n inverted; and by doing this two or three times,
making the inversions and vibrations to coincide, the needle swung through
an arc of 150 deg. or 160 deg..

142. When one end of the helix, which may be called A, was uppermost at
first (B end consequently being below), then it mattered not in which
direction it proceeded during the inversion, whether to the right hand or
left hand, or through any other course; still the galvanometer needle
passed in the same direction. Again, when B end was uppermost, the
inversion of the helix and bar in any direction always caused the needle to
be deflected one way; that way being the opposite to the course of the
deflection in the former case.

143. When the helix with its iron core in any given position was inverted,
the effect was as if a magnet with its marked pole downwards had been
introduced from above into the inverted helix. Thus, if the end B were
upwards, such a magnet introduced from above would make the marked end of
the galvanometer needle pass west. Or the end B being downwards, and the
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 deg.. 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 defl