Electro-magnetic properties in the mines of Cornivall. 137 



the information on these points which may be found in the pages of 

 the American Journal, it is to be hoped that some of its readers may- 

 contribute something more specific, and accompany their statements 

 with the result of experimental engineers, similar to those detailed in 

 the following abstract. J. G. 



The previous experimental researches of the author on the pro- 

 gressive increase of temperature in mines, suggested to him the opin- 

 ion, that this internal heat, which he has so satisfactorily proved to be 

 augmented with the depth, might be connected with electrical action. 

 The fact of such an action his experiments have clearly established. 



His apparatus consisted of small plates of sheet copper, which 

 were fixed in contact with ore in the veins by copper nails, or press- 

 ed closely against it by wooden props, stretched across the " levels" 

 or galleries. Between two of these plates at different stations, and 

 a galvanometer, a communication was made by means of copper 

 wire, one twentieth of an inch in diameter, which was at first coated 

 with sealing wax ; but this prevention v/as afterwards dispensed with. 

 The galvanometer, used for detecting the electric action, consisted 

 simply of a magnetic needle three and a quarter inches long, one 

 eighth of an inch wide, and one twentieth of an inch thick. It was 

 inclosed in a box four inches square and one inch in depth, having a 

 a plated copper wire, one fiftieth of an inch in diameter, coiled round 

 it twenty five times. No magnet was used to neutralize the terres- 

 trial polarity. In some instances nearly three hundred fathoms of 

 copper wire were employed. 



The intensity of the electro-magnetic action differed greatly in 

 different places ; in some cases the deviation of the needle was in- 

 considerable, in others it went completely round the circle. In gen- 

 eral it was greater, caeteris paribus, in proportion to the greater abun- 

 dance of copper ore in the veins, and in some degree perhaps to the 

 depth of the stations ; and where there was little or no ore, there 

 was little or no action. Hence it seems likely, that electro-magnet- 

 ism may become useful to the practical miner in determining with 

 some degree of probability, at least, the relative quantity of ore in 

 veins, and the directions in which it most abounds. When the dis- 

 tance of the plates from each other in a horizontal direction was onl}'- 

 a few fathoms, and the copper ore between them was plentiful, and 

 uninterrupted by non-conducting substances, or the workings in the 

 mine, no action occurred, owing no doubt to the sood conducting 



Vol. XX.— No. L 18 



