258 CAUSE OF THE CHANGES OF RELATIVE 



Obfervatlons and The real annual motion of x muft be 4,6294, in a dire6lIon 



fpeSingThr ^° 20' fouth following. This will carry it over 9^74, in 21,1 



changes of rela- years; and, when combined with the apparent motion which 



trve fituatlon in ^^e folar parallax will occafion, both together will bring it to 

 ftars extremely . ^ . , n 



»ear each other, its proper ditlance from yLeonis, and to a fituation which will 



agree with the laft obferved angle of pofition. 



From what has been faid, it is again evident, that not only as 

 many particular circuraftances mufi: concur in explaining the 

 phenomena of y Leonis as we have pointed out with a Gemi- 

 norum^ but that a very marked condition is added in our fecond 

 double ftar, which requires an adjuftment of velocities in y and 

 X, which fiiall a]fo fit the fame folar motion that was ufed in a 

 Geminorum. And this proves, that every additional double 

 flar whicii requires the fame condition in order to have its ap 

 pearances explained, will inforce the argum.ents which have 

 been ufed, in a compound ratio. 



If, on the other hand, we have recourfe to the fimplicity of 

 the known effcds of attraction, and admit the two ftars of oiir 

 prefent double ftar to be united in one fyftem, all the foregoing 

 difficulties of accoundng for the obferved phenomena will 

 vanifli. Whatever may be the proper motion of the fun, the 

 parallax arifing from that caufe will affeft both ftars equally, 

 on account of their equal diftance from the fun. The proper 

 motion of y Leonis alfo may be in any diredion, and of any 

 given velocity, fuch as will agree beft with aftronomical ob- 

 fervations; fince the motion of a fyftem of bodies will not in- 

 terfere with the particular motion of the bodies that belong to 

 it, fo that our fecondary ftar will continue its revolution round 

 the primary one without difturbance. 



It will now be neceifary to exainine the obferved angles of 

 pofttion, and to compare them wiih calculated ones ; but, as 

 there has been a change in the diftance of the two ftars, it is 

 evident that, if they revolve in circular orbits, the ftiuation of 

 the plane of their revolution muft be conftderably inclined to 

 the line in which we fee the principal ftar. 



Let N F S P, Fig. 2, be the orbit in which x revolves about 

 y placed in the centre. Suppofe a perpendicular to be ercded 

 at 7 leading to O, not expretfed in the figure. By an obferva- 

 tion of Feb. 16, 1782, we have the aiiglc F y .r = 7^^ 37' north 

 following ; and the proportion of the apparent diameter of y to 

 that of X has been given as 5 to 4. It has alfo been afcer^ 



tained 



