C to F, on the down line,
then it takes only a half second to go from C to G, so that the line A
represents the time, and the line H the intensity, a complete cycle
being formed from C, D, F, then through F, E, C, and so on.

[Illustration: _Fig. 112._ ALTERNATING POLARITY LINES]

HOW AN ALTERNATING DYNAMO IS MADE.--It is now necessary to apply these
principles in the construction of an alternating-current machine. Fig.
113 is a diagram representing the various elements, and the circuiting.

[Illustration: _Fig. 113._ ALTERNATING CURRENT DYNAMO]

Let A represent the ring or frame containing the inwardly projecting
field magnet cores (B). C is the shaft on which the armature revolves,
and this carries the wheel (D), which has as many radially disposed
magnet cores (E) as there are of the field magnet cores (B).

The shaft (C) also carries two pulleys with rings thereon. One of these
rings (F) is for one end of the armature winding, and the other ring
(G) for the other end of the armature wire.

THE WINDINGS.--The winding is as follows: One wire, as at H, is first
coiled around one magnet core, the turnings being to the right. The
outlet terminal of this wire is then carried to the next magnet core and
wound around that, in the opposite direction, and so on, so that the
terminal of the wire is brought out, as at I, all of these wires being
connected to binding posts (J, J'), to which, also, the working circuits
are attached.

THE ARMATURE WIRES.--The armature wires, in like manner, run from the
ring (G) to one armature core, being wound from right to left, then to
the next core, which is wound to the right, afterward to the next core,
which is wound to the left, and so on, the final end of the wire being
connected up with the other ring (F). The north (N) and the south (S)
poles are indicated in the diagram.

CHOKING COIL.--The self-induction in a current of this kind is utilized
in transmitting electricity to great distances. Wires offer resistance,
or they impede the flow of a current, as hereinbefore stated, so that it
is not economical to transmit a direct current over long distances. This
can be done more efficiently by means of the alternating current, which
is subject to far less loss than is the case with the direct current.
It affords a means whereby the flow of a current may be checked or
reduced without depending upon the resistance offered by the wire over
which it is transmitted. This is done by means