486
EXPOSITION AT VIENNA.
about fifty feet in length. The trains are supposed to move in the direction indicated by the arrow. The electric magnet S which operates the semaphore, together with the semaphore itself and its fixtures, are placed 200 or 300 feet in advance of the short section a 1 a 2 . The semaphore is the same shown in Plate XI., under class 2.
Opposite the signal apparatus, a battery B is connected to the continuous rail of the track by a wire, 1. From the opposite pole of the battery, two wires, 2 and 3, are conducted to two relays, R and R 1 , and thence to the long and short sections of the other rail, a a 1 and a 1 a 2 respectively. These two relays control the local circuit 4, 5, 6, 7, which operates the semaphore, by means of the local battery E.
The normal position of the semaphore indicates "danger.” But whenever a current is passing through the magnet S, it will indicate "safety,” until the current is interrupted, when a counterbalance weight returns the signal to its former position.
When a train, passing in the direction of the arrow, reaches the short section of rail, its wheels and axles form an electrical connection with the opposite rail, closing the circuit of the relay R 1 , the armature of which in turn closes the local circuit at x. A moment afterward, the advancing train reaches the long section at a 1 , actuating the other relay R in the same manner, and closing the local circuit at y. The local circuit being now complete at x and y , the electromagnet S is charged, and a safety-signal shown, which indicates to the engineer that he may proceed with safety. As soon as the last car of the train has passed the point a 1 , the relay R 1 opens, breaking the local circuit and returning the semaphore to "danger.” The relay R, however, will remain closed while the train is passing over the long section, and the local circuit will, during this time, pass through the wires 6, 7 and 8, including the retaining magnet M. If, therefore, another train should enter upon the short section a 1 a 2 , it would be unable to close the local circuit at x, and thus cause a safety-signal to be shown, because the armature of the relay R 1 would be held fast by the attraction of M.
In this svstem it will be seen that the circuit closers, beinsr