( 329 ) 



as it was produced, but continually found it 

 to be atmofpheric air, which continued to 

 appear during four hours after the fire be- 

 gan to adt : in the laft four hours none was 



produced. 



Dire£ting my eye along the glafs tube 

 iuted to the neck of the matrafs, I could fee 

 the bottom of that vefTel by the light of the 

 fire which furrounded it ; and, attentively 

 obferving it in that part, I began, after it 

 had remained three quarters of an hour in a 

 ilrong fire, to perceive a flight inflation in 

 the vitreous matter, which afterwards in- 

 creafed, and confifted of tumours that rofe 

 extremely flowly from the furface of the 

 fufed glafs, and funk again as flowly ; and 

 fome of whigh, having attained their great- 

 eft dilatation, burft. This kind of flow 

 ebullition extremely refembled that which, 

 making ufe of the fame glafs and many 

 other volcanic fubftances, I obferved in the 

 crucibles of a glafs furnace ; it continued as 

 long as the intenfity of the heat remained 



the fame. 



When 



