52 C. V. L. CHARLIER, 
which is the density (— the number of B-stars per cub-Siriometer) at 
the centre of the galaxy. Within a cube having a volume of 1000 
cub-Siriometers we thus have 2.625 B-stars. 
As long as we consider regions nearer than c, in the XY-plane 
of the Galaxy and nearer than e, in the direction of the poles, the 
density is only slightly smaller than at the centre. Thus in the neigh- 
bourhood of the sun (x = 18, y —0, z — 4) we have to reduce the 
density at the centre by the factor 
Pere Mora 
2x87! 2x13? 
e = e "(appr.) = 0,882 , 
giving a density of 0,032 stars per cub-Siriometer. 
When the distance from the centre is greater than « the den- 
sity decreases rapidly. At a distance of 100 Siriometers from the 
centre, the distance is reduced to 0.01 of that at the centre as long as 
we consider points in the XY-plane of the Galaxy. At the same di- 
stance along the Z-axis the density is reduced to 107 of that in the 
centre. 
The variation of the density in different points of the galactic 
system is graphically illustrated on plates III— V, which will be descri- 
bed below. 
22. The number of stars of type B being rather limited, Pıck- 
ERING has considered it possible to gather from his photographie pla- 
tes all stars in the sky having this spectral type. In the volume 56 
of the Harvard Annals PrckERING gives indeed a catalogue of these 
stars, of which the greater portion have been found in the classifica- 
tion of the Henry Draper Memorial spectra by Mrs Fleming. In all 
there are, in this catalogue, 751 stars of the subclasses Bo, Bi, De, Ba 
and Bs. These 751 stars have been used in the preceding paragraphs 
for deducing the parameters of the Galaxy. An appendix to Vol. 
56 N:o II has been taken into account where certain omissions and 
corrections have been indicated. All these 751 stars are contained in 
the following catalogue. In the catalogue of the B-stars PICKERING 
also includes the stars of the subclass Oe 5 B, which in this Catalogue 
are indicated by the number 5 in italics. By an inadvertency these 
stars, ten in number, have been reckoned as belonging to the sub- 
class B 5. This mistake is, however, of no consequence for the com- 
