314 GEOLOGY OF THE COMSTOCK LODE. 



as having been made. It is to be regretted that in none of the papers is 

 there even an attempt toward fully describing the phenomena quantita- 

 tively. Generally, conclusions are drawn from the deflection of a galvano- 

 meter needle without sufficient consideration of the very jJi'obable variation 

 of the resistance of different circuits. The experiments are, moreover, made 

 individually, not in series or with reference to any definite, preorganized 

 plan. Insomuch, however, as most of the work was done when methods of 

 electric measurement were still in their infancy, these matters are not to be 

 mentioned to the disparagement of the authors. In fact, the reader is sur- 

 prised at the broad view usually taken, at the cautiousness with which 

 hypotheses are stated, and at the number of details and chances of error 

 which are considered. 



HYPOTHESIS UNDERLYING THE PRESENT INVESTIGATION. . 



There can be little doubt that the hypothesis which ascribes to ore- 

 currents a hydro-electric origin is perfectly correct. Fox and Reich them- 

 selves found in the case of terminals of copper and zinc used together, the 

 points tapped being in rock, that currents resulted, the direction of which 

 changed with an exchange of the terminals. I have actually measured the 

 electromotive force in action under these circumstances (see page 322), and 

 found it of the same order as that produced by combining these metals with a 

 liquid in the form of a galvanic element. If, then, there are also ores which 

 possess the electric properties of metals — and that this is the case Fox^ went 

 to some trouble to show — the possibility of ore-currents due to hydro- 

 electric action follows as an immediate consequence. These currents will 

 in general have an origin analogous to those technically known as "local 

 currents" in batteries, while at times they may even be due to the occurrence 

 of a complete natural battery. Thermo-electric hypotheses are unnatural, 

 insomuch as with the temperatures met with, even in the Comstock, it 

 would be necessary to assume values for thermo-electric power which, 

 in compai-ison with those of known substances, are abnormally large. Such 



'R. W. Fox, Phil. Trans., 1., p. 39, 1835. 



