VI. TRAIN TELEGRAPHY. Phelps Induction Train Telegraph.—The principle upon which the train telegraph system of Jlr. Lucius J. Phelps is based is that of induction according to the law that if a current he sent through one of two parallel wires in close proximity to each other. the second wire (on closed circuit) will have a momentary current induced in it, the direction of which will be contrary to that of the primary or -inducing current ; while, if the primary cur rent be interrupted, the induced current will be re versed, i.e., flowing in the same direction as the pri mary current. By utilizing this oft-applied principle, therefore, electrical effects and currents are obtained al a distance from, and without contad with, any source of electricity. Thus. if in Fig. 30. a current be sent through the bottom wire a, a momentary current will be set up in the parallel coil, which current can he utilized to actuate a relay, and through it a sounder. While this particular• employment of a reduced current to actuate a relay is not in itself new, its m^difleation and adaptation is very ingenious. By referring also to the diagram. Fig. 30, the general arrangement of the sending and receiving stations will be seen, that to the right representing the moving car, Taking the terminal station first, we find its principal equipment to consist simply of a main battery, a pole-changing key and a telephone, the latter taking the place of the relay and sounder shown in Fig. 3u, and all connected in the usual way with the line wire.
In this system the line wire is run between the rails, and consists of an insulated copper wire laid in a covered trough composed ef strips of wood hollowed out to receive the wire. Fig,. 31 shows the manner in which the wire is secured and protected, the iuelosing strips resting upon blocks secured to the cross-ties. The ear equipped with this system differs from the ordinary car only in the addition of a pipe running below and along the centre of the car between the trucks, and hung by suspenders. This pipe is situated directly over the line wire, at a height of seven inches, and consists of a two-inch gas pipe. This pipe contains a 1',-inch rubber hose, in which the induction wire of the car is incased. It consists of No.
14 copper wire, single braided and paraffined.
One end of this is first drawn through the pipe, passed up to the ceiling at one end of the car, back to the other end, then down and into the pipe, and the operation is repeated until ninety convolutions are completed.
This forms a continuous circuit about miles in length, and presenting about of a mile of wire parallel with the main line wire upon the track. The circuit throughout is enclosed in a rubber hose, the object in carrying the return leads along the top of the car obviously being to separate. as far as possible. those portions of the wire in which the current flows in opposite directions.
The terminals of the wire so wound around the car are brought together and carried to a transmitting key placed on top of the small compartment situated in one corner of the baggage car, as shown in Fig. 32, which represents the moving telegraph station. The equipment of this station consists of a transmitting key, a " buzzer " or vibrator, a sounder, a polarized relay, and a battery of five quart cells, one of which constitutes the local battery. The terminals of the coil are carried to the key, and connect through the back contact of the latter with the polarized relay, shown in Fig. 33, the construc tion of which will be explained presently. This is the receiving instrument on the car, and closes the local battery circuit through the sounder, which is placed on a sounding-board supported by brackets above the relay. For the transmission of messages from the car, the cur rent from the four cells is passed through the front con tact of the key before mentioned, through the 1 miles of wire in the coil, and through the buzzer, which breaks the current very rapidly and converts the single " click " into a humming sound. This rapidly vibrating current induces similar currents in the main-line wire on the track, and the operator at the terminal station reads the 'Morse characters from a telephone, which reproduces the humming of the " buzzer." If it is desired to receive a message in the car, the operator at the terminal station merely manipulates his key in the usual way, and the pulsations of the current in the main line induce corre sponding effects in the wire placed a few inches above it on the car. The induced currents actuate the delicate relay, and the sounder gives forth its signals in the same way as usual and can be easily heard at a distance of ten • feet even above the din of a moving train.