James Prescott Joule

James Prescott Joule
Born	United Kingdom
Died	October 11, 1889(1889-10-11) (aged 70)
Occupation	Physicist
Known for	Investigations into heat and mechanical energy, conservation of energy principle, first law of thermodynamics, Joule's first law, Kelvin scale

James Prescott Joule (24 December 1818 – 11 October 1889) was a British physicist renowned for his investigations into heat and its connection to mechanical energy, which contributed significantly to the formulation of the conservation of energy principle and the first law of thermodynamics. The SI unit for energy, the joule (J), honors his contributions.

In collaboration with Lord Kelvin, Joule helped establish the absolute thermodynamic temperature scale, now known as the Kelvin scale. He also discovered magnetostriction and identified the relationship between electric current passing through a resistor and the resulting heat produced, a principle referred to as Joule's first law. His groundbreaking work on energy transformations was initially published in 1843.

Early years

James Joule was born in 1818 to Benjamin Joule, a prosperous brewery owner. He received scientific guidance from John Dalton and was influenced by chemist William Henry as well as Manchester engineers Peter Ewart and Eaton Hodgkinson. Interested in electricity from a young age, he and his brother conducted experiments involving electric shocks.

As he matured, Joule took charge of the family brewery but pursued scientific inquiry seriously alongside his business duties. Around 1840, he investigated the possibility of substituting the brewery’s steam engines with electric motors. His early scientific writings appeared in William Sturgeon’s Annals of Electricity. Driven by both commercial efficiency goals and scientific interest, Joule aimed to determine which prime mover offered superior efficiency.

In 1841, he articulated what became known as Joule's first law: the heat produced by an electrical current is proportional to the square of that current multiplied by resistance. He determined that steam engines powered by coal were more cost-effective than zinc-based batteries. To quantify energy output, Joule used the foot-pound, which measures the work required to lift one pound by one foot.

Joule soon shifted his attention from economic considerations toward exploring how work could be extracted and energy transformed. His experiments in 1843 revealed that heat generated within conductors occurred locally, contradicting the prevailing caloric theory that treated heat as an indestructible fluid. Although advocates of caloric theory resisted these findings—citing reversible thermoelectric phenomena—Joule’s research laid essential foundations for modern thermodynamics.

The mechanical equivalent of heat

Through experiments involving his electric motor, Joule estimated the mechanical equivalent of heat as approximately 4.1868 joules per calorie required to raise one gram of water by one kelvin. He presented these findings at the British Association for the Advancement of Science meeting in Cork in August 1843; however, his results initially received little attention.

Persisting in his efforts, Joule pursued a purely mechanical approach by forcing water through a perforated cylinder to generate viscous heating, deriving a mechanical equivalent value consistent with his electrical measurements. This agreement reinforced the concept that work could be converted into heat.

Subsequently, Joule measured heat produced by compressing gases and obtained another estimate for the mechanical equivalent of heat. Although his paper was rejected by the Royal Society in 1844, it was later published in the Philosophical Magazine in 1845. In this publication, he dismissed the Caloric theory, arguing that any framework implying destruction of force was flawed—reflecting his theological belief that only a divine Creator could annihilate energy.

In June 1845, Joule demonstrated his most famous experiment at a British Association meeting in Cambridge. By using a falling weight to rotate a paddle wheel submerged in insulated water, he measured an increase in temperature and calculated a mechanical equivalent value. He subsequently detailed this experiment in a letter to the Philosophical Magazine later that year.

By 1850, Joule had refined his measurement to a value closely matching those established during the twentieth century.

Reception and priority

Joule initially faced skepticism due to his dependence on extraordinarily accurate measurements—he asserted precision within of a degree Fahrenheit (3 mK), a level of exactitude rare for that era. His background in brewing and access to practical instruments, aided by instrument-maker John Benjamin Dancer, enabled such meticulous results. Joule’s experimental work aligned well with theoretical progress made by Rudolf Clausius, who co-developed the concept of energy.

He advanced a kinetic theory of heat, describing it as rotational kinetic energy, which required acceptance of perfectly elastic molecular collisions. At that time, the scientific community was largely unconvinced about the reality of atoms and molecules, despite foundational contributions from scientists such as John Dalton and later Ernest Rutherford.

The dominant caloric theory had certain merits, particularly in providing the basis for Nicolas Léonard Sadi Carnot’s heat engine analysis. It was only subsequently that Lord Kelvin demonstrated Carnot’s mathematical framework held true without presuming the existence of a caloric fluid.

In Germany, Hermann Helmholtz recognized the parallel work of Joule and Julius Robert von Mayer from 1842, crediting both in his 1847 formulation of the conservation of energy. That same year, Joule presented his findings at the British Association meeting in Oxford, where prominent figures including George Gabriel Stokes, Michael Faraday, and William Thomson (later Lord Kelvin) were present. Stokes supported Joule’s concepts; Faraday was impressed yet remained unconvinced; Thomson showed interest but maintained reservations.

Later in 1847, Joule met Thomson in Chamonix. Although their attempt to detect temperature changes at a waterfall was unsuccessful, this encounter set the stage for future cooperation. Initially an advocate for the Carnot–Clapeyron perspective, Thomson expressed early skepticism about caloric theory in 1848 influenced by Joule’s results. While he did not conduct new experiments at that time, by 1851 he acknowledged both Joule’s and Carnot’s roles in explaining heat’s capacity to perform work.

This interaction sparked a fruitful correspondence between 1852 and 1856: Joule conducted experiments while Thomson interpreted data and suggested further investigations. Their collaborative efforts, including identifying the Joule–Thomson effect, played a key role in wider acceptance of Joule’s discoveries and the kinetic theory of gases.

Kinetic theory

Kinetics involves the study of motion, and as a student of Dalton, Joule embraced the atomic theory despite widespread doubt during his time. He was open to the overlooked contributions of John Herapath regarding the kinetic theory of gases and drew inspiration from Peter Ewart’s 1813 essay "On the measure of moving force."

Joule connected his experimental findings to the kinetic theory of heat, proposing that heat represents rotational motion at a molecular level. He also traced intellectual influences from earlier thinkers such as Francis Bacon, Sir Isaac Newton, John Locke, Count Rumford, and Sir Humphry Davy. From Rumford’s research, Joule estimated the mechanical equivalent of heat at 1,034 foot-pounds despite critiques about the precision of these experiments. He observed that Mayer’s measurements were no more exact than those by Rumford.

Joule is credited with describing the sunset phenomenon known as the green flash in an 1869 letter to the Manchester Literary and Philosophical Society, although he only noted its final appearance as bluish green without providing an explanation for its cause.

Published Work

• "The Heat Generated by Metallic Conductors of Electricity and within Battery Cells during Electrolysis," Philosophical Magazine, 1841
• "Calorific Effects of Magneto-Electricity and the Mechanical Value of Heat," Philosophical Magazine, 1843
• "Temperature Variations Caused by the Rarefaction and Compression of Air," Proceedings of the Royal Society of London, 1844
• "Temperature Changes Resulting from Air Rarefaction and Condensation," Philosophical Magazine, 1845
• "The Mechanical Equivalent of Heat," Notices and Abstracts to British Association for Advancement of Science, 1845
• "Evidence for an Equivalent Relationship Between Heat and Mechanical Power," Philosophical Magazine, 1845
• "On the Mechanical Equivalent of Heat," Philosophical Transactions of the Royal Society of London, 1850
• The Scientific Papers of James Prescott Joule, Physical Society, London, 1884
• Collected Scientific Papers, Taylor and Francis, London, 1887

Honours

Joule passed away at his residence in Sale and was laid to rest in Brooklands cemetery. His tombstone bears the inscription "772.55," denoting his 1878 determination of the mechanical equivalent of heat—expressed as the foot-pounds of work necessary to raise one pound of water from to . Additionally, it features a verse from the Gospel of John: "I must work the work of him that sent me, while it is day: the night cometh, when no man can work." In tribute, a local Wetherspoons pub in Sale carries his name as "The J. P. Joule."

Notable distinctions include:

• Fellowship of the Royal Society (1850)
  • Recipient of the Royal Medal (1852) recognizing his paper on the mechanical equivalent of heat
  • Awarded the Copley Medal (1870) for contributions to the dynamical theory of heat
• Presidency of the Manchester Literary and Philosophical Society (1860)
• Twice President of the British Association for the Advancement of Science (1872, 1887)
• Honorary Member of the Institution of Engineers and Shipbuilders in Scotland (1857)
• Honorary degrees bestowed:
  • LL.D. from Trinity College, Dublin (1857)
  • DCL from University of Oxford (1860)
  • LL.D. from University of Edinburgh (1871)
• Civil list pension awarded at £200 annually starting 1878 in recognition of his scientific achievements
• Recipient of the Albert Medal from the Royal Society of Arts (1880) for establishing fundamental links between heat, electricity, and mechanical work—laying scientific groundwork for engineering advancements

A commemorative monument honoring Joule is situated in Westminster Abbey’s north choir aisle, although he is not interred there. His statue by Alfred Gilbert stands within Manchester Town Hall, positioned opposite that dedicated to Dalton.

Family

In 1847, Joule wed Amelia Grimes; she passed away in 1854. The couple had three children: Benjamin Arthur Joule (1850–1922), Alice Amelia (1852–1899), and a son named Joe who died during infancy.

See Also

• Latent heat
• Sensible heat
• Internal energy

Additional resources

• Fox, R, "James Prescott Joule, 1818–1889", featured in

External links

• The scientific papers of James Prescott Joule (1884) – with annotations by Joule
• The joint scientific papers of James Prescott Joule (1887) – annotated by Joule himself
• Classic publications from 1845 and 1847 at ChemTeam On the Mechanical Equivalent of Heat and On the Existence of an Equivalent Relation between Heat and the ordinary Forms of Mechanical Power
• Joule's apparatus for water friction housed at the London Science Museum
• Some Remarks on Heat and the Constitution of Elastic Fluids, featuring Joule's 1851 calculation of gas molecule velocity
• Manuscripts of Joule preserved at University of Manchester Library
• University of Manchester resources on Joule – includes images of his residence and burial site
• Joule Physics Laboratory located at University of Salford