232 ELECTEICITY A SOUECE OF VOLCANIC HEAT. [Ch.XXXIII 



from 



may 



loerhaps, be one of the principal means by 

 whicli heat lost by conduction into space may be restored to 

 tlie planet ; and we may easily imagine that at successive 



geological periods^ when 



mountain chains have been 

 en removed bv snb<^irlA-npa n-i^ 



denudation, when even oceans and continents have chano-ed 

 places, the circulation of electro-magnetic currents and the 

 local concentration of heat due to them may affect new parts 

 of the exterior of the planet. It is scarcely possible to exao-- 



amount 



here alluded to may give rise. ' The silent and slow operation 

 of electricity as a chemical agent is more important/ says 

 Davy, ' in the economy of nature than its grand and impressive 

 operation in lightning and thunder. It may be considered, 

 not only as directly producing an infinite variety of changes, 

 but as influencing almost all which take place ; it would 

 seem, indeed, that chemical attraction itself is only a peculiar 

 form of the exhibition of electrical attraction.' ^ 



Thermo-electricity may be generated by great inequalities 

 of temperature, arising from a partial distribution of volcanic 

 heat. Wherever, for example, masses of rock occur of great 

 horizontal extent, and of considerable depth, which are at 

 one point in a state of fusion (as beneath some active volcano); 

 at another, red-hot ; and at a third, comparatively cold- 



mo 



nean electric currents, if once excited, 



decomposin 



ma} 



Chemical action. 



H 



metallic bases of the earths and alkalies, he threw out the 

 idea that stores of those metals might abound in an tui- 

 oxidised state in the subterranean regions to which water 

 must occasionally penetrate. Whenever this happened, 

 gaseous matter would be set free, the metals would combine 



sufficient 



melt 



o 



» 



This hypothesis was 



chemist 



* Consolations in Travel, p. 271. 



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IS 



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 carbonate 



reverse o 

 resulted 

 The same 

 of heat d 

 a mass o 

 tlierefure 

 active vo^ 

 of eniptit 

 M, Fou 



sheet of 

 access, cei 



the lov.-fr 



state, and 



shiftin 



enveh^ 



^foiin 

 latiou 



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different 



of 



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