( 3^5 ) 



not before in pofleflion ; but I do not con- 

 lider the problem as undeniably folved ; 

 lince to thefe facts a great number of others 

 of a contrary nature may be oppofed, of 

 which, as they are related by writers well 

 deferving credit, I cannot omit the exami- 

 nation. I (hall impartially confider the 

 weight of each, and afterwards give my 

 fincere and unbiaiTed opinion* 



Thefe two fubjeds I (hall proceed to 

 confider in two chapters, between which 

 i (hall infert a very fhort one, containing 

 an account of a chemical difcovery made ia 

 the courfe of my experiments. Thefe will 

 conclude my enquiries relative to thefs 

 truly terrific phenomena. 



Having obferved that the bubbles, vacui- 

 ties and tumours, which are generated by 

 aeriform fluids in many lavas, glafles, and 

 enamels, are likewife produced by the fame 

 fluids in the fame bodies, when expofed to 

 common fire ; I determined to avail myfelf 

 of that means to difcover the nature of 

 Y 3 thefe 



