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