376 
Proceedings of the Poyal Society of Edinburgh. [Sess. 
XXI. — The Systematic Motions of the Stars. (Second Paper.) 
By Professor Dyson. 
(MS. received February 16, 1909. Head March 1, 1909.) 
1. In a previous paper * the hypothesis propounded by Kapteyn that the 
stars are moving in two streams was examined by considering the proper 
motions of stars which were moving more than 20 " a century. By a 
graphical method the directions of these two streams were found with 
results in fair agreement with those found by Kapteyn and Eddington by 
other methods and with different material. It was evident from that paper 
that it would be possible in a large percentage of cases to say with tolerable 
certainty to which stream individual stars of large proper motion belonged. 
The most satisfactory way of doing this seemed to be to compare 
P 
the direction of each star’s proper motion with the direction of the two 
streams already determined. Thus, in the diagram, if P be the north pole, 
S the position of any star, A the direction of Stream I, B that of Stream II, 
and ST the direction of a star’s proper motion, the nearness of ST to SA 
or SB furnishes a criterion as to whether the star belongs to Stream I or 
Stream II. 
The determination of the angles PSA and PSB was made with very 
great ease by Mr W. B. Blaikie’s beautiful device for solving spherical 
triangles. In each case SA and SB were also determined. Although Mr 
* Proc. Royal Soc. Edin ., vol. xxviii. pp. 231-238. 
