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In my obfervations on the pumices of 

 Vulcano I have remarked, that inilead of 

 fwelling in the furnace, and being tranf- 

 formed into an ebullient product, as is al- 

 mod always the cafe with glaffes and comr 

 pad: enamels, they become of lefs bulk, 

 lofe their pores, if they had any before, or, 

 at leaft, contra<St, and therefore become 

 heavier. The prefent pumices do not dif- 

 fer in this refped: from thofe of Vulcano ; 

 and the enamel which they produce in the 

 furnace has a black and fhining ground, in- 

 teifperfed with whitifh fpots, which are 

 feltfpars that, having loft their luftre and 

 tranfparency, are become white. This ena- 

 mel puts the magnetic needle in motion at 

 the diftance of a full line, notvvithftanding 

 that it had no fenfible efFed on it when .in 

 the ftate of pumice. 



There Is no reafon to fuppofe that thefe 

 pumices have ever formed currents, both 

 becaufe they are always found in detached 

 pieces,, and becaufe their pores have not that 

 diredion which is ufually obfervable in 



pumices 



