ON STAR STREAMING. 257 
Star Streaming, By Professor J. C, KAPTEYN. 
[Ordered by the General Committee to be printed in extensa. | 
‘x deriving the constant of precession, and in investigating the motion of 
the sun through space, it is usual to start from the hypothesis that the 
real motions of the stars, the so-called peculiar motions, have no preference 
for any particular direction. 
Of late I have found anomalies in the distribution of the apparent 
proper motions, of so strongly systematic a character that I feel convinced 
that we are compelled to give up this hypothesis. 
It will be the aim of this paper to show the nature of these anomalies, 
and to explain the conclusion to which they lead us. 
It is only just to mention that as early as 1895 Kobold called atten- 
tion to a fact which seems incompatible with a random distribution of the 
direction of the motion of the stars. Had Kobold been more successful 
in separating the systematic motions of the stars from the displacements 
caused by the sun’s motion, he would probably have been led to conclusions 
similar tu those which I am now about to submit to you. 
In order to show clearly the anomaly in the distribution of the proper 
motions here alluded to, it will be necessary to call to mind how this 
distribution must present itself if the hypothesis of the random orienta- 
tion of the motions were really satisfied. 
For this purpose consider a great number of stars very near each other 
on the sphere, say all the stars of such a small constellation as the Southern 
Cross. For convenience’ sake we will even assume them to be all 
apparently situate in the same point S (fig. 1, P) of the sphere, though not 
in space, because their distance would be different. 
The peculiar proper motions of these stars will be distributed some- 
what in the manner indicated in fig. 1, P. 
In addition to this motion, which represents the real motion of the 
stars as seen projected on the sphere, they will have an apparent motion, 
the parallactic motion, which is due to the observer's own motion, or say 
the motion of the solar system, through space. 
These parallactic motions, we all know, are directed away from the 
apex, which is the point where the sun’s motion prolonged meets the 
sphere. For all the stars at S the parallactie motion will be directed 
along Sw. 
The motions as really observed are the resultant of the peculiar and 
the parallactic motion. 
: Thus for the star whose peculiar motion is SB, let Sf be the parallactic 
motion, then the observed motion of that star will be Sd. Likewise the 
observed proper motion of the star having the peculiar motion SC will be 
Se, and so on. 
| Making the composition for all the stars of fig. 1, P, we get the really 
observable motions distributed as in fig. 1, Q. 
From this it must be evident that whereas, according to the hypothesis, 
the distribution of the peculiar motions would be radially symmetrical, 
this symmetry will be destroyed for the observed proper motions. 
There will be a strong preference for motions directed towards the 
1905. 8 
