Kelvin, Lord (William Thomson)

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KELVIN, LORD (WILLIAM THOMSON)

KELVIN, LORD (WILLIAM THOMSON) (1824–1907), British scientist.

The fourth child of James and Margaret Thomson, William Thomson was born in Belfast. His mathematician father taught at the Belfast Academical Institution, well known for its political and religious radicalism. His mother, who came from a Glasgow commercial family, died when William was six. In 1832 his father was offered the chair of mathematics at the University of Glasgow and there continued to exert a profound influence on the education of his children. William enjoyed a broad philosophical curriculum at Glasgow but left without taking a degree in order to enter Peterhouse, Cambridge, as an undergraduate. Following several years of intensive mathematical study he emerged second in the 1845 "Mathematics Tripos," the intensely competitive examinations that ranked final-year students in order of mathematical merit. Enhancing his experimental skills in Paris, he was elected in 1846 as Glasgow University professor of natural philosophy, a post from which he retired in 1899.

In a scientific paper written when he was seventeen, Thomson used Jean-Baptiste-Joseph Fourier's (1768–1830) mathematical treatment of heat flow to replace action-at-a-distance forces in electrostatics with continuous-flow models. His radical approach later inspired James Clerk Maxwell's electromagnetic field theory, which found expression in the celebrated Treatise on Electricity and Magnetism (1873). Thomson himself extended Fourier's techniques to analyze electric signals transmitted through long-distance telegraph wires. Retardation of such signals had raised concerns among telegraph projectors, especially in relation to the economic viability of undersea cables. Thomson's analysis enabled him to advise on the optimum dimensions for projected transatlantic and imperial telegraphs. He also constructed extremely delicate measuring instruments, most notably a "marine mirror galvanometer," for use in telegraphic engineering. For these services to the empire, he was knighted by Queen Victoria in 1866, following completion of the first successful Atlantic telegraph.

Just two years into his professorship at Glasgow, Thomson formulated an "absolute" scale of temperature (later named the Kelvin Scale in his honor) which differed from traditional scales in being independent of any specific substance such as mercury. It depended on Thomson's recent commitment to Sadi Carnot's theory of the motive power of heat in which the "fall" of heat between a high temperature (the boiler) and a low temperature (the condenser) drove a heat engine just as the fall of water drove a waterwheel. Thomson's insight was to correlate temperature difference—the "fall"—with work done rather than with a particular working substance.

These researches took place within a larger context that generated, over the next decade, the new sciences of thermodynamics and energy. In the 1840s the Manchester experimentalist James Joule had been conducting laboratory investigations to determine the quantitative relationship between work done and heat produced. Thomson initially accepted Joule's findings that work could be converted into heat, as in friction, according to an exact equivalent. Committed to Carnot's theory, however, he could not accept the converse that work, once converted into heat, could then simply be recovered as useful work. Aided by similar investigations recently undertaken by the Scottish engineer William John Macquorn Rankine and the German physicist Rudolf Clausius, Thomson produced a reconciliation of Joule and Carnot in 1850–1851. For the production of work or motive power, a "thermo-dynamic engine" (Thomson's name for a heat engine) required two principles, the conversion of an exact amount of heat into the work done and the transfer of a certain amount of heat from high to low temperature. These principles formed the basis for the two laws of thermodynamics. The new science offered the empire's marine engineers—many located in Glasgow—an incentive to design steam engines of much higher pressures, which in accordance with thermodynamic laws would offer greater economy of fuel consumption.

Thomson and Rankine then introduced the terms actual (later kinetic) and potential energy. The laws of energy conservation and dissipation became the foundation of a new "science of energy," and the physics discipline quickly became redefined as the study of energy and its transformations. Thomson and his Edinburgh University colleague Peter Guthrie Tait initiated, but never completed, a vast project to develop an energy perspective in all branches of physical science, which would find embodiment in their Treatise on Natural Philosophy (1867).

Using these energy laws, Thomson arrived at ages for the earth and sun (20–100 million years). He explicitly challenged the geological timescales and assumptions on which Charles Darwin had built his controversial theory of evolution by means of natural selection (1859). The famous evolutionist later admitted that of the many objections raised to his theory, Thomson's proved the most difficult to counter.

Thomson developed his private laboratory into the first university physical laboratory in Britain. The work extended beyond telegraphic testing and invention to the patenting and manufacture of a large range of scientific, industrial, and navigational instruments. The wealth generated enabled him to purchase in 1870 a 126-ton schooner yacht, Lalla Rookh, which served as a laboratory afloat, especially for testing his mariner's compass and mechanical sounding machine. When in 1892 he was elevated to the peerage, he became the first British scientist to be so honored. Taking the title Baron Kelvin from the tributary of the River Clyde that flowed close to the University, Lord Kelvin continued to publish scientific papers until he found a last resting place in Westminster Abbey, not far from the tomb of Sir Isaac Newton.

See alsoScience and Technology.