254 



CfX.'JSE OF THfi CHANGE OF RELATIVE 



Obfcrvstionsand Pollux Tor November 5, 1759, it appears, that a line drawn 

 fpeS!ne*the ' ^^^^ PolluK through Caftor, muft have made an angle of 

 changes of rela- 56^ 32' north preceding with the parallel of that ftar ; and, this 

 ftlrstSe'^cl'" being alfo the pofition of our double ftar, we have an interval 

 near each other, of 43 years and 142 days, for a change of 45° 39', from the 

 time of Dr. Bradley's obfervation to that of my laft meafure of 

 the angle. By this we are now enabled to corre6t our former 

 calculation, which was founded upon a.fuppofition that the firft 

 angle of pofition I had taken vv as perfe/^ ; but this could hardly 

 be expeded, and on examination it appears that the meafure 

 was 2® 40' too little. The annual motion, by our increafed 

 period, is 1° 3',1 ; and the computation of the angles of po- 

 fition in the third column of the following table, as well as the 

 differences contained in the fourth, ate made according to this 

 motion. 



When the refult of this table is compared with that of the 

 former, it will be feen that my obfervations agree not only very 

 well with Dr. Bradley*s pofition, but even give more equally 

 divided ditlerences than beTore, fo that the excefs and differ- 

 ences counteract each other better than in the firft table. 



The time of a periodical revolution may now be calculated 

 from the arch of 45^ 39', which has been defcribed in 43 years 

 and 142 days. The regularity of the motion gives us great 

 leafon to conclude, that the orbit invvhich the fmall fiar moves 



about 



