When the dust of conflict concerning Newton's announcement of the qualities of light had somewhat subsided, he turned to his former discovery, the Law of Gravitation, and bent his mighty mind upon it. The influence of the moon upon the Earth, the tilt of the Earth, the flattening of the poles, the recurring tides, the size, weight and distance of the planets, now occupied Newton's attention. And to study these phenomena properly, he had to construct special and peculiar apparatus. In Sixteen Hundred Eighty-seven the results of his discoveries were brought together in one great book, the "Principia." Newton was forty-five years old then. He was still the Cambridge professor, but was well known in political circles in London on account of having been sent there at various times to represent the University in a legal way. His diplomatic success led to his being elected a member of Parliament. Among other great men whom he met in London was Samuel Pepys, who kept a diary and therein recorded various important nothings about "Mr. Isaac Newton of Cambridge--a schoolteacher of degree, with a great dignity of manner and pleasing Countenance." It seems Newton thought so well of Pepys that he wrote him several letters, from which Samuel gives us quotations. Pepys really claimed the honor of introducing Newton into good society. Among others with whom Newton made friends in Parliament was Mr. Montague, who shortly afterward became Secretary of the Exchequer. Montague made his friend Newton a Warden of the Mint, with pay about double that which he had received while at Cambridge. In this public work Newton brought such talent and diligence to bear that in Sixteen Hundred Ninety-seven he was made Master of the Mint, at a salary of fifteen hundred pounds a year--a princely sum in those days. There is no doubt that the fact that Newton was a devout Churchman and an upholder of the Established Order was a great, although perhaps unconscious, diplomatic move. His delightful personality--gracious, suave, dignified and silent--won for him admiration wherever he would go. In argument his fine reserve and excellent temper were most convincing. Had he turned his attention to the law he would have become Chief Justice of England. In Seventeen Hundred Three he was elected President of the Royal Society, an office he held continuously for twenty-five years, and which tenure was only terminated by his death. In Seventeen Hundred Five the Queen visited Cambridge, and there with much pageantry bestowed the honor of Knighthood which changed Professor Newton into Sir Isaac Newton. But the man himself was still the simple, modest gentleman. The title did not spoil him--he was a noble man from boyhood.