434 
ASTRONOMY: H. SHAPLEY 
A word should be said as to the theoretically important question 
whether the reciprocal crosses differ in their results. No consistent differ- 
ence is observable. Eight of the 31 Fi cows (indicated by an asterisk in 
table 1) had Guernsey dams while 23 had Holstein dams. In their first 
lactation period the cows with Guernsey dams gave less milk but more 
butter-fat, average 6953 pounds of milk, 287 pounds of butter-fat. But 
in the second lactation period, three cows with Guernsey dams give a 
little more than the average amount of milk with exactly the average 
amount of butter-fat. It seems unlikely, therefore, that any sex-linked 
factors are concerned in the case. 
1 Roberts, Elmer. Correlation between the percentage of fat in cow's milk and the 
yield. /. Agric. Res., 14, No. 2, July 8, 1918. 
STUDIES OF MAGNITUDES IN STAR CLUSTERS, X. SPEC- 
TRAL TYPE B AND THE LOCAL STELLAR SYSTEM 
By Harlow Shapley 
Mount Wilson Observatory, Carnegie Institution of Washington 
Communicated by G. E. Hale, August 26, 1919 
In an earlier communication^ it has been suggested that the properties 
of star-streaming and the observed decrease of stellar density with in- 
creasing distance from the sun, as well as other observational phe- 
nomena, can be explained if the sun is shown to be not far from the 
center of a large physically-organized star cluster or cloud, which is 
imbedded in a typical stellar region of the galactic system. Evidence 
of the existence of such a local group, intermingled with stars of the 
galactic field, was found from various sources; in particular, the distri- 
bution of the brighter stars of spectral type B directly supported the 
h3^o thesis that a much flattened local system, of limited extent, sur- 
rounds the sun asymetrically, with its equatorial plane incHned some 12 
degrees to the plane of the Milky Way.^ Until recently we have com- 
monly supposed that this stellar assemblage, which is now called the local 
cluster, constitutes the major part of the known sidereal system; at 
present we hold it to be a very minor part of the galactic organization. 
The completion at the Harvard College Observatory of the first 
three volumes of the Henry Draper Catalogue of stellar spectra permits 
examination of the distribution of the fainter B-type stars as a graphi- 
cal test of the existence, dimensions, and inclination of the local system. 
Miss Cannon has kindly supplied the proof sheets of the third volume 
of the catalogue in advance of publication. The region covered by 
