The Theory of Explqfions, 75 



to wit, to inquire concerning the immediate caufe of the 

 eruption of volcanoes and of earthquakes. 



Whatever may be the agent which kindles and infl;,mes 

 volcanic fubftances, whether it be the ele(3:ric gas which 

 communicates its fire to thofe moft inflammable fubftances, 

 fuch as fulphur, See. or whether it be the fubterranean heat, 

 which, in making its tfcape, fels fire to thofe fubftances, ftill 

 it is certain that atmofpheric air muft be found in great quan- 

 tities in the interior of volcanoes. For, fince the ever memo- 

 rable difcoveries of Lavoifier, of Pricftley, of Scheele, and of 

 Ingenhouz, on combuftion, it is admitted as a demonftrable 

 truth, that the burning of combuftible fubftances is owing to 

 oxygen; that is to fay, it is fixed and abforbed by the body 

 in combuftion, while the caloric and the light, which are 

 combined with it, efcape, in order to form the fla-me, the 

 light, and the heat. In this manner atmofpheric air is one 

 of the efiential agents in fupporting the fire of a volcano. 



Thefe things being premifed, as foon as a volcano is kin- 

 dled and fet on fire, the atmofpheric air which feeds it, as 

 well as the bafes of fulphur, of water, &c. which are alfo 

 converted to the ftate of gafes by the evolution or accumula- 

 tion of heat, are expanded, and break out with a violence and 

 jmpetuofity not to be reftrained by the force of oppofing 

 bodies, and thereby give birth to earthquakes, &c. 



This theoiy is remarkably countenanced by the common 

 and uniform feries of occurrences which follows the eruption 

 of a volcano. In the firft place, as foon as it is kindled, there 

 appears a thick fmoke ; foon after, when the air, &c. become 

 expanded, ftones of enormous bulk are thrown out to great 

 diftances into the aerial regions, accompanied with earth- 

 quake, and agitation of a!! the furrounding country. As 

 foon as the fuperfiaous air is difcharged and fet free, there 

 fucceeds a bright flame, which feems to reftore ferenity to 

 the abyfs, which again, after a fliort time, vomits forth a 

 Ihower of fiery and deftruftive matters. 



To recapitulate : i. The burfting of veflTels in the freezing 



of water is owing to the efcape of atmofpherical air, which 



alfo feparates the ice into irregular maiTes. ISothing is more 



improbable xh-^xi liie expanfion or incrcafed repellency of the 



L 7, particles 



