54 The Ottawa Naturalist. [June-Julv 



and from now on, through condensation continues the temper- 

 ature begins to fall. If, however, the star is very massive, the 

 temperature rises still further and we have the lines of helium 

 appearing with occasionally silicon and at the still higher tem- 

 perature of 20,000 F. and over. 



From this period onward the temperature begins to fall, 

 very slowly of course, with pauses, and yet with a downward 

 trend. The star is shrinking gradually, becoming denser but 

 owing to its density the shrinkage is not so great, the quantity 

 of heat produced does not quite equal that radiated, and 

 the temperature must inevitably fall. Hence it becomes yellower 

 and passes through the same or nearly the same spectral types 

 as in its ascending phase. It is believed that our sun is on the 

 descending scale of temperature, is at a stage where the change 

 is very gradual, where the loss of heat through radiation is 

 nearly neutralized by that gained through shrinkage. It has 

 been calculated that a contraction in its diameter of 300 ft. a 

 year is sufficient to compensate for the heat lost bv radiation. 

 At that rate in some 12,000,000 or 15,000,000 years it will be 

 so dense as to be incapable of further contraction, will then 

 relatively rapidly solidify and cool down and become a dead 

 sun while its attendant planets will soon reach the temperature 

 of outside space 460 F. and all life will become extinct. This 

 comparatively short time that must have elapsed between the 

 time when our globe was in a molten condition and the present, 

 a time which according to the contraction theory can not be 

 more than about 50,000,000 years and which is much too short 

 for the geologists who require the earth to be hundreds or even 

 thousands of millions of years old, may be indefinitely extended 

 on the assumption of the presence of a comparatively small 

 quantity of radio-active material. Even supposing that the 

 energy given off by substances like radium played a very con- 

 siderable part in compensating for the enormous loss due to 

 radidation yet it is inevitable that finally there must be loss of 

 temperature and gradual cooling down of all the stars. 



The plan of evolution here developed which postulates both 

 an ascending and descending scale of temperature differs from 

 that generally held which assumes that the development is from 

 the nebulae to the white and blue stars without intermediate 

 stages and then by descending stages to yellowish and red stars 

 and extinction. Although such a plan, requiring both ascending 

 and descending scales of temperature was formulated' by Sir 

 Norman Lockyer many years ago it did not receive much support 

 and it is only within the last year or two that it has come into 

 favor chiefly by the evidence collected from manv sources by 

 Dr. H. N. Russell of Princeton University. 



