48 THE FITNESS OF THE ENVIRONMENT 



matter of which it is composed. Finally 

 terrestrial chemistry completes the evidence 

 regarding the composition of such astronom- 

 ical bodies; geophysics that regarding their 

 state. The number of extinct suns is prob- 

 ably very great ; Arrhenius thinks it not un- 

 likely that they may be one hundred times 

 more numerous than the luminous stars. 1 



It is more difficult to gain a clear idea of 

 the nebulae, for such aggregations of matter 

 are very diverse in appearance, and none lie 

 near enough to the earth for us to study them 

 as we study the solar system. However, in- 

 vestigation of new stars, of the spiral forms of 

 many nebulae, of the so-called star rifts 

 which appear to be due to the movement of a 

 large body through a nebula, sweeping up 

 smaller bodies and leaving a channel behind, 

 and a variety of considerations dependent 

 upon the modern development of the sciences 

 of physics and chemistry, all contribute to a 

 growing belief that nebulas may often, and 

 sometimes at least do certainly arise from col- 

 lisions between dense bodies. Further, the 

 nature of the processes by which stars may be 

 formed out of nebulae becomes constantly 

 better understood, and while there is small 

 ground to regard our present science of nebulae 



1 " Worlds in the Making," p. 151. 



