150 INORGANIC EVOLUTION. [CHAP. 



his statement that the sun has probably never been, and never will be, 

 much hotter than at present. 



Sir William Huggins's statement as to the ultra-violet spectrum of 

 Arcturus is most interesting, if confirmed. The Kensington series of 

 large .dispersion photographs show an : almost perfect similarity of 

 spectrum with that of the sun, extending to X 3880. 



It is difficult to see any objection, on the ground of unequal 

 masses, even if we grant the similarity of the two spectra. It is only 

 necessary to suppose that Arcturus, like the sun and other solar stars, 

 has passed its hotter stages, and that it may have commenced its 

 condensation before the sun. 



To take another case, f Ursse Majoris and ft Aurigse have spectra 

 which are almost identical, although the masses of the two systems, 

 according to Pickering, are respectively 40 times and 4 '6 times that of 

 the sun. Another very hot star, Spica, has a mass only 2 '6 times that 

 of the sun. 



Dr. Schuster further suggests that it if, not known to me that 

 Ritter has long studied the question of gaseous masses contracting 

 under their own gravitation. In my work which has consisted in the 

 discussion of spectroscopic observations, I was at the outset led to the 

 view that it was not a question of gaseous masses at all, originally, 

 and therefore I did not refer to Bitter's conclusions on this point. 

 Again, I had to face the spectroscopic evidence of a chain of obviously 

 cooling bodies, arid it was a detail to consider the fact that "a radiat- 

 ing and contracting mass is not necessarily a cooling mass," because 

 in spite of this truism a time must certainly come when all bodies will 

 find their temperature reduced. I am aware that Hitter's conclusions 

 regarding the first rise and subsequent fall of temperature of gaseous 

 bodies, are similar to those supported by the spectroscopic evidence of 

 what I have considered to be condensing swarms of meteorites, but it 

 would not have been fair to claim Ritter's conclusions as supporting my 

 own, because the bases of the phenomena considered by us were so 

 different. 



I, perhaps, may be allowed to point out that where Ritter's conclu- 

 sions dp not seem to harmonise with the spectroscopic facts, it may be 

 that, as Professor Perry has pointed out,* a stellar atmosphere is a 

 more complicated thing than the theory of a gaseous mass implies. 

 Even the. spectroscope deals generally only with the reversing layer. 

 . , Professor Perry writes : 



; " He (Bitter) assumes that the radiating layer on the outside of a 



s.tar is of constant mass. He also assumes that the rate of radiation 



is proportional to the fourth power of the average temperature of 



. Nature; vol. Ix, p. 247, 1899." 



