164 COSMICAL ARRANGEMENTS. 



a sufficient amount seriously to alter the adapta- 

 tions of the system.* 



The same examination of the subject by which 

 this is proved, points out also the conditions on 

 which this stability depends. " I have succeeded 

 in demonstrating," says Laplace, " that whatever 

 be the masses of the planets, in consequence of 

 the fact that they all move in the same direction, 

 in orbits of small excentricity, and slightly in- 

 clined to each other their secular inequalities 

 are periodical and included within narrow limits ; 

 so that the planetary system will only oscillate 

 about a mean state, and will never deviate from 

 it except by a very small quantity. The ellipses 

 of the planets have been, and always will be, 

 nearly circular. The ecliptic will never coincide 

 with the equator, and the entire extent of the 

 variation in its inclination cannot exceed three 

 degrees." 



There exists, therefore, it appears, in the solar 

 system, a provision for the permanent regularity 

 of its motions ; and this provision is found in the 

 fact that the orbits of the planets are nearly 

 circular, and nearly in the same plane, and the 

 motions all in the same direction, namely, from 

 west to east.f 



* Laplace Expos, du Syst. du Monde, p. 441. 

 f In this statement of Laplace, however, one remarkable pro- 

 vision for the stability of the system is not noticed. The planets 



