The Great Events by Famous Historians, Volume 12

by Unknown

This correction of Newton's error, and the discovery that a projectile would move in an elliptical orbit when under the influence of a force varying in the inverse ratio of the square of the distance, led Newton, as he himself informs us in his letter to Halley, to discover "the theorem by which he afterward examined the ellipsis," and to demonstrate the celebrated proposition that a planet acted upon by an attractive force varying inversely as the squares of the distances, will describe an elliptical orbit in one of whose foci the attractive force resides.

But though Newton had thus discovered the true cause of all the celestial motions, he did not yet possess any evidence that such a force actually resided in the sun and planets. The failure of his former attempt to identify the law of falling bodies at the earth's surface with that which guided the moon in her orbit, threw a doubt over all his speculations, and prevented him from giving any account of them to the public.

An accident, however, of a very interesting nature induced him to resume his former inquiries, and enabled him to bring them to a close. In June, 1682, when he was attending a meeting of the Royal Society of London, the measurement of a degree of the meridian, executed by M. Picard in 1679, became the subject of conversation. Newton took a memorandum of the result obtained by the French astronomer, and having deduced from it the diameter of the earth, he immediately resumed his calculation of 1665, and began to repeat it with these new data. In the progress of the calculation he saw that the result which he had formerly expected was likely to be produced, and he was thrown into such a state of nervous irritability that he was unable to carry on the calculation. In this state of mind he intrusted it to one of his friends, and he had the high satisfaction of finding his former views amply realized. The force of gravity which regulated the fall of bodies at the earth's surface, when diminished as the square of the moon's distance from the earth, was found to be almost exactly equal to the centrifugal force of the moon as deduced from her observed distance and velocity.

The influence of such a result upon such a mind may be more easily conceived than described. The whole material universe was spread out before him; the sun with all his attending planets; the planets with all their satellites; the comets wheeling in every direction in their eccentric orbits; and the systems of the fixed stars stretching to the remotest limits of space. All the varied and complicated movements of the heavens, in short, must have been at once presented to his mind as the necessary result of that law which he had established in reference to the earth and the moon.

After extending this law to the other bodies of the system, he composed a series of propositions on the motion of the primary planets about the sun, which were sent to London about the end of 1683, and were soon afterward communicated to the Royal Society.

About this period other philosophers had been occupied with the same subject. Sir Christopher Wren had many years before endeavored to explain the planetary motions "by the composition of a descent toward the sun, and an impressed motion; but he at length gave it over, not finding the means of doing it." In January, 1683-1684, Dr. Halley had concluded from Kepler's law of the periods and distances, that the centripetal force decreased in the reciprocal proportion of the squares of the distances, and having one day met Sir Christopher Wren and Dr. Hooke, the latter affirmed that he had demonstrated upon that principle all the laws of the celestial motions. Dr. Halley confessed that his attempts were unsuccessful, and Sir Christopher, in order to encourage the inquiry, offered to present a book of forty shillings value to either of the two philosophers who should, in the space of two months, bring him a convincing demonstration of it. Hooke persisted in the declaration that he possessed the method, but avowed it to be his intention to conceal it for time. He promised, however, to show it to Sir Christopher; but there is every reason to believe that this promise was never fulfilled.

In August, 1684, Dr. Halley went to Cambridge for the express purpose of consulting Newton on this interesting subject. Newton assured him that he had brought this demonstration to perfection, and promised him a copy of it. This copy was received in November by the doctor, who made a second visit to Cambridge, in order to induce its author to have it inserted in the register book of the society. On December 10th Dr. Halley announced to the society that he had seen at Cambridge Newton's treatise De Motu Corporum, which he had promised to send to the society to be entered upon their register, and Dr. Halley was desired to unite with Mr. Paget, master of the mathematical school in Christ's Hospital, in reminding Newton of his promise, "for securing the invention to himself till such time as he can be at leisure to publish it."

On February 25th Mr. Aston, the secretary, communicated a letter from Newton in which he expressed his willingness "to enter in the register his notions about motion, and his intentions to fit them suddenly for the press." The progress of his work was, however, interrupted by a visit of five or six weeks which he made in Lincolnshire; but he proceeded with such diligence on his return that he was able to transmit the manuscript to London before the end of April. This manuscript, entitled Philosophic Naturalis Principia Mathematics and dedicated to the society, was presented by Dr. Vincent on April 28, 1686, when Sir John Hoskins, the vice-president and the particular friend of Dr. Hooke, was in the chair.

Dr. Vincent passed a just encomium on the novelty and dignity of the subject; and another member added that "Mr. Newton had carried the thing so far that there was no more to be added." To these remarks the vice-president replied that the method "was so much the more to be prized as it was both invented and perfected at the same time." Dr. Hooke took offence at these remarks, and blamed Sir John for not having mentioned "what he had discovered to him"; but the vice-president did not seem to recollect any such communication, and the consequence of this discussion was that "these two, who till then were the most inseparable cronies, have since scarcely seen one another, and are utterly fallen out." After the breaking up of the meeting, the society adjourned to the coffee house, where Dr. Hooke stated that he not only had made the same discovery, but had given the first hint of it to Newton.

An account of these proceedings was communicated to Newton through two different channels. In a letter dated May 22d Dr. Halley wrote to him "that Mr. Hooke has some pretensions upon the invention of the rule of the decrease of gravity being reciprocally as the squares of the distances from the centre. He says you had the notion from him, though he owns the demonstration of the curves generated thereby to be wholly your own. How much of this is so you know best, as likewise what you have to do in this matter; only Mr. Hooke seems to expect you would make some mention of him in the preface, which it is possible you may see reason to prefix."