iv/iich ovcurred in Sicili/ in March 1823. 169 



teen miles distant, we were rocked as though we had been 

 upon the sea. Some of the shocks were very violent. The 

 door of my chamber, which I left purposely a-jar, kept a con- 

 tinued beating against its side posts. The shocks lasted as 

 long as the volcano was in operation ; and when the external 

 phaenomena disappeared, the internal fire not being yet ex- 

 tinguished, deep subterranean rumblings and explosions were 

 heard, and shocks felt at each report. 



When the fire invests substances, it rarefies their masses to 

 a great degree; the acquisition of new volume produces a pro- 

 portionate expansion ; and under the action of an enormous 

 accumulation of inflamed matter, a passage is made for it with 

 sudden and fearful energy. The expansion of water, for ex- 

 ample, under a medium pressure of the atmosphere, is 1 728 

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

 At 110° of Reaum. the pressure is equal to four atmospheres 

 only. The explosion of a single barrel of gunpowder shocks and 

 overthrows the whole vicinity. If, then, a subterranean stream 

 of water happens upon places where volcanic fires are burning, 

 it is at once conveited into steam, acquires a density propor- 

 tioned to the resistance of the mass of earth above it, circu- 

 lates about, and agitates the m(;st 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 ex- 

 ternal marks of its existence. It seems that the return of the 

 terrible phaenomenon is owing to the flow of water into places 

 on fire — of water, the streams of which are determined only 

 by accidental causes. 



The vast furnace in the interior of the earth being inflamed, 

 the fire attacks every thing exposed to its influence: some are 

 liquefied, while others are converted to vapour; these, deve- 

 loping their volumes, form a system of force moving with im- 

 measurable 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 

 propoitioned to the quantity of force, to the transmissive power 

 of the body moved, and to various local circumstances favour- 

 able or otherwise to the jiropagation of motion. After having 

 combated with the obstacles which oppose roaring mider the 

 earth like the winds of .Eolus, 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 powei', and they sink into their former state. Oiten, 

 however, they drive befon; them the matter which tlie heat 

 has li(|uefiecl ; and urging it towards the ancient mouths of 



Vol. ().j. Xo.32rJ. 7V/r/rr// 182.'5. Y volcanos. 



