To
the other terminal fasten another piece of wire and ground it on
the water faucet in the house. If there is no faucet in the house,
ground it with a large piece of zinc.
Fasten the other end to one terminal of the transmitter and from
the other terminal of the same run a wire into the ground. The
ground here should consist either of a large piece of carbon, or
several pieces bound tightly together.
[Illustration: A Unique Battery]
If a person speak into the transmitter, one at the receiver can
hear what is said, even though there are no batteries in the
circuit. It is a well known fact that two telephone receivers
connected up in this way will transmit words between two persons,
for the voice vibrating the diaphragm causes an inductive current
to flow and the other receiver copies these vibrations. But in
this experiment, a transmitter which induces no current is used.
Do the carbon and the zinc and the moist earth form a battery?
--Contributed by Wm. J. Slattery, Emsworth, Pa.
** A Cheap Fire Alarm [47]
An electrical device for the barn that will give an alarm in case
of fire is shown in the accompanying diagram.
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