158 
ASTRONOMY: W. S. ADAMS 
her classification of the Harvard spectra, makes the statement that they 
are of about the same intensity as in a Tauri, a typical K5 star.^ 
The classification of the Mount Wilson stellar spectra in accordance 
with the Harvard system, a description of which is given in a previous 
communication,^ is based upon a comparison of the intensities of the 
hydrogen Hues with those of neighboring iron lines which are subject to 
relatively slight variation with type. A series of curves have been con- 
structed giving the relationship between the relative intensities of these 
pairs of lines and the spectral type; and the determination of type is 
thus reduced to an estimation of the intensities of these lines. The 
stars used in the derivation of these curves are almost wholly stars of 
large proper motion, and in many cases have measured parallaxes of 
considerable size. They are, accordingly, stars of relatively low intrin- 
sic brightness in general. This is true especially of the K5-K9 and Ma 
stars, nearly all of which, like 61 Cygni and Groom. 34, are of very low 
absolute luminosity. The curves derived in this way show a regular 
decrease in the intensity of the hydrogen lines throughout the range of 
spectrum employed, the Hnes in K5 stars being fainter than in KO, and 
in the Ma stars fainter than in K5. In fact the hydrogen lines are barely 
visible in most of the M stars used in the construction of the curves . 
When these results are applied to the M stars of high luminosity a 
very anomalous condition is found. The presence of the bands places 
these stars definitely in the M type, but the hydrogen lines are of quite 
abnormal intensity. Thus a Orionis, with bands of type Ma, if classi- 
fied on the basis of its hydrogen lines would become G2. This is the 
most remarkable case found as yet, but all of the high luminosity M 
stars show a strong tendency in the same direction. The results of a 
classification of 48 stars of types Ma to Mc on the basis of the intensities 
of their hydrogen lines may be summarized as follows : 
TABLE I 
TYPE 
NO. OP STARS 
TYPE 
NO. OF STARS 
TYPE 
NO, OP STARS 
G2 
1 
G7 
9 
Ma 
20 
G3 
1 
G8 
10 
Mb 
18 
G4 
3 
G9 
4 
Mc 
10 
G5 
3 
KO 
4 
G6 
11 
Kl 
2 
Accordingly, the most advanced type found for any of these stars from 
a determination of the intensities of their hydrogen lines is Kl, and the 
average type is 07. This is as against an average type of Mb given by 
