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HISTORY OF PHYSICAL ASTRONOMY.

of uniting in one great work all the discoveries that had been effected inPhysical Astronomy. This design appears realised in the MecaniqueCeleste , one of the most stupendous monuments of the human intellectwhich modern civilization can boast of. It consists of five quarto volumes,which were published at different times in the course of the author’s life. Thefirst and second volumes appeared in 1700 ; the third in 1800 ; the fourthin 1805 ; and the fifth in 1825. The whole work is divided into sixteenbooks. Ten of these occupy the first four volumes; the remaining sixcontained in the last volume may be considered as supplementary to theothers. The first book of this immortal production treats of the laws ofequilibrium and motion ; the second, of the law of universal gravitation andof the centres of gravity of bodies ; the third, of the figures of the celestialbodies ; the fourth, of the oscillations of the sea and the atmosphere ; thefifth, of the motions of the celestial bodies about their centres of gravity ;the sixth, of the theory of the planets ; the seventh, of the lunar theory ; theeighth, of the theory of the satellites of Jupiter, Saturn, and Uranus ; theninth, of the theory of comets ; the tenth, of the theory of refraction andother points relative to the system of the world. In the first book of thefifth volume or the eleventh of the whole work, Laplace considers thefigure and rotation of the earth. The twelfth book treats of the attractionand repulsion of spheres and of the laws of the equilibrium and motion ofelastic fluids ; the thirteenth, of the oscillations of the fluids which coverthe surfaces of the planets; the fourteenth, of the motions of the celestialbodies about their centres of gravity ; the fifteenth, of the motions of theplanets and comets ; the sixteenth, of the motions of the satellites. Besidesthe five volumes above mentioned, Laplace composed at different timessupplements to several of the books.

The physical theory of the planetary system is exhibited in the MecaniqueCeleste in a state of almost complete developement. No material progresshas in consequence been effected in this branch of astronomy since thepublication of that immortal work. One discovery of a very remarkablecharacter has indeed been recently added to the long list of triumphswhich adorn its history; but during the present century geometers havebeen mainly occupied in correcting and extending previous results, in im-proving the methods of investigation, and in illustrating the more obscurepoints of the theory.

In reviewing the progress of Physical Astronomy since the close ofNewton’s career, it is impossible not to be struck with the truth of the re-mark. that great occasions always call forth from the bosom of societysuitable minds to cope with the emergencies of the times, and to triumphover opposing difficulties. It has been said that Newton appeared onthe theatre of the world when the materials of the magnificent structureerected by him had been already amassed by the persevering industry ofpreceding ages. The true state of the planetary system had been un-folded by the successive labours of Hipparchus, Copernicus , and Kepler ;the laws of motion had been fully established by Galileo , and his suc-cessors Huygens , Wallis, and Wren; nay, the all-pervading principlewhich animates and controls the bodies of the universe had been dimlysurmised by more than one philosopher. There was still, however,wanting some master-spirit to detect the mutual dependence of thesedisjointed principles, and by a mighty effort of generalization to reduceall the phenomena of the heavens under one dominant law of nature. Theprospect of achieving this grand result was the alluring motive by which