138 
ASTRONOMY: ADAMS AND SHAPLEY 
the plate, though well measurable, is somewhat under-exposed. Es- 
pecial care was taken in adjusting the spectrograph to secure good defi- 
nition in the region of the hydrogen line Hy. As a result the spectrum 
lines are very sharply defined from X 4200 to X 4500, but begin to show 
diffuseness to the red of this point. They are, however, measurable as 
far as X 4600. 
A comparison of the two negatives under a Hartmann spectrocom- 
parator at once showed some important differences beween the two 
spectra.^ These may be summarized as follows. The photograph of 
FIG. 1. SPECTRA OF 5 CEPHEl 
Top: Spectrum near Minimum ot Light 
Bottom: Spectrum near Maximum of Light 
December 24 was taken near the star's maximum of light, and that of 
December 23 not far from minimum. 
7 4578 (maximum) y 4571 (minimum) 
Hydrogen line Hy Strong Much weakened 
Enchanced lines of Fe, Ti, Sr, and Cr Strong Much weakened 
\ 4481, enhanced Mg Very strong Much weakened 
X 4227 of calcium Strong Strengthened 
Low temperature lines of Ca, Fe, Ti, and Cr. . . Weak Strengthened 
Continuous spectrum Strong in violet Weakened in violet 
The observation on the continuous spectrum is made somewhat un- 
certain by the general under-exposure of the plate taken near minimum, 
but the result is apparently as given. The lines on this photograph ap- 
pear to be broader and less sharply defined than those on the plate at 
maximum, and this effect we consider as probably genuine after all neces- 
sary allowance has been made for the difference in the quality of the 
two negatives. There is, however, no evidence of lack of symmetry in 
the spectrum lines either at maximum or minimum, nor of the presence 
of a secondary spectrum. It appears from these observations that the 
changes follow a definite tendency. At maximum the high temperature 
lines are very strong, and the low temperature lines are weak; while at 
minimum the reverse is the case. The conclusion appears to be justi- 
fied that the temperature of the gases constituting the star's absorbing 
envelope is higher at maximum of light than at minimum. 
