290 DISCUSSIONS IN COSMOLOGY. 



miles but by Sirius-distances, each of which comprises 

 millions of miles, so the organic history of the earth 

 must not be calculated by thousands of years, but by 

 palseontological or geological periods, each of which 

 comprises many thousands of years, and perhaps 

 millions or milliards of thousands of years." 



Statements more utterly opposed to the present 

 state of modern science on this subject could hardly 

 well be made. Not only have physicists fixed a limit 

 to the extent of time available to the evolutionist, but 

 they have fixed it within very narrow boundaries. 



Every one will admit that the organic history of our 

 globe must have been limited by the age of the sun's 

 heat. The extent of time that the evolutionist is 

 allowed to assume depends, therefore, on the answer to 

 the question, What is the age of the sun's heat ? And 

 this again depends on the ulterior question, From what 

 source has he derived his energy ? The sun is losing 

 heat at the enormous rate of 7,000 horse-power on every 

 square foot of surface. And were it composed of coal 

 its combustion would not maintain the present rate of 

 radiation for 5,000 years. Combustion, therefore, 

 cannot be the origin of the heat. 



Gravitation has generally been considered by 

 physicists as the only source from which the sun could 

 have obtained his energy. The contraction theory 

 advocated by Helmholtz is the one generally accepted, 

 but the total amount of work performed by gravitation 

 in the condensation of the sun from a nebulous mass 

 to its present size could only have afforded twenty 

 million years' heat at the present rate of radiation. 

 On the assumption that the sun's density increases 

 towards the centre, a few additional million years' heat 

 might be obtained. But on every conceivable supposi- 

 tion gravitation could not have afforded more than 

 twenty or thirty million years' heat. 



