126 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1945 



was the first to show any systematic drifts of great numbers of stars 

 in any particular direction. 



Gustaf Stromberg, at the Mount Wilson Observatory, examined the 

 motions of various classes of stars and uncovered some surprising 

 facts. His analysis of the motions of certain stars that the spectro- 

 scope showed to have very high velocities, 50 miles a second and up, 

 proved that their directions are by no means at random. They seem 

 to be leaving a particular part of the sky because the sun and its 

 planets are moving toward that region. 



The most rapidly moving stars, Stromberg found, are those far-dis- 

 tant groups, each consisting of many thousands of closely associated 

 stars, which are called globular clusters. There are about a hundred 

 of these clusters. 



Thus, these and other men were finding beads of knowledge that 

 eventually had to be strung together to show their relationship. The 

 first to do this was Bertil Lindblad, of the Swedish observatory at 

 Stockholm. He explained the apparent motion of high-velocity stars 

 by fitting them into a theory of galactic rotation. He showed that if 

 we assume the whole Milky Way system of stars to be revolving, then 

 what otherwise appear to be peculiar and unaccountable motions of 

 stars become natural consequences of that revolution. He likened our 

 system of a billion or more stars to the spiral nebulae that can be seen 

 far beyond the limits of the Milky Way and suggested that each of 

 these nebulae is itself a distant island galaxy, seen as a blur of light 

 because we are unable to distinguish any but the brightest individuals 

 among its millions or billions of component stars. 



Lindblad's suggestion was not new, but he was the first to form a 

 complete theory. As far back as the time of Sir William Herschel our 

 system of stars was being likened to the spiral nebulae. Herschel, with 

 the large telescope that his patron George III had enabled him to 

 build, could see many hazy patches of light that he shrewdly guessed 

 might be star systems. The name "island universes," applied to these 

 suppositional galaxies, became common at that time. 



Herschel 's telescopes were not powerful enough to resolve these 

 nebulous objects into separate stars, but he predicted that all such 

 clouds might one day be shown to consist of stars. With his largest 

 telescope he had already proved that some objects which his smaller 

 instruments showed only as glowing spots were really star clusters. 

 What could be more natural than that with means more abundant, 

 even, than those supplied by King George, telescopes might be made 

 that would break up into stars even the most distant spots on the sky? 



This very reasonable guess of Herschel's has since been found to be 

 partly at fault, for the spectroscope, of more modern times, shows in- 

 disputably that some of the nebulae are gaseous and that some are 



