POSITION OF DOUBLE STARS. ^^^ 



being obtained, we (hall alfo have the relative parallax ofobfervations 

 every ftar, not having a proper motion, which is affeded by ^"^ inferences 

 the folar motion. Aftronomical obfervations oh the proper changes of rela- 

 motion of many different ftars, however, will not allow us t©''ve fituation in- 

 account for the motion of a Geminorum in the manner ^^'^^^ nt&t llch^iJx* 

 the foregoing inftance requires ; the hypothefis, therefore, of 

 its being at reft, muft be rejeded. 



(/i) If we place our two motions in O and a, we ftiall be 

 led to the fame conclufion as in the laft hypothefis. The known , 



proper motion of a, and the fituations of the fmall ftar in 

 1779 and 1803, given by my obfervations, will afcertain the 

 apparent motion of x, now -fuppofed to be at reft. Then, 

 fince the change in the place of x muft be intirely owing to the 

 effed of parallax, it will confequently give us, in the fame 

 manner as before, the quantity and diredtion of the motion 

 of the folar fyftem, and the relative diftances of all fuch ftara 

 as are affedled by it. But, here again, the folar motion re- 

 quired for the purpofe is fuch as cannot be admitted ; and the 

 hypothefis is not Maintainable. 



Motion of the three Bodies, 

 (i) There Is now but one cafe more to conftder, which is, 

 according to No. 5, to alTign real motions to all our three 

 bodies ; and this may be done as follows. Suppofe the fun to 

 move towards X Herculis, with the annual velocity 1. 



Let the apparent motion of a, Geminorum be as it is ftated 

 in the aftronomical tables before mentioned; butfuppofe it to 

 arife from a compofition of its real motion with the effed of the 

 fyftematical parallax, as we may call that apparent change of 

 place of ftars which is owing to the motion of the folar fyftem. 

 Let the real motion of x, aided by the effect of the fame pa- 

 rallax, be the caule of the changes in the angle of pofition 

 which my obfervations have given. We may admit the largeft 

 of the two ftars of our double ftar to be of the fecond magni- 

 tude ; and, as we are not to place x too near a, we may fup- 

 pofe its diftance from O to be to that of « from the fame as 3 to 2. 

 In this cafe, O will move from the parallel of an in an angle 

 of 60® 31^ north following, with an apparent annual velocity 

 of ,4536. The motion of a in right afcenfion, may be intirely 

 afcribed to folar parallax; but its change of declination, can- 

 not be accounted for in the fame manner. Let us therefore 

 ^ Vol. VII.— March, 1804.. Q admit 



