താൾ:CiXIV132a.pdf/430

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CXVIII

magnet, instead of the second one the Earth is taken as a Con
ductor. 2) Morse's Key. 447, 2. It is a metallic lever, one
arm pressed upwards by a spring, the other end rests upon a
small metal support in contact with the wire. 3) The Indicator.
447, 3. consists of an electromagnet, which, when by the key
of another station the current is closed, attracts an armature of
soft iron, fixed at the end of a lever (movable about an axis).
At the other end of the lever there is a pencil, which writes, or
a needle, which engraves the signals on a long band of paper
rolled round a drum. When the current is open the lever is
raised by a spring and the pencil removes from the paper.
There is another little electromagnet fixed on a board; the arma
ture of it being attracted, strikes against a bell, and this way the
receiving station is warned, that a despatch is about to be sent.
This instrument is called the Alectrical Adaram. By means
of the relay, which is another auxiliary electromagnet, the cur
rent of a local battery is introduced into the communicator in
order to strengthen the electric force upon the electromagnet,
which has to write a despatch.

§ 300. 10) The Telephone. In the electrical alarum we have
already an instrument, by which signals may be given. The
telephone (recently improved by the Microphone), consists,
as this figure shows, of two corresponding apparatus, one in
A for delivering a message, one in B for receiving one. M is
a strong magnetic rod, one pole connected with a secondary
coil (R), in front of this we see a small thin plate of iron in a
vertical position (P) and before this a mouthpiece, having the
form of a funnel (T). Both ends of the inducing coil in A
are connected by wires with the ends of the coil in B. If
through the mouthpiece in 4 a word is spoken, the sound-waves
will cause the plate of iron to vibrate and each of these vibra

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