observed in some Metalliferous Veins. 275 



quartz or clay intervened between the plates, and the higher one 

 was on the negative side with respect to horizontal currents." 



I had the honour to assist Mr Fox in the first experiments 

 instituted, and, as he mentions, of making many of those detail- 

 ed in his first paper on the subject; I have subsequently extend- 

 ed them to mines in all parts of Cornwall, making in all fifty- 

 seven different series of observations, of which forty-five were 

 either altogether or in part conducted by me, and the following is 

 a brief generalization of many of the results. 



When points at different depths were connected, in thirteen cases 

 the currents were upward ; and in thirty-five downward. 



In thirty-six experiments the direction has been towards, and 

 twenty-onej^rom, the granite. 



The causes exciting the currents will be our next object of 

 inquiry. 



Tn the Reports of the British Association (III. p. 118) Mr 

 Christie has made an objection to the conclusions drawn by Mr 

 Fox/ which I had previously often urged on that gentleman, 

 viz. that the wires employed might, by contact with the ores, 

 have generated the currents observed. Mr Fox has, however, 

 entirely obviated it by a very well contrived experiment, in 

 which the copper plates were sometimes alternately employed 

 with others of zinc, and in some instances zinc alone were used : 

 the direction of the currents were the same whatever the posi- 

 tions and arrangements of the plates. (Reports, Brit. 4ssoc. 9 

 IV. 572). 



But two opinions have, so far as I know, been yet formed as 

 to the origin of these currents, one, that they are thermo-electric ; 



* There have been no observations on any of this class having a north- 

 easterly dip. 



