William Thomson, Lord Kelvin

William Thomson was born in Belfast in 1824 and raised in Glasgow, where his father was a mathematics professor. A prodigy, he entered Glasgow University at ten and went on to Cambridge, becoming professor of natural philosophy at Glasgow in 1846 at the age of twenty-two — a post he held for fifty-three years. He was raised to the peerage as Baron Kelvin in 1892, taking his title from the River Kelvin that runs past the university.

In 1848 Thomson proposed an absolute thermodynamic temperature scale whose zero lies at the point where no more heat can be extracted from a body, independent of any particular substance. The scale followed from Carnot's analysis of heat engines, whose efficiency depends only on temperature; the unit of absolute temperature, the kelvin, is named for him. He worked closely with James Joule, and the Joule–Thomson effect — the cooling of a gas on expansion — emerged from their collaboration.

Thomson was a principal architect of the first and second laws of thermodynamics, giving an early statement of the second law and the principle of energy dissipation. His range was vast, spanning electromagnetism, elasticity, hydrodynamics, and geophysics, where his estimate of the age of the Earth (too low, because he did not know of radioactive heating) famously clashed with geologists and biologists.

He was also a consummate engineer and entrepreneur. His theory of signal transmission and his sensitive galvanometers made the first successful transatlantic telegraph cable possible in 1866, for which he was knighted, and he patented dozens of instruments. He died in 1907 and is buried in Westminster Abbey, next to Newton.