iS8 



ILLUSTRATIONS OF THE 



Som 



the fuggeftions 

 opaque body like 



:ent experiments, feem to make 

 in this query applicable to an 



nous bod 



earth, as well as to lumi- 



fuch as the fu 



The radiation of heat 



d fixed liars 



here there is no ligh 



was firlt rendered probable by the experiments 

 of M. PicTET of Geneva* ; and the only ob- 

 jedions to which the conclufions from thofe ex- 



la 



;nts feemed liable, are 



ery important difcpver 

 f. From thefe it 



• 



moved by the 



of D 



He 



app 



that heat is 



capable of refradl 



and 



fledion, as well as 



light, fo th 



is not abfurd to fuppofe, that 



the beat of great, denfe, and fixed bodies, may he 

 confer 'ued by the grea nefs of the bodies, and the 

 mutual adion and rjea^lion between them and the 



f 



beat which they e7?iit. 



The exillence of fubterraneous heat is Itill 

 further rendered probable from the refearches 

 of Mairan, which tend fo fhew, that there i? 

 another fource of terreflrial heat befides the in-' 

 fluence of the folar rays J. 



Whatever be the truth with regard to thefe 

 conjectures, it is certain, that the firft and ori- 

 ginal fource of heat is independent or burning. 



Burning is an effedi of the concentration of heat ; 



and 



* Effai fur le Feu. 



f Phil. Tranf. i8co. p. .84. 



t Mem. de TAcad. des Sciences, I'jS^, p. 143 



