XIV
TRAIN TELEGRAPHY
Edison, His Life and Inventions, vol. 2 | ||
14.
XIV
TRAIN TELEGRAPHY
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 connect
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
FIG. 1
[Description: Illustration of train telegraphy.]
When the key is pressed down the circuit is closed, and current from the transmitting battery, B, passes through
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 minutiæ of the art for the purpose of this work.
XIV
TRAIN TELEGRAPHY
Edison, His Life and Inventions, vol. 2 | ||