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matrafles broken by this fluid from its exu- 

 berance and the refiflance it met with. I 

 afterwards made in the furnace fome expe^ 

 riments more decifive. I caufed three ma- 

 trafles to be made, on purpofe, of clay, 

 the fides of which were an inch thick, and 

 the belly, which I more than half filled 

 with a cellular lava, four inches and three 

 quarters in diameter ; the neck projected 

 in part from the furnace. At the end of 

 eleven hours the three matralTes were broken 

 in the belly, with feveral filTures, through 

 which the lava iflued. Having afterwards 

 broken up the matralTes, I obferved that 

 they were entirely filled with a glafs full of 

 large bubbles, which did not extend beyond 

 about half the neck, becaufe there the heat 

 was no longer iufficient to keep it in fafion. 

 It was eafy to underftand the caufe of the 

 matrafs breaking. The glafs rarefied by 

 the aeriform vapour, the belly being unable 

 to contain it, had rifen into the neck ; but 

 lofing there its fluidity from the cold, it could 

 advance no further ; and, its inflation in- 

 creafing from the vehemence of the heat, 



the 



