
1922.] The Ninth Indian Science Congress. L.8.C. 49 
spectral type. our information is limited; but Shapley has 
pointed out that stars of the B-type are to be found even 
below the 9th or the 10th mag. but these should be real Milky 
least tendency for crowding near the Milky Way. From a 
tral types, it will be apparent, how for the distant stars the 
galactic condensation is a good Criterion of the mean distance. 
A remarkable relation between a star’s peculiar motion and its 
class of spectrum was discovered by Campbell in 1910, from a 
study of the residual radial velocities of about a thousand 
stars. He pointed out that the average linear velocities in- 
crease with advancing spectral type a result which has also 
been confirmed by Boss from a discussion of transverse motions 
A reasonable explanation for such a progression has been 
offered by Russell from a study of the stellar masses according 
to spectral Type. 
e relationship between the class of Spectrum and lu- 
minosity (absolute magnitude) has been investigated indepen- 
dently by Herzprung and Russell which has resulted in the 
important discovery of the existence of two series of stars which 
have been designated as Giants and Dwarfs. If the absolute 
magnitudes are arranged according to the type of Spectrum, it 
is found that in class B, the two series are coincident, but 
with advancing spectral type the gap between them widens, 
and in Type M, the stars fall into two distinct groups separate 
by a considerable interval. Adam’s extensive determinations 
zero, indicating an average 
luminosity of about a hundred times that of the Sun. The 
for type M is as much as Il magnitu 
The existence of the two series of ; 
has upset all previous conceptions regarding stellar Perse 
in strict order of temperature. If Russell’s views : 
