158 Parallax of 6 1 2 Cygni, deduced from 



one member is a dark body* it is nevertheless far removed from 

 the influence of 6i 2 Cygni, which would account for the as yet 

 unprovedf orbital motion of 61 1 and 61 2 around a centre of 

 gravity common to the two. The probabilities in favor of the 

 existence of such orbital motion, if they really have the same 

 parallax, are fully as strong as are those against the juxtaposition 

 in line of sight of two stars having so nearly the same large ap- 

 parent motion, if they are really separated in space by the dis- 

 tance which this difference of parallax indicates. 



This presents to us therefore one of those cases where the ex- 

 ceedingly strong probability against an event happening is per- 

 haps overruled by its actual occurrence. 



The evidence here presented as to a difference of parallax is at 

 any rate of sufficient weight to demand a more extended series of 

 photographic measures of the same degree of precision as Wil- 

 sing's and extending over more than two years. Perhaps Prof. 

 Wilsing would himself be willing to continue his series of plates. 

 It is also highly desirable to reinforce the evidence of a variable 

 proper motion of 6i x by independent methods, such as is afforded 

 by the spectroscope, for example. 



* Publications of the Lich Observatory, Vol. II, 1894. Page 122. Burnham 

 records his inability to see at 1889.463 and 1889.502 a companion to either 

 star, though using the 36-inch telescope with powers up to 1000. 



f Monthly Notices,Vol. XXXV, page 323. Ast. Nach., Vol. 132, pages 87 and 

 199. Burnham in Tlie Sideral Messenger, Vol. X, page 1, and Mann, ibid. 

 page 13. 



