Lord Kelvin (William Thomson)

Major contributions

• Proposed in 1848 an absolute temperature scale independent of any substance, based on Carnot's theory; the SI unit of temperature, the kelvin, is named after him (see Temperature)
• Stated the second law of thermodynamics in 1851 (the Kelvin, later Kelvin–Planck, statement) and reconciled Carnot's work with Joule's energy conservation (see Second Law)
• With James Joule, discovered the Joule–Thomson effect (1852), the temperature change of a gas expanding through a valve, the basis of many gas liquefiers
• Developed the theory of signal propagation in long submarine cables and invented the mirror galvanometer and siphon recorder, enabling the transatlantic telegraph (1858, 1866)
• Made major contributions to electromagnetism, elasticity and hydrodynamics, and coined the term “kinetic energy” (with Peter Guthrie Tait)

Named concepts

Career

Thomson was born in Belfast and moved to Glasgow when his father became professor of mathematics there. He entered the University of Glasgow at ten, studied at Cambridge (graduating Second Wrangler in 1845), worked briefly in Paris with Henri Victor Regnault, and in 1846, aged 22, became professor of natural philosophy at Glasgow, a post he held until 1899. His meeting with James Joule in 1847 turned him towards energy conservation.

He was knighted in 1866 for his work on the transatlantic cable, made Baron Kelvin of Largs in 1892 (named after the River Kelvin by the university), served as President of the Royal Society from 1890 to 1895, and received the Copley Medal in 1883. He became wealthy through patents on telegraph and navigation instruments. He is buried in Westminster Abbey, next to Isaac Newton.

Key publications

• Thomson, W. (1848). “On an Absolute Thermometric Scale.” Philosophical Magazine, 33, 313–317.
• Thomson, W. (1851). “On the Dynamical Theory of Heat.” Transactions of the Royal Society of Edinburgh, 20, 261–288.
• Thomson, W., Tait, P.G. (1867). Treatise on Natural Philosophy. Oxford: Clarendon Press.

Nobel Prize

Kelvin did not receive a Nobel Prize; the first prizes were awarded in 1901, late in his life, and the committee did not recognise his earlier foundational work.

Historical context

Kelvin is also remembered for confident claims that later proved wrong. Assuming the Earth had cooled by conduction alone from a molten state, he estimated its age at 20 to 400 million years (1862), later narrowing it to 20–40 million, far younger than geologists and Darwin needed. The estimate failed because it ignored radioactive heating, unknown at the time, and, as John Perry argued in 1895, convection in the Earth's interior (see Convection); the accepted age is about 4.5 billion years. The widely quoted line that “there is nothing new to be discovered in physics now” is not found in his writings and is generally regarded as misattributed. His 1900 lecture on “two clouds” over the dynamical theory of heat and light pointed to the problems that relativity and quantum theory would resolve.