Group of the Pleiades. 319 



measures, have operated to diminish the accuracy of Elkin's de- 

 termination of 24 p in his first triangulation by means of position 

 angles and distances from Alcyone. More than nine-tenths of the 

 error made in measuring its distance would enter into the right 

 ascension of 24 p. This would account for the large difference 

 found in the right ascensions, while the declinations from the two 

 triangulations agree very closely. Of course the position derived 

 from Elkin's second triangulation would be quite free from the 

 sources of error just mentioned. For in this case the stars are 

 located by measuring their distances from four fundamental stars 

 forming a quadrilateral large enough to include nearly the whole 

 cluster. There were therefore no short distances in this determina- 

 tion of 24 p. 



The rather large discordance of the photographic position of 

 Alcyone is perhaps due to the imperfection of the photographic 

 images of this comparatively bright star. This discordance amounts 

 to o".47 in right ascension, and o".o7 in declination, if we adopt 

 Elkin's position of Alcyone, which is, for 1873.0: 



* = 54° 59' 4"-2i 8 = 2 3 ° 42' 36". 93 . 



The values given for the precessions and secular variations depend 

 upon the Pulcowa constants, and have been calculated with the aid 

 of the tables given by Elkin. 



The third term of precession, or coefficient of ( ) , is: 



\ioo/ 



— o".o59 in Right Ascension, 



— o". 159 in Declination. 



The total precession to reduce the catalogue places to 1873 + * 

 will therefore be : 



t 2 / t \ 3 



(precession) t + (sec. var.) f- (third term) ( ) . 



200 / \ioo/ 



Annals N. Y. Acad. Sci., VI, April, 1892.— 22 



