reply to the Queries thus addressed to him, that Newton wrote the five remarkable letters already alluded to. By this means some of the great truths of the Newtonian Philosophy were promulgated among a class of readers who would not otherwise have heard of them.1 About the year 1718, Isaac Watts speaks of the exploded Physics of Descartes, and the noble inventions of Sir Isaac Newton, in his "hypotheses of the heavenly bodies and their motions;" and he refers to previous writers who have explained Nature and its operations in a more sensible and geometrical manner than Aristotle, especially those who have followed the principles of that wonder of our age and nation, Sir Isaac Newton. 2 Dr. John Keill was the first person who publicly taught natural philosophy, "by experiments in a mathematical manner." Desaguliers informs us, that this author "laid down very simple propositions, which he proved by experiments, and from these he deduced others more compound, which he still confirmed by experiments, till he had instructed his auditors in the laws of motion, the principles of hydrostatics and optics, and some of the chief propositions of Sir Isaac Newton, concerning light 1 Lord Aston, a great lover of the mathematics, who would gladly be satisfied in a difficulty or two on that science,” requested Mr. Greves and Sir E. Southcote to submit these difficulties to Sir Isaac Newton. Mr. Greves accordingly went on Monday, the 30th November 1702, and gives the following account of the conversation. He owns there are a great many faults in his book, and has crossed it and interleaved it, and writ in the margin of it, in a great many places. It is talked he designs to reprint it, though he would not own it. I asked him about his proof of a vacuum, and said that if there is such a matter as escapes through the pores of all sensible bodies, this could not be weighed . . . . . I find he designs to alter that part, for he has writ on the margin, Materia sensibilis; perceiving his reasons do not conclude in all matter whatsoever."--Edleston's Correspondence, Pref. p. xiv., and Tixall's Letters, II. 152, quoted there. 2 Improvement of the Mind, Part I. chap. xx. Art. vi. and xvi., or his Works, vol. v. pp. 301, 306. and colours. He began these courses in Oxford about the year 1704 or 1705, and in that way introduced the love of the Newtonian philosophy." When Dr. Keill left the University, Desaguliers began to teach the new philosophy by experiments. He commenced his lectures at Harthall, in Oxford, in 1710, and delivered more than a hundred and twenty discourses; and when he went to settle in London in 1713, he informs us that he found "the Newtonian philosophy generally received among persons of all ranks and professions, and even among the ladies by the help of experiments. "2 Such were the steps by which the philosophy of Newton was established in Great Britain. From the time of the publication of the Principia, its mathematical doctrines formed a regular part of academical education, and before twenty years had elapsed, its physical truths were communicated to the public in popular lectures, illustrated by experiments, and accommodated to the capacities of those who were not versed in mathematical knowledge. The Cartesian system, though it may have lingered for a while in the recesses of our universities, was soon overturned; and long before his death, Newton enjoyed the high satisfaction of seeing his philosophy triumphant in his native land. In closing our account of the Principia, and in justification of the high eulogium we have pronounced upon it, we may quote the opinions of two of the most distinguished men of the past or the present age. It may be justly said," observes Halley, "that so many and so valu 66 1 These lectures were first published in Latin in 1718, and afterwards in English in 1721 and 1739, under the title of An Introduction to the true Astronomy, or Astronomical Lectures, read in the Astronomical School of the University of Orford. By John Keill, M.D., F.R.S 2 Desaguliers, ut supra, Preface, pp. viii, x. able philosophical truths, as are herein discovered, and put past dispute, were never yet owing to the capacity and industry of any one man. "The importance and generality of the discoveries," says Laplace, "and the immense number of original and profound views which has been the germ of the most brilliant theories of the philosophers of this century, and all presented with much elegance, will ensure to the work, on the Mathematical Principles of Natural Philosophy, a pre-eminence above all the other productions of human genius." " 1 Phil. Trans. vol. xvi. p. 296. 2 CHAPTER XIII THE NEWTONIAN PHILOSOPHY STATIONARY FOR HALF A CENTURY, OWING GAINS THE PRIZE OFFERED BY THE ENGLISHI BOARD OF LONGITUDE— MOON'S ACCELERATION, AND COMPLETES THE LUNAR THEORY—LAGRANGE'S SOLUTION OF THE PROBLEM OF THREE BODIES AS APPLIED TO THE PLANETS-INEQUALITIES OF JUPITER AND SATURN EXPLAINED BY LAPLACE-STABILITY OF THE SOLAR SYSTEM THE PROOF OF DESIGN —MACLAURIN, LAPLACE, AND OTHERS, ON THE FIGURE OF THE EARTH -RESEARCHES OF LAPLACE ON THE TIDES, AND THE STABLE EQUILIBRIUM OF THE OCEAN-THEORETICAL DISCOVERY OF NEPTUNE BY ADAMS AND LEVERRIER-NEW SATELLITES OF SATURN AND NEPTUNE -EXTENSION OF SATURN'S RING AND ITS PARTIAL FLUIDITY-TWENTYSEVEN ASTEROIDS DISCOVERED – LEVERRIER'S THEORY OF THEM COMETS WITH ELLIPTIC ORBITS WITHIN OUR SYSTEM-LAW OF GRAVITY APPLIED TO DOUBLE STARS-SPIRAL NEBULÆ-MOTION OF THE SOLAR SYSTEM IN SPACE. WHEN Halley remarked that the author of the Principia "seemed to have exhausted his argument, and left little to be done by those who should succeed him," he committed a mistake which, though it had a tendency to check the progress of inquiry, was yet one into which philosophers are apt to fall when their science has made a great start by the discovery of some general and comprehensive law. Had Halley ventured to make this remark at the close of his life, rather than in 1687, he might have found some justification of it in the long interval which elapsed before any brilliant addition had been made to physical astronomy. During the half century which had passed away since the discovery of universal gravitation, no application of it of any importance had been made, and, as Laplace has observed, "all this interval was required for this great truth to be generally comprehended, and for surmounting the opposition which it encountered from the system of vortices, and from the prejudices of contemporaneous mathematicians." The infinitesimal analysis, as it was left by Newton and Leibnitz, was incapable of conducting the physical astronomer to any higher results than those which were consigned in the Principia; and it is a remarkable fact in the history of science, that the very men who spurned the new philosophy of gravitation, were strenuously engaged in improving that very calculus which was destined to establish and extend those great truths which they had so rashly denounced. It has been remarked by Laplace, that "with the exception of his researches on the elliptical motion of the planets and comets, of the attraction of spherical bodies, and of the intensity of gravity at the surface of the sun, and of the planets that are accompanied by satellites, all the other discoveries which we have described were only blocked out by Newton. His theory of the figures of the planets was limited by the supposition of their homogeneity. His solution of the problem of the precession of the equinoxes, though very ingenious and accordant with |