1.8.C. 44 Procs. of the Asiatic Soc. of Bengal. |N.S., XVII, 
available in his time. Herschel’s position of the Solar apex 
R.A. = 262°, D=26° is in sensible accord with modern deter- 
minations. 
As more proper motions became known, the problem 
began to engage increasing attention. Two different methods 
have been developed by Airy and Bessel for determining the 
direction of the Solar motion assuming the random nature of 
the proper motions of the individual stars. A large number 
of investigations based on these methods have been made 
which have resulted in somewhat widely different values for 
the position of the apex. The R.A. in all these determina- 
tions remained very nearly the same while there was a wide 
range in the values for the declination which seemed to depend 
on the magnitudes of the stars employed. Recently Weersma 
of Groningen has found the position of the apex by a method 
originally due to Bravais, which does not proceed on the 
sumptions regarding the masses. His result was A=17'51", 
D=31°'4 which may be taken as the best determination we 
have at present. 
Kapteyn has examined in detail whether the different 
parts of the stellar system are relatively at rest. He finds 
that the velocity of the Sun is approximately independent of 
the system of stars whose proper motions are discussed in the 
solution. Weersma has shown how the position of the apex 
motions being a much better criterion of stellar distances than 
magnitudes, he has shown conclusively that the declination of 
ee e apex does not depend on the distances of the reference 
stars. 
An entirely different value for the coordinates of the Solar 
apex was obtained by Kobold by following Bessel’s mnethad 
It was found difficult to reconcile the positions obtained by 
these different methods until Kobold himself pointed out that 
“the results could be harmonised on the assumption that the 
motus peculiares of stars take place in the plane of the Milky 
Way. some in the direct sense and others in the retrograde 
sense”? This cautious statement was later fully confirmed by 
the brilliant discovery of Kapteyn that the stars show decided 
preferences for motion in two diametrically opposite directions. 
If the stars are assumed to be moving at random and the Sun 
fixed in space, the observed proper motions will be equally 
numerous in all directions, so that the velocity diagram W! 




