[ 145 ] 



Vrill fufficiently account for its relative heat in winter ; while 

 the decompofition of various minerals at ' confiderable depths, 

 will afford a reafonable explanation of the other phzenomcna : 

 fo that thefe obfervations do not at all neceffarily lead us to 

 believe in the exiftence of a central fire, and experiments 

 made at confiderable depths within the earth, evidently tend to 

 difcountenance it. 



Whatever be the truth, whether the general temperature 

 of the earth be an encreafing, a permanent, or decreafing 

 quantity, it is likely that poflerity will be able to form 

 •a probable conclufion on the fubjcd, from a comparifon of 

 future experiments with thofc of the prefent age. But there 

 is another queftion of fufficient importance to us, which may 

 poflibly admit of an earlier anfwer ; Whether the temperature 

 of particular countries be fubje<St to any confiderable variations, 

 which, in the courfe of ages may be capable of influencing 

 their vegetable and animal produdlions, and the affedions of 

 their atmofphere. 



We have experience enough, even in our temperate ifland, 

 to fatisfy us, that the caufes of heat and cold are not abfolutcly 

 uniform ; fince it never happens that two fuccellive years are 

 alike throughout, in the temperature of their feveral months : 

 Inftances have even frequently occurred, wherein the temperature of 

 the month of January has rivalled the genial warmth of May. 



86 



U We 



