ELECTRICAL ACTIVITY OF ORE BODIES. 311 



other respects the method of research was identical with that of Fox. 

 \'. Strombeck made a large number of experiments, but was unable to detect 

 any traces of electric excitation, and, consequently, concludes that Fox's 

 results are not applicable to veins generally, and that even in Cornwall 

 the matter requires further consideration. 



In 1834 Fox again resumed his experiments, with special reference to 

 the objections which had been raised against the validity of his results.^ It 

 having been mooted that the currents observed might in some way owe their 

 origin to the copper contact-plates, he showed that by replacing these by 

 plates of zinc the results remained unaltered. This was the case even when 

 terminals of copper and zinc were used simultaneously. It was, moreover, 

 immaterial whether the contact was produced by plates or whether the ends 

 of tlie wire only were pressed against the vein. By inserting a copper-zinc 

 couple into his circuit Fox found that its effect was in some cases nearly, in 

 others decidedly, overbalanced by the lode currents. Finally, in the interval 

 of four years which had elapsed between these and his former experiments 

 the direction of the currents had remained unchanged. 



In a subsequent paper Fox^ endeavors to classify minerals with refer- 

 ence to their electrical properties. A table of conductivities is contained in 

 his original paper. 



In the Skeers lead mine, near Middleton, Fox^ obtained but feeble 

 currents; at the Coldberry mine, in the same locality, they were absent alto- 

 gether. Lead mines do not in general give evidence of electrical action 

 comparable to that of copper mines — a circumstance which Fox refers to 

 the positions of their ores in liis scale. 



Henwood's^ experiments were made on a larger scale (at times as 

 much as 600 fathoms of copper wire were employed), but otherwise in a way 



'E. W. Fox, "Account of some experiments on the electricity of the copper vein in Huel .Jewel 

 mine." Rep. Br. Assoc, 1834, p. .572. 



-R. W. Fox, "Note on the electric relations of certain metals and metalliferous minerals." Phil. 

 Tr.ans., I., p. 39, 1835. 



■'R. W. Fgx, "Report on some experiments on the electricity of metallic veins, etc." Rep. Br. 

 Assoc, p. 133, 1837. 



* W. J. Henwood, " Surles courauts ^lectriques observes dans les filons de Gomouailles." Aunales 

 des Mines, [3], XL, p. 585, 1837. 



