rmously
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[A].

[A] 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.

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
may be 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 thousands of miles across the magnetic
curves, cutting them in various directions within its mass, as well as at
the surface, it is possible the electricity may rise to considerable
intensity.

192. I hardly dare venture, even in the most hypothetical form, to ask
whether the Aurora Borealis and Australia may not be the discharge of
electricity, thus urged towards the poles of the earth, from whence it is
endeavouring to return by natural and appointed means above the earth to
the equatorial regions. The non-occurrence of it in very high latitudes is
not at all against the supposition; and it is remarkable that Mr. Fox, who
observed the deflections of the magnetic needle at Falmouth, by the Aurora
Borealis, gives that direction of it which perfectly agrees with the
present view. He states that all the variations at night were towards the
east[A], and this is what would happen if electric currents were setting
from south to north in the earth under the needle, or from north to south
in space above it.

[A] Philosophical Transactions, 1831, p. 202.

S 6. _General remarks and illustrations of the Force and Direction of
Magneto-electric Induction._

193. In the repetition and variation of Arago's experiment by Messrs.
Babbage, Herschel, and Harris, these philosophers directed their attent