ASTRONOMY: IV. 5. ADAMS 
\6\ 
bands are stronger. There are occasional exceptions to this rule, as in 
the case of a Orionis, but in general the effect is well marked. Thus if 
we compare the intensity of the hydrogen line Hp in the stars having 
bands of moderate intensity with that in stars in which the bands are 
very strong we find the following result: 
No. of Stars Intensity of Bands Intensity of Hff 
13 Moderate +1.2 
20 Strong +1.7 
It is of interest to note in this connection that the computation of 
the absolute magnitude shows that the Mc stars, in which the bands are 
exceedingly strong, are brighter on the average than those in which the 
bands are less intense. 
Among the high luminosity stars are some with proper motions of 
moderate size. The absolute magnitudes of these stars should average 
somewhat less than those of the very small proper motion stars which 
constitute the remainder of the list. An analysis of the results for the 
48 stars gives the following comparison. M is the absolute magni- 
tude and m the apparent magnitude. 
• No. of Stars Average P.M. Average m Average M 
15 0!'155 5.06 1.54 
33 0.017 5.49 1.29 
After making the necessary correction for the difference in the values 
of the average apparent magnitude we find the large proper motion stars 
to be about 0.7 magnitude fainter than those of small proper motion. 
This furnishes a check on the accuracy of the absolute magnitude de- 
terminations. 
The variations in the intensities of the hydrogen lines and of the two 
lines used in the computation of absolute magnitude form only a part 
of a more general difference in the spectral characteristics of the high 
and the low luminosity M stars. The results of a detailed compar- 
ison of the spectrum of a Orionis (M = —1.0) with that of Lai. 21185 
(M = + 10.6) and of other intrinsically faint stars may be summarized 
as follows: 
a Orionis Lai. 21185 
Enhanced lines, especially those due to Fe, Ti, Sr, and F_ . Strong Weak 
Hydrogen lines Strong Weak 
Low temperature lines of Ca, Ti, Cr, and Sr Weak Strong 
X 4227 of calcium Weak Very strong 
Results of a character very similar to these were found in a compari- 
son of the spectra of a Tauri (K5) and 61 ^ Cygni (K8) two stars differing 
