352 GEOLOGY OF THE COMSTOCK LODE. 



The values for earth-potential again exhibit a marked variation in pass- 

 ing toward the ore-deposit. But, unlike former cases, the passage from points 

 remote to those neai'er the ore-region is one from lower to higher potential. 

 As nothing is known about the distribution of potential with reference to 

 ore bodies, this is not to be regarded as at variance with former results. 

 Not overmuch reliance, however, must be placed on the values of e in this 

 table. They were obtained under unfavorable circumstances, and not 

 checked as in the former cases. 



According to Matteuci,^ a difference of potential exists between points 

 at different levels, in virtue of this fact alone. "Ce courant est ascendant 

 dans la partie mdtallique du circuit ; son intensitt^ augmente i\ mesure que 

 les lignes sont plus longues, et que la difference de niveau entre ces ex- 

 trdmitds est plus grande." But in the present case the direction of the ciu-- 

 rent is not only the opposite of this, but the electromotive force continues 

 to increase even in greater ratio after the highest point of the series has been 

 reached. The effects, therefore, are not such as Matteuci observed. The 

 reader is further referred to page 3 (JO. 



REPETITION OF SOME OF THE EXPERIMENTS AFTER AN INTERVAL 

 OF ABOUT ONE HUNDRED AND THIRTY DAYS. 



The preceding experiments ai'e to be regarded as inconq^lete in two 

 particulars. In the first place, the data are the results of but a single 

 method of measurement, the application of which is not immediately evident; 

 in the second, no criterion of their constancy in point of time has as yet 

 been obtained. The additional results now to be given were obtained on tlie 

 60()-foot level of the Richmond mine, all of the former holes (points tapped), 

 with the single exception of No. I., being used over again. In place of 

 the latter, this having become inaccessible, a fresh hole, about 25 feet to 

 the east of the old one, but also in shale, was drilled. 



The experiments were made after an interval of more than four months 

 from the time at which the original data were obtained. 



Methods. — From an inspection of the magnitude of the electromotive 

 forces contained in the foregoing tables, it will be seen that they fall well 



'Ann. de Chim. et do Phys., (4), T. X., p. 148, 1867. 



