SECT. III. INVARIABLE PLANE. 23 



maximum (N. 81). La Place found that the plane in 

 question is inclined to the ecliptic at an angle of nearly 

 1 34' 15", and that, in passing through the sun, and 

 about midway between the orbits of Jupiter and Saturn, 

 it may be regarded as the equator of the solar system, 

 dividing it into two parts, wh.ch balance one another in 

 all their motions. This plane of greatest inertia, by no 

 means peculiar to the solar system, but existing in every 

 system of bodies submitted to their mutual attractions 

 only, always maintains a fixed position, whence the 

 oscillations of the system may be estimated through 

 unlimited time. Future astronomers will know, from 

 its immutability or variation,, whether the sun and his 

 attendants are connected or not w.th the other systems 

 of the universe. Should there be no link between them, 

 it in.-iy be interred, from the rotation of the sun, that 

 the center of gravity (N. 82) of the system situate within 

 his mass describes a straight line in this invariable plane 

 or great equator of the solar system, which, unaffected 

 by the changes of time, will maintain its stability through 

 endless ages. But, if the fixed stars, comets, or any 

 unknown and unseen bodies, affect our sun and planets, 

 the nodes of th s plane w.ll slowly recede on the plane 

 of that immense orbit which the sun may describe about 

 some most distant center, in a period which it transcends 

 the powers of man to determine. There is every rea- 

 son to believe that this is the case ; for it is more than 

 probable that, remote as the fixed stars are, they in 

 some degree influence our system, and that even the 

 invariabiLty of this plane is relative, only appearing fixed 

 to creatures incapable of estimating its minute and slow 

 changes during the small extent of time and space grant- 

 ed to the human race. " The development of such 

 changes," as M. Poinsot justly observes, " is similar to 

 an enormous curve, of which we see so small an arc, 

 that we imagine it to be a straight line." If we raise 

 our views to the whole extent of the universe, and con- 

 sider the stars, together w.th the sun, to be wandering 

 bodies, revolving about the common center of creation, 

 we may then recognize in the equatorial plane passing 

 through the center of gravity of the universe the only 

 instance of absolute and eternal repose. 



