jB24 CAUSE OF THE CHANGES OF RELATIVE 



Obfervatlons (g) If we ftiould intend to change our ground, and place 



and inferences the two motions in O and Xt it will then be conceded, that the 

 changes of rela- "^°^'^" ^^ ^ '^ °"b' ^" apparent one, which owes its exigence 

 tive fituations into the real motion of the fun. By this, the effed of the folar 

 ^''a'r wcTothL. parallax on any ftar at the fame diftance will be given ; and it 

 cannot be difficult to aflume a motion in x, which fliall, with 

 the effefl of this given parallax, produce the apparent motion, 

 in the direction of a chord from the firft to the laft angle of 

 pofition pointed out by my obfervations; taking care, however, 

 not to place the ftars a and x at the fame diftance from us ; 

 ufing the inverfe ratio of the folar parallax as a multiple in the 

 affigned motion. For inftance, let the fun have a motion of 

 the velocity exprefled as before by S'\5l, and in a dire6lion 

 which makes an angle of 53^^ 13' fouth following with the 

 parallel of a Geminorum ; and let the fmall flar x have a real 

 motion in an angle of 18*^ 40' fouth preceding from the pa- 

 rallel of its filuation, and with a real velocity which, were it 

 at the diftance of a, would carry it through 8^^89. Then, if 

 the diftance of the fmall ftar be to that of the large one as 3 

 to 2, the effefl of the folar parallax upon it will be y of its 

 eff*e6t upon a ; that is, while a, which is at reft, appears to 

 move over a fpace of 3'',5I, in an angle of 53^ 31' north pre- 

 ceding, the paralla6tic change of place in x will be 2", 3 4 in 

 the fame dire6lion. This, though only an apparent motion, 

 will be compounded with the real motion we have afligned to 

 it, but which, at the diftance of », will only appear as l" ,26 ; 

 and the joint effedl of both will bring the ftar from the place 

 in which it was feen 23 1 years ago, to that where now we 

 find it fituated. a, in the fame time, will appear to have had 

 an annual proper motion of — 0"A05 in right afcenfion, and 

 (y',12 in declination towards the north ; and thus all pheno- 

 mena will be explained. 



From this ftateraent, we may draw a confequence of con- 

 ftderable importance. If we fucceed, in this manner, in 

 accounting for the changes obferved in the relative fituation of 

 the two ftars of a double ftar, we ftiall fail in proving them to 

 form a binary fyftem ; but, in lieu of it, we ftiall gain two 

 other points, of equal value to aftronomers. For, as a Ge- 

 minorum, according to the foregoing hypothefis, is a ftar that 

 has no real motion, its apparent motion will give us the velo- 

 city and direction of the motion of the folar fyftem ; and, this 



being 

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