ELECTEICAL ACTIVITY OF ORE BODIES. 



361 



In a particular case the intensity /i obtained by connecting- two lioles 

 in the ordinary manner was 



;, = 101:10^ 



A thin strip of platinum was subsequently introduced into one of the holes 



and firndy pressed against its sides. The intensity i, then measured proved 



to be 



i, = 99:10'; 



or, practically, the same as before. An effect due to the platinum was there- 

 fore absent. 



Two holes, about 18 inches apart, were drilled in solid rock and con- 

 nected as usual. The measureinents made for difference of potential, by 

 the original method, gave, in four successive experiments, different bags 

 being used for each, 



1) e = -i- 1:1(/ 



2) e:=-l:10-' 



3) e = ±0:10-' 



4) e = ±0:l(:P, 



or zero, as from the proximity of the holes it ought to be. 



Finally, the potential of a number of points lying between Nos. V and 

 VIL, on the 600-foot level of the Richmond mine, was determined. A zero 

 method being used, it was only necessary to put the terminal bags in con- 

 tact with the rock at the points chosen, by allowing them to recline against 

 the wall. Care was taken to prevent any part of the copper wire from 

 touching it. Two points, A and J5, wei'e thus established between VII. and 

 VI.; three, C, B, and i^, between VI. and V. The following table gives the 

 results, the potential of No. VIII. being put equal to zero, as before: 



Table XX. 



