SHAPLEY— STAR CLUSTERS. 345 



probable genetic relationships to open clusters support that view. 



It may be that the thousands of sub-organizations in the galactic 



system, such as open clusters, star streams, moving groups like those 



in Ursa Major and Taurus, wide pairs of stars of common motion, 



long-period visual binaries, all oringinate in these in-falling globular 



clusters ; it may be, too, that the galactic system itself, which possibly 



is little else than a great mixture of disintegrating minor systems, 



owes its beginning and subsequent growth to globular clusters. But 



whatever its origin and destiny, it is clear that the sidereal system, 



as it now stands out, is a giant in mass and volume compared with 



the region around the sun to which we have usually confined our 



stellar investigations. 



Mount Wilson Observatory, 

 Pasadena, Calif. 

 March, 1919. 



