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§§ 192, 193] preparations for a new edition of the Principia, besides going on with the lunar theory, but the work was again interrupted in 1695, when he received the valuable appointment of Warden to the Mint, from which he was promoted to the Mastership four years later. He had, in consequence, to move to London (1696), and much of his time was henceforward occupied by official duties. In 1701 he resigned his professorship at Cambridge, and in the same year was for the second time elected the Parliamentary representative of the University. In 1703 he was chosen President of the Royal Society, an office which he held till his death, and in 1705 he was knighted on the occasion of a royal visit to Cambridge.

During this time he published (1704) his treatise on Optics, the bulk of which was probably written long before, and in 1709 he finally abandoned the idea of editing the Principia himself, and arranged for the work to be done by Roger Cotes (1682–1716), the brilliant young mathematician whose untimely death a few years later called from Newton the famous eulogy, "If Mr. Cotes had lived we might have known something." The alterations to be made were discussed in a long and active correspondence between the editor and author, the most important changes being improvements and additions to the lunar theory, and to the discussions of precession and of comets, though there were also a very large number of minor changes; and the new edition appeared in 1713. A third edition, edited by Pemberton, was published in 1726, but this time Newton, who was over 80, took much less part, and the alterations were of no great importance. This was Newton's last piece of scientific work, and his death occurred in the following year (March 3rd, 1727).

193. It is impossible to give an adequate idea of the immense magnitude of Newton's scientific discoveries except by a free use of the mathematical technicalities in which the bulk of them were expressed. The criticism passed on him by his personal enemy Leibniz that, "Taking mathematics from the beginning of the world to the time when Newton lived, what he had done was much the better half," and the remark of his great successor Lagrange (chapter, § 237), "Newton was the 16