98 F. W. Very — A Cosmic Cycle. 



This gives Arcturus a mass 125 times that of the sun, even if 

 its mean density is no greater than the sun's,' leading to the 

 conclusion that great mass may still be associated with stage 

 (B), which is therefore determined by the elimination of sub- 

 stances essential to stage (A). 



Have we any evidence as to the nature of these eliminated 

 substances ? * In answer to this question, I must refer to Sir 

 J. E\ Lockyer's researches,* which indicate that helium, the 

 metalloids, and some unknown substances, as well as (in a few 

 cases) the substance characterized by the series of spectral lines 

 discovered by Pickeringf in f Puppis (perhaps an allotropic 

 form of hydrogen needing rarefaction and a high temperature 

 for its manifestation), are distinctive of the stars which I have 

 included in stage (A). Hydrogen at its greatest development 

 and the metals belong peculiarly to stage (B). But there must 

 be an intermediate stage connecting the two. Let us suppose 

 that the metalloids are on the whole the most unstable elements 

 and the first to be eliminated, but that before their complete 

 extinction the first stage of condition (B) is entered — that of 

 the Sirian or hydrogen stars (B t ) — and that there is still enough 

 explosive energy left to cast off, but not enough to completely 

 sever from the system such bodies as the major planets. These 

 bodies will retain in their interior substance a larger proportion 

 of metalloids and other light substances, giving them small 

 density, a much more probable assumption than that their com- 

 position is the same as that of the earth and their low density 

 due to incandescence, for since the outer planets are on this 

 hypothesis much the oldest, they have long since cooled to 

 terrestrial surface conditions. The abundance of hydrogen in 

 stars of the Sirian type and the presence of hydrogen in the 

 atmospheres of the outer planets may be noted. 



(B a ). The next stage in condition (B) is that of the Procyon 

 or hydrogen-iron stars. At this point may be placed the birth 

 of the terrestrial planets whose mean density points to an abun- 

 dance of iron and metals of similar specific gravity in their 

 interiors. 



(B 3 ). The explosive activity of the sun at the present time 

 is only capable of producing cometary births ; and this condi- 

 tion is most favorable to that quiet, continuous sunshine which 

 is needed for life on planetary worlds. 



The question : Which are the hottest stars ? needs to be put 

 somewhat more definitely. If we ask : Which stars are hottest 

 at the center? the present hypothesis answers that the solar 



* " On the Chemical Classification of the Stars," Proc. R. S. London, vol. lxv, 

 p. 186, 1899. Not all of the lines designated as unknown are new. "Asterium " 

 is only another name for helium (first subordinate series of " parhelium "). 



f E. C. Pickering, Astro-physical Journal, vol. v, p. 92, 1897. 



