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306 THE BOY ELECTRICIAN

is due to the fact that the armature winding is composed
of a very large number of turns of wire. The more turns
that are placed on the armature, the higher its voltage will
be. The current or amperage of a large telephone magneto
wound with a large number of turns of fine wire is very low.
Too low in fact to be used for anything except ringing a
bell or .testing. Winding the armature with fewer turns
of large wire reduces the voltage and increases the am-
perage so that the current will light a small lamp or may
be used for other purposes. The winding does not change
the principle of the magneto, it merely changes its am-
perage and voltage.

The magneto may be mounted On a wooden base-board
and screwed to a table, so that the handle may be turned
without inconvenience. A small strip of copper, called a
brush, should be fastened to the base with ' a screw and
brought to bear against the end of the insulated pin. The
brush should be connected to a binding-post with a piece
of wire. A second wire leading to a binding-post should
be connected to the frame of the magneto. When the
handle is turned rapidly, currents may be drawn from the
two binding-posts.

The current is of the kind known as alternating, that is
to say, itflows first in one direction, then reverses and flows
in the other.

In order to make the machine give direct current, it must
be fitted with a commutator. This is somewhat diflicult
with some magnetos but the following plan may be carried

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