PROPER MOTION OF THE STARS. 195 



light on two mutually dependent problems ; namely, the mo- 

 tion of the solar system,* and the position of the center of 

 gravity in the heaven of the fixed stars. That which can 

 only be reduced in so very incomplete a manner to numerical 

 relations, must for that very reason be ill calculated to throw 

 any clear light on such causal connection. Of the two prob- 

 lems just mentioned, the first alone (especially since Arge- 

 lander's admirable investigation) admits of being solved with 

 a certain degree of satisfactory precision ; the latter has been 

 considered with much acuteness by Miidler, but, according 

 to the confession of this astronomer himself,! his attempted 

 solution is, in consequence of the many mutually compensa- 

 ting forces which enter into it, devoid " of any thing like evi- 

 dence amomiting to a complete and scientifically certain 

 proof." 



After carefully allowing for all that is due to the preces- 

 sion of the equinoxes, the nutation of the earth's axis, the 

 aberration of light, and the change of parallax caused by the 

 earth's revolution round the sun, the remaining annual mo- 

 tion of the fixed stars comprises at once that which is the 

 consequence of tlie translation in sjmce of the ivhole solai 

 system, and that also which is the result of the actual propei 

 motion of the fixed stars. In Bradley's masterly labors on 

 nutation, contained in his great treatise of the year 1748, we 

 meet with the first hint of a translation of the solar system, 

 and in a certain sense, also, with suggestions for the most 

 desirable methods of observing it.$ " For if our own solar 

 system be conceived to change its place with respect to ab- 

 solute space, this might, in process of time, occasion an ap- 

 parent change in the angular distances of the fixed stars ; 

 and in such a case, the places of the nearest stars being more 

 afiected than of those that are very remote, their relative 

 positions might seem to alter, though the stars themselves 

 were really immovable. And, on the other hand, if our own 

 system be at rest, and any of the stars really in. motion, this 

 might likewise vary their apparent positions, and the more 

 so, the nearer they are to us, or the swifter their motions are, 

 or the more proper the direction of the motion is, to be ren- 

 dered perceptible by us. Since, then, the relative places of 



* Cosmos, vol. i., p. 146. t Madler, Astronomie, s. 414. 



X Arago, ill his Annnaire pour 1842, p. 383, was the first to call at- 

 tention to this remarkable passage of Bradley's. See, in the same An- 

 nuaire, the section on the translation of the entire solar system, p. 389- 

 399. 



