52 POPULAR LECTURES AND ADDRESSES. 



Suppose it is a great burning mass, a great mass 

 of material not yet combined, but ready to combine, 

 a great mass of gun-cotton, a great mass of gun- 

 powder, or nitro-glyccrine, or some other body 

 having in small compass the potential elements 

 of a vast development of energy. We may imagine 

 that to be the case, and that he is continually 

 burning from the combustion of elements within 

 himself ; or we may imagine the sun to be merely 

 a heated body cooling ; but imagine it as we please, 

 we cannot estimate more on any probable hypo- 

 thesis, than a few million years of heat. When I 

 say a few millions, I must say at the same time, 

 that I consider one hundred millions as being a 

 few, and I cannot see a decided reason against 

 admitting that the sun may have had in it one 

 hundred million years of heat, according to its 

 present rate of emission, in the shape of energy. 

 An article, by myself, published in Macmillaris 

 Magazine for March, 1862, on the age of the sun's 

 heat, 1 explains results of investigation into various 

 questions as to possibilities regarding the amount 



1 Republished as Appendix (I'-) t<> Thomson and Tail's Natural 

 Philosophy, Yol i., Part ii., 2nd ed. (1885). 



