d
was at a maximum when the motion was perpendicular to the magnetic
direction.

178. When the wire was bent into other forms and moved, equally strong
effects were obtained, especially when instead of a rectangle a double
catenarian curve was formed of it on one side of the galvanometer, and the
two single curves or halves were swung in opposite directions at the same
time; their action then combined to affect the galvanometer: but all the
results were reducible to those above described.

179. The longer the extent of the moving wire, and the greater the space
through which it moves, the greater is the effect upon the galvanometer.

180. The facility with which electric currents are produced in metals when
moving under the influence of magnets, suggests that henceforth precautions
should always be taken, in experiments upon metals and magnets, to guard
against such effects. Considering the universality of the magnetic
influence of the earth, it is a consequence which appears very
extraordinary to the mind, that scarcely any piece of metal can be moved in
contact with others, either at rest, or in motion with different velocities
or in varying directions, without an electric current existing within them.
It is probable that amongst arrangements of steam-engines and metal
machinery, some curious accidental magneto-electric combinations may be
found, producing effects which have never been observed, or, if noticed,
have never as yet been understood.

* * * * *

181. Upon considering the effects of terrestrial magneto-electric induction
which have now been described, it is almost impossible to resist the
impression that similar effects, but infinitely greater in force, may be
produced by the action of the globe, as a magnet, upon its own mass, in
consequence of its diurnal rotation. It would seem that if a bar of metal
be laid in these latitudes on the surface of the earth parallel to the
magnetic meridian, a current of electricity tends to pass through it from
south to north, in consequence of the travelling of the bar from west to
east (172.), by the rotation of the earth; that if another bar in the same
direction be connected with the first by wires, it cannot discharge the
current of the first, because it has an equal tendency to have a current in
the same direction induced within itself: but that if the latter be carried
from east to west, which is equivalent to a diminution of the m