Engineering Wonders of the World
Volume I

236 ENGINEERING WONDERS OF THE WORLD. Fig. 19.—AUTOMATIC SIGNAL ON AN AMERICAN HIGH-SPEED INTERURBAN RAILWAY. THE POINT ON THE SEMAPHORE INDICATES THAT THE SIGNAL IS AUTOMATIC. POWER IS OBTAINED FROM THE “LIVE” RAIL OF THE TRACK. down when the signal is cleared. Were a train to overrun a signal, a trip cock (C), attached to the leading car truck, would strike the trigger, admit air to the train pipe, and apply the brakes in exactly the same manner as if the pressure were released by means of the motorman’s valve or by the breaking in two of the train. Now, as the brakes are sufficiently powerful to pull up an electric train in 400 feet, the overlap and its guarding trigger provide sufficient protec- tion to a train in the section beyond against a train overrunning from behind. On steam railways the overlap is increased from 400 feet to 400 yards ; and the automatic “ stop ” signal at the entrance of a section is supplemented by a distant or warning signal at the entrance Automatic of the preceding section. We Signalling- on Steam would ask the reader’s atten- Railways tion to Fig. 21. On each signal post are two arms—the upper (8), a “ stop ; ” the lower (D), a “ distant.” The signals are so interconnected electrically that each “stop” controls the “distant” on the