The call-bell has nothing to do with the telephone. It is
operated by a small magneto-generator,--a very near relative of the
dynamo-the current from which is sent over the telephone circuit (the
same wires) when the small crank is turned. Sometimes the question
occurs: "Why ring one's own bell when one desires to ring only that at
the central office?" The answer is that both bells are in the same
circuit. If the circuit is uninterrupted your bell will ring when you
ring the other, and a bell at each end of your circuit is necessary in
any case, else you could not yourself be called.
When the receiving instrument is on its hook its weight depresses the
lever slightly. This slight movement _connects_ the bell circuit
and _disconnects_ the telephone circuit. Take it off the hook and
the reverse is effected.
The long-distance telephone differs from the ordinary only in larger
conductors, improved instruments, and a metallic circuit--two wires
instead of the ordinary single wire and ground connections.
[Illustration: TELEAUTOGRAPH TRANSMITTING INSTRUMENT.
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