494 Mr. Fox's Experiments on Subterranean Electricity 



In some instances the cylinders of copper pyrites were al- 

 lowed to remain in solutions of sulphate of copper in the bent 

 tube for several weeks, when deposits of oxide of iron were 

 found coating the inside of the tube about the negative pole. 

 These results remind one of the ochrey appearance observed 

 in rocks inclosing much vitreous copper, a fact noticed by my 

 friend Joseph Carne ; and it may be worth while to inquire 

 how far the proportion of "gossan" in copper veins may be 

 connected with the quantity of vitreous ore contained in them. 



Since the foregoing experiments were made, I have obtained 

 an electro-type copper plate J^ inch long, l£ wide and J$ of 

 an inch thick, by the agency of these subterranean currents. 

 The apparatus consisted of a porous earthenware vessel, rest- 

 ing on wooden legs in a larger one; both were partly filled 

 with solutions of sulphate of copper, an engraved copper plate 

 attached to the negative wire being placed in the outer vessel, 

 and another plate of copper attached to the positive wire in 

 the inner one. After a few days it was observed that crystals 

 of copper had been formed on the negative plate, but it was 

 nearly two months before the apparatus was removed from the 

 circuit, when the deposited metal was detached from the plate, 

 having received its impression, vi insita terr^. Whilst 

 this experiment was in progress at the surface, the water, as I 

 have before mentioned, invaded the mine, but without inter- 

 rupting the process ; it appeared, indeed, that the electric ac- 

 tion was rather increased than diminished by this circumstance. 



Before the influx of the water, an ore-point in the north vein 

 was connected with rock near the south vein (generally the 

 wall of the vein), and an ore-point in the south vein was like- 

 wise connected with rock near the north vein, in both which 

 cases currents more or less feeble were detected passing to- 

 wards the latter through the wires, which were insulated, as 

 before, by wooden poles stretched at intervals across the gal- 

 leries. It is probable that the moisture on the rocks con- 

 ducted the electricity from the ore to the metal, however im- 

 perfectly, and when different metals, as platinum and zinc, 

 were successively substituted for the copper in contact with 

 the rocks, the currents were modified in their force according 

 to the metal employed, but were seldom changed in their di- 

 rection. The action was most decided when the place of con- 

 tact with the rock was near ore ; and sometimes the end of the 

 wire, or rather the piece of copper attached to it, was rubbed 

 by an assistant against the walls of one of the veins or the sides 

 of a "cross-cut" between them. Under these circumstances 

 the astatic needle was several times suddenly much deflected, 

 and the parts of the rocks from which this increased action 



