from a tree, led his thoughts upon the subject of gravity; and, reflecting on the power of that principle, he began to consider, that, as this power is not found to be sensibly diminished at the remotest distance from the centre of the earth, to which we can rise, neither at the tops of the loftiest buildings, nor on the summits of the highest mountains, it appeared to him reasonable to conclude, that this power must extend much further, than is usually thought."Why not as high as the moon?" said he to himself; " and if so, her motion must be influenced by it; perhaps she is retained in her orbit by it; however, though the power of gravity is not sensibly weakened in the little change of distance at which we can place ourselves from the centre of the earth, yet it is very possible that, at the height of the moon, this power may differ in strength much from what it is here." To make an estimate of what might be the degree of this diminution, he considered with himself, that if the moon be retained in her orbit by the force of gravity, no doubt the primary planets are carried about the sun by the like power; and by comparing the periods of the several planets with their distances from the sun, he found, that if any power like gravity held them in their courses, its strength must decrease in the duplicate proportion of the increase of distance. This he concluded, by supposing them to move in perfect circles, concentric to the sun, from which the orbits of the greatest part of them do not much differ. Supposing, therefore, the force of gravity, when extended to the moon, to decrease in the same manner, he computed whether that force would be sufficient to keep the moon in her orbit. In this computation being absent from books, he took the common estimate in use among the geographers and our seamen, before Norwood had measured the earth, namely, that sixty miles make one degree of latitude; but as that is a very erroneous supposition, each degree containing about sixty-nine and one-third of our English miles, his computation upon it did not make the power of gravity, decreasing in a duplicate proportion to the distance, answerable to the power which retained the moon in her orbit; whence he concluded, that some other cause must at least join with the action of the power of gravity on the moon. For this reason he laid aside for that time, any further thoughts upon the matter. Mr. Whiston (in his Memoirs, p. 33.) says, he told him that he thought Des Cartes's vortices might concur with the action of gravity. Nor did he resume this enquiry on his return to Cambridge, which was shortly after. The truth is, his thoughts were now engaged upon his newly projected reflecting telescope, of which he made a small specimen with a metallic reflector spherically concave. It was but a rude essay, chiefly defective by the want of a good polish for the metal. This instrument is now in the possession of the Royal Society. In 1667, he was chosen fellow of his college, and took the degree of master of arts. And in 1669, Dr. Barrow resigned to him the mathematical chair at Cambridge, the business of which appointment interrupted, for a while, his attention to the telescope; however, as his thoughts had been for some time chiefly employed upon optics, he made his discoveries in that science the subject of his lectures for the first three years after he was appointed mathematical professor: and having now brought his theory of light and colours, to a considerable degree of perfection, and having been elected a Fellow of the Royal Society, in January 1672, he communicated it to that body, to have their judgment upon it; and it was afterwards published in their Transactions, viz. "of February 19, 1672. This publication occasioned a dispute upon the truth of it, which gave him so much uneasiness, that he resolved not to publish any thing further for a while upon the subject; and in that resolution he laid by his optical lectures, although he had prepared them for the press. And the analysis by infinite series, which he had intended to subjoin to them, unhappily for the world, underwent the same fate, and for the same reason. In this temper he resumed his telescope: and observing that there was no absolute necessity for the parabolic figure of the glasses, since, if metals could be ground truly spherical, they would be able to bear as great apertures as men could give a polish to, he completed another instrument of the same kind. This answering the purpose so well, as, though only half a foot in length, to show the planet Jupiter distinctly round, with his four satellites, and also Venus horned, he sent it to the Royal Society, at their request, together with a description of it, with further particulars; which were published in the Philosophical Transactions for March, 1672. Several attempts were also made by that society to bring it to per fection; but for want of a proper composition of metal, and a good polish, nothing succeeded, and the invention lay dormant till Hadley made his Newtonian telescope in 1723. At the request of Leibnitz, in 1676, he explained his invention of Infinite Series, and took notice how far he had improved it by his method of Fluxions, which however he still concealed, and particularly on this occasion, by a transposition of the letters that make up the two fundamental propositions of it, into an alphabetical order; the letters concerning which are inserted in Collins's "Commercium Epistolicum," printed 1712. In the winter, between the years 1676, and 1677, he found out the grand proposition, that, by a centripetal force acting reciprocally as the square of the distance, a planet must revolve in an ellipsis, about the centre of force placed in its lower focus, and, by a radius drawn to that centre, describe areas proportional to the times. In 1680 he made several astronomical observations upon the comet that then appeared; which, for some considerable time, he took not to be one and the same, but two different comets; and upon this occasion several letters passed between him and Mr. Flamsteed. He was still under this mistake, when he received a letter from Dr. Hook, explaining the nature of the line described by a falling body, supposed to be moved circularly by the diurnal motion of the earth, and perpendicularly by the power of gravity. This letter put him upon enquiring anew what was the real figure in which such a body moved; and that enquiry convincing him of another mistake which he had before fallen into concerning that figure, put him upon resuming his former thoughts with regard to the moon; and Picart having not long before, riz. in 1679, measured a degree of the earth with sufficient accuracy, by using his measures, that planet appeared to be retained in her orbit by the sole power of gravity; and, consequently, that this power decreases in the duplicate ratio of the distance; as he had formerly conjectured. Upon this principle he found the line described by a falling body to be an ellipsis, having one focus in the centre of the earth. And finding by this means, that the primary planets really moved in such orbits as Kepler had supposed, he had the satisfaction to see that this enquiry, which he had undertaken at first out of mere curiosity, could be applied to the greatest purposes. Hereupon he drew up about a dozen propositions, relating to the motion of the primary planets, round the sun, which were communicated to the Royal Society in the latter end of 1683. This coming to be known to Dr. Halley, that gentleman, who had attempted the demonstration in vain, applied, in August, 1684, to Newton, who assured him that he had absolutely completed the proof. This was also registered in the books of the Royal Society; at whose earnest solicitation Newton finished the work, which was printed under the care of Dr. Halley, and came out about Midsummer, 1687, under the title of" Philosophiæ Naturalis Principia Mathematica," containing, in the third book, the cometic astronomy, which had been lately discovered by him, and now made its first appearance in the world: a work which may be looked upon as the production of a celestial intelligence rather than of a man. This work, however, in which the great author has built a new system of natural philosophy, upon the most sublime geometry, did not meet at first with all the applause it deserved, and was one day to receive. Two reasons concurred in producing this effect: Des Cartes had then got full possession of the world. His philoso phy was indeed the creature of a fine imagination, gaily dressed out: he had given her likewise some of nature's fine features, and painted the rest to a seeming likeness of her. On the other hand, Newton had, with an unparalleled penetration and force of genius, pursued nature up to her most secret abode, and was intent to demonstrate her residence to others, rather than anxious to describe particularly the way by which he arrived at it himself: he finished that piece in that elegant conciseness, which had justly gained the ancients a universal esteem. In fact, the consequences flow with such rapidity from the principles, that the reader is often left to supply a long chain of reasoning to connect them, so that it required some time before the world could understand it. The best mathematicians were obliged to study it with care, before they could make themselves masters of it; and those of a lower rank durst not venture upon it, till encouraged by the testimonies of the more learned. But at last, when its value came to be sufficiently known, the approbation which had been so slowly gained, became universal, and nothing was to be heard from all quarters, but one general burst of admiration. "Does Mr. Newton eat, drink, or sleep, like other men?" says the Marquis De l'Hospital, one of the greatest mathematicians of the age, to the English who visited him. "I represent him to myself as a celestial genius entirely disengaged from matter." In the midst of these profound mathematical researches, just before his Principia went to the press in 1686, the privileges of the University being attacked by James the Second, Newton appeared among its most strenuous defenders, and was on that occasion appointed one of their delegates to the High-commission Court; and they made such a defence, that James thought proper to drop the affair. Our author was also chosen one of their members for the Convention Parliament, in 1688, in which he sat till it was dissolved. Newton's merit was well known to Mr. Montague, then Chanceller of the Exche quer, 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 assistant in it; and accordingly, in 1696, he was appointed Warden of the Mint, in which employment he rendered very signal service to the nation. And three years after he was promoted to be Master of the Mint, a place worth 12 or 1500l. per annum, which he held till his death. Upon this promotion he appointed Mr. Whiston his deputy in the mathe. matical professorship at Cambridge, giving him the full profits of the place, which appointment itself he also procured for him in 1703. The same year our author was chosen President of the Royal 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 heterogeneous mixture of light, and the production of colours thence arising, he had employed a good part of his time in bringing the experiment upon which the theory is founded, to a degree of exactness that might satisfy himself. The truth is, this seems to have been his favourite invention; thirty years he had spent in this arduous task, before he published it in 1704. In infinite series and fluxions, and in the power and rule of gravity, in preserving 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 further separation, in the discovery of the different refrangibilities of these particles thus separated; and that these constituent rays had each its own peculiar colour inherent in it; that rays falling in the same angle of incidence have alternate fits of reflection and refraction; 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 though it necessary to be himself the last finisher of it. In fact, the affair that chiefly employed 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 distance, between light and other bodies, by which both the reflections and refractions, as well as inflections, of the former, were constantly produced. To ascertain the force and extent of this principle of action was what had all along engaged 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 physics; and, if we look upon his queries as containing the history of a great man's first thoughts, even in that view they must be always at least entertaining and curious. This 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 inventions were intended for the public so long before as 1672; but were laid by then, in order to prevent his being engaged on that account in a dispute about them. And it is not a little remarkable that, even now, this last piece proved the occasion of another dispute, which continued for many years. Ever since 1684, Leibnitz had been artfully working the world into an opinion, that he first invented 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 Scholium to the 2nd lemma of the 2nd 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 Leipsic, where an account is given of this book, the author of that account ascribed the invention to Leibnitz, intimating that Newton borrowed it from him. Dr. Keill, 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 considering all the papers and letters relating to the point in controversy, decided in favour of Newton and Keill; as is related at large in the life of the last-mentioned gentleman; and these papers themselves were published in 1712, under the title of "Commercium Epistolicum Johannis Collins," 8vo. In 1705, the honour of knighthood was conferred upon our author by Queen Anne, in consideration of his great merit. And in 1714, he was applied to by the House of Commons, for his opinion upon a new method of discovering the longitude at sea by signals, which had been laid before them by Ditton and Whiston, in order to procure their encouragement; but the petition was thrown aside upon reading Newton's paper delivered to the committee. The following year, 1715, Leibnitz, with the view of bringing the world more easily into the belief that Newton had taken the Method of Fluxions from his Differential Method, attempted to foil his mathematical skill by the famous problem of the trajectories, which he, therefore, proposed to the English by way of challenge; but the solution of this, though the most difficult proposition he was able to devise, and what might pass for an arduous affair to any other, yet was hardly any more than an amuse. ment to Newton's penetrating genius: he received the problem at 4 o'clock in the afternoon, as he was returning from the Mint; and, though extremely fatigued with business, yet he finished the solution before he went to bed. tice to the Elector of Hanover, so when that prince was raised to the British throne, Newton came more under the notice of the court; and it was for the immediate satisfaction of George the First, that he was prevailed on to put the last hand to the dispute about the invention of fluxions. In this court, Caroline, Princess of Wales, afterwards Queen consort to George the Second, happened to have a curiosity for philosophical inquiries; no sooner, therefore, was she informed of our author's attachment to the House of Hanover, than she engaged his conversation, which soon endeared him to her. Here she found, in every difficulty, that full satisfaction which she had in vain sought for elsewhere; and she was often heard to declare, publicly, that she thought herself happy in coming into the world at a juncture of time which put it in her power to converse with him. It was at this Princess's solicitations that he drew up an abstract of his Chronology; a copy of which was at her request communicated about 1718, to Signior Conti, a Venetian nobleman, then in England, upon a promise to keep it secret. But, notwithstanding this promise, the abbé, who while here had also affected to shew a particular friendship for Newton, though privately betraying him, as much as lay in his power, to Leibnitz, was no sooner got across the water, into France, than he dispersed copies of it, and procured an antiquary to translate it into French, as well as to write a confutation of it. This, being printed at Paris, in 1725, was delivered as a present, from the bookseller that printed it, to our author, that he might obtain, as was said, his consent to the publication; but though he expressly refused such consent, yet the whole was published the same year. Hereupon Newton found it necessary to publish a defence of himself, which was inserted in the Philos. Trans. Thus, he who had so much all his life long been studious to avoid disputes, was unavoidably all his lifetime, in a manner, involved in them; nor did this last dispute even finish at his death, which happened the year following. Newton's paper was republished in 1726, at Paris, in French, with a letter of the Abbé Conti, in answer to it; and the same year some dissertations were printed there by Father Souciet, against Newton's Chronological Index; an answer to which was inserted, by Halley, in the Philos. Trans. No. 397. Some time before this business, in his As Leibnitz was Privy-Councellor of Jus 80th year, our author was seized with an incontinence of urine, thought to proceed Newton's character has been attempted by Mr. Fontenelle and Dr. Pemberton, the substance of which is as follows. He was of a middle stature, and somewhat in clined to be fat in the latter part of his life. His countenance was pleasing and venerable at the same time, especially when he took off his peruke, and shewed his white hair, which was pretty thick. He never made use of spectacles, and lost but one tooth during his whole life. Bishop Atterbury says, that in the whole air of Sir Isaac's face and make, there was nothing of that penetrating sagacity which appears in his compositions; that he had something rather languid in his look and manner, which did not raise any great expectation in those who did not know him. His temper, it is said, was so equal and mild, that no accident could disturb it. A remarkable instance of which is related as follows. Sir Isaac had a favourite little dog, which he called Diamond. Being one day called out of his study into the next room, Diamond was left behind. When Sir Isaac returned, having been absent but a few minutes, he had the mortification to find that Diamond having overset a lighted candle among some papers, the nearly finished labour of many years was in flames, and almost consumed to ashes. This loss, as Sir Isaac was then very far advanced in years, was irretrievable; yet without once striking the dog, he only rebuked him with this exclamation: "Oh! Diamond! Diamond! thou little knowest the mischief thou hast done!" He was indeed of so meek and gentle a disposition, and so great a lover of peace, that he would rather have chosen to remain in obscurity, than to have the calm of life ruffled by those storms and disputes, which genius and learning always draw upon those that are most eminent for them. From his love of peace, no doubt, arose that unusual kind of horror which he felt for all disputes: a steady unbroken attention, free from those frequent recoilings inseparably incident to others, was his peculiar felicity; he knew it, and he knew the value of it. No wonder then that controversy was looked on as his bane. When some objections, hastily made to his discoveries concerning light and colours, induced him to lay aside the design he had taken of publishing his optical lectures, we find him reflecting on that dispute, into which he had been unavoidably drawn, in these terms; "I blamed my own imprudence for parting with so real a blessing as my quiet, to run after a shadow." It is true this shadow, as Fontenelle observes, did not escape him afterwards, nor did it cost him that quiet which he so much valued, but proved as much a real happiness to him as his quiet itself; yet this was a happiness of his own making; he took a resolution from these disputes, not to publish any more concerning that theory, till he had put it above the reach of controversy, by the exactest experiments, and the strictest demonstrations; and accordingly it has never been called in question since. In the same temper, after he had sent the manuscript to the Royal Society, with his consent to the printing of it by them; yet upon Hook's injuriously insisting that he himself had demonstrated Kepler's problem before our author, he determined rather than be again involved in a controversy to suppress the third book; and he was very hardly prevailed upon to alter |