ASTRONOMY: SHAPLEY AND NICHOLSON 
423 
tensity at maximum absorption of the undisplaced spectral line. It has 
also been assumed that the setting for the position of a line is such that 
the area under the intensity curve is divided equally and that the 
eflect of absorption which is less than \ /J will not be appreciated; 
the results, however, are but sHghtly affected by the value assumed, 
provided it is within reasonable limits. 
The lines of the spectrum of h Cephei are much wider at minimum 
than at maximum light (and velocity)."^ Those shown in figures 3a 
and 3b are of the same width as observed in the case of 5 Cephei at 
minimum and maximum, respectively, when a stellar spectograph of 
h'"gh dispersion and resolving power is used. The change observed in 
line width, according to results by Adams and by Young,^ appears to 
have twice the period and about three times the amphtude of the 
variation which would be produced in a pulsating star by the distri- 
bution of velocity over the stellar disk; this latter variation, therefore, 
although it might be measurable if isolated, would probably be com- 
pletely masked by the larger variation due to other causes. 
Since practically all of the asymmetry is above the limit | any 
deviation from a symmetrical form of the absorption lines would at all 
phases of the pulsation be inconspicuous on a spectrogram, and the lines 
would appear to be shifted bodily. The asymmetry would be most 
pronounced at maximum when the lines are comparatively narrow; but 
even then it seems doubtful if it could be observed if we are right in 
assuming that the lines for a Cepheid at maximum are best represented 
by curves such as those shown in figure 3, with values of x between J 
and 1. 
We conclude from these results that it is doubtful if either the periodic 
broadening or the slight asymmetry of the lines, due to a distribution 
of velocity over the stellar disk in accordance with the pulsation 
hypothesis, could be observed by any method thus far used. 
1 Shapley, Harlov/, Mt. Wilson Contr., No. 99, Astrophys. Chicago, III, 41, 1915 (291- 
306), pp. 292-295. 
2 Jeans, J. H., Mon. Not. R. Astr. Sac, London, 73, 1917 (28-36), p. 35. 
3 Wadsworth, F. L. O., Phil. Mag., London, Series V, 43, 1897 (317-343). 
* Adams, W. S., Observatory, London, 42, 1919 (167-168). 
^ Young, R. K., /. R. Astr. Soc. Canada, Toronto, Can., 13, 1919 (45-54). 
