With wonderful sagacity Newton traced the consequences of the law of gravitation.  He showed that the earth must be an oblate spheroid, formed by the revolution of an ellipse round its lesser axis.  He showed how the tides were caused by the moon, and how the effect of the moon’s action upon the earth is to draw its fluid parts into the form of an oblate spheroid, the axis of which passes through the moon.  He also applied the law of gravitation to explain irregularities in the lunar motions, the precession of the equinoctial points, and the orbits of comets.

In the “Principia” Newton published for the first time the fundamental principle of the fluxionary calculus which he had discovered about twenty years before; but not till 1693 was his whole work communicated to the mathematical world.  This delay in publication led to the historical controversy between him and Leibnitz as to priority of discovery.

In 1676 Newton had communicated to Leibnitz the fact that he had discovered a general method of drawing tangents, concealing the method in two sentences of transposed characters.  In the following year Leibnitz mentioned in a letter to Oldenburg (to be communicated to Newton) that he had been for some time in possession of a method for drawing tangents, and explains the method, which was no other than the differential calculus.  Before Newton had published a single word upon fluxions the differential calculus had made rapid advances on the Continent.

In 1704 a reviewer of Newton’s “Optics” insinuated that Newton had merely improved the method of Leibnitz, and had indeed stolen Leibnitz’s discovery; and this started a controversy which raged for years.  Finally, in 1713, a committee of the Royal Society investigated the matter, and decided that Newton was the first inventor.

IV.—­Later Years of Newton’s Life

In 1692, when Newton was attending divine service, his dog Diamond upset a lighted taper on his desk and destroyed some papers representing the work of years.  Newton is reported merely to have exclaimed:  “O Diamond, Diamond, little do you know the mischief you have done me!” But, nevertheless, his excessive grief is said for a time to have affected his mind.

In 1695 Newton was appointed Warden of the Mint, and his mathematical and chemical knowledge were of eminent use in carrying on the recoinage of the mint.  Four years later he was made Master of the Mint, and held this office during the remainder of his life.  In 1701 he was elected one of the members of parliament for Oxford University, and in 1705 he was knighted.

Towards the end of his life Newton began to devote special attention to the theological questions, and in 1733 he published a work entitled “Observations upon the Prophecies of Daniel and the Apocalypse of St. John,” which is characterised by great learning and marked with the sagacity of its distinguished author.  Besides this religious work, he also published his “Historical Account of Two Notable Corruptions of Scripture,” and his “Lexicon Propheticum.”