Pierre Simon Laplace, marquis de, a French astronomer and mathematician, born at Beau-mont-en-Auge, Lower Normandy, March 23, 1749, died in Paris, March 5, 1827. Of the events of his early life he seldom spoke after he had attained rank and distinctions, but he is known to have been of humble origin, and to have been enabled by the assistance of rich friends to study at the college of Caen and at the military school of Beaumont, whence at the age of 18 he went to Paris with letters of introduction to D'Alembert and others. D'Alembert at first took no notice of him; but receiving from him a remarkable paper on the general principles of mechanics, he at once interested himself in behalf of the young stranger, and by his influence procured him in 1768 or 1769 a professorship of mathematics in the military school of Paris. Thenceforth for more than half a century Laplace devoted himself to the pursuit of science with an ardor and industry productive of the most beneficial results, and which his participation in public business and politics never seriously interrupted. In 1773, when he was barely 24 years of age, his papers on the calculus and various astronomical questions, read before the academy of sciences, procured his admission into that body as an associate.

A few years later he became examiner of the pupils of the royal artillery corps, and in 1785 he was elected a member of the academy of sciences. He subsequently lectured on analysis at the normal school, served in the board of longitude, and presented to the council of 500 a report of the proceedings of the institute from its establishment. The revolution drew him into the sphere of politics, in which he accomplished nothing worthy of his fame, and in which the ignoble traits of his character were prominently displayed. At first he appears to have been a radical republican, and it is said that in 1796 he was one of a deputation who were presented at the bar of the council of 500 to swear eternal hatred to royalty. Two years later he paid his court to Gen. Bonaparte, fresh from his Italian campaigns, thus securing his election to the institute; and after the overthrow of the directory he was intrusted by the first consul with the department of the interior. So little capacity did he display in this office, however, that within six weeks he was superseded by Lucien Bonaparte, being appointed to a seat in the senate.

Napoleon in his exile at St. Helena, with more point than justice, complained that Laplace "carried the spirit of the infinitesimal calculus into the management of business." In fact, the department was then one of the most difficult in France to manage, and a more experienced statesman than Laplace might have failed to discharge its functions properly. Under Napoleon he was made vice president and chancellor of the senate, a count of the empire, an officer of the legion of honor, and was the recipient of many other distinctions. He nevertheless turned against his benefactor when misfortunes overtook him, voted for his deposition in 1814, and was rewarded by Louis XVIII. with the title of marquis. He also suppressed in the second edition of his Theorie des proba-bilites (Paris, 1814) the dedication to "Napoleon the Great," contained in the edition of 1812, in which, as in the dedication to vol. iii. of the Mecanique celeste, of which he did not live to publish a second edition, he had expressed himself under lasting obligations to Napoleon for numerous benefits.

During the hundred days he refrained from presenting himself at the Tuileries, and after the second restoration of the Bourbons his employments were chiefly of a scientific character, the most important being the presidency of the commission for reorganizing the polytechnic school, and that of the academy of sciences. - As a physicist Laplace occupies a position second to that of no mathematical philosopher since Newton, and to his labors the science of astronomy owes the discovery of the invariability of the major axes of the planetary orbits, and of the great inequality of the motions of Jupiter and Saturn, the settlement of the problem of the acceleration of the mean motion of the moon, the theory of Jupiter's satellites, and other important laws. In his knowledge of physical principles he was probably superior to any contemporary analyst; and his invention, in conjunction with Lavoisier, of the calorimeter for measuring the capacities of bodies for heat, his discovery of the cause of the discrepancy between the theoretical and observed velocity of sound, his rules for barometrical measurement, and his theories regarding capillary attraction, tides, and atmospheric refraction, show that in some of the most important branches of general physics his mind was not less actively and profitably employed than in mathematical analysis.

The crowning glory of his scientific career was his Mecanique celeste, a book which has been truly said to have had no predecessor, and which must wait for a second Laplace to arise ere it finds a rival. In it he sought to digest on a uniform scientific basis the abundant materials relating to the application of analysis to physical astronomy, which had been accumulating during nearly a century, and which, written in various languages, with differing notations and in various stages of scientific progress, presented a mass of matter not only difficult of access, but almost incomprehensible to any but the most recondite student. The result of his labors appeared in 16 books, published in 5 vols. 4to, with four supplements, between 1799 and 1825, and arranged as follows: - vol. i.: book i., "On the General Laws of the Equilibrium of Motion;" book ii., " On the Law of Universal Gravitation and the Motion of the Centres of Gravity of the Heavenly Bodies;" - vol. ii.: book iii., " On the Figure of the Heavenly Bodies;" book iv., " On the Oscillations of the Sea and the Atmosphere;" book v., " On the Motions of the Heavenly Bodies around their Proper Centres of Gravity " (Paris, 1799; republished in 1829-30); - vol. iii.: book vi., "On the Theory of the Planetary Motions;" book vii., " On the Theory of the Moon," and supplement i., " On the two great Inequalities of Jupiter and Saturn " (Paris, 1804); - vol. iv.: book viii., " On the Theory of the Satellites of Jupiter, Saturn, and Uranus;" book ix., "On the Theory of Comets;" book x., " On different Points relative to the System of the World," and supplements ii. and iii., comprising the "Theory of Capillary Action" (Paris, 1805); - vol. v.: book xi., " On the Figure and Rotation of the Earth;" book xii., " On the Attraction and Repulsion of Spheres, and the Laws of the Equilibrium and Motion of Elastic Fluids;" book xiii., " On the Oscillation of the Fluids which cover the Planets;" book xiv., "On the Motions of the Heavenly Bodies around their Centres of Gravity;" book xv., " On the Motions of the Planets and Comets;" book xvi., " On the Motions of the Satellites," and supplement iv., " On the Development in Series of the Radical which expresses the Mutual Distance of two Planets" (Paris, 1823-'5). " Within this immense programme," says Professor Nicol, "placed as if parenthetically, one finds the most striking notices on almost every important problem of mechanical physics, any one of which would have made the fortune of an ordinary mathematician." In consequence, however, of his almost total neglect to refer to the labors of his predecessors or contemporaries in this, and indeed in all his works, it is difficult for the student to know how much of it belongs to Laplace and how much to others; and he has therefore, not without apparent reason, been sometimes considered more of a compiler than a discoverer.

The name of Lagrange, his great contemporary and friend, is rarely mentioned, and one of the latter's finest analytic discoveries is on one occasion cursorily referred to as " the formula No. 21 of the second book of the Mecanique celeste." In like manner the claims of Taylor and Mac-laurin to the theorems passing under their names are ignored, while his references to himself are innumerable. With all needful restorations and acknowledgments, however, almost any one of the original researches of Laplace contained in the Mecanique celeste is sufficient to stamp him as one of the greatest of mathematicians. The only translation of this work is that by Dr. Bowditch of Salem, Mass., with full commentaries, published at Boston. (See Bowditch, Nathaniel.) Mrs. Somerville's " Mechanism of the Heavens " is a summary of a portion of the work. Laplace's remaining works consist of his Theorie analytique des probabilites, the most mathematically profound treatise on the subject which has yet appeared, and containing his celebrated method for the approximation to the values of definite integrals (Paris, 1812; 3d ed., 1820, with four supplements); his Exposition du systeme du rnonde (2 vols. 8vo, 1796; 6th ed., containing a eulogium on the author by Baron Fourier, 4to, 1835), "a resume of all modern astronomy, unsurpassed for perspicuity and elegance in any scientific literature," translated by Prof. Pond; and over 40 important memoirs, principally on astronomical subjects, published between 1772 and 1823. Of the three works above named, an edition in 7 vols. 4to (Paris, 1843-'7) was published under government auspices.

He died after a short illness. It is commonly related that his last words were: "What we know is of small amount; what we do not know is enormous." But De Morgan states, apparently with authority, that the last words of the great astronomer were different. During his illness, says De Morgan, " he thought much on the great problems of existence, and often muttered to himself, Qu'est ce que c'est que tout cela ! After many alternations, he appeared at last so permanently prostrated that his family applied to his favorite pupil, Poisson, to try to get a word from him. Poisson paid a visit, and after a few words of salutation said: ' I have good news for you. A letter has been received at the bureau of longitudes from Germany, announcing that M. Bessel has verified by observation your theoretical discoveries upon the satellites of Jupiter.' Laplace opened his eyes and answered with deep gravity: 'Man pursues nothing but chimeras.' He never spoke again." He has been accused of holding materialistic views; but his writings give no evidence of a tendency in that direction, and the subject is one which he is known to have avoided.

As a scientific writer he was perspicuous and elegant, and his Systeme du monde, as a specimen of style, is called by Arago "one of the most perfect monuments of the French language."