64 



Eutherfurd Photographic Measures of 



The figures at the tops of the columns are the numbers of the 

 plates to which the columns are applicable as determined by their 

 values of P 2 . Selecting, therefore, the proper column and using 

 S 2 as the argument in the body of the table (where it is expressed 

 in units of the fourth decimal place), one will find in the first col- 

 umn the desired value of S 2 P 2 , expressed in divisions of the scale. 

 Column ten of Table V gives the total proper motion correction. 



14. A correction for parallax of the principal star was next ap- 

 plied. Using Auwers's values of the coordinates of 61 1 Cygni 

 reduced to 1873.0 



h m s 



a = 21 01 12.329 

 6 = 38° 07' 33.40 



and the almanac values of r and ©, the radius vector and longi- 

 tude of the sun respectively, the values of S 3 , £ 4 , P 3 and P 4 

 were computed by the formulae 



g sin G = sin S cos 

 g cos Cr,= sin a 



h sin H= sin S sin a 

 h cos H= — cos t) 



/sin F=h sin (-ET-f e) 

 / cos F= — cos a cos e 



S 3 =fsin(p + F) 

 Si=g sin (p + G) 



F 3 = — r sin Q 

 P 4 = — r cos © 



The value of p used here was the mean of the position-angles 

 after correction for proper motion and orientation variation, as 

 described in paragraphs 17 and 19. The values of P 3 and P 4 are : 



