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 science into his curriculum than was then to be found at the great public schools. Having competed unsuccessfully for an entrance scholarship at St. John’s College, Cambridge, in 1863, and again at Trinity in 1864, Darwin entered Trinity in the autumn of 1864 without a scholarship, and read mathematics with [q.v.], the well-known ‘coach’. Two years later Trinity elected him to a foundation scholarship, and in January 1868 he graduated as second wrangler and was awarded the second Smith’s prize. The autumn of the same year saw him elected a fellow of his college.

Although Darwin had generally been expected to do well in his examinations, no one, and least of all himself, had so far recognized that he possessed quite exceptional mathematical ability, and his place in the tripos was higher than he had ventured to hope for. Having at this time no idea of finding his life’s occupation in mathematics or science, he began reading for the bar; he was called in 1874, but he never practised. His health, which had frequently given trouble in his boyhood, grew much worse after he had taken his degree, and he began to suffer seriously, as his father had done before him, from digestive troubles and general weakness. Successive treatments at Malvern, Homburg, and Cannes produced no cure, although from 1873 onwards he gradually improved under the care of (Sir) Andrew Clark.

This period of ill-health resulted in Darwin’s abandoning all thought of a legal career; and in October 1873 he returned to Cambridge and settled in rooms in Trinity. At this time he was writing articles on oddly miscellaneous subjects, such as ‘Development in Dress’, ‘Restriction to Liberty of Marriage’, a ‘Defence of Jevons’, and ‘Cousin Marriages’. About 1875 a more distinctly scientific trend became noticeable, in papers on slide-rules, equipotential lines, elliptic integrals; and finally the memoir On the Influence of Geological Changes on the Earth’s Axis of Rotation, read before the Royal Society in 1876 and published in the Society’s Philosophical Transactions (1877), marked his definite entry into serious scientific life. He was proposed for the Royal Society in 1877 and elected a fellow in 1879. After his Trinity fellowship had expired (in 1878) he continued to live in Cambridge, holding no official position but pursuing research on cosmogony. In 1883 the Plumian professorship of astronomy and experimental philosophy fell vacant through the death of [q.v.], and Darwin was elected, although only, if we may trust a note in his diary, by the votes of five out of the nine electors. In 1884 he married, and his family life was conspicuously happy in spite of the continual handicap of his indifferent health.

The main part of Darwin’s scientific life was occupied by lines of research which originated out of his memoir of 1876. Sir William Thomson (afterwards Lord Kelvin) had been asked by the Royal Society to report on the suitability of this paper for publication; and out of the ensuing correspondence and conversations resulted a friendship which terminated only with the death of the older man, as well as a lifelong devotion of the younger to problems of the past history of the earth and of the solar system. Generally speaking, Darwin’s earliest papers dealt solely with the earth; those of his next epoch were concerned with the earth-moon system; later papers survey the whole solar system and even to some extent the whole universe of stars, but always with reference to the problems of past history and development. The object of most of these papers is to put general conjectures to the test of precise numerical calculations. The method is well illustrated in his 1876 paper already mentioned. Geologists, impressed by the apparent evidence of successive ice-ages, and naturalists, arguing from the present and supposed past distributions of terrestrial life, had promulgated the hypothesis of former extensive wanderings in the position of the earth’s pole and violent variations in the obliquity of the ecliptic. Darwin showed, by numerical calculation, that so long as the earth has remained rigid, the north pole can never have been distant more than about 3° from its present position. The possibility of cataclysmic adjustments of the earth’s shape may somewhat increase this figure, but in no event is a change to the extent assumed by geology dynamically possible.

The next series of papers, on the earth-moon system, are marked by the hypothesis that ‘tidal friction’ played a prominent part in the development of the system. As a result of viscosity, the tides raised in our earth by the moon will always have their points of high tide a little in advance of the positions they would occupy if the whole earth were perfectly fluid. The result is a force ever checking the speed of the earth’s rotation and increasing the distance between  145