ELECTRICAL ACTIVITY OF ORE BODIES. 



339 



Tajsle X — Coiitimu'd. 

 THIRD SERIES. 



FOURTH SERIES. 



FIFTH SERIES. 



SIXTH SERIES: 



' In these cases three consecntive exchanges of the terminals were made, their positions in Nos. 1 and 3 and In Nos. 2 

 ftnd 4 being the same. 



The values for electromotive force contained in Tables VIII. and X. 

 are now to be referred to one and the same origin. For this purpose it 

 will be convenient to select a point having an extreme position Point I., 

 50('-foot level, is of this kind. As there is no means of assigning an abso- 

 lute value to the potential of this point, it may be arbitrarily called zero, in 

 which case the electromotive force between it and any succeeding point will 

 be identical with the potential of tlie latter. In the following table (XI.) 

 the potentials of all the points on the 400 and 600-foot levels have been 



