KELVIN, WILLIAM THOMSON, BARON British physicist, the second son of James Thomson, LL.D., professor of mathematics in the University of Glasgow, was born at Belfast, Ireland, on June 26, 1824, his father being then teacher of mathematics in the Royal Academical Institution. In 1832 James Thomson accepted the chair of mathematics at Glasgow.
In 1841 William Thomson entered Peterhouse, Cambridge, and in 1845 took his degree as second wrangler and won the first Smith's Prize. At that time there were few facilities for the study of experimental science in Great Britain. Thomson therefore had recourse to Paris, and for a year worked in the laboratory of Regnault, who was then engaged in his classical researches on the thermal properties of steam. In 1846, he accepted the chair of natural philosophy in the University of Glasgow, which he filled for 53 years, attaining universal recognition as one of the greatest physicists of his time. The Glasgow chair was a source of inspiration to scientific men for more than half a century, and many of the most advanced researches of other physicists grew out of the numerous suggestions made by Thomson. One of his earliest papers dealt with the age of the earth. Thomson's calcu lations on the conduction of heat showed that at some time between 20 millions and 400 millions, probably about ioo mil lions, of years ago, the physical conditions of the earth must have been entirely different from those which now obtain. This led to a long controversy with geologists in which the physical principles held their ground.
In 1847 Thomson first met James Prescott Joule at the Oxford meeting of the British Association. Joule's views of the nature of heat strongly influenced Thomson's mind, with the result that in 1848 Thomson proposed his absolute scale of temperature, which is independent of the properties of any particular thermo metric substance, and in 1851 he presented to the Royal Society of Edinburgh a paper on the dynamical theory of heat, which reconciled the work of N. L. Sadi Carnot with the conclusions of Count Rumford, Sir H. Davy, J. R. Mayer and Joule, and placed the dynamical theory of heat and the fundamental prin ciple of the conservation of energy in a position to command universal acceptance. It was in this paper that the principle of
the dissipation of energy, briefly summarized in the second law of thermodynamics, was first stated.
Although his contributions to thermodynamics may properly be regarded as his most important scientific work, it is in the field of electricity, especially in its application to submarine telegraphy, that Lord Kelvin is best known to the world at large. From 1854 he is most prominent among telegraphists. The stranded form of conductor was due to his suggestion ; but it was in the letters which he addressed in that year to Sir G. G. Stokes, and which were published in the Proceedings of the Royal Society (1855), that he discussed the mathematical theory of signalling through submarine cables, and enunciated the conclusion that in long cables the retardation due to capacity must render the speed of signalling inversely proportional to the square of the cable's length. Thomson set to work to overcome the difficulty by im provement in the manufacture of cables, by the production of copper of high conductivity and the construction of apparatui which would readily respond to the slightest variation of the cur rent in the cable. The mirror galvanometer and the siphon recorder, which was patented in 1867, were the outcome of these researches. Thomson's work in connection with telegraphy led to the production in rapid succession of instruments adapted to the requirements of the time for the measurement of every electrical quantity, and when electric lighting came to the front a new set of instruments was produced to meet the needs of the electrical engineer.
When W. Weber in 1851 proposed the extension of C. F. Gauss's system of absolute units to electromagnetism, Thomson took up the question, and, applying the principles of energy, calculated the absolute electromotive force of a Daniell cell, and determined the absolute measure of the resistance of a wire from the heat produced in it by a known current. In 186i Thomson induced the British Association to appoint its first famous committee for the determination of electrical standards.