ELECTEICAL ACTIVITY OF ORE BODIES. 323 



strength, so that all the phenomena are identical with those which would be 

 obtained in the laboratory. The eflfect of polarization in distorting the true 

 value of the lode currents was frequently noticed, but it would be super- 

 fluous to repeat the data here. 



It is necessary therefore, in order to obtain satisfactory results, to apply 

 all the refinements that have been developed for problems of this character. 

 In making an attempt of this kind in the mines on the Comstock, however, 

 unusually great difficulties would be encountered. At the outstart, the fact 

 that the observer is compelled to operate with wet hands must be considered 

 as prejudicial to delicate physical experimentation. But there is a more 

 fundamental difficulty. It will be remembered that the ore of the Comstock 

 Lode is argentite accompanied by gold, probably in the metallic state, finely 

 disseminated in quartz. At the time of the experiments the mines without 

 exception were working in comparatively barren parts of the vein, so that 

 there was actually more mineral possibly possessing electrical properties 

 (iron pyrites, etc.) in the rocks than ore in the ore-stopes. In such a case 

 the term "ore body" is scarcely applicable at all. 



The result of circumstances of this kind, regarded from an electrical 

 point of view, can be expressed as follows: Either there will be no electric 

 action at all, since each little granule of ore or pyrite may be considered as 

 surrounded by an insulating envelope of either quartz or country rock — 

 whether the latter be considered as an insulator or an electrolyte is imma- 

 terial — or the whole District, vein and rock, is to be regarded as the field 

 of electric action. In the latter case an equal difficulty occurs, insomuch as 

 within the limited space open to the observer the variation of potential will 

 be inappreciable. In short, from the peculiar distribution of mineral matter, 

 electric excitation is not local in comparison with the space accessible for 

 experimentation. 



The unusual difficulty with which a correct interpretation of results 

 would be attended, not to mention the loss of time occasioned by the fact 

 that, in consequence of the heat, experimentation cannot be long continued, 

 finally induced me to abandon the matter at the Comstock altogether — at 

 least until definite results could be obtained in a more favorable locality. 



