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NEW persons, which so disturbed his tranquillity that he threatened to be no longer "a slave to philosophy," but "resolutely to bid adieu to it eternally except what he might do for his own private satisfaction, or leave to come out after him." Finding "mathematical speculation at least dry if not somewhat barren," Newton thought of studying law, and became a candidate for the law fellowship in February, 1673. Dr. Barrow, however, gave the appointment to his rival as being the senior candidate. In consequence, probably, of this disappointment, the Royal Society at his desire "excused him" from its weekly payments; and when his fellowship was about to expire the crown permitted him to hold the Lucasian chair with a fellowship, without the obligation of taking holy orders. On the 9th December, 1675, Newton communicated to the Royal Society "a theory of light and colours, containing partly an hypothesis," to explain the properties of light in his former papers, and also the colours of thin plates. This hypothesis was to such an extent a modification of Descartes and Hook's undulatory theory that after the reading of it Hook said "that the main of it was contained in his Micrographia," an assertion which led to a controversy between the two philosophers which had an amicable termination. In having published this hypothesis Newton is supposed by Dr. Young to have considered an ethereal medium as necessary for the production of light; but he himself distinctly states that his hypothesis was "not propounded to be believed;" "that light is neither ether nor its vibrating motion;" and that "an erroneous supposition" is involved in such a hypothesis. In prosecuting his researches respecting gravity he was led by the laws of Kepler to the great law that gravity decreased as the square of the distance; but not possessing an accurate measure of the earth's radius, he could not reconcile the force of gravity at the earth's surface with that which takes place at the distance of the moon. Having heard, however, of Picard's measure of the earth's diameter, he succeeded in 1684 in proving that the force of gravity at the earth's surface, four thousand miles from its centre, was about exactly equal to that which kept the moon in her orbit at the distance of two hundred and forty thousand miles from the earth, and consequently that all the primary planets were retained by the same force in their orbits round the sun, and all the secondary planets in their orbits round their primaries. These discoveries were described in a treatise, "De Motu Corporum," which he showed to Halley at Cambridge in 1684, and which was afterwards completed and communicated to the Royal Society early in 1685. This treatise is supposed to have been part of his Lucasian lectures. It was doubtless the germ of his great work entitled "Philosophiæ Naturalis Principia Mathematica," the first book of which was presented to the society on the 20th April, 1686; the second in March, 1687; the third on the 6th of April, 1687; and the work published at the expense of Dr. Halley about the middle of the same year. A recent edition, under the care of Roger Cotes, was published in 1713, and a third edition edited by Dr. Pemberton in 1726. We have already seen that Newton had invented the method of fluxions in 1665. In June, 1669, he communicated to Dr. Barrow his "Analysis per equationes numero terminorum infinitas," in which the method of fluxions is explained. The contents of this work had been circulated throughout Europe, and were therefore known to foreign mathematicians though the work itself was not published till 1711. The principle of the calculus was published in the "Principia" in 1687, and its algorithm in 1699 in the second volume of Wallis' works. The doctrine of fluxions (the calculus of differences) was discovered also by Leibnitz, and hence a controversy arose on the question of priority which agitated the mathematical world for nearly two centuries, and which can hardly be said to have terminated. The following is the verdict pronounced by Sir David Brewster in his Life of Newton:—

1. That Newton was the first inventor of the method of fluxions in 1666; that the method was incomplete in its notation, and that the fundamental principle of it was not published to the world till 1687. 2. That Leibnitz communicated to Newton in 1677 his Differential Calculus, with a complete system of notation, and that he published it in 1684.

While Newton was engaged in writing the second and third books of the "Principia," an arbitrary act of James II. called him into public notice. He was one of a deputation which the university sent to government to resist a mandamus from the crown for granting to a monk the degree of master of arts. Judge Jeffreys rebuked the deputation—"As most of you are divines," said he, "go away and sin no more lest a worse thing come unto you." "Under this rebuke," Sir David Brewster remarks, "and in front of such a judge, the most ferocious that ever sat upon the judgment-seat, stood the immortal author of the 'Principia,' who had risen from the invention of its problems to defend the religion which he professed and the university which he adorned. The mandate which he resisted—a diploma to a monk—was in one sense an abuse of trivial magnitude, unworthy of the intellectual sacrifice which it occasioned; but the spark is no measure of the conflagration which it kindles, and the arm of a Titan may be required to crush what the touch of an infant might have destroyed." Owing to the part which Newton took on this occasion he was chosen to represent the university in the house of commons, and he sat in parliament from January, 1689, till its dissolution in February, 1690. As Newton was not returned to the next parliament, his friends exerted themselves to procure for him the presidency of King's college, Cambridge; and when they failed in this attempt they applied in vain for the mastership of the Charter-house school. In the autumn of 1692 his health began to give way. For nearly a year he had suffered from loss of appetite and want of sleep, which produced a degree of nervous irritability which gave rise to a report that he had become insane. It has been proved, however, that this rumour was wholly groundless, as he composed at this period his four celebrated letters to Dr. Bentley, solved difficult problems, and carried on important chemical inquiries. Having completed the great researches which it had been the business of his life to carry on, he and his friends had expected some national recognition of his services to science Charles Montague, whom he had known as a fellow of Trinity college and as a colleague in the Convention parliament, had long been anxious to serve his friend. Having been appointed chancellor of the exchequer, and found it necessary to restore to its proper value the adulterated coin of the realm, he appointed Newton in 1695 warden of the mint, with a salary of £600 per annum. In 1699 he succeeded to the mastership of the same establishment, with a salary of from £1200 to £1500 a year. In the same year the French Academy of Sciences elected him one of their eight foreign associates. In studying the lunar theory he had occasion, between 1694 and 1696, to correspond with Flamsteed, the astronomer royal, for the purpose of obtaining the results of his lunar observations at Greenwich. Flamsteed gave his observations with some reluctance, and a misunderstanding took place which compromised the character of both. In 1703, when Newton was elected president of the Royal Society, he was anxious for the publication of the Greenwich observations; and having mentioned their importance to the prince-consort, the prince offered to be at the expense of reducing and publishing them. Articles of agreement were accordingly drawn up, and referees appointed. Flamsteed failed to fulfil his part of the contract, and a grave quarrel arose, in which he denounced Newton as his enemy. Mr. Baily, in his life of Flamsteed, having had access only to the documents left by the astronomer, has represented Newton as having not only acted unjustly in the matter, but given way to "sudden ebullitions of temper, and apparent perversity of conduct." Sir David Brewster, however, having obtained a true copy of the articles of agreement, and other documents not known to Mr. Baily, has placed this question in its true light—a light much less favourable to Flamsteed than to Newton. While this controversy was going on, Newton received the honour of knighthood on the 16th April, 1705, when the queen with the prince-consort was passing through Cambridge to her residence at Newmarket. The court was held in Trinity lodge; and the royal guests were entertained at a dinner of so sumptuous a character that the university was obliged to borrow £500 to pay the expense of it. On the death of Queen Anne in 1714, and the accession of George I., Charles Montague was created Earl of Halifax, and appointed first lord of the treasury. From his intimacy with Newton he became acquainted with his niece, Catherine Barton, a lady of wit and beauty; and such was his admiration of her that he bequeathed to her the rangership and lodge of Bushy park, with £5000 and an annuity of £200, purchased in Sir Isaac Newton's name. Though reckoned a woman of strict honour and virtue, this legacy gave rise to unmerited suspicions, which had no existence during the life of Halifax, and we regret to say that attempts have been recently made to give a colour to the transaction equally