DEPARTMENT OF MERIDIAN ASTROMETRY.* 



Benjamin Boss, Director. 



The activities of the Department during the last year may be 

 grouped under four general heads: investigations of stellar motions, 

 reduction of observations, preparations for the General Catalogue, 

 and preparations for future work. 



INVESTIGATIONS OF STELLAR MOTIONS. 

 PARALLAXES. 



In order to determine as accurately as possible the real space 

 motions of the stars it has been found necessary to reconcile as well as 

 possible the various series of stellar parallax observations, utilizing 

 all available material. A preliminary system was already completed 

 when a large number of unpublished parallaxes were very generously 

 offered by Professors Schlesinger, Mitchell, Frost, and Miller, and it 

 became necessary to revise the system. While the last approximation 

 to definitive results has not been completed, several conclusions will 

 not be materially altered. 



The trigonometrical parallaxes obtained by the photographic pro- 

 cess are in general of a high degree of excellence; and their relative 

 weights are very approximately represented by the probable errors 

 assigned by the authors to their observations. While systematic 

 corrections depending upon progression in right-ascension have been 

 derived, in addition to constant corrections, they are very small and 

 might easily vanish with the accumulation of data, though the effect 

 appears to be well marked in some instances. 



The mean probable error of the parallaxes derived according to 

 Adams's method are of an order comparable to those determined by 

 the trigonometrical method, but the probable error varies with the 

 size of the parallax. As Adams's system is founded upon trigono- 

 metrical parallaxes, certain corrections to it are to be expected with the 

 accumulation of results. Thus, it appears that for very small paral- 

 laxes a considerable minus correction must be applied. This may be 

 partly accounted for if Adams used small positive parallaxes in fixing 

 this part of the curve, more or less neglecting the minus parallaxes. 

 After the application of all the corrections, Adams's results were 

 treated for effect depending upon spectral classification. It was 

 anticipated that a decided dispersion effect would be found, but curi- 

 ously enough an approximately linear correction developed, positive 

 for M-class dwarfs. It was also surprising to find that the probable 

 error of a parallax derived from a single plate was not improved by the 

 employment of several plates. 



*Address: Dudley Observatory, Albany, N. Y. 



211 



