Joule’s theories did not initially find acceptance among his peers was the very small temperature degrees he used as proof in his experiments. He claimed that he could measure temperature to within one-two-hundredth of a degree, which his detractors doubted was possible. Eventually, however, scientists realized the importance of using extremely precise measurements to prove theories that would otherwise remain almost impossible to demonstrate.

Bibliography

Atkins, Peter. The Laws of Thermodynamics: A Very Short Introduction. Oxford: Oxford UP, 2010. Print. Presents an overview of the four laws of thermodynamics. Includes a description of how each law works and discusses its practical and scientific significance.

Joule, James Prescott. The Scientific Papers of James Prescott Joule. Cambridge: Cambridge UP, 2011. Print. Reprint of Joule’s papers detailing his work on heat and energy. Discusses heat measurement, electromagnets, and thermodynamics. Originally published by the Physical Society of London between 1885 and 1887.

Reynolds, Osborne. Memoir of James Prescott Joule (Volume 1). Cambridge: Cambridge UP, 2011. Print. Reprint of Joule’s biography, written by his colleague, Osborne Reynolds (1842–1912). Includes details about Joule’s early life and discusses the significance of his scientific achievements. Originally published in 1892.