360 POPULAR LECTURES AND ADDRESSES. 



that of water (and, therefore, that his mass cools 

 considerably less than 100 C. in 700 years, a con- 

 clusion which, indeed, we could scarcely avoid on 

 simply geological grounds), the physical principles 

 we now rest on fail to give us any reason for 

 supposing that the sun's specific heat is more 

 than 10,000 times that of water, because we cannot 

 say that his expansibility in volume is probably 

 more than 1/400 per i Cent. And there is, on 

 other grounds, very strong reason for believing 

 that the specific heat is really much less than 

 10,000. For it is almost certain that the sun's 

 mean temperature is even now as high as 14,000 

 Cent. ; and the greatest quantity of heat that we 

 can explain, with any probability, to have been 

 by natural causes ever acquired by the sun (as we 

 shall see in the third part of this article), could not 

 have raised his mass at any time to this tempera- 

 ture, unless his specific heat were less than 10,000 

 times that of water. 



We may therefore consider it as rendered highly 

 probable that the sun's specific heat is more than 

 ten times, and less than 10,000 times, that of liquid 



