On the Electro-magnetism of Veins of Copper-Ore in Cornwall. 1 7 



face ; but none of that rock is observable in situ nearer than 

 about Glenmalur, eight or ten miles to the westward ; where 

 the interesting phenomenon is observable of regular alterna- 

 tions of granite and mica slate. 



The lode on which the experiment was made is very large, 

 and appears to be more distinctly defined than most of the 

 others. It consists principally of clay and soft clay-slate and 

 friable quartz, through which the ores (chiefly gray copper-ore 

 with some mundic, and a small portion of yellow copper-ore,) 

 traverse in various directions in thick ribs and bunches, the 

 continuous direction of which I could not satisfactorily ascer- 

 tain. The experiment was made on this lode in a level about 

 25 fathoms from the surface, driven about 8 fathoms in a 

 south-west direction from the shaft. The galvanometer being 

 fixed in the level about 4 fathoms in that direction from the 

 shaft, the end of one wire was placed against the ore ground 

 in the " end" or extremity of the level about 4? fathoms further 

 in the same direction, the other end of it being placed in the 

 western receptacle of the instrument. The end of another 

 wire was placed against a mass of ore near the shaft ; and on 

 inserting the opposite extremity of it in the eastern recep- 

 tacle, it had the effect of repelling the north end of the needle 

 towards the west, showing the wire in the western receptacle 

 to be negative, and the other of course positive. The oscil- 

 lations of the needle reached about 18°. 



I am, Gentlemen, yours, &c. 

 Peupellick, near Lostwithiel, Tho. Petherick. 



Jan. 25, 1833. 



IV. On the Electro-magnetism of Veins of Copper-Ore in Corn- 

 wall, By Mr. John Bennetts. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 



CINCE the discovery of electrical currents in the mines of 

 ^ Cornwall, by Mr. R. W. Fox, the galvanometer has been 

 applied to a veins in various copper-mines with more or less 

 effect. 



In my experiments the electro-galvanic action has borne 

 some proportion to the quantity of copper-ore in those parts 

 of the vein with which the wires of the galvanometer have been 

 brought into contact. 



When the vein produces but little copper-ore, I have found 

 but little action ; but my experiments have not been suffi- 

 ciently numerous to lay down a rule as to the relation ex- 



Third Series. Vol. 3. No. 13. July 1833. D 



