XXV. On the electro-magnetic properties of metalliferous veins in the mines 
of Cornwall. By Robert Were Fox of Falmouth. Communicated hy the 
President. 
Read June 10th, 1830. 
In one of my communications to the Cornwall Geological Society on the 
high temperature of the interior of the earth, I ventured to express a belief that 
mineral veins, and the internal heat, are connected with electrical action. This 
opinion, founded as it was on the curious arrangement of the veins, &c. in pri- 
mitive rocks, I have had the satisfaction to find confirmed by experiments 
made in some of the mines of Cornwall; and, I doubt not that the existence of 
electricity in metalliferous veins similarly circumstanced, and capable of con- 
ducting it, will prove to be as universal a fact, as the progressive increase of 
temperature under the earth’s surface is now admitted to be, much as my 
conclusions on this point were at one time controverted. 
In my first experiment I did not succeed in detecting any electricity; but in 
my second I had the gratification to observe considerable electrical action. 
My apparatus consisted of small plates of sheet copper, which were fixed in 
contact with ore in the veins by copper nails, or pressed 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 afterwards this precaution was dispensed 
with. 
* It may be proper to describe the galvanometer employed in making many of my electro-magnetic 
experiments. The magnetic needle was three inches and a quarter long, one-eighth of an inch wide, 
and one-twenty-eighth thick. It was inclosed in a box four inches square and one inch in depth, 
having a plated copper wire one-fiftieth of an inch in diameter coiled round it twenty-five times. No 
magnet was used to neutralize the terrestrial polarity. In my earlier experiments a less delicate gal- 
vanometer was employed. 
3 F 
MDCCCXXX. 
