On the Electro-magnetic Properties of metalliferous Veins in the Mines 

 of Cornwall. By Robert Were Fox, of Falmouth. Communicated 

 by the President. Read June 10, 1830. [Phil. Trans. 1830, p. 399.] 



The author having been led from theory to entertain the belief 

 that a connexion existed between electric action in the interior of 

 the earth, and the arrangement of metalliferous veins, and also the 

 progressive increase of temperature in the strata of the earth "jas we 

 descend from the surface, proceeded to the verification of this opinion 

 by experiment. His first trial was unsuccessful ; but in the second 

 he obtained decisive evidence of considerable electrical action in the 

 mine of Huel Jewel in Cornwall. His apparatus consisted of small 

 plates of sheet copper, which were fixed in contact with one in the 

 veins by copper nails, or else wedged closely against them with wood- 

 en props stretched across the galleries. Between two of these plates 

 at different stations, a communication was made by means of copper 

 wire one twentieth of an inch in diameter, which included a gal- 

 vanometer in its circuit. In some instances, 300 fathoms of copper 

 wire were employed. 



The intensity of the electric currents was found to differ consider- 

 ably in different places ; it was generally greater in proportion to 

 the greater abundance of copper ore in the veins, and in some de- 

 gree also to the depth of the stations. Hence the discovery of the 

 author seems likely to be of practical utility to the miner in discover- 

 ing the relative quantity of ore in veins, and the directions in which 

 it most abounds. The electricity thus perpetually in action hi mines 

 does not appear to be influenced by the presence of the workmen 

 and candles, or even by the explosion of gunpowder in blasting. 



The author's experiments enable him to give a table of the relative 

 powers of conducting galvanic electricity possessed by various metal- 

 liferous minerals. This power, he remarks, appears to bear no ob- 

 vious relation to any of the electrical or other physical properties of 

 the metals themselves, when in a proper state, or to the proportions 

 in which they exist in combination. He proceeds to point out va- 

 rious facts relative to the position of veins, and . the arrangement of 

 their contents, which he thinks are irreconcileable with any of the 

 hypotheses that have been devised to explain their origin. 



He observes that ores which conduct electricity have generally 

 some conducting substances interposed in the veins between them 

 and the surface ; a structure that appears to bear a striking analogy 

 to the ordinary galvanic combinations. He is of opinion that the 

 intensities both of heat and of electricity, and consequently of mag- 

 netism, increase in proportion to the depths of the strata under the 

 surface of the earth ; that they have an intimate connexion with one 

 another ; and that the discovery of electrical currents in various and 

 frequently opposite directions, in different parts of the same mine, 

 may perhaps, hereafter, afford a clue to explain the declination and 

 variation of the magnetic needle. 



