210 COSMOS. 



not a drop of rain falls for ten months together, the natives 

 consider the repeated shocks of earthquakes, which do not 

 endanger the low reed-huts, as auspicious harbingers of fruit- 

 fulness and abundant rain. 



The intimate connexion of the phenomena which we have 

 considered is still hidden in obscurity. Elastic fluids are 

 doubtlessly the cause of the slight and perfectly harmless 

 trembling of the Earth's surface, which has often continued 

 several days (as in. 1816, at Scaccia, in Sicily, before the 

 volcanic elevation of the island of Julia), as well as of the 

 terrific explosions accompanied by loud noise. The focus of 

 this destructive agent, the seat of the moving force, lies far 

 below the Earth's surface ; but we know as little of the extent 

 of this depth as we know of the chemical nature of these 

 vapours that are so highly compressed. At the edges of two 

 craters, Vesuvius and the towering rock which projects beyond 

 the great abyss of Pichincha, near Quito, I have felt periodic 

 and very regular shocks of earthquakes, on each occasion from 

 20 to 30 seconds before the burning scoriae or gases were 

 erupted. The intensity of the shocks were increased in pro- 

 portion to the time intervening between them, and conse- 

 quently to the length of time in which the vapours were 

 accumulating. This simple fact, which has been attested by 

 the evidence of so many travellers, furnishes us with a general 

 solution of the phenomenon, in showing that active volcanoes 

 are to be considered as safety-valves for the immediate neigh- 

 bourhood. The danger of earthquakes increases when the 

 openings of the volcano are closed, and deprived of free com- 

 munication with the atmosphere ; but the destruction of Lisbon, 

 of Caracas, of Lima, of Cashmir in 1554,* and of so many 

 cities of Calabria, Syria, and Asia Minor, shows us, on the 

 whole, that the force of the shock is not the greatest in the 

 neighbourhood of active volcanoes. 



As the impeded activity of the volcano acts upon the shocks 

 of the Earth's surface, so do the latter react on the volcanic 

 phenomena. Openings of fissures favour the rising of cones 

 of eruption, and the processes which take place in these cones, 

 by forming a free communication with the atmosphere. A 



* On the frequency of earthquakes in Cashmir, see Troyer's German 

 translation of the ancient Radjataringini, vol. ii., p. 297, and Carl v. 

 HUgel, Reisen, bd. ii. s. 184. 



