372 LAPLACE. 



epoch at which the major axis of the earth's orbit coincided 

 with the line of the equinoxes, and the epoch at which it stood 

 perpendicular to that line. By calculation, he found the 

 former of these epochs to be referable to the year 4107, B.C., 

 and the latter to the year 1245, A.D. He accordingly sug- 

 gested that the latter should be used as a universal epoch for 

 the regulation of chronological occurrences. 



(B.) 



The Mecanique Celeste. This stupendous monument of 

 intellectual research consists, as stated by the author, of five 

 quarto volumes. The subject-matter is divided into sixteen 

 books, and each book again is subdivided into several chap- 

 ters. Vol. I. contains the first and second books of the work ; 

 Vol. II. contains the third, fourth, and fifth books ; Vol. III. 

 contains the sixth and seventh books ; Vol. IV. contains the 

 eighth, ninth, and tenth books ; and, finally, Vol. V. contains 

 the remaining six books. In the first book the author treats 

 of the general laws of equilibrium and motion. In the second 

 book he treats of the law of gravitation, and the movements 

 of the centres of gravity of the celestial bodies. In the third 

 book he investigates the subject of the figures of the celestial 

 bodies. In the fourth book he considers the oscillations of 

 the ocean and the atmosphere, arising from the disturbing 

 action of the celestial bodies. The fifth book is devoted to 

 the investigation of the movements of the celestial bodies 



O 



around their centres of gravity. In this book the author 

 gives a solution of the great problems of the precession of the 

 equinoxes and the libration of the moon, and determines the 

 conditions upon which the stability of Saturn's ring depends. 

 The sixth book is devoted to the theory of the planetary 

 movements ; the seventh, to the lunar theory ; the eighth, to 

 the theory of the satellites of Jupiter, Saturn, and Uranus ; 

 and the ninth, to the theory of comets. In the tenth book 

 the author investigates various subjects relating to the system 

 of the universe. Among these may be mentioned the theory 



