With an armament of mathematical methods which had been perfected since the days of Newton by the labors of two or three generations of mathematical inventors, Laplace essayed in his “Celestial Mechanics” to unravel the mysteries of the heavens. It will hardly be disputed that the book which he has produced is one of the most difficult books to understand that has ever been written. The investigations of Laplace are, generally speaking, of too technical a character to make it possible to set forth any account of them in such a work as the present. He did, however, publish one treatise, called the “System of the Universe,” in which, without introducing mathematical symbols, he was able to give a general account of the theories of the celestial movements, and of the discoveries to which he and others had been led. In this work Laplace laid down the principles of the nebular theory, which, in modern days, has been generally accepted. The nebular theory gives a physical account of the origin of the Solar System, and has already been explained in this volume. Bach advance in science seems to make it more certain that this hypothesis substantially represents the way in which our Solar System has grown to its present form. Not satisfied with a career which was merely scientific, Laplace sought to connect himself with public affairs. Napoleon appreciated his genius, and desired to enlist him in the service of the state. Laplace was appointed to the office of minister of the interior. The experiment was not successful, for he was not by nature a statesman. In despair of Laplace’s capacity as an administrator, Napoleon declared that he carried the spirit of his infinitesimal calculus into the management of business. Indeed, Laplace’s political conduct hardly admits of much defense. While he accepted the honors which Napoleon showered on him in the time of his prosperity, he seems to have forgotten all this when Napoleon could no longer render him service. Laplace was made a marquis by Louis XVIII. During the latter part of his life the philosopher lived in a retired country-place at Arcueile. Here he pursued his studies, and, by strict abstemiousness, preserved himself from many of the infirmities of old age. He was endowed with remarkable scientific sagacity; but above all his powers his wonderful memory shone pre-eminent. His “Celestial Mechanics” is, next to Newton’s “Principia,” the greatest of astronomical works. He died on March 5, 1827, in his seventy-eighth year, his last words being, “What we know is but little, what we do not know is immense.” LEVERRIER.