The world-wide reputation, as a mathematician and physicist, which Sir William Thomson has acquired, is a sufficient plea for giving him the foremost place in our sketches of University professors. Born in Belfast in June, 1824, Sir William has entered upon the forty-eighth year of his age. His father, Dr. James Thomson, was the author of several mathematical text-books, and occupied for some time the position of lecturer on mathematics at the Royal Academical Institute in Belfast, from whence he was transferred to the mathematical professorship of Glasgow University. The subject of our present sketch commenced his University life at the early age of eleven years. Both in the chemistry classes of Dr. Thomas Thomson, and in the astronomical lectures of Dr. Nichol, he showed himself an exceedingly apt student, and gained numerous prizes. In 1845, he graduated as second wrangler and first Smith's prizeman at Cambridge University. On Sir William's career as a Cambridge student we find the following interesting paragraph in an article recently supplied to one of the leading magazines:—"When quite a boy at Cambridge, still in his teens, he was a contributor to mathematical journals both in France and England. It might have been supposed that he was a lonely student, dwelling in a tower, like Erasmus or Roger Bacon, quite cut off from the unsympathetic mob of his brother collegians. On the contrary, Thomson was one of the best oarsmen of his day, and an immense favourite with his brother under-graduates. This taste for the water has always accompanied him. He had made many valuable excursions in his beautiful yacht Lalla Rookh; and his knowledge of the theory and practice of sailing is said to be extraordinary. The occasion of his taking his degree proved an ovation still recollected, and recorded in the annals of Cambridge. There was not the least doubt in the University but that the youthful Peterhouse man was the mathematical genius of the day. 'Eclipse was first and the rest nowhere.' But the rumour arose that there was a 'dark man' at St. John's, who possessed a wonderful power of throwing off paper-work at examinations with the regularity of a machine. One of the examiners subsequently described himself as petrified at the papers thrown off, as if by the velocity of a steam-engine, on the part of the Johnian. At the Cambridge Senate House examinations speed is everything; and when two men are pretty evenly balanced the muscular power of the wrist settles the day. Thomson was Second Wrangler, and a little more time for writing would have made him Senior Wrangler. For the Smith's Prize he of course distanced the Senior Wrangler and all other competitors. The worthy Johnian, who supplanted him for the blue ribbon of the University, was, irrationally enough, very unpopular, and has subsequently been lost sight of in scientific history. Before Sir William Thomson there was a great career. At twenty-one he was a fellow of his college. At twenty-two he was a Professor of Natural Philosophy at the University of Glasgow. When little more than out of his teens, Sir William Thomson became editor of the Cambridge and Dublin Mathematical Journal, through which a great impetus was given to the study of pure and applied mechanics; and before the era of the Atlantic Cable he contributed many papers on telegraphy to the Royal Society, in connection with which he made the acquaintance and enjoyed the esteem of such men as Faraday and Brewster. The Natural Philosophy Chair in Glasgow University he has raised to a high rank—perhaps the highest of its kind in the world, and students come from far and near to sit at the feet of this Gamaliel among the physicists of his day and generation."

The Bakerian lecture, entitled "The Electro-Dynamic Properties of Metal," was delivered by Sir William Thomson in 1855, and by that and kindred contributions to scientific literature he was rapidly laying the foundation of his great reputation. In 1854 he published a series of investigations, by which he shows that the capacity of the conducting wire for the electric charge depends on the ratio of its diameter to that of the gutta percha covering; and in the face of much opposition he established what is now known as the "law of squares," which asserts that the rate of transmission is inversely as the square of the length of the cable. These results were of much utility in their bearing on the working of submarine cables, and it is not too much to affirm that it was to Sir William Thomson's counsel that the success of the Atlantic Cable is in great part due. His mirror galvanometer was the first instrument that could be applied with anything like satisfactory results to submarine telegraphy. More recently, however, he has invented and patented another instrument, called the "syphon recorder," which was exhibited publicly for the first time at the opening of the British India Submarine Telegraph. The special feature of the "syphon recorder" is a minute capillary syphon, which, while it continually discharges ink against a moving paper, is by means of a delicate electro-magnetic arrangement caused to move from side to side according to the electric pulses passed through the cable, and from the record thus obtained of these motions the message is deciphered. From trials lately made on the Falmouth, Gibraltar, and Malta lines, it has been ascertained that 25 words per minute can be registered through a cable 800 miles long. It is also a recommendation to the "syphon recorder" that it can be worked by very low battery power, and therefore tends to the preservation of the cable. Among Sir William's other inventions we may specially mention an electrometer, which has now assumed a very complete form. His divided-ring electrometer admitted of accurate measurements, in skilled hands, of fractions of a Daniell's cell; his portable electrometer admits of readings from 10 or 20 cells upwards; but his new reflecting electrometer gives as much as 100 divisions on the scale for one single cell of the battery. In Mr. Varley's patent of 1860, he describes a method which he employed to make the one plate charge itself, and on this principle he constructed a large electrical machine, which he exhibited at a soiree of the Royal Society of 1869-70. This machine has been adopted by Sir William Thomson for maintaining the charge in his electrometer. The new electrometer is really a combination of three inventions—of Sir William Thomson's portable electrometer to indicate whether or no the instrument is sufficiently charged; of the replenisher by Mr. Varley for charging or discharging; and of the quadrant electrometer for reading off the minute tensions measured. The instrument is in its present form so practically useful that it has been largely used in connection with telegraphic cables, and Mr. Varley has calculated tables to enable any electrician at a glance to infer from two readings by this electrometer the insulating power of any telegraphic cable.

Sir William Thomson is no specialist. Many people are accustomed to associate his name with the Atlantic Cable, and with that alone. This, however, is a great mistake, for he has made many important additions to the science of magnetism, respecting which he published a number of valuable papers between the years 1847 and 1851. He has also displayed extraordinary acumen and intelligence in the investigation of the nature of heat. Neither should it be forgotten that Sir William has speculated a great deal on the ultimate constitution of matter—an inquiry which has occupied the attention of all great physicists in modern times. Last year he published in Nature an article which, running from four different lines of argument, seeks to establish proof of the absolute magnitude of the atoms of matter. Of this argument Tyndall says:—"William Thomson tries to place the ultimate particles of matter between his compass points, and to apply to them a scale of millimetres."

In the EncyclopÆdia Britannica, Sir William has published an article describing the instruments—chiefly invented by himself—which were used in laying the Atlantic Cable. In the same contribution he describes the expeditions undertaken in 1857 and 1858 for the purpose of laying the Atlantic Cable, and the difficulties that had to be encountered in that great enterprise. This he was eminently qualified to do from his experience as acting electrician on board the Agamemnon during the progress of the work which resulted in the completion, in August, 1858, of the Atlantic Cable, and the astonishment of the world at finding the two opposite shores of the great ocean placed in instantaneous communication with each other. For some time after the cable was laid he remained at Valentia, endeavouring to bring his galvanometer to still greater perfection. From the subsequent failure of the Atlantic Cable, and until it was finally established as a successful "institution," Sir William was busily employed in seeking to make more perfect and easy the difficult science of submarine telegraphy; and in the expeditions of 1865 and 1866, which he accompanied, his counsel and assistance proved of inestimable value.

From the Royal Society of Edinburgh Sir William received the Keith Prize for the years 1862 and 1863. On the occasion of the award, Sir David Brewster, the Vice-President of the Society, thus referred to the many valuable papers he had communicated to the Society during the seventeen years of his connection with it:—"These papers, and others elsewhere published, relate principally to the theories of Electricity, Magnetism, and Heat, and evince a genius for the mathematical treatment of physical questions which has not been surpassed, if equalled, by that of any living philosopher. In studying the mathematical theory of Electricity, he has greatly extended the general theorems demonstrated by our distinguished countryman, Mr. Green; and was led to the principle of 'electrical images,' by which he was enabled to solve many problems respecting the distribution of electricity on conductors, which had been regarded as insoluble by the most eminent mathematicians in Europe. In his researches on Thermo-dynamics, Professor Thomson has been equally successful. In his papers 'On the Dynamical Theory of Heat,' he has applied the fundamental propositions of the theory to bodies of all kinds, and he has adduced many curious and important results regarding the specific heats of bodies, which have been completely verified by the accurate experiments of M. Joule. No less important are Professor Thomson's researches on Solar Heat, contained in his remarkable papers 'On the Mechanical Energy of the Solar System;' his researches on the Conservation of Energy, as applied to organic as well as inorganic processes; and his fine theory of the dissipation of Energy, as given in his paper 'On a Universal Tendency in Nature to the Dissipation of Mechanical Energy.' To these we may add his complete theory of Diamagnetic Action, his investigations relative to the Secular Cooling of our Globe, and the influence of internal heat upon the temperature of its surface." Sir David Brewster, after referring to other works, added that "the important conclusions which he obtained from 'The Theory of Induction in Submarine Telegraphy,' have found a valuable practical application in the patent instrument for reading and receiving messages, which he so successfully employed in the submarine cable across the Atlantic; and when that great work is completed, his name will be associated with the noblest gift that science ever offered to civilisation. By his delicate electrometer, his electric spark recorder, and his marine and land relation galvanometer, he has provided the world of thought with the finest instruments of observation and research, and the world of action with the means of carrying the messages of commerce and civilisation which have yet to cross the uncabled oceans that separate the families of the earth."

In 1866, after the Atlantic Telegraph Cable had been successfully laid, Sir William Thomson received the honour of knighthood from the Crown. On the same occasion he was presented with the freedom of his adopted city—Glasgow. The degree of LL.D. was conferred on him successively by Trinity College, Dublin, by Cambridge and by Edinburgh Universities, and that of D.C.L. by Oxford. He is a Fellow of the London Royal Society, as well as that of Edinburgh; and he is an honorary and corresponding member of several learned societies abroad.

On the loss of H.M.S. Captain, a Commission was appointed to investigate the merits of designs for ships of war. Of that Commission Sir William Thomson is a valuable and valued member, from his intimate acquaintance with dynamical science and the theory of stability. Sir William also conducts the operations of two committees appointed by the British Association to investigate the subject of Tides and Underground Temperature, the results of which are expected to settle many points of physical theory. The circumstances of Sir William Thomson's election to the presidential chair of the British Association for the Advancement of Science, and the remarkably able address which he delivered in opening the late Edinburgh meeting, are of such recent occurrence that they need not be recapitulated.

Sir William Thomson married, in 1852, a daughter of the late Walter Crum, Esq., F.R.S., who has predeceased him. He is a Liberal in politics, and no one has taken a more active part than he in forwarding the interests of the Liberal candidates for the representation of the Universities.