TRANSACTIONS OF THE SECTIONS. 35 



was let out till it reached to the second point of contact, near which 

 the multiplier was placed, and the two ends of the fine wires connected 

 with it. The multiplier, with double needle, and very sensible, be- 

 longed to a thermo-electric apparatus of Melloni, made by Oertling of 

 Berlin. In order in some measure to judge of its delicacy, it may be 

 mentioned, that a current, from a pair of zinc and copper plates of 

 only one inch square, placed in water very weakly acidulated, drove 

 the needle up to the button, placed at 90°, to prevent further deviation ; 

 that an iron wire connected with two brass wires, placed in the multi- 

 plier, by the mere heating with the hand of the point of contact, pro- 

 duced a deviation of from 10° to 20°, according to the temperature 

 communicated. The following results were obtained: — 1. Two ore 

 points, separated by a non-metalliferous mass, or between which there 

 occurs a cross vein, or a space where the vein is worked out, give rise 

 to an electric current in a metallic wire connecting them. This law 

 was determined by seventeen experiments with every variety in them, 

 so as to obviate all objections. 2. Two ore points, in uninterrupted 

 metallic connection with one another, induce no electrical current 

 through a wire connecting them. 3. If only one disc be connected 

 with an ore point, and the other with the timbering, or be held in the 

 hand, there is no effect produced on the multiplier. This result was 

 confirmed several times. 4. If an ore point be connected with masses 

 of ore already won, a current sometimes manifests itself, and sometimes 

 there is none. 5. When an ore point is connected with non-metallife- 

 rous rock, frequently no current takes place ; frequently, however, a 

 current, always feeble, occurs in the connecting wire. This result does 

 not agree with that of Fox and Hen wood, who never detected a cur- 

 rent. Professor Reich performed the experiment eighteen times. 



With respect to the cause of the electrical currents, observed in 

 metalliferous veins, three difi^erent opinions have been broached. 

 They have been ascribed, 1, to general electric currents at the earth's 

 surface, produced either entirely or in part by the earth's magnetism : 

 2, to hydro-electric, and 3, to thermo-electric actions of the various 

 metallic components of the vein. The first hypothesis, according to 

 Reich, is refuted by the independence of the direction of the currents 

 on their position relatively to the earth's axis. Thermo-magnetism he 

 holds to be incapable of producing such strong currents, as the strong- 

 est currents are observed exactly where the two points were separated 

 by a non-metallic conductor; and he concludes that there remains 

 only the hydro-electric action of the metallic components of the vein 

 to account for the phenomena. In respect to the extent of the devia- 

 tion of the multiplier, it is to be borne in mind, that there can be no 

 immediate conclusion drawn from this as to the electric difference of 

 the substances coming into play ; for it depends on the resistance to 

 conduction in the entire circuit, which again depends on the dimensions 

 and nature of the intervening rock, as also on the more or less perfect 

 contact between the copper disc and the ore, and between the disc 

 and the wire. 



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