otion
communicated to it from the earth (172.), then the electric current from
south to north is rendered evident in the first bar, in consequence of its
discharge, at the same time, by means of the second.

182. Upon the supposition that the rotation of the earth tended, by
magneto-electric induction, to cause currents in its own mass, these would,
according to the law (114.) and the experiments, be, upon the surface at
least, from the parts in the neighbourhood of or towards the plane of the
equator, in opposite directions to the poles; and if collectors could be
applied at the equator and at the poles of the globe, as has been done with
the revolving copper plate (150.), and also with magnets (220.), then
negative electricity would be collected at the equator, and positive
electricity at both poles (222.). But without the conductors, or something
equivalent to them, it is evident these currents could not exist, as they
could not be discharged.

183. I did not think it impossible that some natural difference might occur
between bodies, relative to the intensity of the current produced or
tending to be produced in them by magneto-electric induction, which might
be shown by opposing them to each other; especially as Messrs. Arago,
Babbage, Herschel, and Harris, have all found great differences, not only
between the metals and other substances, but between the metals themselves,
in their power of receiving motion from or giving it to a magnet in trials
by revolution (130.). I therefore took two wires, each one hundred and
twenty feet long, one of iron and the other of copper. These were connected
with each other at their ends, and then extended in the direction of the
magnetic meridian, so as to form two nearly parallel lines, nowhere in
contact except at the extremities. The copper wire was then divided in the
middle, and examined by a delicate galvanometer, but no evidence of an
electrical current was obtained.

184. By favour of His Royal Highness the President of the Society, I
obtained the permission of His Majesty to make experiments at the lake in
the gardens of Kensington-palace, for the purpose of comparing, in a
similar manner, water and metal. The basin of this lake is artificial; the
water is supplied by the Chelsea Company; no springs run into it, and it
presented what I required, namely, a uniform mass of still pure water, with
banks ranging nearly from east to west, and from north to south.

185. Two pe