342 GEOLOGY OF TBE COMSTOCK LODE. 



same position relatively to the holes, are usually very nearly of the same 

 value, from which i" generally differs, frequently having even the opposite 

 sign. 



Potential. — Betwccn the values of e for the first three, and for the last 

 three series, there is usually a good agreement. The means (e^ and e.^ of these 

 series, however, often show a lack of accordance which is greater than 

 was expected. The discrepancies occur j^jrincipally in the results obtained 

 on the .'i 00-foot level, and it was at first thought that they were largely to be 

 referred to the fact that a solution of sodic sulphate was used as an outer 

 liquid in the holes. In No. 11, Table XL, for instance, this liquid, instead of 

 soaking into the rock, as usvial, remained in the hole, gradually becoming con- 

 centrated by -evaporation. In the repetition of the experiment, therefore, the 

 exterior liquids in P. C. and X. were not of the same concentration, so that a 

 discrepancy would not seem remarkable. Subsequent experiments, how- 

 ever, hardly corroborated this supposition. Another large difi"erence occurs 

 in the case of No. 27 of the same table; but for this hole it was impossi- 

 ble to obtain constant results, though the experiments were many times 

 repeated. I am at a loss to account for this fact. 



The actual relation between potential and distance will, of course, be 

 exceedingly complex, and it would be little shoit of a waste of time to 

 endeavor with the data at command to arrive at an empirical form for 

 this function. On the other hand, a graphic representation of the change 

 of potential due to a corresponding change of distance is certainly desira- 

 ble. Accordingly, I have discarded more elaborate mathematical means and 

 have represented the relation in question by the following- simple plan: If all 

 points on the 400 and 500-foot levels be joined by straight lines with Point 

 I. oa the 500, the horizontal projections of these will lie within a sector 

 whose center is at I. and whose bounding radii subtend an angle of 31° 

 approximately. It should be noted (Table XII.) that on passing through 

 the ore bodies the variation of bearing is nuich smaller; that it is large 

 both for points near I., where the actual length of arc subtended, however, is 

 small, and for points on the 400-foot level, where, though the actual length 

 of subtended arc is large, as all points are remote from ore ;i smaller change 

 of ])Ot(_'ntial may be expected. Bearing in mind, therefore, that the object 



