426 



COMPARISON OF CATALOGUES OF STARS. 



COMPARISON OF THE FOUR CATALOGUES UNDER CONSIDERATION BY MEANS 



OF THEIR PROPER MOTIONS. 



Since the proper motion is a direct function of the time, it is possible to determine 

 the exact amount by which two catalogues will differ at the expiration of a qjiven 

 time. If the two systems of proper motions differ systematically, these systematic 

 errors will be introduced into the catalogues themselves. In general, the constant 

 part of the deviation may be considered as a function of the precession constant. The 

 explanation of the variable part in any given case is for the most part exceedingly 

 difficult. For example : it is easy to account for the systematic deviations between 

 Auwers and Boss, by referring them to the corresponding deviations between the 

 system of Bradley on the one hand and the mean of the systems of Bessel, Struve, 

 and Argelander on the other, but I have found it impossible to trace the origin of the 

 differences between these fundamental systems. I give below the comparison of each 

 authority with Auwers. Columns I. and II. contain the values of A/a and A// for the 

 first and the second twelve hours of right ascension respectively. The proper motions 

 of the secondary catalogue form the basis of the comparison in the Harvard College 

 Observations ; the corresponding values were communicated by Dr. Auwers to Pro- 

 fessor Pickering for facilitating the reductions in Vol. XII. of the Annals. In the 

 comparison with Safford in right ascension, A//, involves the change from the con- 

 stants of Bessel to those of Struve. I have assumed the mean value to be the 

 constant part of the deviation. 



Auwers minus Harvard College. 



