312 GEOLOGY OP THE COMSTOCK LODE. 



analogous to that of Fox. They contain a thorough corroboration of the 

 results of the latter. He, moreover, insists that currents are only obtained 

 in the ease where the points tapped are in vein matter, being most decisive 

 for copper pyrites, vitreous and black copper ore, galena and blende; that 

 between points in barren rock electric action is altogether absent. After a 

 number of theoretical considerations — to which the paper is largely devoted — 

 he concludes that the currents are probably of thermo-electric origin, and 

 that they are certainly purely local. 



Some time after, all of Fox's experiments were again repeated and the 

 results confirmed throughout by Reich.^ Although the heating of one of 

 the points of contact in the case where both were applied to the same vein 

 produced a decided thermo-electric effect, quantitatively this was so small as 

 to furnish grounds against Kenwood's hypothesis. Reich is convinced that 

 Fox's currents are hydro-electric phenomena. When a point in ore was con- 

 nected with one in rock, the currents were not only much smaller — proba- 

 bly on account of the greater resistance in this case — but if plates of copper 

 and zinc were used together as terminals, a commutation of these invariably 

 produced a corresponding change in the direction of the current. 



In Fox's last paper on the subject, the effect of the cont-act plates is 

 again carefully considered. But even with one terminal of zinc, the other 

 of copper, "the current continued to deflect the needle from 50° to 60°, 

 notwithstanding that any action between the copper * * * * and the 

 zinc * * * * if it had existed would have been in the opposite direction 

 and have tended more or less to counteract the influence of the actual cur- 

 rent." The galvanometer referred to consisted of forty-eight turns of brass 

 wire wrapped around a 2-inch needle, on a pivot. The lode current in a case 

 observed was found to remain constant for a period of eight months. Toward 

 the end of the paper mention is made of experiments in which one or both 

 terminals were in rock. In this case the results were similar to those of 



'F. Reich, "Notizubcr elektrische Stiiime auf Erzgiingeu." Pogg. Auu., XLVIII., p. 287, 183!). 

 'R. W. Fox, "Some experiments on subterranean electricity, made at Pennance mine near Fal- 

 mouth." Phil. Mag., [3], XXIII., pp. 457 and 491, ie43. 



