'Baj.l— Parallax of 61 (A) Cygni. 



211 



i, h, g, H, G, are the well-known constants in the Nautical Alma- 

 nac ; t is the year in which the observation was made ; a is the right 

 ascension of 61 Cygni. 



In order to free the observations from the grosser part of the 

 effects of the large proper motion of 61 Cygni, I have assumed that 

 the small comparison star is at rest, and that the preceding star A has 

 the annual proper motion assigned to it by Argelander, viz. : 



+ 3"-232. 



"When these various corrections have been applied, the following 

 are the values of the differences of declination : — 



1877. 

 July 3, 

 6, 



19, 



22, 



24, 

 Aug. 4, 



12, 



31, 

 Sept. 3, 



21, 



27, 

 Oct. 1, 



16, 

 23, 

 25, 

 29, 

 2, 

 13, 



Nov. 



66" 



879 



66 



899 



66 



739 



66 



927 



66 



901 



66 



798 



66 



867 



66 



959 



66 



695 



66 



942 



66 



897 



66 



•888 



67 



304 



67 



013 



67 



195 



67 



021 



67 



369 



67 



300 



67 



344 



1877. 







Dec. 13, 



67" 



701 



14, 



67 



474 



17, 



67 



482 



19, 



67 



326 



29, 



67 



350 



30, 



67 



553 



1878. 







Jan. 31, 



67 



659 



Mar. 24, 



67 



273 



24, 



67 



433 



31, 



67 



252 



April 1, 



67 



001 



17, 



67 



224 



24, 



67 



161 



27, 



66 



852 



May 18, 



66 



851 



28, 



66 



688 



June 1, 



67 



341 



Assuming that the true mean value of the difference of declina- 

 tion is 67"- 150 + X, that the true relative proper motion of A and the 

 comparison star is 3"-232 + x', that tt is the annual parallax, and that 

 k is the difference in the coefficients of aberration for the two stars, 

 then the observations yield thirty-six equations, which, being solved 

 in the usual manner, give 



X = + 0"-0274 ± 0"-0210 

 x' = -Q -0943 ± -1218 

 7r -+0 -4654 ± -0497 

 Tc = + -0330 ± -0493 



I subjoin the various determinations of the annual parallax of 



E. I. A. PROC, VOL. II., SEE. III. SCIENCE. R 



