ASTRONOMY: H. SHAPLEY 
279 
The hundred or so brightest short-period Cepheids (cluster-type 
variables) in the galactic system do not show a marked concentration 
to the plane of the Milky Way. This result is not conclusive, however. 
There are hundreds of known variable stars in low galactic latitudes 
whose periods and variations are not yet recognized. If, as may well 
be the case, these prove to be short-period Cepheids which appear 
faint because of distance, though intrinsically fairly luminous, our ideas 
relative to their galactic concentration will need modification. In fact, 
we probably have much more complete information about the Cepheid 
variables in w Centauri than in our own system, and for the former the 
information is also homogeneous. 
Summary. (1) When based on photographs with exposures long 
enough to show ten or twenty thousand stars, the study of stellar dis- 
tribution in the so-called globular clusters reveals an underlying ellip- 
tical symmetry that may be universally present. (2) The 130 bright- 
est stars of color class B in Messier 13 show a distinct preference for 
the sectors containing the axis of symmetry, which was previously 
found for faint stars but is not shown by the thousand brightest objects 
of all color classes. (3) The Cepheid variables in Messier 13 also aline 
themselves along this axis. (4) The southern cluster co Centauri shows 
a conspicuous elliptical distribution, even when only the brightest 5000 
stars are examined. (5) The 128 short-period variables in this cluster 
show a much higher concentration toward the axis of symmetry than 
do the other stars. (6) Because of the analogous condition in our 
Galaxy, the peculiar concentration of blue stars and variables strongly 
supports the hypothesis that these axes of symmetry in reality repre- 
sent the projections of more or less oblate systems of stars ; and it indi- 
cates that in this flattened form, which appears not only as a character- 
istic of various kinds of nebulae, but also of the solar system, of the 
whole galactic system, and now even of globular clusters, we have a 
property that is general and fundamental in the dynamics of stellar 
groups. 
1 Pease, F. G., and Shapley, H., these Proceedings, 3, 1917, (96-101). 
2 Shapley, H., ML Wilson Contrih. No. 116, 1915, (1-92). 
' lUd., page 87. 
* Bailey, S. I., Ann. Obs. Harvard Coll., Cambridge, 38, 1902, (1-252), page 5. 
^ Bailey, S. I., Astr. and Astroph., Northfield, Minn., 12, 1893, (689-692). 
« Shapley, H., loc. cit., and Observatory, London, 39, 1916, (452-456), page 456. 
