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Kelvin, Lord Thomson, William (1824-1907) was a British physicist who first proposed the use of the absolute scale of temperature, in which the degree of temperature is now called the kelvin in his honour. Thomson also made other substantial contributions to thermodynamics and the theory of electricity and magnetism, and he was largely responsible for the first successful transatlantic telegraph cable. Kelvin was born William Thomson in Belfast on 26 June 1824. His father was Professor of Mathematics at Belfast University and both he and his older brother James Thomson (1822-1892), who also became a prominent physicist, were educated at home by their father. In 1832 Thomson' s father took up the post of Professor of Mathematics at Glasgow University, and Thomson himself entered the university two years later at the age of ten to study natural philosophy (science). In 1841, Thomson went on to Cambridge University, graduating in 1845. He then travelled to Paris to work with Henri Regnault (1810-1878) and in 1846 took up the position of Professor of Natural Philosophy at Glasgow, where he created the first physics laboratory in a British university. Among his many honours were a knighthood in 1866, the Royal Society's Copley Medal in 1883, the Presidency of the Royal Society from 1890 to 1894 and a peerage in 1892, when he took the title Baron Kelvin of Largs. Kelvin retired from his chair at Glasgow in 1899 and died at Largs, Ayrshire, on 17 December 1907. Thomson's early work, begun in 1842 while he was still at Cambridge, was a comparison of the distribution of electrostatic force in a region with the distribution of heat through a solid. He found that they are mathematically equivalent, leading him in 1847 to conclude that electrical and magnetic fields are distributed in a manner analogous to the transfer of energy through an elastic solid. James Clerk Maxwell (1831-1879) later developed this idea into a comprehensive explanation of the electromagnetic field. From 1849 to 1859, Kelvin also developed the discoveries and theories of paramagnetism and diamagnetism made by Michael Faraday (1791-1867) into a full theory of magnetism, developing the terms magnetic permeability and susceptibility, and arriving at an expression for the total energy of a system of magnets. In electricity, Kelvin obtained an expression for the energy possessed by a circuit carrying a current and in 1853 developed a theory of oscillating circuits that was experimentally verified in 1857 and was later used in the production of radio waves. In Paris in 1845, Kelvin was introduced to the classic work of Sadi Carnot (1796-1832) on the motive power of heat. From a consideration of this theory, which explains that the amount of work produced by an ideal engine is governed only by the temperature at which it operates, Kelvin developed the idea of an absolute temperature scale in which the temperature represents the total energy in a body. He proposed such a scale in 1848 and set absolute zero at -273°C (-459°F), showing that Carnot's theory followed if absolute temperatures were used. However, Kelvin could not accept the idea then still prevalent and accepted by Carnot that heat is a fluid, preferring to see heat as a form of motion. This followed Kelvin's championing of the work of James Joule (1818-1889), 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, which had been advanced independently in 1850 by Rudolf Clausius (1822-1888). In 1852 Kelvin also produced the idea that mechanical energy tends to dissipate as heat, which Clausius later developed into the concept of entropy. Kelvin and Joule collaborated for several years following their meeting, Joule's experimental prowess matching Kelvin's theoretical ability. In 1852 they discovered the Joule-Thomson effect, which causes gases to undergo a fall in temperature as they expand through a nozzle. The effect is caused by the work done as the gas molecules move apart, and it proved to be of great importance in the liquefaction of gases. Kelvin was also interested in the debate then taking place about the age of the Earth. Hermann Helmholtz (1821-1894) in 1854 gave a value of 25 million years for the Earth's lifetime, assuming that the Sun gained its energy by gravitational contraction. Kelvin came to a similar conclusion in 1862, basing his estimate on the rate of cooling that would have occurred from the time the Earth formed, and reaching an age of 20 million to 400 million years with 100 million years as the most likely figure. Furthermore, the cooling would have produced volcanic upheavals that would have limited the time available for the evolution of life. Although both estimates were far too low, neither scientists knowing of the nuclear processes that fuel the Sun and the radioactivity that warms the Earth, their figures were taken seriously and helped to bring about theories of mutation to explain evolution. Kelvin's knowledge of electrical theory was applied with great practical value to the laying of the first transatlantic telegraph cable. Kelvin pointed out that a fast rate of signalling could only be achieved by using low voltages, and that these would require very sensitive detection equipment such as the mirror galvanometer that he had invented. The first cable laid in 1857 broke and high voltages were used in the second cable laid a year later as Kelvin's predictions were not believed. The cable did not work, but a third cable laid in 1866 using Kelvin's ideas was successful, and it was for this achievement that he received a knighthood. Kelvin was also very concerned with the accurate measurement of electricity, and developed an absolute electrometer in 1870. He was instrumental in achieving the international adoption of many of our present-day electrical units in 1881. Kelvin was one of the greatest physicists of the nineteenth century. His pioneering work on heat consolidated thermodynamics and his understanding of electricity and magnetism paved the way for the explanation of the electromagnetic field later achieved by Maxwell. Author not available, Kelvin, Lord Thomson, William (1824-1907). , The Hutchinson Dictionary of Scientific Biography, 01-01-1998. |
