056 CAUSES OF THK CHANGES OF RELATIVE 



Obfcrvationsand lowing. The fum of thefe angles gives 1 3** 58', for the change 

 fpeaing the " ^^^^ ^^^ taken place in 21 years and 38 days. To account for 

 change of reia- this, we are to have recourfe, as before, to the various motions 

 t° t'tdr °f 'he three bodies, 

 near each other. 



Single Motions. 



(a) The motion of x alone cannot be admitted, lince it is 

 known that y Leonis is not at reft. The annual proper motion 

 of this ftar, according to M. De la Lande, is + 0'^38 in right 

 afcenfion, and 0'^04< in declination towards the fouth. 



(b) 7 cannot be the only moving body; becaufe its mo- 

 tion in right afcenfion only, which, in 2 1 , 1 years, at the parallel 

 of y, amounts to 7'^49, would have long ago taken it away from 

 the fmall ftar. ^ 



(c, d, e,) The fun cannot be the only moving body ; becaufe 

 its motion in right afcenfion will not account for that of 7 

 Leonis, which ftar therefore cannot be at reft. And, if we 

 were willing to give up the former aflTumed folar motion, in 

 order to fix upon fuch a one as would explain the motion of r, 

 we fliould be under a iieceflity to contradict the united evi- 

 dence of the proper motions of many principal ftars which are 

 in oppolition to it. 



Double Motions, 



(/) When two motions are propofed, we cannot fix upon 7 

 and X for the moving bodies, unlefs we ftiould fet afide the 

 folar motion, and this, we know, cannot properly admit of a 

 doubt. 



(g) That we cannot allow O and x to be the two bodies in 

 motion, follows from the infufficiency of the folar motion to 

 account for that of 7, which muft be real, or at leaft partly fo. 



(A) If O and 7 are the moving bodies, the given fituations of 

 X, in the years 1782 and 1783, point out an apparent motion 

 of ar, which muft be intirely owing to the folar parallax ; and, 

 therefore, thofe who will admit this hypothefis, muft grant the 

 difcovery of the motion of the folar fyftem, and of the propor- 

 tional parallax of the two ftars y and x. Let us however exa- 

 mine whether any motion of the fun, fuch as we can admit, 

 will account for the change of pofition and diftance pointed out 

 by my obfervalions of the fmall ftar near y Leonis. 



The 



