through the magnetic field of the magnet (A), it becomes, in a measure,
a magnet of its own and tries to set up in business for itself as a
generator of electricity. But when the loop leaves the magnetic field,
the magnetic or electrical impulse in the wire also leaves it.

THE MOVEMENT OF A CURRENT IN A CHARGED WIRE.--Your attention is
directed, also, to another statement, heretofore made, namely, that when
a current from a charged wire passes by induction to a wire across
space, so as to charge it with an electric current, it moves along the
charged wire in a direction opposite to that of the current in the
charging wire.

Now, the darts show the direction in which the current moves while it is
approaching and passing through the magnetic field. But the moment the
loop is about to pass out of the magnetic field, the current in the loop
surges back in the opposite direction, and when the loop has made a
revolution and is again entering the magnetic field, it must again
change the direction of flow in the current, and thus produce
alternations in the flow thereof.

Let us illustrate this by showing the four positions of the revolving
loop. In Fig. 103 the loop (B) is in the middle of the magnetic field,
moving upwardly in the direction of the curved dart (A), and while in
that position the voltage, or the electrical impulse, is the most
intense. The current used flows in the direction of the darts (C) or to
the left.

In Fig. 104, the loop (A) has gone beyond the influence of the magnetic
field, and now the current in the loop tries to return, or reverse
itself, as shown by the dart (D). It is a reaction that causes the
current to die out, so that when the loop has reached the point farthest
from the magnet, as shown in Fig. 105, there is no current in the loop,
or, if there is any, it moves faintly in the direction of the dart (E).

[Illustration: _Figs. 103-106._ ILLUSTRATING ALTERNATIONS]

CURRENT REVERSING ITSELF.--When the loop reaches its lowest point (Fig.
106) it again comes within the magnetic field and the current commences
to flow back to its original direction, as shown by darts (C).

SELF-INDUCTION.--This tendency of a current to reverse itself, under the
conditions cited, is called self-induction, or inductance, and it would
be well to keep this in mind in pursuing the study of alternating
currents.

You will see from the foregoing, that the alternations, or the change of
direction of the current