142 
ASTRONOMY: ADAMS AND SHAPLEY 
would be shifted toward longer wave-lengths with reference to the stel- 
lar lines by amounts corresponding to the observed pressure displace- 
ments. It seems to us probable that this is the explanation of at least 
the principal part of the observed difference, although differential radial 
currents in the star's atmosphere may account for a portion of it. 
An important confirmation of this result is furnished by Mr. St. 
John's measurements of the displacements of solar lines relative to the 
arc spectrum lines of iron. He has kindly furnished us with the pro- 
visional values obtained for the lines given in Table I, and from these 
we find: first, that the small pressure shift fines are displaced toward 
the red in the sun relative to the arc fines by an average amount of 
0.009 angstrom; second, that the large pressure shift lines are displaced 
toward the violet 0.004 angstrom. These differences are in the same 
direction as in the case of 5 Cephei and the absolute amount is of much 
the same order. Thus we find: 
Sun Large A lines — Small A lines = —0.013 A = —0.9 km 
b Cephei " " = -1.2 km 
It is well known that the pressures in the upper portions of the sun's 
atmosphere where the stronger fines of the spectrum appear to find 
their origin are extremely low. 
A comparison of the velocities given by the enhanced lines in 5 Cephei 
with those given by such as are not enhanced indicates a distinct shift 
of the former toward longer wave-lengths. In the case of the photo- 
graph taken near maximum the difference amounts to -}-0.86 km, or 
about +0.012 angstrom. The other photograph gives a similar value 
of larger amount. A difference of the same character was found by 
Adams some years ago for the enhanced lines in the spectra of Sirius and 
Procyon.* The values were +0.90 km for Sirius and +0.58 for Pro- 
cyon, with which the result found for 5 Cephei is in very fair agreement. 
It is probable that the explanation of these results is to be found mainly 
in radial convection currents in the stellar atmospheres. 
^ Belopolsky and Lohmann at Pulkova have described some differences in the intensities 
of the lines at maximum and minimum light, but the dispersion employed makes it impos- 
sible to identify the lines with certainty. 
2 Moore, Lick Ohs. Bull., 7, 153 (1913). 
3 Luizet, Ann. VUniv. Lyon, N. S., 33, 42 (1912). 
^Astrophys. J., 33, (1911). 
