ELECTRICAL ACTIVITY OF ORE BODIES. 365 



CONCLUDING REMARKS. 



On reviewing the results described it is strikingly evident that the 

 electromotive forces met with are invariably small, very frequently, indeed, 

 quite at the limit of the accurately measurable. It is true that the elec- 

 trically active material was probably galena, which, as Fox long ago ol)- 

 served, is unfavorable for observations like the present. It is a question, 

 however, whether results much larger than these will generally be obtained. 

 I cannot believe that Reich's earnest appeal for general research in the 

 direction of electric prospecting has been altogether disregarded. There 

 is much more to lead one to infer that many undertook the study of the 

 question, but, disappointed with feeble reactions and discordant results, 

 abandoned the matter altogether. Reich, at the end of his last paper, 

 gives a list of the apparatus desirable, which, however, except whei-e the 

 action is so intense as it was found to be in Cornwall, and to a less extent 

 at Freiberg, would certainly be insufficient. 



The very large currents obtained in the localities just mentioned ren- 

 dered it not improbable, at the outstart of the present investigation, that 

 important conclusions might be drawn from the results of a minute mag- 

 netic survey^ of the interior of the mines, or across the vein on the surface; 

 and preparations for such a purpose were, in fact, made. But the currents 

 obtained galvanometrically dictated the abandonment of this project. 



The study of the electric activity of ore bodies should be carried out 

 on a broader basis than was possible in the present case, to reach the best 

 results. A single line of survey, or the investigation of the variation of 

 potential in a single drift, is far from sufficient. The endeavor should be 

 made to map the equipotentials as surfaces traversing the whole mine, care- 

 fully considering their position and contour relatively to any ore already 

 in sight, and their change of form on leaving it. The inferences to be drawn 

 herefrom would certainly compare in value with those of a purely geological 



'Fox himself entertained an idea of this kind. 



