482
EXPOSITION AT VIENNA.
to set his out-door signal at block, so as to prevent a second train passing down ; to set the disc in his box to correspond with the semaphore ; to notify the station above him that the train has passed, in order that the latter may unblock his signal ; and to notify the station below that the train is coming. The first of these operations is performed by turning the " semaphore winch ” from left to right, so as to rest against the point f, which lowers the right arm of the semaphore, signifying "block.” (This is the present position of the left- hand winch and the left-hand arm on the "up-line” side.) The second and third operations are performed together, as follows : The plunger marked T 2 is depressed (which could not before be done), carrying down with it the metallic spring a, which is cut off from W 1 and connected to 5, and also carrying down the spring rod G, which presses the pawl c into the notch on the axis of the winch. The handle K of the magneto-inductor is then turned, which causes alternate positive and negative currents to flow along the commutator marked -f- and the wire in connection therewith, and through the right coil of the electro-magnet E 2 , thence by 6, a, L 1 , i 1 and P 1 out on the line L 1 . The electro-magnet E 2 , actuated by alternate positive and negative currents, alternately attracts and repels an armature swinging between the ends of the two coils. On the upper end of this armature is a bell- hammer, which strikes the right hand and centre bells; on the lower end is an escapement which works into the teeth of the half-white, half-red index placed behind the right hand glass disc shown in fig. A. A sliding weight on the stem of the plunger T 2 presses down upon the opposite end of the index, and, as the escapement moves back and forth, the index is raised, tooth by tooth, until the red takes the place of the white behind the glass, and the box-signal corresponds with the semaphore. The depression of G has allowed a lever l to press against the shoulder H on the rod, and, as the index rises, its axis, half of which is cut out, prevents the lever l from returning. The rod G, therefore, holds down the pawl c, and prevents the out-door semaphore from being unblocked until the index is brought back to white , or " line clear .” This will be understood by reference to the left side of the diagram.