William Thomson, 1st Baron Kelvin

William Thomson, 1st Baron Kelvin (26 June 1824 – 17 December 1907) was a British mathematician, mathematical physicist and engineer.

Born in Belfast, he was the professor of Natural Philosophy at the University of Glasgow for 53 years. There he undertook significant research on the mathematical analysis of electricity, and was instrumental in the formulation of the first and second laws of thermodynamics. He contributed significantly to unifying physics, which was then in its infancy of development as an emerging academic discipline. He received the Royal Society's Copley Medal in 1883 and served as its president from 1890 to 1895. In 1892 he became the first scientist to be elevated to the House of Lords.

Absolute temperatures are stated in units of kelvin in Lord Kelvin's honour. While the existence of a coldest possible temperature, absolute zero, was known before his work, Kelvin determined its correct value as approximately −273.15 degrees Celsius or −459.67 degrees Fahrenheit. The Joule–Thomson effect is also named in his honour.

Kelvin worked closely with the mathematics professor Hugh Blackburn in his work. He also had a career as an electrical telegraph engineer and inventor which propelled him into the public eye and earned him wealth, fame and honours. For his work on the transatlantic telegraph project, he was knighted in 1866 by Queen Victoria, becoming Sir William Thomson. He had extensive maritime interests and worked on the mariner's compass, which previously had limited reliability.

Kelvin was ennobled in 1892 in recognition of his achievements in thermodynamics, and of his opposition to Irish Home Rule, becoming Baron Kelvin, of Largs in the County of Ayr. The title refers to the River Kelvin, which flows near his laboratory at the University of Glasgow's Gilmorehill home at Hillhead. Despite offers of elevated posts from several world-renowned universities, Kelvin refused to leave Glasgow, remaining until his retirement from that post in 1899. Active in industrial research and development, he was recruited around 1899 by George Eastman to serve as vice-chairman of the board of the British company Kodak Limited, affiliated with Eastman Kodak. In 1904 he became Chancellor of the University of Glasgow.