ASTRONOMY: ADAMS AND JOY 
131 
and eight spectral divisions in the two cases respectively. There is, however, 
a small systematic difference in spectral type at both maximum and minimum, 
the types given here being on the average slightly earlier. 
It is clear from the very special character of the variations in the spectra 
of the Cepheid variables that it is doubtful if they can be regarded as furnish- 
ing direct evidence as to the order of evolution of stars in general. In the 
normal succession of spectral types changes in intensity of the hydrogen 
lines are accompanied by numerous important changes in many features of 
the spectrum which appear to remain essentially unaltered in the spectra of 
the Cepheids. 
Reference has been made to certain differences in the spectra of these stars 
at maximum and minimum of light other than those in the hydrogen lines. 
The most important of these are: (1) a shift of the maximum of the con- 
tinuous spectrum toward shorter wave-lengths at maximum of light, a result 
found by Albrecht 3 : (2) a general slight widening of the spectral lines at 
minimum: (3) an increase in the intensity of the so-called 'enhanced' lines 
at maximum. The last two characteristics were noted in the investigation of 
the spectrum of 8 Cephei by Adams and Shapley 6 . The change in the enhanced 
Jines is probably most significant in its bearing on the variation of absolute 
magnitude. The three lines principally used for the determination of abso- 
lute magnitudes of stars of this type of spectrum are all strongly enhanced 
and it seems probable, as we have suggested previously, that enhanced lines 
as a class vary with luminosity. Accordingly we have compared the intensi- 
ties of some of the more prominent enhanced lines in the spectra of these 
variables with their intensities in the solar spectrum, and also on the photo- 
graphs taken at maximum and minimum of light. In all cases these lines are 
much more intense in the stellar spectra, and to a less degree more intense 
at maximum than at minimum of light. Among the lines are the following: 
4077 Sr 4233 Fe 4290 Ti 4385 Fe 4584 Fe 
4215 Sr 4246 Y 4376— 4534 Ti 
Of these X 4077 shows the largest difference, being fully five times as strong 
in some of the stellar spectra as in the sun. With the aid of the reduction 
curves for absolute magnitude, the difference in the intensities of the three 
lines X 4077, 4215 and 4290 at maximum and minimum of light may be con- 
verted into differences of magnitude. They give for the average of the nine 
stars the values 0.8, 1.3 and 0.6, respectively, or a mean of 0.9. This is in 
very fair agreement with the average variation in apparent magnitude of 0.7 
for the same stars. 
Two other features of the spectra of this class of variables may be referred 
to briefly. The first is the marked difference in the relative intensities of the 
hydrogen lines when compared with the solar spectrum. In the sun the line 
H/3 is considerably more intense than ITy, but in all of the Cepheid spectra 
the reverse is the case, H7 being much stronger than H0. At minimum of 
