■Earthquakes in Sicily. 227 



santly belched out towards heaven, and whose approach was 

 announced by horrid roarings and explosions which filled the 

 air to a great distance. Each explosion was accompanied by 

 shocks ; and as the interval between them was of but a few 

 minutes duration, the city and country to a vast extent were 

 in a continued undulation. For many days at Catania, 

 eighteen 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 1 left purposely ajar, kept a 

 continued beating against its side posts The sho. ks lasted 

 as long as the volcano was in operation, that is, for more than 

 nine months ; and when the external phenomena disappear- 

 ed, the internal fire not being yet extinguished, deep subter- 

 ranean rumblings and explosions were heard, and shocks felt 

 at each report. 



When the tire invests substances, it rarefies their masses to 

 a great degree ; the acquisition of new volume produces a 

 proportionate expansion; and under the action of an enor- 

 mous accumulation of inflamed matter, a passage is made for 

 it with sudden and fearful energy. The expansion of 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 110° of Rea. the pressure is equal to four at- 

 mospheres only. The explosion of a single barrel of powder, 

 shocks and overthrows the whole vicinity. If, then, a sub- 

 terranean stream of water happens upon places where vol- 

 canic 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 accidental causes. 



The vast furnace in the interior of the earth being inftamed,^ 

 the fire attacks every thing exposed to its influence, some 

 are liquified, 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 di- 

 mensions ; and this effect is transmitted by the solid earth, 

 to -distances proportioned to the quantity of force, to the 



