James Joule, English physicist, 1882.

UNITED KINGDOM - JULY 02: Engraving by C H Jeens from the periodical �Nature�, published 26th October 1882. James Joule (1818-1889) is best known for his experimental establishment of the mechanical theory of heat. In 1847 Joule met the Scottish physicist William Thomson, Baron Kelvin of Largs (1824-1907), who recognised the importance of Joule�s work and went on to collaborate with him on a series of papers. In 1848 Joule became a fellow of the Royal Society. From 1852 Joule and Thomson worked together to try and verify predications made previously by Thomson in relation to thermodynamics. This led to the so-called Joule-Thomson effect, based on a slight deviation from the work on gases by H V Regnault. (Photo by SSPL/Getty Images)