vn the 29th of August, 1874. 133 



in eruptions elsewhere that the outward flow of the lava ceases 

 when the shocks are felt. 



It suffices to mention the earthquakes which agitated the east- 

 ern side of Etna when the external manifestations of the erup- 

 tion of 1865 had just ceased, specially that terrible one in the 

 neighbourhood of Giarre, which destroyed the village called 

 Fondo Macchia. These earthquakes gradually decreased in 

 number and intensity in the direct ratio which is observed in the 

 movement of the lava in an eruption, which by gradually checking 

 itself soon ceases altogether. The eruptive apparatus, still hot and 

 smoking and placed thus along an abyss of lava, we must believe 

 will now remain inactive, and that a great eruption is not to be 

 expected as imminent; since it seems strange to admit that 

 when the intensity of the volcanic force has reached the point of 

 creating this imposing apparatus, it should then have chosen to 

 interrupt its course after a few hours' eruption, in order to 

 resume it again afterwards. The truth is more probably, as I 

 have said, that in the dislocation and breaking up of the conso- 

 lidated strata of the mountain the mass of lava has found a way 

 of penetrating more quietly into the caverns of the earth, devia- 

 ting from the axis of eruption, and deriving its mechanical force 

 from the gases and vapours, from which in time it may acquire 

 such dynamic energy as to cause explosions capable of driving it 

 out to the surface with the ordinary phenomena of eruption. 



It is very probable that a future eruption of Etna, when it 

 takes place, will happen on the side of the mountain already 

 opened, where certainly the lava will find less difficulty in coming 

 to the surface. 



This last eruption of Etna has enriched the history of vol- 

 canoes with a new and important page, and the appearance of 

 this preparation for a great eruption which remains inactive is of 

 interest in the annals of volcanic science. It remains quite un- 

 changed by any emission of volcanic matter, but, remaining fully 

 open, seems to give material testimony to the fact of nature 

 having been surprised and disturbed in one of her great opera- 

 tions. Indeed any one who may wish to form a clear idea of 

 how an explosion in a great volcano, outside of the central crater, 

 begins, and by means of what mechanism it is completed, can 

 now visit and observe with attention the interesting localities of 

 the eruption of August 1874. 



This disturbance of Etna which we have described is not an 

 isolated one in the Italian volcanic system. 



In the nearest island of Vulcano, after a century's inactivity, 

 a new abyss opened in the large crater nine months before the 

 eruption of Etna (from the 20th of September to the 20th of 

 October, 1873). This was accompanied by an eruption of 



