few years Newton turned his attention to his optical work. In 1668 he made his first reflecting telescope; it had an aperture of about one inch and was six inches long, and with it Newton saw Jupiter's satellites (Maccl. Corr. ii. 289). He never held any college office, but in 1669 he assisted Dr. Barrow, Lucasian professor, with an edition of his ‘Optical Lectures.’
At the end of 1668 Mercator had published his ‘Logarithmotechnia,’ in which he showed how to calculate the area of an hyperbola. A copy of this was sent by John Collins (1625–1683) [q. v.] to Barrow, and shown by him to Newton. Newton recognised that the method was in the main the same as the more general one he had already devised for finding the area of curves and for solving other problems, and showed his manuscripts to Barrow. Barrow was delighted, and wrote on 20 July 1669 to Collins, promising to send the papers of ‘a Friend of mine here that hath an excellent genius to these Things.’ The papers were sent, but without any mention of the name of the author, on 31 July, and on 20 Aug. Barrow writes: ‘I am glad my Friend's paper gives you so much satisfaction; his name is Mr. Newton; a Fellow of our College, and very young … but of an extraordinary genius and Proficiency in these things’ (Comm. Epist. pp. 1, 2, London, 1712). The title of the paper, printed from a manuscript in Collins's handwriting found among his papers after his death, and compared with Newton's own copy, is ‘De Analysi per Æquationes numeri terminorum infinitas.’ The main part of this manuscript was published by Newton in 1704 as an Appendix to his ‘Optics.’ Collins, writing to Strode in 1672, after stating that Barrow had sent him Newton's paper, proceeds: ‘Equibus et aliis quæ prius ab authore cum Barrovio communicata fuerant, patet illam methodum a dicto Newtono aliquot annis antea excogitatam et modo universali applicatam fuisse.’
In the autumn of 1669 Barrow resigned the Lucasian chair, and Newton was chosen to succeed him. Part of his time during 1669 and 1670 was occupied in writing notes and additions to a Latin translation of Kinckhuysen's ‘Algebra.’ (See Correspondence with Collins, Maccl. Corr. ii. 281.) He also at this time was led to conclude from his optical experiments that it was impossible to perfect the refracting telescope, and he applied himself to improving his reflecting instrument. The second telescope made by him was sent up to the Royal Society in December 1671, and is described in the ‘Philosophical Transactions,’ vii. 4004. Towards the end of the same year he was busy enlarging his method of infinite series. This paper was never finished, but was published in 1736 in a translation by Colson. Pemberton states that he had persuaded Newton ‘to let it go abroad,’ and hoped to receive from him papers to supply what was wanted when he died. About the same time he prepared an edition of the ‘Optical Lectures,’ twenty in number, which he had delivered as Lucasian professor. These were not published till 1729, when there was printed a copy, which he had given to David Gregory, the Savilian professor at Oxford.
At the end of this year Newton was proposed for election as a fellow of the Royal Society by Seth Ward, bishop of Salisbury. He was elected on 11 Jan. 1672, and about this time his correspondence with Henry Oldenburg [q. v.], secretary of the Royal Society, commenced (see Newton Correspondence with Cotes, edited by Edleston, 1850, App. p. 240; Maccl. Corr. ii. 311). The earliest letters relate mainly to the telescope. He was pleased at his election, and writes: ‘I shall endeavour to show my gratitude by communicating what my poor and solitary endeavours can effect towards the promoting philosophical design.’ This promise was soon fulfilled, for on 8 Feb. Oldenburg read a letter, dated 6 Feb., from Newton, containing his ‘New Theory about Light and Colours’ (Phil. Trans. vi. 3075).
The letter contained an account of the experiments with the prism bought in 1666 to try the celebrated phenomena of colours. The experiments showed conclusively that ‘Light consists of Rays differently refrangible;’ that ‘Colours are not Qualifications of Light derived from Refractions of Natural Bodies, as is generally believed, but original and connate properties which in divers Rays are divers;’ that ‘to the same degree of refrangibility ever belongs the same colour, and to the same colour ever belongs the same degree of refrangibility. The least refrangible rays are all disposed to exhibit a red colour. … the most refrangible rays are all disposed to exhibit a deep violet colour,’ and ‘this species of colour is not mutable by refraction, nor by reflexion from natural bodies,’ while ‘white light is ever compounded, and to its composition are requisite all the aforesaid primary colours mixed in proper proportion.’
It was ordered that ‘the author be solemnly thanked for this very ingenious discourse, and be made acquainted that the society think very much of it.’ It was further ordered that this discourse be entered in the register book, and that the Bishop of Salisbury, Robert Boyle [q. v.], and Robert Hooke [q. v.] be desired to peruse and consider it, and to bring in a report of it to the society.
