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WHILE the one-time art of telegraphing to
and from moving trains was essentially a wireless
system, and allied in some of its principles to
the art of modern wireless telegraphy through
space, the two systems cannot, strictly
speaking be regarded as identical, as the
practice of the former was based entirely on the
phenomenon of induction.
Briefly described in outline, the train
telegraph system consisted of an induction
circuit obtained by laying strips of metal along
the top or roof of a railway-car, and the
installation of a special telegraph line running
parallel with the track and strung on poles of
only medium height. The train, and also each
signalling station, was equipped with regulation
telegraph apparatus, such as battery, key,
relay, and sounder, together with
induction-coil and condenser. In addition,
there was a special transmitting device in the
shape of a musical reed, or "buzzer." In
practice, this buzzer was continuously operated
at a speed of about five hundred vibrations per
second by an auxiliary battery. Its vibrations
were broken by means of a telegraph key into long
and short periods, representing Morse
characters, which were transmitted inductively
from the train circuit to the pole line or vice
versa, and received by the operator at the other
end through a high-resistance telephone receiver
inserted in the secondary circuit of the
induction-coil.
The accompanying diagrammatic sketch of a simple
form of the system, as installed on a car, will
probably serve to make this more clear.
An insulated wire runs from the metallic layers
on the roof of the car to switch S, which is
shown open in the sketch. When a message is to
be received on the car from a station more or
less remote, the switch is thrown to the left to
con- nect with a wire running to the telephone
receiver, T. The other wire from this
receiver is run down to one of the axles and
there permanently connected, thus making a
ground. The operator puts the receiver to his
ear and listens for the message, which the
telephone renders audible in the Morse
characters.
If a message is to be transmitted from the car
to a receiving station, near or distant, the
switch, S, is thrown to the other side, thus
connecting with a wire leading to one end of the
secondary of induction-coil C. The other end
of the secondary is connected with the grounding
wire. The primary of the induction-coil is
connected as shown, one end going to key K and
the other to the buzzer circuit. The other side
of the key is connected to the transmitting
battery, while the opposite pole of this battery
is connected in the buzzer circuit. The
buzzer, R, is maintained in rapid vibration by
its independent auxiliary battery, B.
When the key is pressed down the circuit is
closed, and current from the transmitting
battery, B, passes through primary of the
coil, C, and induces a current of greatly
increased potential in the secondary. The
current as it passes into the primary, being
broken up into short impulses by the tremendously
rapid vibrations of the buzzer, induces
similarly rapid waves of high potential in the
secondary, and these in turn pass to the roof
and thence through the intervening air by
induction to the telegraph wire. By a continued
lifting and depression of the key in the regular
manner, these waves are broken up into long and
short periods, and are thus transmitted to the
station, via the wire, in Morse characters,
dots and dashes.
The receiving stations along the line of the
railway were similarly equipped as to apparatus,
and, generally speaking the operations of
sending and receiving messages were substantially
the same as above described.
The equipment of an operator on a car was quite
simple consisting merely of a small lap-board,
on which were mounted the key, coil, and
buzzer, leaving room for telegraph blanks. To
this board were also attached flexible conductors
having spring clips, by means of which
connections could be made quickly with
conveniently placed terminals of the ground,
roof, and battery wires. The telephone
receiver was held on the head with a spring, the
flexible connecting wire being attached to the
lap board, thus leaving the operator with both
hands free.
The system, as shown in the sketch and
elucidated by the text, represents the operation
of train telegraphy in a simple form, but
combining the main essentials of the art as it
was successfully and commercially practiced for a
number of years after Edison and Gilliland
entered the field. They elaborated the system
in various ways, making it more complete; but
it has not been deemed necessary to enlarge
further upon the technical minutiae of the art
for the purpose of this work.
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