206 



CARNEGIE INSTITUTION OF WASHINGTON. 



estimated with about the same certainty that it can be derived from 

 the laborious counts of thousands of stars. The accompanying tabu- 

 lation shows the close agreement of the two methods, and justifies 

 the extension of the work by means of estimates to the southern 

 clusters that are unavailable for work with the Mount Wilson tele- 

 scopes. 



Using the Franklin-Adams charts to supplement Mount Wilson 

 plates, Mr. and Mrs. Shapley have now studied the form of 41 globular 

 systems and have examined the orientation of the major axes with 

 respect to the plane of the Galaxy. The images of about one-fourth 

 of the systems appear to be nearly circular, a result to be expected 

 from a random distribution of the assumed galactic planes. Two or 

 three clusters are decidedly asymmetrical, but the remainder show 

 distinct and approximately symmetrical ellipticity. 



A Theory of Star-Streaming. 



The center of the galactic system, as outlined by the globular clus- 

 ters, lies in a direction 90° from the center indicated by studies of the 

 motions and luminosities of the brighter stars. Moreover, the first 

 center is more than 100 times as distant as the second. Investigating 

 the probable meaning of this discrepancy from the standpoint of the 

 larger galactic system, Mr. Shapley finds that a large, open, flattened 

 star-cluster exists in the neighborhood of the sun, with its central 

 plane inclined about 12° to the galactic plane; its center is some 50 

 parsecs to the north of the mid-plane of the Galaxy, as defined by 

 distant stars and the galactic clouds. The investigation also yields 

 information relative to the extent of the cluster and its spectral 

 constituency. 



We thus come to the rather obvious hypothesis that the phenomena 

 of star-streaming are simply the results of the motion (as seen from our 

 moving position in the solar system) of this local cluster through the 

 general star-fields of the galactic system, supplemented by the internal 

 orbital motions of the cluster stars. The sun, probably a field star, is by 

 chance near the center of this immense moving system, which con- 

 tains a majority of the conspicuous stars in the sky, including nearly 



