DEPARTMENT OF MERIDIAN ASTROMETRY.* 



Benjamin Boss, Director. 

 STELLAR MOTIONS. 



Most of the methods of dealing with preferential motion fail when 

 applied to the B-type stars on account of their small peculiar motions^ 

 together with their small average parallax, their pecuhar distribution 

 in a belt almost coincident with the galaxy, and their uneven distribu- 

 tion along this belt. 



Since the close agreement of the apex of solar motion as derived from 

 the proper-motions of the B-type stars, with the apex derived from all 

 types combined, indicates that the motions of the B-type stars are 

 symmetrical with respect to the general system, a simple method has 

 been employed for the determination of any existing preference of 

 motion among them. 



The B-type stars of the PreUminary General Catalogue have been 

 grouped in areas according to their natural grouping in the sky, and a 

 center of motion has been determined from the actual proper-motions. 

 The position-angles and amount of proper-motion from this center were 

 graphically represented by smooth curves whose abscissae represent 

 position-angle and whose ordinates represent amount of proper-motion. 

 The curves thus determined were mostly very smooth, with definite 

 maxima, each maximum indicating the existence of preferential motion. 



When the paths leading from the center of the areas in the direction 

 of the preferences of motion were plotted, it became apparent that 

 with one exception each area contained a clearly marked preference 

 for motion in the plane of the B-type stars, a plane shghtly inchned to 

 the path of the galaxy. In addition, many of the curves indicated a 

 second maximum, showing the existence of a strong tendency for a 

 portion of the B-type stars to leave their own plane. There was noth- 

 ing of a systematic character in this tendency. Thus the investiga- 

 tion shows that while the motions of a large proportion of the B-type 

 stars will preserve their present plane, contrary to existing notions, the 

 scattering of the stars, which becomes so apparent in later types, has a 

 well-marked beginning in the B-type stage. 



The same method will subsequently be apphed to stars of later types. 



Mr. Raymond is at present working on the determination of prefer- 

 ential motion of the stars by a new method, devised by him several years 

 ago. This method takes account of the amounts as well as of the 

 direction of the proper-motions; it is a modification of that used by 

 Newcomb in his paper "On the position of the Galactic and other 

 principal planes toward which the stars tend to crowd" (Carnegie Inst. 



♦Address, Dudley Observatory, Albany, New York. 

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