354 POPULAR LECTURES AND ADDRESSES. 



solar radiation is at present compensated, to any 

 appreciable degree, by heat generated by meteors 

 falling in ; and, as it can be shown that no 

 chemical theory is tenable, 1 it must be concluded 

 as most probable that the sun is at present merely 

 an incandescent liquid mass cooling. 



How much he cools from year to year, becomes 

 therefore a question of very serious import, but it 

 is one which we are at present quite unable to 

 answer. It is true we have data on which we 

 might plausibly found a probable estimate, an< 

 from which we might deduce, with at first sigl 

 seemingly well-founded confidence, limits, not vei 

 wide, within which the present true rate of 

 sun's cooling must lie. For we know, from tl 

 independent but concordant investigations 

 Herschel and Pouillet, that the sun radiates evei 

 year from his whole surface about 6 x io 30 (si: 

 million million million million million) times 

 much heat as is sufficient to raise the temperature 

 of i Ib. of water by i Cent. We also have 

 excellent reason for believing that the sun's 

 1 " Mechanical Energies of the Solar System." See note p. 351. 



