An Introduction to the History of Science

by Walter Libby

Willughby, F., Historia Piscium. 1686.

Ray, John, Historia Plantarum. 2 vols., 1686-88.

Flamsteed, John, Tide-Table for 1687.

Newton, Isaac, Philosophiæ Naturalis Principia Mathematica. Autore Is. Newton. Imprimatur: S. Pepys, Reg. Soc. Præses. Julii 5, 1686. 4to. Londini, 1687.

After the Society had ordered that Newton's Mathematical Principles of Natural Philosophy should be printed, it was found that the funds had been exhausted by the publication of Willughby's book on fishes. It was accordingly agreed that Halley should undertake the business of looking after it, and printing it at his own charge, which he had engaged to do. Shortly after, the President of the Royal Society, Mr. Samuel Pepys, was desired to license Mr. Newton's book.

It was not merely by defraying the expense of publication that Halley contributed to the success of the Principia. He, Wren, Hooke, and other Fellows of the Royal Society, concluded in 1684 that if Kepler's third law were true, then the attraction exerted on the different planets would vary inversely as the square of the distance. What, then, would be the orbit of a planet under a central attraction varying as the inverse square of the distance? Halley found that Newton had already determined that the form of the orbit would be an ellipse. Newton had been occupied with the problem of gravitation for about eighteen years, but until Halley induced him to do so, had hesitated, on account of certain unsettled points, to publish his results.

He writes: "I began (1666) to think of gravity extending to the orb of the moon, ... and thereby compared the force requisite to keep the moon in her orb with the force of gravity at the surface of the earth, and found them answer pretty nearly." As early as March of that same year Hooke had communicated to the Society an account of experiments in reference to the force of gravity at different distances from the surface of the earth, either upwards or downwards. At this and at every point in Newton's discovery the records of co-workers are to be found.

By Flamsteed, the first Royal Astronomer, were supplied more accurate data for the determination of planetary orbits. To Huygens Newton was indebted for the laws of centrifugal force. Two doubts had made his meticulous mind pause—one, of the accuracy of the data in reference to the measurement of the meridian, another, of the attraction of a spherical shell upon an external point. In the first matter the Royal Society, as we have seen, had been long interested, and Picard, who had worked on the measurement of the earth under the auspices of the Académie des Sciences, brought his results, which came to the attention of Newton, before the Royal Society in 1672. The second difficulty was solved by Newton himself in 1685, when he proved that a series of concentric spherical shells would act on an external point as if their mass were concentrated at the center. For his calculations henceforth the planets and stars, comets and all other bodies are points acted on by lines of force, and "Every particle of matter in the universe attracts every other particle with a force varying inversely as the square of their mutual distances, and directly as the mass of the attracting particle." He deduced from this law that the earth must be flattened at the poles; he determined the orbit of the moon and of comets; he explained the precession of the equinoxes, the semi-diurnal tides, the ratio of the mass of the moon and the earth, of the sun and the earth, etc. No wonder that Laplace considered that Newton's Principia was assured a preëminence above all the other productions of the human intellect. It is no detraction from Newton's merit to say that Halley, Hooke, Wren, Huygens, Bulliau, Picard, and many other contemporaries (not to mention Kepler and his predecessors), as well as the organizations in which they were units, share the glory of the result which they coöperated to achieve. On the contrary, he seems much more conspicuous in the social firmament because, in spite of the austerity and seeming independence of his genius, he formed part of a system, and was under its law.