I 
38 ASTRONOMY: G. ST ROM BERG 
GROUP 
NO. 
M 
m 
7T 
km. 
I 
509 
0.76 
4.83 
Of 015 
13.11 
II 
513 
2,08 
5.09 
0.025 
17.13 
III 
260 
6.05 
6.82 
0.070 
25.88 
Each group contains stars of spectral types F, G and K, the third group, com- 
prising the faintest stars, also including 11 stars of the dwarf M type. The 
symbol t denotes the geometrical mean of the parallaxes, which is readily 
derived by the formula 
5 log 7r = M — m — 5. 
In accordance with the method of Charlier, the sky has been divided into 
48 equal areas situated symmetrically with reference to the galactic equator. 
If star streaming is studied on the basis of the ellipsoidal or the two drift theory, 
opposite areas may be combined by assuming that the stream motion is the 
same in all parts of the space. 
Since the sun, however, is not situated at the center of the stellar system, 
but at a distance from it probably comparable with the mean distance of the 
later type stars used in this investigation, we might, according to the theory 
of Turner 3 and Eddington, 4 conceive the stream-motion to be due to the gen- 
eral attraction of the stellar system. It would then differ from point to 
point and be related to the position of the center and the central plane of the 
stellar system. Such a theory is supported by Kapteyn's 5 suggestion that 
there is an acceleration of the first stream; i.e., that the velocity of the first 
stream is different in different parts of the space. 
In order to test for the existence of such a varying stream-motion, I have 
tried to express the average radial velocity as a rational integral function of 
the direction-cosines of the line of sight such that the radius vector of the sur- 
face thus defined equals the average radial velocity. Using only terms of 
second order we can in this way determine the stream-motion, if the latter is 
constant (Eddington 6 ). If the stream motion is variable this must be marked 
by the existence of asymmetrical (odd) terms in the analytical representation 
of the surface. 
In this investigation terms to the third order inclusive have been 
determined. 
If terms of the second order alone are included, opposite areas in the sky 
may be combined. The resulting directions of the axes of maximum radial 
velocity 0 are thus: 
GROUP I 
GROUP II 
GROUP III 
a 
8 
a 
5 
OL 
8 
km. 
16.14 
98° 
+ 5° 
km. 
20.98 
86° 
+ 10° 
km. 
32.4 
100° 
+ 34' 3 
