PROSPECTING. 143 



method. It was found that the distribution of potential along the length of 

 the drift, even after an interval of four months, has not materially changed, 

 and that on passing from barren rock toward and across the ore body, 

 small, though decided, variations of potential were encountered in its 

 vicinity. 



"Results. — The electrical effects observed were too distinctly pro- 

 nounced 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 practical 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 suffi- 

 ciently coincident 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 currents in 

 the Richmond mine were not due to the ore bodies is exceedingly improb- 

 able. But unfortunately they are so weak as to require an almost imprac- 

 ticable 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 in Eureka. It is not unlikely, for example, 

 that galena, cinnabar, and the copper sulphosalts 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 investigations in this direction." 



Fig. 5, page 144, represents the plotted curve resulting from Dr. Barus's 

 determination of potentials, and Fig. 6, same page, represents the curve 

 resulting from the plotting of the assay values of the samples taken from 

 the points I., II., up to XVIII. In plotting the electric as well as the assay 

 curve, the linear distances between the points I. and II., I. and III., etc., 

 are taken as the abscissas, the values of the potentials being the ordi- 

 nates in the electric curve, and the assay values being the ordinates in 

 the assay curve. Beyond the point XVIII. no samples were taken, as it 

 was not possible to find Dr. Barus's points. The assays were made some 



