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This experiment may be - tried by- any boy with the
equipment he probably has already around his .shop.
Twenty-five to thirty turns of wire wound. around a card-
board tube five or six inches in diameter will serve as a
coil. Two such coils, an ordinary telephone transmitter, a
telephone. receiver and a couple of dry. cells are all that is

The diagram in the accompanying illustration shows
how the apparatus is arranged. The coils may be used




FIG. 238. —A Simple Wireless Telephone.

Speech directed into the Transmitter can be heard in the Receiver, although there is no direct
electrical connection between the two. ‘

several inches apart 'and the voice will be clearly heard in
the receiver. -

Such ' an outfit is, however, only experimental, and if it
is desired to make a practical set, the coils, etc., must be
much larger in diameter and contain a greater number of

Larger coils are made by first drawing a circle four feet
in diameter on the floor of the “ shop ” or attic. Then

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