i»081T10N OF DOUBLE STARS.' Q^'J 



The joint efFed of proper motion and parallax, has carried y Obfervatlons anrt 

 from its fituation in 1782 to that where we now find it. The l"^^!"^^' ''^^ 



ipecting the 



fmall ftar, having all this time, in appearance, accompanied y, change of rela» 



muft have gone through a fpace of 7^98, in a diredion whicl) Jj^^/f^^f,'^", '" 



makes an angle of 8^ 30' fouth following with the parallel of „gaf each other. 



y, in order to be at its prefent di fiance from it, and at the fame 



time to have undergone the required change of its angle of po- 



lition. Now, as the fuppofition we are examining requires this 



fmall ftar to be a6iually at reli, it will be neceiTary to ailign to 



the fun an oppofite motion of the fame velocity, in order to 



make that of x only an apparent one. The confequence of this 



will be a retrograde motion of the fun, which it is well known 



cannot be admitted^ 



Motion of the three Bodies, 



(i) A motion of all the three bodies, is the only way left to 

 explain the phenomena of our double ftar ; and I (hall noW 

 again point out the very particular circumftances vvhich it is 

 requifite fliould all happen together, to produce the intended 

 effea. 



ILei the motion of the fun, with the fame annual velocity 1, 

 as in the cafe of a Geminorum, be dire6led towards x Herculis. 

 Then the effed of this motion will (hew itfelf at the place of 

 y Leonis, in the annual velocity of ,3314, and in a direftioh 

 which makes an angle of 31** 1 1'' fouth preceding with the pa- 

 rallel of thatftar. In this calculation, I have admitted thedif- 

 tance of the largeft of the two ftars of 7 from the fun to be 5> 

 that of a- Geminorum being 2. But, if any other diftance 

 fhould hereafter be con(idered as more probable, the calcula- 

 tion may be ea(ily adapted to it. The confequence of the pa- 

 rallax thus produced on y Leonis in 21,1 years, will be an ap- 

 parent motion of 2''',788 fouth preceding^ in the abovemen- 

 tioned direction ; and, on i, it will be in the fame time, and 

 in the fame direction, l'',09i. As the fmall ftar muft not be 

 too near y, we have, in tlie calculation, fuppofed it to be at 

 the diftance of 4 from O. 



The real annual proper motion of y is required to be 3,5202; 

 and its direction muft make an angle of 3** 40' north following 

 with the parallel. B.y this motion alone, y would have palTed 

 Over a fpace of 9^'87 in 21,1 years; but, when it is combined 

 with the apparent motion ariling from parallax, the ftar will 

 come into its prefent fituation. 



Vol. VII.— April, 1804. S The ' 



