6-2 EARTHQUAKES. [Lesson xx xv. 



<luced by the filtration of water, and other causes, 

 they inflame : the inflaming will produce a great 

 quantity of vapourizcd air,the spring of which, com- 

 pressed in a small space, like that of a cavern, will 

 not only shake the earth immediately above, but 

 will search for passages, in order to make its escape. 

 It will therefore naturally force its way through 

 those parts where it meets least obstruction, and 

 will proceed through any channels or caverns 

 where it can find a passage. This subterraneous 

 .air or vapour will also produce in its passage a 

 noise and motion proportioned to its force and 

 the resistance it meets with : and these effects will 

 be continued till it finds a vent, perhaps in the sea, 

 or till its force be diminished by being greatly ex- 

 panded. This explanation corresponds entirely 

 with all the phenomena that are observed respect- 

 ing Earthquakes : for they proceed with a wave- 

 like motion, and are felt at different places, not at 

 the same instant, but at different times in propor- 

 tion to the distance. 



Yet plausible as the above hypothesis may ap- 

 pear, it is objected against by several of the modern 

 philosophers, who, in opposition thereto, assert, 

 that Earthquakes are produced by an accumulation 

 of the electric fluid in the bowels of the earth. 



Mr. Nicholson, in his Introduction to Natural 

 Philosophy, says, t( It is extremely probable, that 

 " Earthquakes owe their original to the discharge 

 " between a cloud and the earth, in a hie;hly elec- 

 " trie state, or even between two clouds." In 

 .support of this opinion, he advances the following 



arguments : 





