Kelvin, William Thomson (1824-1907)

Irish physicist who introduced the kelvin scale, the absolute scale of temperature. His work on the conservation of energy in 1851 led to the second law of thermodynamics. He was knighted in 1866, and made a baron in 1892.

Kelvin's knowledge of electrical theory was largely responsible for the first successful transatlantic telegraph cable. In 1847 he concluded that electrical and magnetic fields are distributed in a manner analogous to the transfer of energy through an elastic solid. From 1849 to 1859 Kelvin also developed the work of English scientist Michael Faraday into a full theory of magnetism, arriving at an expression for the total energy of a system of magnets.

Kelvin was born in Belfast and educated at Glasgow University (which he entered at the age of ten) and Cambridge. He was professor of natural philosophy at Glasgow 1846-99, and there created the first physics laboratory in a British university.

Based on the theories of French physicist Sadi Carnot on the motive power of heat, in 1848 Kelvin proposed an absolute temperature scale in which the temperature represents the total energy in a body. Kelvin differed from Carnot in seeing heat as a form of motion, an idea derived from the work of James Joule, whom Kelvin met in 1847, on the determination of the mechanical equivalent of heat. In 1851 Kelvin announced that Carnot's theory and the mechanical theory of heat were compatible provided that it was accepted that heat cannot pass spontaneously from a colder to a hotter body. This is now known as the second law of thermodynamics. In 1852 Kelvin also produced the idea that mechanical energy tends to dissipate as heat.

Kelvin was very concerned with the accurate measurement of electricity, and developed an absolute electrometer in 1870. He was instrumental in achieving the international adoption in 1881 of many of our present-day electrical units. He also invented a tide gauge and predictor, an improved compass, and simpler methods of fixing a ship's position at sea.