STUDIES IN STELLAR STATISTICS. 11. 19 
The mean errors in R are difficult to determine. I estimate 
them to about 0.5 Sir/st. year. 
Hence it seems probable that the correlation between A and m 
is real. It should imply that the more distant stars of the spectral 
type B would have a fainter luminosity than the nearer ones. It is 
necessary to discuss, somewhat in detail, the bearing of this conclusion. 
If all stars of the spectral type 2 do possess the same tempe- 
rature and the same radius — as has been hitherto accepted in this 
investigation — then the value of À ought to be independent of the 
apparent magnitude (m) of the stars. Accepting the conclusion 
that À varies with m we are obliged to assume that either the tempe- 
rature or the radius (or both) of these stars are dependent on m. The 
variability of the radius would imply that the bigger stars would be 
more condensed near the centre of the Milky Way, a conclusion by 
no means improbable, which is however in this case counterbalanced 
by our assumption that the stars of the spectral type 2, as far as 
they possess the same temperature, ought to have also nearly the 
same radius. 
We are thus induced to inspect more closely the hypothesis of 
the equal temperatures of the stars of the spectral type B. Insisting 
upon our assumption regarding the close correlation between tempera- 
ture and the nature of the spectrum, we have to consider the diffe- 
rent kinds of the spectra brought together under the common title 
»spectral type D». 
It is well known that the Harvard observers, having first intro- 
duced the spectral types B, A, PF, G etc. by and by found it ne- 
cessary to insert between these principal types a series of subclasses, 
often a number of ten — which are however not all represented in 
the catalogues. Thus we find in the interval between B and A the 
subclasses 
Bae bt Bs.) Bi Bar B9; 
Of these Bs and Bo are suitably taken together with type A. 
The spectral type B is thus composed of the following 5 subclasses, 
BIO UB B 25 Ban Diss 
Moreover there are, in all, three stars classified as B4 and Be, 
which are not here taken into consideration. 
