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EXPOSITION AT VIENNA.
To fulfil these requirements, the switch-lever at Barnes must "control” (in the sense of change) the position of the semaphore at Putney, and the semaphore at Putney must, with the aid of the Putney signal-man, whose business it is to acknowledge on the bell the signal received from Barnes, indicate at Barnes its obedience to -the switch-lever, thus furnishing a "control” in the continental sense of acknowledgment.
The natural position of the semaphore is at arrest, both in the out-cloor signals and in the miniature copy (shown at Fig. B). In the signal system the out-door semaphore is always required to be changed to follow the indications of the one in the signal-box.
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Suppose a train to be waiting at Putney until another shall have passed Barnes, leaving the section between the two stations clear. As soon as the first train passes Barnes, the latter throws his switch-lever to off. This closes the circuit of a galvanic battery, whose current passes through the magnet A (Fig. B) of the semaphore at Putney, attracting the armature lever B, and by the very simple mechanism shown in the cut, lowering the arm of the semaphore to "line clear.”
The signal-man at Putney then lowers the arm of the outdoor signal, permitting the train to pass on towards Barnes. He then signals its approach to Barnes by depressing the "piston-key” or "plunger” b (Fig. A), which closes as often as depressed, the circuit of the third or bell-wire. There are two batteries for use on this wire, one of which has its positive, and the other its negative pole to the ground. The armature lever B of the semaphore magnet is connected to one of the contact points of the plunger b , the other being connected to the wire to Barnes. The positive pole of one battery is connected to the point E (Fig. B) and the negative pole of the other to the point F, between which points the armature lever B works. It follows then that when the semaphore is at "arrest” the current thrown on the line by depressing the plunger would be from one battery through E, and when the semaphore is at "line clear” it would be from the other battery through F.
The semaphore at Putney being in the latter position, the depression of the plunger throws the current on the bell-wire from the battery connected to F.