SUMMARY. 403 



line of survey, moreover, lay completely outside of the ore body, and all 

 the points tapped were in rock essentially of the same kind. The measure- 

 ments were made in various galvanometric ways, and the results were subse- 

 quently checked by a "zero" method. It was found that the distribution 

 of potential along the length of the drift, even after an interval of four 

 months, had not materially changed, and that, on passing from barren rock 

 towards and across the ore body, small though decided variations of poten- 

 tial were encountered in its vicinity. 



Results. — The electrical effects observed were too distinctly pronounced 

 to be referable to an aggregate of incidental errors, and they were of the 

 character which must have been produced had the ore bodies been the seat 

 of an electromotive force. The experiments made cannot be said to have 

 settled the question as to whether lode currents will or will not be of prac- 

 tical assistance to the prospector. Indeed, as yet it cannot even be asserted 

 with full assurance that the currents obtained are due to the ore bodies. 

 What has been observed is simply a local electrical effect sufficiently coin- 

 cident with the ore body to afford in itself fair grounds for the assumption 

 that these contained the cause. Giving the investigations of Fox and Reich 

 proper weight, however, the supposition that the cun-ents in the Richmond 

 mine were not due to the ore bodies is extremely improbable. But, unfor- 

 tunately, they are so weak as to require an almost impracticable delicacy in 

 the researches designed to detect and estimate them. It is highly probable 

 that under certain circumstances more powerful currents are generated than 

 those found at Eureka. It is not unlikely, for example, that galena, cinna- 

 bar, and the copper sulpho-salts produce electrical effects of far greater 

 magnitude, and that the method might be readily available for the discovery 

 of such ores. The results thus give much encouragement to further inves- 

 tigations in this direction. 



Method proposed. — lu the experiments thus far made, the variation of poten- 

 tial along a single line of electric survey only has been determined. It is 

 obvious, however, that in order to derive the full benefits from such a method a 

 number of these surveys must be cooi-dinated. An endeavor should be made, 

 by passing toward and from the ore body in all directions, actually to deter- 

 mine the contours and positions of the equipotential surfaces. It is not im- 



