Metalliferous Veins. 171 



portions at different depths, the currents have in thirteen in- 

 stances been upward, and in thirty-five cases downward. 



In thirty- six experiments the current has been towards the 

 granite, and in twenty-one others it has taken an opposite 

 direction. 



We are not aware whether Messrs Fox and Henwood have, 

 in their experiments, sufficiently guarded against all the causes 

 of error which present themselves when we seek for the exist- 

 ence of electro-chemical currents by means of the multiplier. 

 The results they have announced are of such importance as 

 regards the electro-chemical re-actions which operate in veins, 

 that we must discuss them. 



To enable the reader to judge and appreciate the accuracy of 

 Mr Fox's process, we will remind him, that when two plates of 

 platina, in communication with the extremities of the wire of a 

 multiplier, are immersed in distilled water, a current is imme- 

 diately produced by the difference of the actions exercised by 

 the liquid on the foreign bodies adhering to the surfaces of the 

 plates. This effect almost invariably takes place when the pre- 

 caution is not taken to remove the foreign substances which 

 adhere to the surfaces of the platina when they are taken out 

 of the water. If, instead of platina, we employ copper, the 

 current is still more decided. As the surfaces are not the same, 

 the water affects them differently. 



Now Mr Fox, in his experiments, has used plates of copper 

 and he has attached them to the metalliferous veins with iron* 

 nails, or strongly pressed them on by means of wooden stays. 

 These two plates are connected with a multiplier by means of 

 a copper wire. 



Might it not happen, that the water which adheres more or 

 less to the sides of the mine galleries, and which does not every 

 where contain the same salts, might have the same effect on the 

 copper as in the experiment just described ? It would be \ery 

 desirable for Mr Fox to make his experiments on perfectly dry 

 conductors of electricity. The objection which we have just 

 made would thus be obviated.-|- 



* Note on page 168. 



+ There was no moisture except in the air, where a current was detected 

 in Levant Mine. W. J. H. 



