276 Mr Kenwood on the Electric Currents 



the other, voltaic. Both these were alluded to by Mr Fox, who, 

 however, now seems to prefer the latter, and this also appears 

 to be the opinion of Strombeck. If voltaic, they must of course 

 be accompanied by chemical decompositions ; What substances, 

 then, undergo these changes under ground ? Our iron pyrites 

 is a bisulphuret, and very little liable to decompose under ordi- 

 nary circumstances ; and if oxygen were obtained for the pur- 

 pose, we would still have an excess of sulphur to dispose of, of 

 which we found no traces in our veins. The ores of copper, 

 zinc, &c., it may be said, are changing their forms ; why then, 

 when broken out of the lodes, are they so constantly " unsullied 

 and bright ?" We should have expected that decompositions 

 generating such enormous quantities of electricity, would have 

 produced a more visible effect on their surfaces. 



But we have seen that sulphuric salts have not been detected 

 in the mineral waters of Cornwall ; and no one who has descend- 

 ed into the mines has ever been struck by the chemical changes 

 going on ; the sulphate of copper which in such a case should 

 have ,been an abundant product, is scarcely ever met with. It 

 is true that atmospheric influence, aided by the percolating wa- 

 ter, and a rather elevated temperature, would have been ex- 

 pected to induce many chemical changes, but where is the evi- 

 dence of their progress ? 



As a greater development of voltaic electricity would accom- 

 pany an elevation of temperature,* and as the heat increases as 

 we descend, it would follow that the most deeply seated cur- 

 rents should be the most energetic, but nothing of the kind 

 occurs. 



We have no reason to believe that there is any constant differ- 

 ence in the mineral contents of the water in different rocks, and 

 it certainly appears that no general law regulating their exist- 

 ence and nature, has yet been discovered. 



It has, however, been shewn, that the various ores of copper 

 are commonly contained in rocks of different characters, and 

 this would indicate the probability of electric currents being ex- 

 cited, even if the liquid be the same in both cases. 



All .metals and many ores, among the latter the sulphurets of 



* Faraday, 3d series, Phil. Mag. IV., 414. 



