THE SUN COOLING OFF. 409 



duce the temperature of the sun two and one fifth degrees 

 annually. During the human period of 6000 years, the 

 temperature would have been reduced more than 19,000 

 degrees. At such a rate of cooling it is obvious that the 

 sun must speedily cease to warm our planet sufficiently to 

 sustain vegetable and animal life. But it is certain that 

 the sun's high temperature has been maintained during 

 almost countless ages anterior to the commencement of the 

 human era. Those Titanic reptiles which could luxuriate 

 only under tropical warmth flourished a hundred thousand 

 years before the world was prepared for man; and those 

 rank, umbrageous ferns, whose forms we trace upon the 

 roof-shales of a coal mine, existed before the reptile horde, 

 and purified the air for their respiration. 



What unseen cause has perpetuated, for a million of 

 years, those solar fires ? Kepler asserted that the firma- 

 ment is as full of comets as the sea is of fishes, and Newton 

 conjectured that these comets are the fuel-carriers of the 

 sun. Alas ! Ave only know that the wandering comet, 

 though flying in tantalizing proximity to the sun, but ac- 

 celerates its speed and hurries onward, as virtue hastens 

 past the vortex of ruin. Is it a chemical action which 

 maintains the solar heat ? The most efficient chemical ac- 

 tion for this purpose is combustion. Now, if the sun were 

 a solid mass of coal, its combustion would only suffice for 

 the brief space of forty-six centuries to replenish the solar 

 system with its vivifying influence. Is it the effect of the 

 sun's rotation on his axis? Such rotation could generate 

 no heat without the resistance of another body. Even if 

 that other body were present, a calculation based upon the 

 sun's mass and his rate of rotation shows that the heat 

 generated could only supply the expenditure for the space 

 of one hundred and eighty-three years. 



There exists, nevertheless, a means of recuperation to the 

 S 



