Newton's merit was well known to Mr. Montague, then Chancellor of the Ex chequer, and afterwards Earl of Halifax, who had been bred at the same college with him ; and when he undertook the great work of recoining the money, he fixed his eye upon Newton for an assist ant in it ; and accordingly, in 1696, he was appointed Warden of the Mint, in which employment he rendered very sig nal service to the nation. And three years after he was promoted to be Mas ter of the Mint, a place worth 12 or 15001. per annum, which he held till his death. Upon this promotion he appoint. ed Mr. Whiston his deputy in the mathe matical professorship at Cambridge, giv ing him the full profits of the place, which appointment itself he also procur ed for him in 1703. The same year our author was chosen President of the Roy al Society, in which chair he sat for 25 years, namely, till the time of his death ; and he had been chosen a member of the Royal Academy of Sciences at Paris, in 1699, as soon as the new regulation was made for admitting foreigners into that society.
Ever since the first discovery of the he terogeneous mixture of light, and the pro duction of colours thence arising, he had employed a good part of his time in bring ing the experiment, upon which the theo ry is founded, to a degree of exactness that might satisfy himself. The truth is, this seems to have been his favourite in vention ; thirty years he had spent in this arduous task, before he published it in 1704. In infinite series and fluxion', and in the power and rule of gravity in pre serving the solar system, there had been some, though distant, hints given by others before him; whereas in dissecting a ray of light into its primary constituent particles, which then admitted of no fur ther separation ; in the discovery of the different refrangibilities of these parti cles thus separated: and that these con stituent rays had each its own peculiar colour inherent in it ; thut rays falling in the same angle of incidence have alter nate fits of reflection and reNiction ; that bodies are rendered transparent by the minuteness of their pores, and become opaque by having them large; and that the most transparent body, by having a great thinness, will become less pervious to the light ; in all these, which make up his new theory of light and colours, he was absolutely and entirely the first starter ; and as the subject is of the most subtile and delicate nature, he thought it necessary to be himself the last finisher of it.
In fact, the affair that chiefly employ ed his researches for so many years was far from being confined to the subject of light alone. On the contrary, all that we know of natural bodies seemed to be comprehended in it ; he had found out that there was a natural action, at a dis tance, between light and other bodies, by which both the reflections and refrac tions, as well as inflections, of the former were constantly produced. To ascer
tain the force and extent of this princi ple of action was what had all along en gaged his thoughts, and what, after all, by its extreme subtlety, escaped his most penetrating spirit. However, though he has not made so full a discovery of this principle, which directs the course of light, as he has in regard to the power by which the planets are kept in their courses, yet he gave the best directions possible for such as should be disposed to carry on the work, and furnished matter abundantly sufficient to animate them to the pursuit. He has, indeed, hereby opened a way of passing from optics to an entire system of ph7sics ; and, if we look upon his queries as contain ing the history of a great man's first thoughts, even in that view they must be always at least entertaining and cu rious.
The same year, and in the same book with his Optics, he published, for the first time, his Method of Fluxions. It has been already observed, that these two in ventions were intended for the public so long before as 1672 ; but were laid by then, in prder to prevent his being en gaged on that account in a dispute about them. And it is not &little remarkable that, even now, this last piece proved the oc casion of another dispute, which continu ed for many years. Ever since 1684, Leibnitz had been artfully working the world into an opinion, that he first invent ed this method. Newton saw his design from the beginning, and had sufficiently obviated it in the first edition of the " Principia," in 1687, (viz. in the Scho lium to the 2d lemma of the 2d book) : and with the same view, when he now published that method, he took occasion to acquaint the world that he invented it in the years 1665 and 1666. In the " Acta Eruditorum" of Leipaic, where an ac count is given of this book', the author of that account ascribed the invention to Leibnitz, intimating that Newton borrow. ed it from him. Dr. Keil!, astronomical professor at Oxford, undertook Newton's defence ; and after several answers on both sides, Leibnitz complaining to the Royal Society, this body appointed a committee of their members to examine the merits of the case. These, after con sidering all the papers and letters relat ing to thejaoint in controversy, decided in favour of Newton and Ke ill ; as is relat ed at large in the life of the last mention ed gentleman ; and these papers them selves were published in 1712, under the title of " Commercium Epistolicum Jo liannis Collins," 8ro.