176 MR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 
very irregular, and were in succession referred to other causes than that sought 
for. The different condition of the water as to purity on the two sides of the 
river ; the difference in temperature ; slight differences in the plates, in the 
solder used, in the more or less perfect contact made by twisting or other- 
wise ; all produced effects in turn : and though I experimented on the water 
passing through the middle arches only ; used platina plates instead of copper ; 
and took every other precaution, I could not after three days obtain any satis- 
factory results. 
190. Theoretically, it seems a necessary consequence that where water is 
flowing, there electric currents should be formed : thus, if a line be imagined 
passing from Dover to Calais through the sea, and returning through the land 
beneath the water to Dover, it traces out a circuit of conducting matter, one 
part of which, when the water moves up or down the channel, is cutting the 
magnetic curves of the earth, whilst the other is relatively at rest. This is a 
repetition of the wire experiment (171.), but with worse conductors. Still 
there is every reason to believe that electric currents do run in the general 
direction of the circuit described, either one way or the other, according as 
the passage of the waters is up or down the channel. Where the lateral ex- 
tent of the moving water is enormously increased, it does not seem improbable 
that the effect should become sensible; and the gulf stream may thus, perhaps, 
from electric currents moving across it, by magneto-electric induction from the 
earth, exert a sensible influence upon the forms of the lines of magnetic 
variation*. 
191. Though positive results have not yet been obtained by the action of the 
earth upon water and aqueous fluids, yet, as the experiments are very limited 
in their extent, and as such fluids do yield the current by artificial magnets 
(23.), (for transference of the current is proof that it maybe produced (213.),) 
the supposition made, that the earth produces these induced currents within 
itself (181.) in consequence of its diurnal rotation, is still highly probable 
(222. 223.) ; and when it is considered that the moving masses extend for 
Theoretically, even a ship or a boat when passing on the surface of the water, in northern or 
southern latitudes, should have currents of electricity running through it directly across the line of 
her motion ; or if the water is flowing past the ship at anchor, similar currents should occur. 
