a7id of the Phenomena of Volcanoes. 347 



continued shocks of a sort of hydraulic lever 1400 leagues in 

 length ♦. 



Heretofore certain objections might be brought against this 

 theory, in so far as related to the formation of muriatic acid from 

 the union of hydrogen with chlorine. It was not admitted by 

 chemists, that water was able to decompose a metallic chloride. 

 Berzelius, however, has recently proved by direct experiment, 

 that water does decompose the chloride of silicium (and also that 

 of aluminium. Tr.) 



The heat emanates, as we have said, from the line of contact 

 between the non-oxidized nucleus of the globe, and its oxidized 

 crust, and is attributable, in a great degree, to the chemical ac- 

 tion which takes place in that region. 



We must add, however, that there exists a secondary cause 

 for its production, in the electric currents which result from the 

 contact of two beds composed of heterogeneous materials. Si- 

 milar currents exist even on the earth's surface, as is shown by 

 their influencing the magnetic needle ; but they are less energetic, 

 on account of the slighter conducting power of these oxides. 



Similar effects, we cannot doubt, are taking place equally in 

 the interior, whilst the direction which the currents affect may 

 be suspected to be determined by the action of the sun, which, 

 heating successively different meridians, diminishes in this man- 

 ner for the time the conductibility of the corresponding portions 

 of the more superficial beds of the earth's crust. 



• Mr Lyell, in the last edition of his Principles of Geology, vol. ii. p. 284, 



has combated the doctrine of a central heat upon principles similar to these 



" Granting for a moment," says he, " that the tides in this internal matter 

 can have become so feeble, as to be incapable of lifting up every six hours the 

 fissured shell of the earth, may we not ask, whether during eruptions, jets of 

 lava ought not to be thrown out from the craters of volcanoes, when the tides 

 arise, and whether the same phenomenon would not be more conspicuous in 

 Stromboli, where there is always lava boiling in the crater ? Ought not the 

 fluid, if connected with the interior ocean, to disappear entirely on the ebb- 

 ing of its tides ?" 



The same author suggests an ingenious mode of reconciling the theory of 

 volcanoes which has been advocated above, with his own fundamental prin- 

 cijHe, that the changes going on in the earth are calculated so to counterba- 

 lance each other, as to produce an endless repetition of the same phenomena. 

 He suggests, that the hydrogen resulting from the water decomposed by the 

 alkaline and earthy bases, may react upon the oxides, and by reducing them 

 to tlieir metallic state, fit them for the same purposes again and again." 



