ON STELLAR DISTRIBUTION AND MOVEMENTS. 



257 



concentrated than is the case in the moving clusters, where they appear 

 to be at ordinary stellar distances. The question must be left open. 

 Another peculiarity, which can hardly be considered here, but which 

 reminds us how exceedingly complicated is the problem we are trying 

 to unravel, has been found by Hinks 20 ; according to his investigations 

 practically all the globular clusters are concentrated into one-half of the 

 celestial sphere. 



A great interest is added to the problem of stellar motions by the 

 discovery, actually made last year, but foreshadowed for several years, 

 that the stars of the later types of spectrum have larger individual 

 motions than those of earlier types. The table gives the most com- 

 plete evidence — that of Campbell; it confirms an earlier table by 



Mean Velocities of Stars. 21 



Kapteyn," and Boss " has also found confirmatory evidence from the 

 angular motions. Properly considered, I think that this relation of 

 spectral type and velocity is one of the most startling of the results 

 of modern astronomy. For the last forty years astrophysicists have 

 been studying the spectra and forming their systems by which they 

 arrange the stars in order of evolution. However plausible may be their 

 arguments, one would have said that their hypotheses must be for 

 ever outside the possibility of confirmation. Yet if this result is right, 

 we have a totally different criterion by which the stars are arranged 

 in the same order. If it is really true that the mean motion of a class 

 of stars measures its progress along the path of evolution, we have a 

 new ■ and powerful aid to the understanding of the steps of stellar 

 development. 



The facts now brought before us direct attention to the very deep- 

 lying question, How must we account for the individual motions of 

 the stars? It appears that as we trace back the life-history of a star, 

 its velocity is found to be smaller and smaller; in the Orion stage it 

 was only about one-third of what it will ultimately become. It seems 

 right to infer that the stars are born with little or no individual motion. 

 Assuming that the gravitational action of other stars is responsible for 

 the motion subsequently accumulated, this might be thought to point 

 to stars being developed from a primordial matter not subject to 



20 Monthly Notices, lxxi., p. 693. 



21 Campbell, Lick Observatory Bull., No. 196. 



22 Astrophyiscal Journ., xxxi., p. 258. 



23 Astron. Journ., No. 623-24, p. 198. 

 1911. 



