( 2>d>^ ) 



iv"hen I have fpoken of volcanic produds 

 become ebullient within the crucibles, and 

 alfo of thofe which have pafled into fuch a 

 ftate by the adion of fubterranean fires ; 

 nor do I conceive that it will be contro- 

 verted by any perfons. Whoever has feen 

 fuch produdiions, will admit that this fup- 

 pofition is fupported by the flrongeft evi« 

 dence. 



But what may be the nature of thi$ 

 fluid ? We cannot imagine it to be atmo- 

 fpheric air which occupied the pores of the 

 pulverifed glafs contained in the matrafs, 

 fmce this muft have been expelled at the 

 very beginning of the fufion ; whereas the 

 tumours on the furface of the liquid glafs 

 were produced in the ftrongeft heat of the 

 fire, and continued as long as it remained ; 

 an inconteftable proof that, then, the fluid 

 in queftion copioufly iiivefted and agitated 

 the vitreous mafs. This fluid, likevvife, 

 cannot be called permanent, like the differ- 

 ent aeriform gafes, fince, w^ere it fo, it would 

 have colle(5ted on the mercury. I therefore 



began 



