Prof. Ferrara on the Earthquakes in Sicily in 1823. 363 



water, for example, under a medium pressure of the atmosphere, is 1728 

 times its first volume, and it increases in the ratio of the heat. At 230° 

 of Fahr. the pressure is equal to four atmospheres only. The explosion of 

 a single barrel of powder, shocks and overthrows the whole vicinity. If, 

 then, a subterranean stream of water falls upon places where volcanic 

 fires are burning, it is at once converted into steam, acquires a density 

 proportioned to the resistance of the mass of earth above it, circulates 

 about, and agitates the most solid mountains and great tracts of land, until, 

 losing its heat in the cavities of the earth, it returns to the state of water, 

 without having given any external marks of its existence. It seems that 

 the return of the terrible phenomenon is owing to the flow of water into 

 places on fire — of water, the streams of which are determined only by ac- 

 cidental causes. 



The vast furnace in the interior of the earth being inflamed, the fire at- 

 tacks every thing exposed to its influence, some are liquefied, while others 

 are converted to vapour ; these, developing their volumes, form a system 

 of force moving with immeasurable power. The subterranean cavities, 

 little able to contain them, are violently convulsed in all their dimensions ; 

 and this effect is transmitted by the solid earth, to distances proportioned 

 to the quantity of force, to the transmissive power of the body moved, and 

 to various local circumstances favourable, or otherwise, to the propagation 

 of motion. After having combated with the obstacles which oppose them, 

 roaring under the earth, like the winds of iEolus, to find an outlet from 

 the places in which they were produced, they circulate in various canals, 

 until a cold temperature deprives them of the heat which gave them such 

 power, and they sink into their former state. Often, however, they drive 

 before them the matter which the heat has liquefied ; and urging it to- 

 wards the ancient mouths of volcanoes, discharge it in flaming rivers 

 in the midst of the terrible phenomena which they themselves produce. 



Urged by the passion for observation, I have often descended into the 

 horrid cavity of the crater, and approached near the blazing brink of the 

 new orifices which have vomited forth streams of fire in my own time; 

 I have seen immense torrents of aqueous vapour urged from the vast chim- 

 ney, whose base is lost in the deep furnaces below ; I have been bathed 

 in the water, to which the vapour was reduced by the low temperature of 

 the atmosphere into which it entered ; often have I seen it fall in fine 

 showers all aroand me. Having penetrated into the recesses of the globe, it 

 is in this manner forced out again by the heat to which it is exposed. I 

 have observed the hydrogen gas ; one time burning with its peculiar 

 colour; at another, bursting forth with a loud, deep explosion ; the sul- 

 phuric and muriatic vapours, whitening the immense clouds of smoke, 

 and filling all the air with their suffocating breath ; or, seizing upon the 

 solid substances around, remaining fixed upon them. Fused substances, 

 forced up by the elastic vapours, are disgorged from the same mouths, 

 spread about in torrents of fire, and consolidated by the contact of the air. 

 Is it not possible that the seat of these products may not be extremely 

 deep, and that yet they may reach the surface ? Who knows, but, in 



