TERRESTRIAL MAGNETO-ELECTRIC INDUCTION. 
175 
against, no effect was obtained; and it appeared that even such dissimilar sub 
stances as water and copper, when cutting the magnetic curves of the earth 
with equal velocity, perfectly neutralized each other’s action. 
187- Mr. Fox of Falmouth has obtained some highly important results re- 
specting the electricity of metalliferous veins in the mines of Cornwall, which 
have been published in the Philosophical Transactions*. I have examined 
the paper with a view to ascertain whether any of the effects were probably 
referable to magneto-electric induction ; but, though unable to form a very 
strong opinion, believe they are not. When parallel veins running east and 
west were compared, the general tendency of the electricity in the wires was 
from north to south ; when the comparison was made between parts towards 
the surface and at some depth, the current of electricity in the wires was from 
above downwards. If there should be any natural difference in the force of 
the electric currents produced by magneto-electric induction in different sub- 
stances, or substances in different positions moving with the earth, and which 
might be rendered evident by increasing the masses acted upon, then the wires 
and veins experimented with by Mr. Fox might perhaps have acted as dis- 
chargers to the electricity of the mass of strata included between them, and 
the directions of the currents would be those observed as above. 
188. Although the electricity obtained by magneto-electric induction in a 
few feet of wire is of but small intensity, and has not as yet been observed ex- 
cept in metals, and carbon in a particular state, still it has power to pass 
through brine (23.) ; and, as increased length in the substance acted upon pro- 
duces increase of intensity, I hoped to obtain effects from extensive moving- 
masses of water, though still water gave none. I made experiments therefore 
(by favour) at Waterloo Bridge, extending a copper wire nine hundred and 
sixty feet in length upon the parapet of the bridge, and dropping from its ex- 
tremities other wires with extensive plates of metal attached to them to com- 
plete contact with the water. The wire therefore and the water made one con- 
ducting circuit ; and as the water ebbed or flowed with the tide, I hoped to 
obtain currents analogous to those of the brass ball (161.). 
189. I constantly obtained deflections at the galvanometer, but they were 
* 1830. p. 399. 
