water contained in the fissures and 

 cavities of the part falling in would come 

 in contact with the fire and be almost 

 instantly raised into vapour. From the 

 first effort of this vapour, a cavity would 

 be formed (between the melted matter 

 and superincumbent earth) filled with 

 vapour only, before any motion would 

 be perceived at the surface of the earth : 

 this must necessarily happen, on account 

 of the compressibility of all kinds of earth 

 and stones, etc.; but as the compression 

 of the materials immediately over the 

 cavity would be more than sufficient to 

 make them bear the weight of the super- 

 incumbent matter, this compression must 

 be propagated on account of the elasticity 

 of the earth in the same manner as a pulse 

 is propagated through the air. And 

 again, the materials immediately over 

 the cavity, restoring themselves beyond 

 their natural bounds, a dilatation will 

 succeed to the compression; and these 

 two following each other alternately, for 



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