Group of the Pleiades. 279 



Star. 



E. — W. 



Pleione 



—30" 



Atlas 



—40 



Merope 



—32 



Asterope 



—30 



Maia 



— 20 



Anon. I 



—30 



Taygeta 



—50 



Electro. 



—26 



Celceno 



—40 



Mean —3l" 



The close agreement of this mean with that found above, affords 

 a striking confirmation of the necessity of the correction just dis- 

 cussed, nor does it seem necessary to compare further the Eastern 

 and Western impressions. The omission of the correction would 

 result in making the final adopted mean position angles of all stars 

 observed on the ten plates too great by 1 7". If the distance between 

 the two impressions of the central star were quite large, the effect 

 might be greatly increased. 



The tables also give at the foot the final adopted means of the 

 distances and position angles, together with their probable errors as 

 derived from the internal agreement of the separate values. These 

 probable errors have been computed from the sums of the residuals, 

 not the sums of squares. For the position angles, the probable 

 error is first given in seconds, and followed by the equivalent dis- 

 placement in arc of a great circle, corresponding to the distance of 

 the star. The final means will be assembled in another table in the 

 next section. 



