PORTION OF THE COSMOS. MULTIPLE STARS. 213 



it the motions of its companion, we find, from the observa- 

 tions hitherto made, that the companion describes round 

 the principal star a conic section in the focus of which the 

 latter is placed ; or an ellipse in which the radius vector 

 of the revolving body passes over equal areas in equal 

 times. Exact measurements of angles of position and of 

 distances, adapted for determinations of orbits, have already 

 shewn, in the case of a considerable number of double stars, 

 that the companion moves round the principal star con- 

 sidered as a body at rest, in obedience to the same gravi- 

 tating forces which prevail in our solar system. This well- 

 established conviction, gained within scarcely a quarter of 

 a century, marks one of the great epochs in the history of 

 the development of the higher cosmical knowledge. Celes- 

 tial bodies, to which the name of fixed stars (assigned by 

 ancient usage) is still given, although they are neither 

 affixed to the heavenly vault nor motionless, have been seen 

 to occult each other. The knowledge of the existence of 

 partial systems, the several parts of which have motions 

 referable to and dependent on each other, extends our 

 views the more- widely as those motions are again sub- 

 ordinated to more general ones. 



The table on the next page contains the Elements of the 

 orbits of six double stars, the determinations of which ap- 

 pear entitled to principal confidence. 



