OP ARTS AND SCIENCES. 399' 



XXIII. 



ON THE REDUCTION OF DIFFERENT STAR CATA- 

 LOGUES TO A COMMON SYSTEM. 



By William A. Rogers. 



Presented May 9th, 1883. 



The communication of Professor Safford, in the March number of 

 the Monthly Notices of the Royal Astronomical Society, cites in a 

 forcible way some of the causes of discrepancies in stellar co-ordinates 

 to which too little attention has hitherto been paid. Incidental!}' he 

 refers to the class of errors which are introduced in the computation 

 of the systematic corrections necessary to reduce different catalogues 

 to a common system. Without this reduction it is impossible to ob- 

 tain the element proper motion with the degree of precision which 

 modern observations call for. 



It is unfortunate that this necessity exists, since considerable un- 

 certainty must always remain in the determination of these corrections. 

 One of the serious demands of instrumental astronomy at the present 

 time is the independent determination at a few widely separated 

 observatories of all the elements which define stellar positions, without 

 direct reference to any assumed fundamental system. The Catalogue 

 of A. G. Publication XIV. by Dr. Auwers is probably more nearly 

 free from systematic errors than any hitherto constr^ucted ; but the 

 independent researches of Professor Boss show that the fundamental 

 observations in declination from about 1815 to 1845 differ as a sys- 

 tem from the Auwers-Bradley system by an amount which cannot be 

 neglected. 



Since it is obviously impracticable to redetermine the instrumental 

 constants with which the different catalogues to be compared have 

 been constructed, by a direct reference to the fundamental system to 

 which they are to be referred, and with these constants to deduce new 

 co-ordinates, we must seek the best method of deriving the systematic 



