tenure of fellowship, was a rather bold step. No engagement was then made. In 1824 he was elected a fellow of his college. He also obtained the post of assistant mathematical tutor, and in addition took some private' pupils. While engaged in this work he prepared a volume called Mathematical Tracts, on subjects which were either deficient at the University, or else not presented in readable form, namely, Lunar Theory, Figure of the Earth, Precession and Nutation, and the Calculus of Variations. The volume was printed by the University Press, and brought its author both reputation and some money. This book, published in 1826, applied the continental notation of the calculus and it exerted a great influence on the study of mathematical physics at Cambridge.
Whewell was senior to Airy in academic standing by seven years. In 1826 they made experiments on gravity in the Dolcoath mine in Cornwall. One pendulum was swung at the top of the mine, the other at the bottom. After numerous observations of their periods in these positions, the one down below was sent up to be compared with the other at the top; when it emerged at the top, the experimenters were surprised and mortified to find the basket on fire, and hence the observations had to be abandoned. This same year the Lucasian professorship of mathematics fell vacant; a Head of one of the colleges sought to capture it as a sinecure; Charles Babbage, who had taken only a poll degree at Cambridge, also applied; and so did Airy. Babbage and the Head mutually destroyed one another, with the result that Airy was elected. Airy improved his academic standing, but not his income; the salary was only £100, and the position involved the giving up of some tuition work. He was not yet in a position to sacrifice his fellowship by marriage. He immediately issued a printed notice that he would give professional lectures in-the next term. There had been no lectures on Experimental Philosophy (Mechanics, Hydrostatics, Optics) for many years. The University in general looked with great satisfaction on such vigorous reform; but there were difficulties to surmount; no allotted term for the lectures, no allotted hour of the day, scarce any available
