On Volcanos and Earthquakes. 19 



and gases are exhausted, when the lava has flowed out for 

 some time, the eruption decreases, and finally is stopped, be- 

 cause the column of lava in the crater, being of a density 

 superior to the water of the sea, chokes the passage, and the 

 volcano must then resume its quiet operation. 



But, why should I endeavour to describe what must hap- 

 pen ? Let us rather ascertain what has happened, and see 

 whether the facts recorded agree with the theory here pre- 

 sented. 



One of the first historians who gives an account of Ve- 

 suvius, is, I believe, Pliny the younger. We read in his 

 Epist. XX. lib. vi. these remarkable words : 



" Preterea mare in se resorberi et tremore terras quasi repelli 

 videbamus. Certe processerat littus, multa animalia maris sic- 

 cis arenis detinebat. Ab altero latere nubes atra et horrenda 

 ignei spiritus tortis vibratisque discursibus rupta, in longas flam* 

 marum figuras dehiscebat ; fulgoribus illse et similes et majores 

 erant." 



The retreat of the sea, and its sudden return by the effect 

 of the elasticity of the fluids, seems to be one of the best as- 

 certained facts. 



Eruption of Vesuvius, 1730, by Nicliolas Cyrillus, Phil. Trans. 



vol. 37. 



*' March 8th. Vesuvius sends forth a great smoke and stream 

 of fire, with hollow rumbling. 9th. The following night Vesu- 

 vius thundered as it were twice. 10th, 11th, 12th. The clouds 

 hide the smoke and fire. 13th. Smoke lessened. 14th. In the 



evening, after eight o'clock, the fire arose to a vast height 



Pumice stones, red hot, of two or more ounces weight, were 

 driven several miles like a shower of hail." 



The blazing flame, hollow rumbling, throwing up of smoke^ 

 ashes, and stone, are but the natural results already antici- 

 pated. 



Collection of various papers concerning Earthquakes felt in Eng- 

 land in \7bO. Phil. Trans, vol. AQ. 

 " The mighty concussion was felt precisely at the same instant 

 of time, being about half an hour after twelve at noon. Let us 

 reflect on the vast extent of this trembling, one hundred miles 

 in length, and forty in breadth, which amount to four thousand 

 square miles in surface. That this should be put into such a^ 



