Metalliferous Veins. 169 



he has observed that positive electricity takes a direction from 

 north to south, although he has seen the contrary in some cases. 

 In veins which dip towards the north, the east is generally posi- 

 tive, and the west negative. He has found, in comparing the 

 relative states of veins at different depths, that the lower sta- 

 tions appear negative in relation to the higher. He has, how- 

 ever, found some exceptions, particularly when a cross-vein of 

 quartz or clay intervenes between the plates. There is, there- 

 fore, no regular order in the direction of the currents. 



If, indeed, there were a progressive increase of negative elec- 

 tricity as we descend in the mines, this phenomenon would 

 agree with the progressive elevation of temperature. The elec- 

 trical effects are not influenced, according to his account, by 

 the presence of workmen and their lights, or by the explosion 

 of gunpowder. Sec. 



All the substances that form part of metalliferous veins are 

 far from possessing the conducting powers necessary to allow 

 the passage of currents transmitted by the metallic portions. 

 He classes among the conductors copper nickel, copper pyrites, 

 vitreous copper-ore, iron pyrites, arsenical pyrites, galena, arse- 

 nical cobalt, the crystallized peroxide of manganese, and tetra- 

 hedral copper- glance (Fahlerz). Among the non-conductors 

 he places the sulphurets of silver, of mercury, of antimony, of 

 bismuth, of arsenic (realgar), of manganese, and of zinc, the 

 combinations of the metals with oxygen and the acids. 



Mr Fox assures us, that he has discovered that the beds of 

 clay-slate (killas) in Cornwall appear to possess the property of 

 conducting free electricity in a slight degree, but only in the 

 direction of their cleavage. This effect can be attributable only 

 to the water interposed. 



With regard to the electric properties of metallic veins, he 

 remarks, that substances which conduct electricity have gene- 

 rally, at least in this country (Cornwall), non-conducting bodies 

 intervening in the veins, between them and the surface. He 

 mentions the tin veins, which are generally intersected by those 

 of copper. When their horizontal bearings do not coincide, the 

 conducting veins traverse the non-conductors. 



Mr Henwood, who has been engaged since Mr Fox in expe- 

 riments on the electric currents in the Cornish mines, has stated, 



