Lord Kelvin

• 1. Introduction

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  In 1845, at the University of Cambridge, an examiner named Robert Leslie Ellis is said to have sized up a graduating student. He reportedly told a fellow examiner, "You and I are just about fit to mend his pens." The student was William Thomson, a young man from Belfast who would later be known as Lord Kelvin. His name now sits on the unit that measures absolute temperature. Yet he was also an engineer, an inventor and a public figure. He remained something of a celebrity on both sides of the Atlantic until his death.

  What did a young man from Belfast do to earn that kind of awe from his examiners? How did a professor of natural philosophy become a man whose face ended up on a banknote? And why did a physicist so influential in the study of heat cling to estimates about the Earth that later physics overturned?

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• 2. Boyhood and Cambridge

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  Margaret Thomson died in 1830, when her son William was six years old. William had been born on the 26th of June 1824 in Belfast. His father, James Thomson, taught mathematics and engineering at the Royal Belfast Academical Institution and was the son of an Ulster Scots farmer. Four boys and two girls in the family survived infancy. William and his elder brother James were tutored at home by their father, while the younger boys learned from their elder sisters. The elder brother was marked out for most of their father's encouragement and money, and he was prepared for a career in engineering.

  In October 1833 the family moved to Glasgow, a year after James Thomson was appointed professor of mathematics at the University of Glasgow. In 1834, aged ten, William began studying at that university. This was no sign of unusual brilliance. The university provided much of an elementary school's teaching for able pupils, and ten was a typical age to start. The children also saw a wider world than their father's farming childhood had offered. They spent mid-1839 in London, and the boys were tutored in French in Paris. Language study ranked high among the family's priorities.

  At twelve, William won a prize for translating Lucian of Samosata's Dialogues of the Gods from Ancient Greek into English. In the academic year 1839/1840 he won the class prize in astronomy for his Essay on the figure of the Earth. The essay showed an early gift for mathematical analysis and creativity. Throughout his life he would return to the problems it raised as a way of coping with personal stress.

  Joseph Fourier's Analytical Theory of Heat drew the young Thomson toward what was then called continental mathematics. Many British mathematicians, still working in the shadow of Sir Isaac Newton, resisted it. Philip Kelland even wrote a critical book attacking Fourier. That book prompted Thomson's first published scientific paper, a defence of Fourier signed with the pseudonym P.Q.R. His father submitted it to The Cambridge Mathematical Journal, and a second paper followed almost immediately.

  On holiday with his family in Lamlash in 1841, Thomson wrote a third and more substantial P.Q.R. paper. It linked the mathematics of heat conduction to the mathematics of electrostatics. James Clerk Maxwell would later describe that analogy as one of the most valuable science-forming ideas.

  Later in 1841, his father installed him at Peterhouse, Cambridge, with extensive letters of introduction and ample accommodation. Thomson took up sculling and won the Colquhoun Sculls in 1843. He also enjoyed classics, music and literature, but science was the real love of his intellectual life. In 1845, under the tuition of William Hopkins, he graduated as second wrangler. He also took the first Smith's Prize, which, unlike the tripos, tests original research.

  That same year he gave the first mathematical treatment of Michael Faraday's idea that electric induction passes through an intervening medium, called a dielectric, rather than by action at a distance. He also devised the method of electrical images, a powerful tool for problems in electrostatics. Partly in response to his encouragement, Faraday began research in September 1845 that led to the discovery of the Faraday effect. That effect showed that light and magnetic phenomena are related.

  In June 1845 he was elected a fellow of St Peter's, as Peterhouse was often called. He then spent time in the Paris laboratory of Henri Victor Regnault. In 1846 he was appointed to the chair of natural philosophy at the University of Glasgow. At 22, he wore a professor's gown and lectured to a class he had joined as a first-year student only a few years earlier. He would hold that post for 53 years.

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• 3. The Absolute Scale

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  In 1847 Thomson went to the annual meeting of the British Association for the Advancement of Science in Oxford, already known as a precocious and maverick scientist. There he heard James Prescott Joule make yet another attempt to discredit the caloric theory of heat. That theory underpinned the heat engine theory of Sadi Carnot and Émile Clapeyron. Joule argued that heat and mechanical work can be converted into each other at a fixed rate. Thomson was intrigued but sceptical, and he retreated further into the Carnot-Clapeyron school.

  Thomson predicted that the melting point of ice must fall as pressure rises. Otherwise, the expansion of water as it freezes could be exploited to build a perpetual motion machine. Experimental confirmation in his laboratory strengthened his convictions.

  In 1848 he grew dissatisfied that the gas thermometer gave only an operational definition of temperature. So he proposed an absolute scale. On it, a unit of heat falling from one degree to the next lower degree would yield the same mechanical effect at any temperature. Such a scale would be, in his words, "quite independent of the physical properties of any specific substance." Picturing heat as a waterfall, he reasoned that a point would be reached where no more heat could pass. That was absolute zero, a notion Guillaume Amontons had speculated about in 1702.

  Carnot's Reflections on the Motive Power of Heat, published in French in 1824, the year of Thomson's birth, had estimated that point at minus 267. Thomson calibrated his scale against measurements published by Regnault. The value he determined was approximately minus 273.15 degrees Celsius, or minus 459.67 degrees Fahrenheit.

  Thomson did not send Joule a copy of his paper. When Joule eventually read it, he wrote to Thomson on the 6th of October. He claimed that his studies had shown heat turning into work, and that he planned further experiments. Thomson replied on the 27th of October. He said he was planning experiments of his own and hoped the two sides could be reconciled.

  In January 1849 Thomson read a critique of Carnot's original publication to the Royal Society of Edinburgh, still convinced the theory was sound. Over the next two years he ran no new experiments, yet he grew dissatisfied with Carnot and persuaded by Joule. In February 1851 he sat down to set out his new thinking. The paper went through several drafts as he tried to reconcile Carnot with Joule.

  During that rewriting, Thomson seems to have entertained the ideas behind the second law of thermodynamics. In Carnot's theory, wasted heat was simply gone. Thomson held instead that it was "lost to man irrecoverably; but not lost in the material world". His theological beliefs led him to carry the idea out to the whole cosmos, which produced the notion of a universal heat death. In a draft passage he argued that no physical action could ever restore the heat emitted from the Sun, and that the Sun was not inexhaustible. He compared the process to a clock running slower and slower, though he was unsure whether it would stop for ever.

  In the final publication, Thomson stepped back from this radical version. He declared that the theory of the motive power of heat rests on two propositions, one due to Joule and the other to Carnot and Clausius. He then stated a form of the second law. It says that, by inanimate means, no mechanical effect can be drawn from any portion of matter by cooling it below the temperature of the coldest surrounding objects. He admitted that only the thinking of Sir Humphry Davy and the experiments of Joule and Julius Robert von Mayer had swayed him. Experimental demonstration of heat turning into work, he said, was still outstanding.

  Joule wrote back as soon as he read the paper, with comments and questions. That began a fruitful collaboration, mostly by letter, which ran from 1852 to 1856. Joule conducted experiments, and Thomson analysed the results and suggested further ones. Among its discoveries was the Joule-Thomson effect, sometimes called the Kelvin-Joule effect. Their published results did much to win acceptance for Joule's work and for the kinetic theory.

  In 1862 Thomson used the second law to formulate a paradox against an infinitely old universe, known as Kelvin's paradox. William Rankine later extended it. Over his career Thomson published more than 650 scientific papers and applied for 70 patents, though not all were issued.

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• 4. The Atlantic Cable

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  In September 1852, Thomson married his childhood sweetheart, Margaret Crum, the daughter of Walter Crum. Her health broke down on their honeymoon, and for the next 17 years her suffering distracted him. Though eminent in the academic world, he was obscure to the general public.

  On the 16th of October 1854, George Gabriel Stokes wrote to Thomson in an effort to rekindle his interest in his work. He asked Thomson's opinion of some experiments by Faraday on the proposed transatlantic telegraph cable. Faraday had shown that a cable's construction limits how fast messages can be sent, which in modern terms is bandwidth. Thomson seized the problem and published a response that same month. He framed his results as an achievable data rate and as the revenue the venture might earn. In 1855 he stressed that cable design would decide profitability. He argued that signalling speed through a given cable falls in inverse proportion to the square of its length.

  In 1856 Wildman Whitehouse, electrician of the Atlantic Telegraph Company, disputed Thomson's results at a meeting of the British Association. Whitehouse may have misread his own experiments, and he was surely feeling financial pressure, since plans for the cable were well under way. He believed Thomson's figures implied the cable must be abandoned as practically and commercially impossible. Thomson answered in a letter to the popular Athenaeum magazine, which put him in the public eye. He recommended a larger conductor with a larger cross section of insulation. He thought Whitehouse no fool, and suspected he might have the practical skill to make the existing design work.

  In December 1856 Thomson was elected to the board of directors of the Atlantic Telegraph Company. He became scientific adviser to a team in which Whitehouse was chief electrician and Sir Charles Tilston Bright was chief engineer. Whitehouse still got his way on the specification, backed by Faraday and Samuel Morse. In August 1857 Thomson sailed aboard the cable-laying ship HMS Agamemnon, while Whitehouse stayed ashore because of illness. The voyage ended after 380 miles, when the cable parted. Thomson responded by publishing in the Engineer a full theory of the stresses in laying a submarine cable. It showed that a line paying out at constant speed in uniform depth sinks along a straight slant from where it enters the water to where it touches the bottom.

  By 1858 Thomson had developed a complete system for operating a submarine telegraph, capable of sending one character every 3.5 seconds. He patented its key elements that year, the mirror galvanometer and the siphon recorder. The board insisted that he join the 1858 expedition without any pay. In return, he secured a trial of his mirror galvanometer alongside Whitehouse's equipment, which the board had been unenthusiastic about. Thomson found his access unsatisfactory, and a disastrous storm in June 1858 sent the Agamemnon home. In London the board was ready to give up and sell the cable to limit its losses. Thomson, Cyrus W. Field and Curtis Lampson argued for another attempt and won. Thomson insisted that the technical problems could be solved.

  During the voyages he had developed an engineer's instincts and a talent for solving practical problems under pressure. He often took the lead in emergencies and was unafraid to help with manual work. A cable was completed on the 5th of August.

  Thomson's fears were then realised. Whitehouse's apparatus proved insufficiently sensitive, and Thomson's mirror galvanometer had to replace it. Whitehouse kept insisting that his own equipment was providing the service. He then tried desperate remedies and fatally damaged the cable with a jolt of high voltage from five-foot induction coils at Valentia Island, the cable's eastern landfall. When the cable failed completely, Whitehouse was dismissed. Thomson objected and was reprimanded by the board for interfering. He later regretted giving in too readily to many of Whitehouse's proposals.

  A joint committee of inquiry, set up by the Board of Trade and the Atlantic Telegraph Company, put most of the blame on Whitehouse. It found that underwater cables were notoriously unreliable, but that most of the problems came from known and avoidable causes. Thomson sat on a five-member committee asked to recommend a specification for a new cable, and it reported in October 1863. In July 1865 he sailed on the cable-laying expedition of the SS Great Eastern. Technical problems dogged the voyage, and the cable was lost after 1200 miles. The project was abandoned. A further attempt in 1866 laid a new cable in two weeks, and then recovered and completed the 1865 cable.

  The public feted the enterprise as a triumph, and Thomson enjoyed a large share of the adulation. Queen Victoria knighted him, along with the other principals of the project, on the 10th of November 1866, making him Sir William Thomson. To exploit his inventions for long submarine cables, he went into partnership with C. F. Varley and Fleeming Jenkin. With Jenkin he also devised an automatic curb sender, a kind of telegraph key for sending messages on a cable.

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• 5. Life at Sea

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  Thomson's wife, Margaret, died on the 17th of June 1870, and he resolved to change his life. In September he bought a 126-ton schooner, the Lalla Rookh. He was already devoted to the sea, and he used the vessel as a base for entertaining friends and scientific colleagues.

  He had taken part in laying the French Atlantic submarine cable in 1869. With Jenkin he later served as engineer for the Western and Brazilian and the Platino-Brazilian cables, assisted by the vacation student Alfred Ewing. In 1873 he was present at the laying of the Pará to Pernambuco section of the Brazilian coast cables. His maritime interests continued in 1871, when he was appointed to the Board of Enquiry into the sinking of HMS Captain.

  In June 1873 Thomson and Jenkin were aboard the Hooper, bound for Lisbon with 2500 miles of cable, when the cable developed a fault. An unscheduled 16-day stop in Madeira followed. There Thomson became good friends with Charles R. Blandy and his three daughters. On the 2nd of May 1874 he sailed for Madeira in the Lalla Rookh. Approaching the harbour, he signalled to the Blandy residence, "Will you marry me?" Frances Anna Blandy, called Fanny, signalled back "Yes". They married on the 24th of June 1874, and she was 13 years his junior.

  Thomson was an enthusiastic yachtsman, and his time aboard the Agamemnon and the Great Eastern may have deepened his love of the sea. He introduced a new method of deep-sea sounding in which a steel piano wire replaced the ordinary hand line. The wire glides so easily to the bottom that "flying soundings" can be taken while the ship runs at full speed. He added a pressure gauge to register the depth of the sinker. Around the same time he revived the Sumner method of finding a ship's position and calculated a set of tables to apply it.

  During the 1880s Thomson worked to perfect an adjustable compass. It corrected the errors caused by magnetic deviation as ships used more and more iron. Movable iron masses at the binnacle cancelled the ship's own magnetism. His design was steadier and less hampered by friction than the older instruments. Much of it developed principles identified by George Biddell Airy and others, and it added little novel physical thinking. Energetic lobbying and networking won the Admiralty's acceptance.

  Biographers disagree about the compass story. Scientific biographers have often cast naval administrators as dim-witted opponents of a superlative mind. Writers sympathetic to the Navy portray a talented and enthusiastic man with some real knowledge of the sea. In that telling, he turned a handful of modest ideas into a commercial monopoly for his own manufacturing firm. He is said to have used his reputation in the law courts to beat down even small claims of originality from others. The truth probably lies somewhere between the two extremes.

  Charles Babbage had been among the first to suggest that a lighthouse might signal a distinctive number through occultations of its light. Thomson pointed out the merits of Morse code for the purpose. He urged that the signals use short and long flashes to represent dots and dashes.

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• 6. Electricity and the Aether

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  In 1893 Thomson headed an international commission to decide the design of the Niagara Falls power station. He believed direct current transmission was superior. Even so, he endorsed the alternating current system of Westinghouse, which had been demonstrated at that year's Chicago World's Fair. After Niagara, he still held that direct current was the better system.

  Thomson did more than any electrician before him to bring accurate methods and devices to the measurement of electricity. As early as 1845 he pointed out that the results of William Snow Harris agreed with the laws of Charles-Augustin de Coulomb. In 1857 he described his divided ring electrometer in the Memoirs of the Roman Academy of Sciences. It was based on the electroscope of Johann Gottlieb Friedrich von Bohnenberger. He built a series of instruments, including the quadrant electrometer, that covered the whole field of electrostatic measurement. His current balance, also called the Kelvin balance or Ampere balance, served to specify the ampere precisely. From around 1880 the electrical engineer Magnus Maclean helped with his experiments.

  On the 26th and the 27th of June 1906, the International Electrotechnical Commission held its preliminary meeting in London. It unanimously elected Thomson its first president in acknowledgement of his work on electrical standardisation. The proposal came from Alexander Siemens of Great Britain, seconded by Mr Mailloux of the US Institute of Electrical Engineers.

  Around 1859 Thomson worked briefly on atmospheric electricity and contributed a great deal in a short time. He adapted electrometers from his telegraph work into instruments for measuring the electric field of the air, and tested them at Glasgow and on holiday on Arran. His Arran measurements were so rigorous and well calibrated that they can be used to infer air pollution from the Glasgow area. His water dropper electrometer was used for many years at Kew Observatory and Eskdalemuir Observatory. One was still in operational use at Kakioka Observatory in Japan until early 2021. He may also have unwittingly recorded electrical effects of the Carrington Event, a significant geomagnetic storm, in early September 1859.

  Between 1870 and 1890, the vortex atom theory was popular among British physicists and mathematicians. It held that an atom was a vortex in the aether, and Thomson pioneered it. The seventeenth-century vortex theory of René Descartes used three kinds of matter, tied to the emission, transmission and reflection of light. Thomson instead imagined a single continuous medium. About 60 scientific papers were written by roughly 25 scientists. Following the lead of Thomson and Tait, the branch of topology called knot theory was developed.

  In 1884 Thomson led a master class at Johns Hopkins University on Molecular Dynamics and the Wave Theory of Light. He compared the acoustic wave equation for sound in air with an electromagnetic wave equation, presuming a luminiferous aether that could vibrate. Among the group were Albert A. Michelson and Edward W. Morley, who later performed the Michelson-Morley experiment, which found no aether. A. S. Hathaway took notes and duplicated them with a papyrograph. Thomson amended the text, and it was typeset and published in 1904. His mechanical models ultimately failed for electromagnetism. Starting from that 1884 lecture, he became the first scientist to formulate the hypothetical concept of dark matter, and he tried to locate some "dark bodies" in the Milky Way.

  On the 27th of April 1900 he gave a widely reported lecture at the Royal Institution, titled "Nineteenth-Century Clouds over the Dynamical Theory of Heat and Light". The two dark clouds were confusion over how matter moves through the aether, including the puzzling Michelson-Morley result, and signs that the equipartition theorem of statistical mechanics might break down. The first led to the theory of relativity, and the second to quantum mechanics. In 1905 Albert Einstein published his annus mirabilis papers. One explained the photoelectric effect using Max Planck's energy quanta, and another described special relativity. A third explained Brownian motion through statistical mechanics, giving a strong argument that atoms exist.

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• 7. A Young Earth

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  Thomson's first estimate of the Earth's age, in 1864, ran from 20 to 400 million years. The wide range came from his uncertainty about the melting temperature of rock, which he equated with the Earth's interior temperature. It also reflected uncertainty about the thermal conductivities and specific heats of rocks. His interest in heat conduction and his youthful work on the figure of the Earth made cooling a natural line of attack. Over the years he refined his arguments and cut the upper bound by a factor of ten. In 1897 Kelvin settled on an estimate of 20-40 million years.

  Thomson was a creationist in a broad sense, but he was not a flood geologist, a view that had lost mainstream scientific support by the 1840s. He held that the laws of thermodynamics operated from the birth of the universe. In his picture, the Solar System and other structures organised and evolved, followed by a gradual heat death. He argued that the Earth had once been too hot to support life, in contrast to uniformitarianism, the view that conditions had stayed constant since the indefinite past. He contended that "This earth, certainly a moderate number of millions of years ago, was a red-hot globe...."

  Charles Darwin's On the Origin of Species appeared in 1859. Thomson saw the Earth's short habitable age as a challenge to Darwin's picture of slow natural selection producing diversity. He favoured a version of theistic evolution sped up by divine guidance. He even proposed that life on Earth had evolved from plants whose seeds were carried from other planets by meteorites. His calculations showed that the Sun could not have shone long enough for slow evolution, unless an energy source beyond Victorian science was heating it.

  In 1895 his former assistant John Perry published a paper challenging Kelvin's assumption of low thermal conductivity inside the Earth. That would imply a much greater age, but the paper had little immediate impact. The discovery in 1903 that radioactive decay releases heat changed the picture. In 1904 Ernest Rutherford famously argued, in a lecture Kelvin attended, that this was the unknown energy source Kelvin had allowed for. Even so, the estimate was not overturned until the development of radiometric dating of rocks in 1907.

  Kelvin eventually paid off a gentleman's bet with Strutt on the importance of radioactivity in the Earth's geology. He never publicly acknowledged the point, because he believed he had a much stronger argument limiting the Sun's age to no more than 20 million years. Without sunlight, he reasoned, the sediment record on the Earth's surface could not be explained. At the time, the only known source of solar energy was gravitational collapse. The paradox was truly resolved only when thermonuclear fusion was recognised in the 1930s. Modern cosmology still recognises a Kelvin period in a young star's life. During it the star shines from gravitational energy, which Kelvin calculated correctly, before fusion and the main sequence begin.

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• 8. Predictions, Peerage and Farewell

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  When Röntgen's discovery of X-rays was announced at the end of 1895, Kelvin was entirely sceptical and took the news for a hoax, according to his biographer Silvanus P. Thompson. Röntgen then sent him a copy of his memoir. On the 17th of January 1896, Kelvin wrote back that he was "very much astonished and delighted" and congratulated Röntgen warmly. In May 1896 he had his own hand X-rayed.

  His view of aviation was less happy. In 1896 he refused an invitation to join the Aeronautical Society. He wrote that he had "not the smallest molecule of faith in aerial navigation other than ballooning". In a newspaper interview in 1902 he predicted that "No balloon and no aeroplane will ever be practically successful." In 1898 he predicted that only 400 years of oxygen supply remained on the planet, given the rate at which combustibles were burning.

  A famous line about physics being finished is often credited to Kelvin, but there is no evidence he said it. The claim, widespread since the 1980s, says nothing new remains to be discovered and only more precise measurement is left. It paraphrases Albert A. Michelson, who said in 1894 that most of the grand underlying principles seemed firmly established. Philipp von Jolly made similar statements earlier. The attribution probably springs from confusion with Kelvin's 1900 lecture, which did the opposite by pointing to coming revolutions.

  In 1892 Kelvin became the first scientist elevated to the House of Lords. He took the title Baron Kelvin, of Largs in the County of Ayr, in recognition of his thermodynamics and of his opposition to Irish Home Rule. The name comes from the River Kelvin, which flows near his laboratory at Gilmorehill in Hillhead, home of the University of Glasgow. The title died with him, since he left neither heirs nor close relations. He refused offers of elevated posts from several world-renowned universities and stayed in Glasgow until he retired in 1899.

  Around 1899 George Eastman recruited him as vice-chairman of the board of Kodak Limited, the British company affiliated with Eastman Kodak. In 1904 Kelvin became Chancellor of the University of Glasgow. The 1902 Coronation Honours list, published on the 26th of June 1902, made him a Privy Councillor and one of the first members of the new Order of Merit. He received the order from the King on the 8th of August 1902 and was sworn of the council at Buckingham Palace on the 11th of August 1902.

  Kelvin lived at Netherhall, a mansion in Largs that he built in the 1870s. In his later years he often travelled to his townhouse at 15 Eaton Place, off Eaton Square in Belgravia, London. He remained a devout Christian, and attendance at chapel was part of his daily routine. On the 23rd of May 1889 he addressed the Christian Evidence Society on how his faith supported and informed his scientific work.

  In November 1907 Kelvin caught a chill, and his condition worsened until he died at Netherhall on the 17th of December. At the request of Westminster Abbey, the undertakers Wylie & Lochhead prepared an oak coffin lined with lead. On a dark winter evening the cortege set off for Largs railway station, about a mile away. Large crowds watched it pass, and shopkeepers closed their premises and dimmed their lights. The train left at 8:30 pm for Kilmarnock, where the van was attached to the overnight express to St Pancras railway station in London.

  Kelvin's funeral took place on the 23rd of December 1907, and the Abbey was crowded. Representatives came from the universities of Glasgow and Cambridge. Others came from France, Italy, Germany, Austria-Hungary, Russia, the United States, Canada, Australia, Japan and Monaco. His grave lies in the nave, near the choir screen and close to the graves of Isaac Newton, John Herschel and Charles Darwin. Darwin's son, Sir George Darwin, was one of the pall-bearers. At the same time, a service was held at St Columba's Episcopal Church in Largs, and the University of Glasgow held a memorial service in the Bute Hall.

  Kelvin is also remembered on the Thomson family grave in Glasgow Necropolis. The Hunterian Museum at the University of Glasgow keeps a permanent exhibition of his papers, instruments and artefacts, including his smoking-pipe. The Clydesdale Bank put him on its £20 note in 1971, and he now appears on its £100 note holding his adjustable compass, with a map of the transatlantic cable behind him. In 2011 he was inducted into the Scottish Engineering Hall of Fame. The botanist William Trownson named Mount Kelvin, in New Zealand's Paparoa Range, after him. Every year since 2019, World Refrigeration Day has fallen on the 26th of June, chosen to celebrate his birth date.

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