EARTHQUAKES. 181 



gated along the sea-bottom from the shores, and give rise to 

 the terrible sea-waves, of which such memorable examples 

 were furnished by the earthquakes of Lisbon, Callao de Lima, 

 and Chili. When, on the contrary, the earthquakes start 

 from the sea bottom itself, from the realm of Poseidon, the 

 earth-shaker (^ffeiai^Owv, Kivrjot^Owv), and are not accom- 

 panied by upheaval of islands (as in the ephemeral exist- 

 ence of the island of Sabrina or Julia), an unusual rolling 

 and swelling of the waves may still be observed at points 

 where the navigator would feel no shock. The inhabitants of 

 the desert Peruvian coasts have often called my attention to 

 a phenomenon of this kind. Even in the harbour of Callao, 

 and near the opposite island of San Lorenzo, I have seen, 

 wave upon wave suddenly rising up in the course of a few 

 hours to more than 10 or 15 feet, in perfectly still nights, 

 and in this otherwise so thoroughly peaceful part of the South 

 Sea. That such a phenomenon might have been the conse- 

 quence of a storm which had raged far off upon the open sea, 

 was by no means to be supposed in these latitudes. 



To commence from those commotions which are limited 

 to the smallest space, and evidently owe their origin to the 

 activity of a volcano, I may mention in the first place how 

 when sitting at night in the crater of Vesuvius at the foot 

 of a small cone of eruption with my chronometer in my hand, 

 (this was after the great earthquake of Naples on the 26th of 

 July, 1805, and the eruption of lava which took place seven- 

 teen days subsequently), I felt a concussion of the soil of 

 the crater very regularly every 20 or 25 seconds, imme- 

 diately before each eruption of red hot cinders. The cinders, 

 thrown up to a height of 50 60 feet fell back partly into 

 the orifice of eruption, whilst a part of them covered the 

 walls of the cone. The regularity of such a phenomenon 

 renders its observation free from danger. The constantly 

 repeated small earthquake was quite imperceptible beyond 

 the crater, even in the Atrio del Cavallo and in the Her- 

 mitage del Salvatore. The periodicity of the concussion 

 shows that it was dependent upon a determinate degree of 

 tension which the vapours must attain, to enable them to 

 break through the fused mass in the interior of the cone 

 of cinders. In the case just described no concussions were 

 telt on the declivity of the ashy cone of Vesuvius, and in an 



