312 R LAPLACE. 
If a celestial body, the moon, for example, gravitated 
solely towards the centre of the earth, it would describe 
a mathematical ellipse; it would strictly obey the laws 
of Kepler, or, which is the same thing, the principles of 
mechanics expounded by Newton in the first sections of 
his immortal work. 
Let us now consider the action of a second force. Let 
us take into account the attraction which the sun exer- 
cises upon the moon, in other words, instead of two 
bodies, let us suppose three to operate on each other, the 
Keplerian ellipse will now furnish merely a rough indi- 
cation of the motion of our satellite. In some parts the 
eel 
attraction of the sun will tend to enlarge the orbit, and 
will in reality do so; in other parts the effect will be the 
reverse of this. In a word, by the introduction of a 
third attractive body, the greatest complication will suc-- 
ceed to a simple regular movement upon which the mind 
reposed with complacency. 
If Newton gave a complete solution of the question 
of the celestial movements in the case wherein two 
bodies attract each other, he did not even attempt an 
analytical investigation of the infinitely more difficult 
problem of three bodies. The problem of three bodies 
(this is the name by which it has become celebrated), 
the problem for determining the movement of a body 
subjected to the attractive influence of two other bodies, 
was solved for the first time, by our countryman Clairaut.* 
istic French names which it is possible to imagine, whose maternal 
grandfather was M. Gros, whose paternal great-grandfather was a 
French officer, a native of Paris, who never wrote except in French, 
and who was invested in our country with high honours during a 
period of nearly thirty years;—ought to be regarded as a French- 
man although born at Turin.— Author. 
* The problem of three bodies was solved independently about the 
