18 On Volcanos and Earthquakes. 



ing ; minerals, sand, and stones are melting, vitrifying, ancJ 

 running at the bottom of the cavern in the shape of lava, of 

 wliich it forms a permanent lake in fusion, just as melted iron 

 is collected at the bottom of a casting furnace. These things 

 being in this situation, if a sudden vacuum is produced, what 

 will happen ? But I may be stopped here, and be asked, 

 how can a sudden vacuum be produced ? I see many cau- 

 ses why it may, but the most simple and natural, and conse- 

 quently the least objectionable one, is, that after a certain 

 time, a number of years that cannot be foreseen, for it is not 

 periodical, a layer of the coal being burnt, reduced to ashes, 

 the mineral to lava, the ground above, no longer supported, 

 crumbles down, with a rumbling noise ; a new surface of 

 cold ground is put in contact with the overheated air and 

 vapours, and a sudden condensation is produced ; a partial 

 vacuum follows : it is so sudden, that it communicates a 

 tremor to the surrounding ground, which is felt as the first 

 shock of an earthquake. This vacuum produces in its turn 

 a violent aspiration, that brings down the water of the sea 

 itself, and of all the streams that may communicate with that 

 furnace. Then, a reverse effect is produced ; water coming 

 in contact with the melted lava and the burning coals, is 

 acted upon in two different ways ; a part is vaporised, and 

 another part decomposed ; steam and hydrogen gas are pro- 

 duced in immense abimdance ; these fluids must open their 

 passage ; water is repulsed back into the sea, which rises 

 above its natural level, under the appearance of a huge tide 

 or wave ; another part may be thrown off through the gap- 

 ing ground, and even may issue mixed with the flames of the 

 mountains. In the meanwhile, new shocks are felt, until the 

 weakest point has yielded to the combined powers of the 

 steam and gases, actuated by the heat and a pressure of eight 

 hundred atmospheres. Generally, the former crater, filled 

 in part with loose stones, lava, and ashes of the preceding- 

 eruption, is the weakest point ; all is thrown up ; a column 

 of fire, produced by the burning hydrogen, is raised to the 

 clouds; ashes, the result perhaps of twenty years' combustion, 

 in sufficient quantity to bury villages and cities, and stones 

 of ail sizes, loosened, are projected to an immense distance ; 

 and, finally, the lava, swept away by the steam, gases, and 

 blowing air, is raised up to the summit of the crater, or runs 

 on one side of the mountain, after having broken open a pas- 

 sage by its enormous mass and weight. When the steam 



