366 VIEWS OF NATURE. 



iii which Herculaneum, Pompeii, and Stabiae were de 

 stroyed. 



The hot aqueous vapour which issued from the crater 

 during the eruption, and diffused itself through the atmosphere 

 formed, on cooling, a dense cloud, which enveloped the column 

 of ashes atfd fire, that rose to an elevation of between 9000 

 and 10,000 feet above the level of the sea. So sudden a 

 condensation of vapour, and, as Gay Lussac has shown, the 

 formation of the cloud itself, tended to increase electric tension. 

 Flashes of forked lightning darted in all directions from the 

 column of ashes, while the rolling thunder might be clearl} 

 distinguished from the deep rumbling sounds within the vol- 

 cano. In no other eruption had the play of the electric force- 

 been so powerfully manifested as on this occasion. 



On the morning of the 26th of October the strange report 

 was circulated that a stream of boiling water was gushing 

 from the crater, and pouring down the cone of cinders. Mon- 

 ticelli, the zealous and learned observer of the volcano, soon 

 perceived that this erroneous report originated in an optical 

 illusion, and that the supposed stream of water was a great 

 quantity of dry ashes which issued like drift sand from a 

 crevice in the highest margin of the crater. The long drought, 

 which had parched and desolated the fields before this erup- 

 tion of Vesuvius, was succeeded, towards the termination of 

 the phenomenon, by a continued and violent rain, occasioned 

 by the volcanic storm which we have just described. A simi- 

 lar phenomenon characterizes the termination of an eruption 

 in all zones of the earth. As the cone of cinders is usually 

 wrapped in clouds at this period, and as the rain is 

 poured forth with most violence near this portion of the vol- 

 cano, streams of mud are generally observed to descend from 

 the sides in all directions. The terrified peasant looks upon 

 them as streams of water that rise from the interior of the 

 volcano and overflow the crater, while the deceived geologist 

 believes that he can recognise in them either sea-water 01 



