Lord Kelvin(1824–1907)

William Thomson was born at 12 College Square East in Belfast on 26 June 1824, the fourth of seven children of James Thomson, a self-taught mathematics tutor from County Down who had walked himself into a chair at the Royal Belfast Academical Institution and then in 1832 into the chair of mathematics at the University of Glasgow. The family moved to Glasgow when William was eight. His mother Margaret died of cholera the following year. James raised the seven children alone, taught them mathematics on the dining table from the textbooks he wrote himself, and put William and his older brother James into the University of Glasgow as students at the ages of ten and twelve respectively. By thirteen William was reading Fourier's Théorie analytique de la chaleur, the work that would shape his physics for the rest of his life.

He went up to Peterhouse, Cambridge in 1841 at sixteen, came out Second Wrangler in 1845, and spent the summer of that year in Paris in Victor Regnault's laboratory absorbing the experimental tradition of French physics. He was elected to the chair of natural philosophy at the University of Glasgow in 1846, aged twenty-two, on the strength of testimonials from Stokes, Faraday and Liouville. He held the chair for fifty-three years. His teaching laboratory at Glasgow was the first physics teaching laboratory in the British Isles. Twelve of his students were elected Fellows of the Royal Society.

In 1848 Thomson published On an Absolute Thermometric Scale, the paper that defined the temperature scale on which water freezes at 273.15 degrees and which has no theoretical lower bound below zero. The Kelvin scale, named for him after his peerage, is the temperature scale of all modern physics. In 1851 he published On the Dynamical Theory of Heat, the paper that contains in section twelve the first general statement of what we now call the second law of thermodynamics: that no engine can convert heat to work without rejecting some of the heat to a colder reservoir. The first law had been stated by Joule and Mayer in the previous decade; Thomson's second law was the constraint that gave the conservation of energy the direction of an arrow.

Through the 1850s and 1860s Thomson did the most successful piece of consulting engineering of the nineteenth century. The 1858 attempt to lay a telegraph cable from Valentia in Ireland to Heart's Content in Newfoundland had failed within weeks of completion; the cable's signalling had been destroyed by the high voltages the consortium's chief electrician Edward Whitehouse had insisted on using. Thomson, brought in as scientific adviser, designed the mirror galvanometer (1858) and later the siphon recorder (1867) that could read a faint signal at the end of a two-thousand-mile copper wire under three miles of seawater, and showed mathematically that the cable had to be made of thicker, lower-resistance copper. The 1866 Great Eastern expedition under his supervision laid the cable that worked; it carried the first commercial transatlantic message that summer, and a permanent transatlantic communications link has existed every day since. He was knighted on the foredeck of the Great Eastern at Brest in November 1866. His maritime compass (1876) and his deep-sea sounding machine (1872) became standard equipment on every ship of the Royal Navy.

He was raised to the peerage as Baron Kelvin of Largs in 1892, the first scientist to be elevated for his work alone. He was president of the Royal Society for five years (1890 to 1895), received the Order of Merit on its inauguration in 1902, and on his death in 1907 was buried in Westminster Abbey beside Isaac Newton, the first scientist since Newton to receive that honour. His late-career resistance to Rutherford's evidence of atomic decay (1903) and his dismissal of heavier-than-air flight as practically impossible (1895) are the qualifications a serious assessment of his work has to make. The Kelvin scale that bears his name runs in every laboratory in the world. The Thomson name in modern physics carries his weight as the man who built the bridge between Newton and the twentieth century.