American telegraphy and encyclopedia of the telegraph; systems, apparatus, operation (1909)
Maver, William, jr. [from old catalog] · New York, Maver publishing company · leaf 606
as shown at A, fromwhich it is conducted by smallerpipes to air chambers on the postssupporting the semaphores. T h eelectrical portion of the system isutilized to open valves which admitthe compressed air into the air cham-bers. The semaphores, of which there aretwo at the entrance of each block,… … tlie home scmapliore; the lower one, semaphore. 496 AMERICAN TELEGRAPHY. When both semaphores are set at right anales to the supporting post, as atC?in the figure, it is an intimation that a train is on the block guarded by thosesemaphores, and when thus set they are said to be in the danger…
Telegraph
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