ioo POPULAR LECTURES AND ADDRESSES. 



" eration. For example, is it not possible that the 

 " prodigious x temperature which would seem to 

 " exist at ioo miles below the surface, all the 

 " metallic bases may behave as mercury does at a 

 " red heat, when it refuses to combine with oxy- 

 " gen ; while, nearer the surface, and therefore at a 

 " lower temperature, they may enter into combina- 

 " tion (as mercury does with oxygen a few degrees 

 " below its boiling point) and so give rise to a heat 

 " which is totally distinct 2 from that which they 

 " possess as cooling bodies ? And has it not also 

 " been proved by recent researches that the quality 

 " of the atmosphere may immensely affect its per- 

 " meability to heat, and consequently profoundly 

 " modify the rate of cooling of the globe as a 

 " whole ? 



" I do not think it can be denied that such 

 " conditions may exist and may so greatly affect 

 " the supply and the loss of terrestrial heat as to 



1 Docs this imply internal fluidity? If so, it is to he rejected. 

 " Prodigious" seems too strong a word for any temperature below 

 the melting point of the material. 



'-' 15y no means so : Imt, on the contrary, an essential part of the 

 heat emitted by the composite mass in cooling. 



