CHAPTER XVII. 



THE PROBABLE ORIGIN AND AGE OF THE SUN'S HEAT. 



Age of the Sun's Heat according to the Gravitation Theories. — 

 Testimony of Geology as to the Age of Life on the Globe. — 

 Evidence from "Faults." — Rate of Denudation. — Age of the 

 Stratified Rocks as determined by the Rate of Denudation. 



Age of the Sun's Heat according to the Gravitation 

 Theories. — The total annual amount of radiation from 

 the whole surface of the sun is 8340 x 10 30 foot-pounds. 

 To maintain the present rate of radiation it would 

 require the combustion of about 1500 lbs. of coal per 

 hour on every square foot of the sun's surface ; and 

 were the sun composed of that material it would all 

 be consumed in less than 5000 years. The opinion 

 that the sun's heat is maintained by combustion 

 cannot be entertained for a single moment. Mr. 

 Lockyer has suggested that the elements of the sun 

 are, owing to its excessive temperature, in a state of 

 dissociation, and some have supposed that this fact 

 might help to explain the duration of the sun's heat. 

 But it must be obvious that, even supposing we were 

 to make the most extravagant estimate of the chemical 

 affinities of these elements, the amount of heat derived 

 from their combination could at most give us only a 

 few thousand years additional heat. Under every 

 conceivable supposition, the combustion theory must 

 be abandoned. 



It is now generally held by physicists that the 



