wire circuit.

Faraday's great discovery was, in fact, that when the pole of a magnet
is moved into, or moved out of, a coil of wire, the motion produces,
while it lasts, currents of electricity in the coil. Such currents are
known as "induced currents;" and the action is called magneto-electric
"induction." The momentary current produced by plunging the magnet pole
into the wire coil or circuit is found to be in the opposite direction
to that in which a current must be sent if it were desired to attract
the magnet pole into the coil. If the reader will look back to Fig. 10
he will see that a north magnet pole is being attracted in from behind
into a circuit round which, as he views it, the current flows in an
opposite sense to that in which the hands of a clock move round. Now,
compare this figure with Fig. 12, which represents the generation of a
momentary induced current by the act of moving the north pole, N, toward
a wire ring, which is in this case connected with a little detecter
galvanometer, G. The momentary current flows round the circuit (as seen
by the spectator from the front) in the _same_ sense as the movement of
the hands of a clock. The induced current which results from the motion
is found, then, to be in a direction exactly opposed to that of the
current that would itself produce the same movement of the magnet pole.
If the north pole, instead of being moved toward or into the circuit,
were moved away from the circuit, this motion will also induce a
transient current to flow round the wire, but this time the current will
be in the same sense as that in Fig. 10, in the opposite sense to that
in Fig. 12. Pulling the magnet pole away sets up a current in the
reverse direction to that set up by pushing the pole nearer. In both
cases the currents only last while the motion lasts.

[Illustration: Fig. 12.]