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. [Illustration: _Portrait by John Van der Bank_ _By permission of W. A. Maxwell & Co._ SIR ISAAC NEWTON] Shortly after the founding of the Royal Society, correspondence, for which a committee was appointed, had been adopted as a means of gaining the coöperation of men and societies elsewhere. Sir John Moray, as President, wrote to Monsieur de Monmort, around whom, after the death of Mersenne, the scientific coterie in Paris had gathered. This group of men, which toward the close of the seventeenth century regarded itself, not unnaturally, as the parent society, was in 1666 definitely organized as the Académie Royale des Sciences. Finally, Leibnitz, who had been a Fellow of the Royal Society as early as 1673, and had spent years in the service of the Dukes of Brunswick, was instrumental in the establishment in 1700 of the Prussian Akademie der Wissenschaften at Berlin.