398 



COMPARISON OF CATALOGUES OF STARS. 



Act 



AS 



The residuals under Auwers minus P' and Auwers minus H. C. 0. involve compar- 

 atively large accidental errors. Those under Auwers minus Struve, and especially 

 those under Auwers minus Safford, are nearly free from accidental errors. While 

 there is a close agreement between the values. — i? and O — C, in every case, it is 

 obvious that in the first two cases there is little to choose between the two methods, 

 but that in the last two cases, the graphic method yields the best results. 



The choice of the method to be used depends, for the most part, upon the magni- 

 tude of the accidental errors, but unfortunately it is often impossible to decide whether 

 the errors are real or accidental. The graphic method is by far the most expeditious, 

 and with hardly an exception it may be safely followed. 



