made in Pennance Mine. 493 



circuit acting in an opposite direction to the electricity from 

 the mine, the deflection showed a difference in favour of the 

 latter, and indeed this was the case when the interposed cloth 

 was moistened by a very weak solution of common salt. 



The electro-magnetic and decomposing effects of these sub- 

 terranean currents also afforded unequivocal evidence of their 

 energy. A helix of copper wire fixed round a small horse- 

 shoe-shaped bar of iron, was placed in the circuit formed by 

 the wires from the veins, when the bar became so magnetized 

 as to cause a compass needle l| inch long, at the distance of 

 nearly half an inch, to oscillate through an arc of about 70°, 

 when the circuit was alternately made and broken a few times. 



A solution of hydriodide of potash was found to have been 

 decomposed after it had been left in the circuit for rather more 

 than a day. 



The endosmose action occurred in various experiments, but 

 it may be sufficient to give one example. Sulphate of copper 

 in solution was put into both branches of a U-shaped glass 

 tube with clay in the bent part of it, the surface of the fluid 

 in one branch standing half an inch above that in the other. A 

 piece of silver wire was plunged into each of them, the upper 

 end passing out through sealing wax, with which the extremi- 

 ties of the tube were stopped, and the apparatus was placed 

 upright in the circuit, with the wire in the higher column of 

 the fluid connected with the negative wire. In the course of 

 a few days this column was found to have risen one-eighth of 

 an inch, the other having fallen in an equal degree, showing 

 that the greater pressure of the higher column was superseded 

 by the force of the electric action. 



When small cylinders of copper pyrites were substituted 

 for the silver wires in the branches of the bent tube, not only 

 did the endosmose action occur, but the copper ore, forming 

 the negative pole, had its surface gradually changed to vitreous 

 copper in the course of two or three days*, the other ore-pole 

 remaining unaltered. The same change was produced, and 

 apparently with equal facility, when solutions of other salts, as 

 carbonate of soda or common salt, were substituted for that of 

 sulphate of copper in both branches of the tube. The cylin- 

 ders of copper pyrites used in these experiments were long 

 enough for the upper ends to project above the mouths of the 

 tube, where the opposite wires were attached to them respect- 

 ively, and these were well coated with sealing-wax dissolved 

 in alcohol, to prevent the access of moisture to any part of the 

 metal, and indeed all but the lower portions of the ore were 

 coated in like manner. 

 * Some of the ore thus changed was at the last Polytechnic Exhibition. 



