Professor de la Rive on Electricity. 277 



escape from volcanoes, are altogether favourable to this opinion. 

 Latterly M. Boussingault, at the termination of his chemical 

 researches upon the nature of the elastic fluids which are disen- 

 gaged from the volcanoes near the equator, has found that these 

 fluids are the same in the different volcanoes, namely, that they 

 consist of watery vapour in very large quantity, of carbonic acid, 

 and hydro-sulphuric acid gases, and sometimes of sulphureous 

 vapours. The presence of hydrogen shews, that there must have 

 been decomposition of water, and that of sulphur, that this sub- 

 stance is found mixed, on the surface of the metallic nucleus, 

 along with the highly oxidable metals of which the nucleus is 

 probably formed. This union is still more natural, inasmuch 

 as the temperatures at which sulphur and these metals become 

 solid very nearly approximate. An analysis of the mineral 

 springs of the Cordilleras, for which we are also indebted to M. 

 Boussingault, has proved that they contain sulphuretted hydrogen 

 gas, as in truth, nearly almost all mineral springs do ; which 

 seems to demonstrate that they proceed from vapours and gases 

 which, arising from the surface of the affected metallic nucleus, 

 find their way through the fissures, and condense themselves in 

 the cavities which the mountains contain, whence finally they 

 flow into the plains. The presence of carbonic acid, which al- 

 most invariably accompanies the sulphuretted hydrogen gas, is 

 probably owing to carbonates, which lie in the neighbourhood of 

 the bed that is attacked, and which are decomposed by the 

 strong heat which the chemical action generates. 



The result of the preceding short exposition, viz. that there 

 exists a chemical action which is going forward at a certain 

 depth beneath the surface of the earth, seems thus to be demon- 

 strated. Hence not only volcanoes, and earthquakes, and mi- 

 neral springs, and the increase of temperature as we penetrate 

 into the oxidised crust, become of easy explication, but the pro- 

 duction of electrical currents becomes a necessary consequence of 

 the same chemical action. As to the general direction of the 

 currents, it will depend upon the relative position of the nega- 

 tive elements, which are the substances already oxidated, and 

 the positive elements, which are the metals of which the surface 

 of the nucleus is formed ; and as this position may change, we 

 ^an understand how the variations in the direction of the needle 



