[Illustration: FIG. 229.--Principle of the motor.]
It is easy to see that long-continued rotation would be impossible in
the arrangement of Figure 228, since the twisting of the suspending
wire would interfere with free motion. If the motor is to be used for
continuous motion, some device must be employed by means of which the
helix is capable of continued rotation around its support.
In practice, the rotating coil of a motor is arranged as shown in
Figure 229. Wires from the coil terminate on metal disks and are
securely soldered there. The coil and disks are supported by the
strong and well-insulated rod _R_, which rests upon braces, but which
nevertheless rotates freely with disks and coil. The current flows to
the coil through the thin metal strips called brushes, which rest
lightly upon the disks.
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