soft iron in its place, inversion of the whole produced the same effect.

144. When the soft iron bar was taken out of the helix and inverted in
various directions within four feet of the galvanometer, not the slightest
effect upon it was produced.

145. These phenomena are the necessary consequence of the inductive
magnetic power of the earth, rendering the soft iron cylinder a magnet with
its marked pole downwards. The experiment is analogous to that in which two
bar magnets were used to magnetize the same cylinder in the same helix
(36.), and the inversion of position in the present experiment is
equivalent to a change of the poles in that arrangement. But the result is
not less an instance of the evolution of electricity by means of the
magnetism of the globe.

146. The helix alone was then held permanently in the magnetic direction,
and the soft iron cylinder afterwards introduced; the galvanometer needle
was instantly deflected; by withdrawing the cylinder as the needle
returned, and continuing the two actions simultaneously, the vibrations
soon extended through an arc of 180°. The effect was precisely the same as
that obtained by using a cylinder magnet with its marked pole downwards;
and the direction of motion, &c. was perfectly in accordance with the
results of former experiments obtained with such a magnet (39.). A magnet
in that position being used, gave the same deflections, but stronger. When
the helix was put at right angles to the magnetic direction or dip, then
the introduction or removal of the soft iron cylinder produced no effect at
the needle. Any inclination to the dip gave results of the same kind as
those already described, but increasing in strength as the helix
approximated to the direction of the dip.