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.p. He accordingly sug- 
gested that the latter should be used as a universal epoch for 
the regulation of chronological occurrences. 
(B.) 
The Mécanique Céleste—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 
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 
a ae Poe 
