TIME AND SPACE DOUGLAS 



149 



volume, and tempei'ature as the giant stars. Prof. H. N. Russell's 

 famous Giant and Dwarf theory of Stellar Evolution suggested 

 that a star begins its career as a very large mass of gas, highly 

 inflated and miicli less dense than air. This Avould slowly contract 

 by gravitational influence, growing hotter and hotter and brighter 

 and brighter. This period would embrace its life as a giant star. 

 When contraction had reached such a point that, upon the old view, 

 the gas laws could no longer be considered as even approximately 

 representing the state of the star, then at this critical point of balance 

 between mass, density, and temperature, further gravitational con- 

 traction would of necessity be accompanied by decrease of tempera- 

 ture and of luminosity. This period constituted the dAvarf stage 

 of a star's career. Now this theory is thrown into a new light by 

 Eddington's results. If the nuiss of a star be constant throughout 



Deneb^^ ,,Oqq yjVSinus O 



Betel^euse 



jyj\Krueger 60 



kSt^ 



Fir; 



Diagram of stellar evolution 



its life, Eddington's formula shows that there can be very little 

 alteration in luminosity in spite of contraction, and hence the evolu- 

 tion of a single star as outlined above is an impossibility. If as an 

 alternative interpretation the mass of a star is gradually diminish- 

 ing, being actually consumed away to maintain the supply of energy 

 which a star is continuously radiating, then Russell's theory of 

 evolution may be retained as indicating the probable sequence of 

 stellar change, but with this difference that, though the effective or 

 surface temperature may decrease during the latter stages, the 

 internal temperature will continue to rise. 



LOSS OF MASS 



A great deal thus turns on whether the mass of a radiating star 

 can actually be considered to be diminishing. There are, further- 

 more, two ways of looking at this question. 

 76041—26 11 



