POSITION OF DOUBLE STARS. <g(?5 



The obfervations I have made on this ftar, are not fufficient Obfervatlons 

 to dire6l us in the inveftigatlon of the nature of the motion by re'keaw'th? 

 which this change is occafioned. changes of rela^ 



We may however be certain, that with regard to ftlrs?x"tremely" 



pear each otbetf 

 Single Motions. 



(a, h) Neither x nor ^ can be fiippofed to be the onlj^ mov- 

 ing bodies, without contradidting the highly probable argu- 

 ments for the fun's motion. 



(c, d) If we admit the fun to be the moving body, the ftars 

 ^ and X being at reft, we may calculate the effe6l of the folar 

 parallax upon them, asfollows. Let O move towards xHerculis, 

 with the annual velocity l,asin thecafeofaGeminorum; then, 

 from the fituation and magnitude of the large ftar of ^ Herculis, 

 which we will fuppofe 4m, the effed of the folar motion at^ 

 will be only ,0522 ; and, at x^ fuppofed to be at the diftance 5m, 

 it will be ,04-18. This will fliow itfelf at the parallel of ^ in a 

 dire6lion of 25^* 5' north preceding, the folar motion being in 

 the oppofite dire6lion fouth following. But this parallax will 

 only produce, in 20 years and 10 months, an apparent change 

 of 0-' ,444 in ^, and of 0" ,355 in x\ and will feparate th© 

 (lars, inftead of bringing them to a conjun6tion. 



(e) A conliderable advantage may be gained, by placing* 

 at a little more than ^ the diftance of ^ from O. For as, in the 

 above-mentioned time, this would make the efFe6l of parallax 

 upon it l" ,18, a conjun6lion fliould now take place. But then 

 the ftars, though very near each other, would not be quite in 

 contad; much lefs could one of them occafion an occultation 

 of the other. The fuppofition alfo, that the fmall ftar fhould 

 be only -y of the diftance of thp large one from us, is not very 

 favourable to the hypothefis. 



' ' 3 Serpentis. 



This double ftar ha? undergone a very confiderable change 

 fn the angle of pofition, but none in the diftance of the two 

 ' "ftars. The 5th of September, 1 7^2, an accurate meafure of the 

 pofition was 42** 48' fouth preceding; and February 7, 1802, it 

 meafured 61® 27' fouth preceding. In 19 years and 155 days, 

 therefore, the fmall ftar has moved, in a retrograde order, over 

 gn arch of 18« 39'. 



¥vcry 



