OF THE COSMOS. MOTION OF THE SOLA.R SYSTEM. 193 



the position in space to be assigned to them, so the know- 

 ledge of the measure and direction of their proper motion 

 (i. e. of the changes experienced by the relative positions 

 of self-luminous bodies) conducts us to two problems depen- 

 dent on each other ; viz., the motion of our solar system, 

 ( 318 ) and the situation of the centre of gravity of the whole 

 heaven of the fixed stars. What can as yet only be reduced 

 in so very incomplete a manner to numerical relations, must 

 for that very reason be ill adapted for the clear mani- 

 festation of casual connection. Of the two last named pro- 

 blems, the first only has received a solution, in particular by 

 Argelander's excellent investigation, which can be viewed as 

 in some degree of a satisfactory defmiteness ; the second, in 

 which so many opposing and mutually compensating forces 

 are concerned, has been treated with great ingenuity by 

 Madler : but, according to that astronomers own avowal, ( 319 ) 

 the attempted solution is deficient in " all the evidences of a 

 complete and scientifically adequate demonstration/'' 



After carefully separating and deducting all that belongs 

 to the precession of the equinoxes, the nutation of the 

 earth's axis, the aberration of light, and the parallactic change 

 occasioned by the earth's revolution round the Sun, the 

 remaining annual motion of the fixed stars still includes 

 both the effects of the movement of translation of the en- 

 tire solar system in space, and those of the true proper 

 motion of the fixed stars themselves. In Bradley's ad- 

 mirable investigation of nutation in his great work in 1748, 

 we find the first expressed anticipation of the translation of 

 the solar system, and also an indication of the method of 

 observation most desirable to be pursued for its discovery. 

 " If/' says he, ( 32 ) " it should be found that our planetary 



VOL. III. 



