358 



Proceedings of the Royal Irish Academy, 



Mean Results of the Observations of the Difference in Declination between 

 61 (B) Cygni and BD + 38°, 4351, reduced for Refraction and 

 Reduction. 



Date. 



Difference. 



Date. 



Difference. 



Date. 



Difference. 



1878. 





1879. 





1879. 





Sept. 18, 



73" -657 



Nov. 17, 



73"-609 



April 30, 



72"-ll7 



„ 20, 



73 -633 



„ 21, 



73 -507 



May 4, 



72 -229 



„ 23, 



73 -579 



„ 25. 



73 -615 



8, 



71 -907 



„ 25, 



73 -613 



„ 28, 



73 -437 



„ 15, 



71 -602 



Oct. 13, 



73 -520 



Dec. 1, 



73 -554 



„ 22, 



71 -640 



„ 24, 



73 -698 



5, 



73 -436 



June 10, 



71 -530 



„ 25, 



73 -528 



8, 



73 -442 



„ 15, 



71 -345 



„ 28, 

 „ 29, 



73 -739 

 73 -537 



30, 

 1879, 

 Jan. 8, 



73 -268 

 73 -400 



„ 28, 

 July 26, 



71 -169 

 70 -853 



„ 31, 



73 -707 



„ 15, 



73 -370 



Sept. 17, 



70 -424 



Nov. 1, 



73 -802 



„ 18, 



73 -325 



Oct. 2, 



70 -816 



8, 



73 -633 



April 10, 



72 -512 







„ 16, 



73 -552 



„ 16, 



72 -348 







A glance at these results exhibits, in a conspicuous manner, the large 

 proper motion of 61 (B) Cygni relatively to the star which has been 

 chosen for comparison. To clear the observations from the grosser 

 part of the effects of proper motion, it became necessary to adopt an 

 approximate value of the relative annual proper motion in declination. 

 The former series of observations had conclusively established the fact 

 that the comparison star is not affected by any considerable proper 

 motion. I therefore felt warranted in assuming Argelander's value of 

 the absolute proper motion of 61 B Cygni in declination as approxi- 

 mately the relative proper motion. The value in question is + 3"-016 

 [Fositiones Media, p. 27). 



The mean epoch of the entire series of 'observations is 1879"069. 

 The mean value of the observed differences of declination is 72"-85549. 

 The assumed epoch is 1879-0, whence, applying a correction of + -20865 

 for proper motion, we have as the adopted mean difference of declina- 

 tions at the epoch 73"-06414. 



