William Thomson Kelvin, 1st Baron

The thermodynamics studies of the Scottish physicist William Thomson, b. June 26, 1824, d. Dec. 17, 1907, led to his proposal (1848) of an absolute scale of temperature. The Kelvin absolute temperature scale, developed later, derives its name from the title--Baron Kelvin of Largs--that he received from the British government in 1892. Thomson also observed (1852) what is now called the Joule-Thomson effect--the decrease in temperature of a gas when it expands in a vacuum.

Thomson served as professor of natural philosophy (1846-99) at the University of Glasgow. One of his first projects was to calculate the age of the Earth, based on the rate of cooling of the planet--assuming it had once been a piece of the Sun. (His result--20 to 400 million years--was far short of the current estimate of 4.5 billion years.) Greatly interested in the improvement of physical instrumentation, he designed and implemented many new devices, including the mirror-galvanometer that was used in the first successful sustained telegraph transmissions in transatlantic submarine cable. Thomson's participation in the telegraph cable project formed the basis of a large personal fortune.