136 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1!)12. 



the origin of spectrum limes. With four negative electrons revolving 

 about a positive central body, 12 of the mysterious lines were explained, 

 and with these several others which were attributed with no great 

 certainty to hydrogen and helium. 



This demonstration, of course, leaves much to be desired. But 

 it is evident in what direction we must proceed to complete it. It is 

 very probable that hydrogen and helium, because of their complex 

 spectra, are not simple elements. What glory it would be if by 

 some well-chosen process we could decompose either of them and 

 make the complete spectrum of nebulium appear in our laboratory! 

 Astronomers could then hand over to the chemists a conquest even 

 more precious than was the discovery of helium. 



While waiting for the realization of this bold synthesis we con- 

 tinue to proceed by analysis and classification. All the conclusions 

 formerly held about nebulae demand revision because of the amount 

 and value of the recently obtained photographic evidence. Re- 

 cently A. R. Hinks ^ has devoted himself to such an analysis. With 

 his wonted precision he has defined the characteristics which distin- 

 guish the various classes of nebulae and star clusters and has found 

 for each class its law of distribution in the heavens. We must dis- 

 card the convenient and very simple law which stated the frequency 

 of the occurrence of nebulae and clusters as a function of the galactic 

 latitude only. 



There is a clearly marked distinction between the stellar and plane- 

 tary nebulae as well as between the annular and spiral ones. This 

 fact gave Stratton ^ a strong argument against the theory of T J. eT. 

 See, who attributed a common origin to the last two kinds. The 

 cosmogony of See, far outrunnmg the possibility of experimental 

 evidence, creates other difficulties, and it seems to us that it has 

 made no progress since its appearance toward being accepted. The 

 same thing can be said of the mutual collisions of stars. Bickerton ^ 

 has come forward as an advocate of them, and they should, accord- 

 ing to him, give birth to double stars as well as to planetary systems. 

 A hazardous theory may prove useful because of the verifications it 

 necessitates. For instance. Monk* showed tliat we ought to keep tab 

 on the displacements of the spectrum lines so as to know m advance 

 of imminent collisions, and Forbes ^ demonstrated that by a similar 

 process we could obtain evidence concernmg the rotation of certain 

 stars about their centers. An attempt with encouraging results has 

 already been made as to the latter problem at the Allegheny Observ- 

 atory. 



1 Monthly Notices, May, 1911. 



2 The Observatory, September, 191 1. 



' Session of the Royal Astronomical Society, Jan. 2o, 1911. 

 * The Observatory, vol. 24, p. 202. 

 » Monthly Notices, vol. 72, p. 378. 



