THEORY CONFIRMED BY PHENOMENA. 71 



says, " Aqueous vapors are evolved copiously from a crater 

 during eruptions, and often for a long time subsequently to 

 the discharge of scoria and lava. These vapors are con- 

 densed in the cold atmosphere surrounding the high vol- 

 canic peak, and heavy rains are thus caused in countries 

 where, at the same season, and under ordinary circumstan- 

 ces, such a phenomenon is entirely unknown. 



We learn from history, that a heavy shower of sand, 

 pumice, and lapilli, sufficiently great to render Pompeii and 

 Herculaneum uninhabitable, fell for eight successive days 

 and nights, in the year 79, accompanied by violent rains. 



94. Journal of Royal Institution, vol. 1, page 302. 

 Rain and hail in an eruption of Vesuvius, on 25th March, 

 1828, are mentioned, and also on 5th July of same year. 

 Quarterly Jour, of Sci. Lit. and the Arts, vol. 5, page 201. 

 In an eruption of Vesuvius, on 25th December, 1817, there 

 was a hail storm, accompanied with red sand. Jour. Sci. 

 and Arts, vol. 19, page 230. A hail storm occurred during 

 an irruption of Mount J^tna, 21st June, 1813. In vol. 20, 

 page 358, G. Poulettsrope, in a work on volcanoes, says, 

 It must be noticed, that from the action of the volcano on 

 the atmosphere, clouds are generally formed in it, which 

 produce falls of rain, often causing torrents, or even inun- 

 dations. 



95. If the reader will examine the writings of M. Du 

 Carla in the Oserv. sur la Physique, he will find the most 

 triumphant proofs of the influence both of mountains and 

 volcanoes in forming clouds and rain. Indeed, the author 

 goes so far as to say that the eternal rains in Northern Peru 

 around the volcanoes there, which are always in blast, draw 

 away the vapor from Southern Peru, and thus prevent it 

 from raining there. 



96. Cumuli or column clouds are formed in the fol- 

 lowing manner; air at the surface of the ground be- 

 low becomes heated, as it always does in clear, calm days, 



