Mrs. Newton, seeing that her son's propensities were not those of a farmer,again sent him to Grantham school. After remaining there nine months, he went to Trinity College, Cambridge, where he was admitted on the 5th June, 1660, in the 18th year of his age. In this favoured situation the peculiar talents of Mr. Newton began to display themselves. The ardour with which he prose cuted his studies, and the rapidity of his progress, at tracted the notice of his teachers, and acquired lum the admiration and friendship of Mr. (afterwards Dr ) Bar row, who was then a fellow of Trinity College. The works which he now perused with avidity were, Saun derson's Logic, Kepler's Optics, the Geometry ol Des cartes, and the Arithmetic of Infinites of Dr. Wallis. The Elements of Euclid, and the works of the ancient geometers, occupied less of his attention than they were justly entitled to ; but he appears to have been carried away' by the seductions of analysis, and he afterwards expressed his regret to Dr. Pemberton, " that he had applied himself to the works of Descartes and other al gebraical writers, before he had considered the Elements of Euclid with thc attention which they deserved." In 1664, Mr. Newton took the degree of bachelor of arts, and it appears, from somc of his accounts of expenses, that he bought in that year a glass prism, for the pur pose of examining experimentally Descartes' doctrine of colours. There is no reason, however, for believing that he began so early to obtain the results which after wards excited so much notice, for he was interrupted in the midst of his researches by the 'appearance of the plague at Cambridge in 1665, which compelled him to quit his studies, and retire to his own property in the country. During the two years which he now spent in the country, his mind, as might naturally have been ex pected, was absorbed in philosophical speculations ; and it was in this peaceful seclusion that lie received the first glimpse of those splendid discoveries which have elevated his name above that of all other men, and shed rcnown upon tho country that gave him birth. When seated alone in a garden, the accidental fall of an apple fixed his thoughts on the subject of gravity. In re flecting upon this property of matter, and considering that it seemed to experience no diminution at the tops either of the highest buildings or the loftiest mountains, be was led to conjecture that it might extend far bey ond the earth and its atmosphere, and even to the orbit of the moon. In this view of the matter, Ile considered the moon as nothing more than a falling body, constantly deflected to the earth from the rectilineal path in which it had been projected, and it became an easy matter to ascertain the force of gravity at the distance of the moon, and to determine if it emanated from the same source as that which exhibited itself in falling bodies at the surface of the earth. In attempting, however, to make the calculation, he employed the erroneous but common estimate among geographers, that sixty miles make one degree of the meridian, and having with such imperfect data obtained a result which opposed his theo retical speculations, he concluded that the moon must be influenced by some other course than that which pro duced the fall of heavy bodies.
At various times after he procured his prism, in 1664, Newton had directed his attention to the subject of op tics. He began by grinding lenses in the final of some of the conic sections, with the view of correcting their spherical aberration, and in the belief that this was the only imperfection to which the telescope was liable. His success, however, did not equal his expectations ; and he was led to study the nature of light itself, by repeating with his prism some of the experiments made by Grimaldi. The brilliancy of the prismatic colours struck him with surprise, and his attention was parti cularly fixed on the oblong figure of the spectrum. Ac cording to the received laws of refraction, the image of thc sun ought to have been exactly circular, in place of an oblong form. This irregularity Newton at first supposed to be only accidental, and in attempting to find its cause, he was led to discover the compound or he terogeneous nature of colourless light, and to deter mine the different refrangibilitics of thc coloured rays which entered into its composition. This important dis covery explained to him at once the causc of the imper fections of refracting telescopes, and having computed the amount of the error arising from the different re frangibility of the rays of light, he found it to exceed some hundreds of times that. which was occasioned by
the spherical form of the lenses. By such steps New ton was led to study the reflection of light, and ht. speedily saw that by mcans ol a reflecting material, ca pable of being polished as highly as glass, and having an exact parabolic form, he could construct a telescope free from all the errors produced by the compound na ture of light.
In 1666 Newton was elected a Fellow of Trinity Cul lege, and in the sante year he took his degree of Mas ter of Arts. Dr. Barrow, who was now Lucasian Pro fessor of AIathematies at Cambridge, having resolved to confine his attention to theology, resigned his chair in favour of Mr. Newton, who was thus obliged to re linquish for a while his practical researches respecting the improvement of the telescope. Having resolved. however, to complete his optical inquiries, he made them the subject of his lectures during the first three years of his appointment, and had thus ample opportunities, not only of repeating his former experiments, but of re-considering his doctrine of colours, and bringing It into a systematic form.
On the 23d December, 1671, the Lord Bishop of Sa rum proposed Mr. Newton as a member of the Royal Society ; and, on the Ilth January, 1672, he was elected a Fellow of that learned body. At the same meeting, a. telescope sent by Mr Newton from Cambridge, was CN hibited to the Society, and it was agreed that the secre tary should send a description of it to Mr. Huygens at Paris, for the purpose of securing for the inventor the honour which belonged to him. On the 25th January, Mr. Oldcnburgh read to the Society a letter from Mr. Newton, concerning " an intimation of a. considerable discovery he intends to send to the Society to be consi dered and examined." This discovery, which was laid before that body on the 8th February, was his new doc trine of the different refrangibility of the rays of light. It was received with peculiar commendation, and the society agreed to the immediate printing of it. in order to secure " the author against the arrogations of others." On the 9th December, 1675, another paper of New ton's was read, " containing partly an hypothesis to ex plain the properties of light, and partly the principal phenomena of the various colours exhibited by thin plates or bubbles, esteemed by him to be of a more difficult consideration, yet to depend also on the said properties of light." On the 16th December, when the remainder of this paper was read, " Mr Hook said that the main of it was contained in his Micrography, which Mr. New ton, in some particulars, had only carried further." In a few days Mr. Newton wrote a reply to this charge, which was read on the 20th January, i 676. " He stated the difference between his hypothesis and that of Mr. Book, in his Micrography ; the result of which is, that he (Mr. Newton) had nothing in common with Mr. Hook, but a supposition that ether is a medium suscep tible of vibrations, of which supposition Mr Newton saith he makes quite a different use ; Mr. Hook sup posing it light itself, which Mr. Newton does not Be sides, that he explains very difTerently from Mr Hook, the manner of refraction and reflexion, and the nature and production of colours in all cases, and CNCII in the colours of transparent substances. Mr. Newton says he explains every thing in a way so differing from Mr. Hook, that the experiments Ile grounds his discourse upon destroy all Hook saith about them. And that the two main experiments, without which the manner of production of those colours is not to bc found out, Were not only unknown to Air. Hook, when hc wrote his 'Mi crography, but even last spring, as he understood, by mentioning them to the said Alr. Hook " Immediately after the letter which contained these sharp observations on Air. Hook's unfounded claims, there was read another paper by Mr. Newton, containing his " Theory of the Colours of Natural Bodies," which pleased the com pany so well, that they were anxious to have it pub lished. Sir Isaac, however, expressed his wish that the publication of his Observations upon Colours should be suspended for a while, as he intended to complete them by some additional experiments and observations.