13-15] 
The Galactic System 
15 
Table II. Star-densities ( Kapteyn ). 
Ellipsoid 
No. 
Semi 
major 
axis 
(parsecs) 
Semi 
minor 
axis 
(parsecs) 
Relative 
Star- 
density 
Stars 
per cubic 
parsec 
Volume 
of Shell 
(cubic 
parsecs) 
Number 
of Stars 
Centre 
1 
602 
118 
1-000 
0631 
o-ioo 
0063 
1-79X10 8 
0-1 X 10 8 
II 
1010 
198 
0-398 
0-040 
6-66 
0-3 X 10« 
III 
1510 
296 
0-251 
0-025 
19-8 
0 -6 X 10 8 
IV 
2106 
413 
0-158 
0-016 
48-4 
1-OxlO 8 
V 
2820 
553 
0100 
0 010 
107 
1-3 xlO 8 
VI 
3656 
717 
0-063 
0-006 
226 
1-8 X 10 8 
VII 
4600 
902 
0040 
0-004 
388 
2-0 X 10 8 
Vili 
5675 
1114 
0-025 
0-002 
702 
2-3 x 10 8 
IX 
6960 
1365 
0-016 
0-002 
1270 
2-5 xlO 8 
X 
8465 
1660 
o-oio 
0001 
2210 
2-6X10 8 
— 
— 
— 
0-03 
0003 
4980 
14-5X10 8 
The first four columns are given by Kapteyn. The next column gives the 
number of stars per cubic parsec over the spheroid in question, calculated 
for a central density of one star per 10 cubic parsecs, our estimated density of 
stars in the neighbourhood of the sun. Kapteyn’s own figures were rather less 
than half of these, as he estimated the central density to be only 00451 
stars per cubic parsec, or about one star per 22 cubic parsecs. 
The general distribution implied in Kapteyn’s scheme is shewn dia- 
grammatically in fig. 2. This represents a section through the central axis of 
the system; if the section is supposed to be parsec in thickness, each 
dot represents a single star. 
0 1000 2000 3000 4000 5000 
Scale, par secs 
Fig. 2. Density of Distribution of Stars surrounding the Sun (Kapteyn). 
(On right, the Andromeda Nebula M. 31 (Plate I) on the same scale.)