William Thomson, Lord Kelvin

William Thomson, known as Lord Kelvin, was one of the most eminent scientists of the nineteenth century and is best known today for inventing the international system of absolute temperature that bears his name.

KelvinScottish-Irish physicist William Thomson, better known as Lord Kelvin, was one of the most eminent scientists of the 19th century and is best known today for inventing the international system of absolute temperature that bears his name. He made contributions to electricity, magnetism, thermodynamics, hydrodynamics, geophysics and telegraphy and other fields, publishing more than 650 papers during his lifetime. Thomson was also an extremely skilled engineer who patented some 70 inventions and was involved heavily in the laying of the first transatlantic telegraph cable. For that successful effort he was knighted by Queen Victoria in 1866. The Baron was raised to peerage in the 1890s, and became known as Lord Kelvin of Largs.

Thomson was born in Belfast, Ireland, the fourth of seven children. His mother died in his youth, and his father, James, was solely responsible for most of his upbringing. The family relocated to Scotland in the early 1830s, where James accepted the mathematics chair at the University of Glasgow. The elder Thomson was a strict guardian guided in his ways by the Presbyterian Church, but he and his second son, William, were very close. It was from his father that William Thomson became acquainted early with mathematics, including developments in the field that were so new that they had not yet been published in textbooks. Thomson was admitted to the University of Glasgow at the age of 10 and flourished academically at the institute, where he first read The Analytical Theory of Heat by Jean Baptiste Joseph Fourier. The methods of the French mathematician were controversial among British scientists at the time, and Thomson’s first published papers, which appeared when he was only a teenager under the pseudonym P.Q.R., were defenses of Fourier’s work. Instead of condemning Fourier’s mathematics, Thomson suggested that they could be used to study other forms of energy besides heat, such as electrical currents.

Following his years at the University of Glasgow, Thomson entered Cambridge in 1841. When he graduated four years later, he received highest honors. His interest in French mathematical and scientific methods then inspired him to travel to Paris, where he gained experience in the experimental side of physics by working in the laboratory of Henri-Victor Regnault. When in 1846 the University of Glasgow needed to fill its chair of natural philosophy, Thomson received the appointment with the help of his father, despite being just 22 years old. He returned to Scotland from France and was content to remain associated with the University of Glasgow throughout his career, though he received offers from other academic institutes.

While still a student at Cambridge, Thomson embarked on a comparative study of the distribution of electrostatic force and the distribution of heat through a solid that led him to conclude that the two are mathematically equivalent. This work, published as "On the uniform motion of heat in homogeneous solid bodies, and its connection with the mathematical theory of electricity," was the foundation of his later work involving electric and magnetic fields. Moreover, Thomson’s efforts in this area would provide the groundwork for James Clerk Maxwell’s theory of electromagnetism, as Maxwell himself openly admitted.

Thomson’s influence on another great scientific mind is notable as well. In 1845, Thomson mathematically analyzed Michael Faraday’s magnetic lines of force and wrote a letter to him in August of that year explaining how his calculations predicted that magnetic fields should affect the plane of polarized light. Faraday had many years before experimented with light and magnetism, but without observing any connection between the two. Encouraged by Thomson’s prediction, Faraday decided to readdress the problem and began a new series of experiments in his laboratory. By mid-September he had proven that magnetism and light are related, discovering what has come to be known as the Faraday effect.

Similar to Faraday, Thomson seems to have been guided by the idea that there is unity among all types of matter and energy. Over the course of his career, he made significant strides in unifying various theories, integrating the work of Charles Augustin de Coulomb and Siméon-Denis Poisson, for instance, with that of Faraday. He also applied the ideas he developed with George Gabriel Stokes regarding hydrodynamics to atomic theory and electrical theory, and united James Joule’s dynamical theory of heat, which he gradually came to accept, to his own dynamical theory of electricity and magnetism. Collaboration was clearly very important to Thomson, who had made many important connections in the scientific world when he was young through his father and even more when he was older due to his own initiative. The meeting between Joule and Thomson in 1847, for example, was very fruitful for both. In the 1850s, their collaboration led to Thomson’s positing a version of the second law of thermodynamics (heat cannot be spontaneously transferred from a colder to a hotter body) and the discovery of the Joule-Thomson effect, in which the temperature of a gas is lowered via expansion from high pressure to low pressure. In addition, Thomson’s work in thermodynamics resulted in his development of the absolute temperature scale that is commonly known as the Kelvin scale.

Thomson garnered great esteem for these and other scientific developments, being elected to the Royal Society of London in 1851, winning its Royal Medal in 1856, the Copley Medal in 1883, and serving as the president of the society from 1890 to 1895. He also served as president of the Royal Society of Edinburgh and the British Association for the Advancement of Science. He was the recipient of countless honorary degrees. It was his feats in engineering, however, that gained him great wealth. The success of the first transatlantic cable had been dependent not only on his supervisory role in the project, but also on a telegraph receiver he patented known as a mirror galvanometer. Following the laying of the cable, Thomson’s galvanometer and a later device he invented called the siphon recorder were in high demand as a network of submarine cables was built to span the globe. The money he received from the sale of the patented devices and his partnership in two engineering firms that specialized in consulting services for the establishment of such cables was sufficient to provide him with a very comfortable life on a baronial estate and enough funds to often entertain large numbers of guests on his 126-ton yacht.

In his later years, Thomson became embroiled in the controversy surrounding the evolutionary theory of Charles Darwin. Basing his calculations on his understanding of thermodynamics and the work of Fourier, Thomson estimated the ages of the sun and the Earth, and based on these estimations speculated that it was impossible for life to evolve over the vast expanses of time associated with Darwinism. T.H. Huxley, commonly known as Darwin’s bulldog, publicly denigrated Thomson’s claims in an address to the Geological Society of London. A less contentious interest developed by Thomson in the latter part of his life involved the sea. His yachting experiences led him to devise a number of useful devices, such as sounding equipment, an analog computer for calculating tide tables, and a type of compass.

It is not a coincidence that a number of instruments for measuring electricity are also included in his list of inventions, for Thomson considered quantification an essential aspect of science. His leadership on the Committee on Electrical Standards of the British Association for the Advancement of Science greatly influenced the standardization and adoption of many of the units that are still utilized in the field of electricity today, such as the volt and ohm. According to Thomson, who died at his estate on December 17, 1907:

“when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely in your thoughts advanced to the state of science, whatever the matter may be.”