274 Mr Henwood on the Electric Currents 



many which afford copper, and in most cases where there was 

 a continuous mass of copper-ore between the points examined, no 

 electricity was detected. In some instances, however, where all 

 the intervening space consisted of rich copper-ore, most ener- 

 getic action was detected. The general fact, however, appeared 

 to be, that in such cases the currents were most feeble ; and 

 where the continuity of a mass of ore was broken either by an 

 unproductive part of the lode itself, or by a cross-course^ the cur- 

 rents were strongest. Copper pyrites, vitreous copper-ore, black 

 copper-ore, galena, and blende, w r ere among the contents of the 

 veins in which the largest development of electricity obtained. 

 But it is in the metallic parts of the veins alone in which these 

 currents have been detected ; for, notwithstanding the same means 

 were employed both on the earthy contents of the lodes and 

 ON THE ROCKS THEMSELVES (as in the tin veins), no trace of 

 electricity has in any one case been discovered in either of them. 



The lead veins in the carboniferous limestone of North Wales 

 were also found by Mr Fox (Cornwall GeoL Trans. IV. 23.) 

 destitute of electric currents. Herr Von Strombeck has repeat- 

 ed the experiments in some E. and W. veins, traversing the clay- 

 slate and grey wacke-slate near St Goar on the Rhine ; the con- 

 tents of one vein were copper pyrites, grey copper-ore, and 

 galena ; and of the other, carbonate and phosphate of lead, grey 

 copper-ore, brown iron-ore, and a little blende, spathose iron, and 

 galena. In neither case, however, could he detect traces of elec- 

 tricity. (Archivfilr Mineralogie^ fyc. Von Karsten, VI. 431 ; 

 and Bulletin de la Societe Geologique de France, V. 53.) 



In his announcement of the discovery, Mr Fox said (Phil. 

 Trans. 1830, p. 399), " the direction of the positive electricity 

 was in some cases from east to west, and in others from west to 

 east ; and when parallel veins were compared, its general ten- 

 dency was, I think, from north to south, though in several in- 

 stances it was the reverse. In veins having an underlie towards 

 the north, the east was commonly positive with respect to the 

 west ; but in veins dipping towards the south the contrary was 

 observed, with one exception only, and that under unusual cir- 

 cumstances. In comparing the relative states of veins at diffe- 

 rent depths, the lower stations appeared to be negative to the 

 upper ; but exceptions sometimes occurred when a cross vein of 



