James Prescott Joule (1818-1889)

British physicist, famous for his research into electricity and thermodynamics.

James was educated at home until he was 15, after which time he went to work in the family brewery. However, he and his older brother continued their education part-time with private tutors in Manchester.

From 1834 until 1837, they were taught chemistry, physics, the scientific method and mathematics by the famous English chemist John Dalton.

In 1839 Joule began a series of experiments involving mechanical work, electricity and heat. In 1840, he sent a paper entitled On the Production of Heat by Voltaic Electricity to the prestigious Royal Society in London. The Royal Society showed little enthusiasm for Joule's paper, however, and published only a brief summary of his findings.

In 1843 Joule calculated the amount of mechanical work needed to produce an equivalent amount of heat. This quantity was called 'the mechanical equivalent of heat'. Again he presented a paper on his findings - this time to the British Association for the Advancement of Science. Response was again unenthusiastic. Several leading journals also declined to publish papers on Joule's work. Many British scientists were sceptical - Joule's findings challenged the caloric theory of heat which most physicists believed in at that time. In the caloric theory, heat was believed to be a 'subtle' fluid -an undefined form of matter.

Joule's work remained largely ignored until 1847, when it came to the attention of William Thomson, later Lord Kelvin. Other enthusiastic supporters were Michael Faraday and George Stokes. In 1849, Joule read his paper titled On the Mechanical Equivalent of Heat to the Royal Society, with Faraday as his sponsor. The following year it was published and Joule was elected a member of the society.

The principle of energy conservation involved in Joule's work gave rise to the new scientific discipline known as thermodynamics. While not the first to suggest this principle, Joule was the first to demonstrate its validity.

William Thomson recognised the importance of Joule's work, and in 1852 began working with him. Together they worked on a number of important experiments to confirm some of the predictions being made in this new discipline. The most famous of these experiments involved the decrease in temperature associated with the expansion of a gas without the performance of external work. This cooling of gases as they expand is known as the 'Joule Thomson effect', and the principle provided the basis for development of the refrigeration industry.

From 1872 onwards Joule's health deteriorated and he did little further work. He died at Sale, Cheshire, England, on October 11, 1889.

The SI unit for amount of heat is named in Joule's honour.