Engineering Wonders of the World
Volume I

RAILWAY SIGNALLING. 239 telegraphic communication with one another, and that the signalmen at the ends of a section must co-operate before a staff is withdrawn, even if the number of staffs in a pair of instruments is even. This com- bination of human and mechanical control is necessary for the convenient regulation of traffic. Fig. 25.—ramp (r) for operating an automatic AUDIBLE SIGNAL IN CAB OF LOCOMOTIVE. A System of Audible Signalling. A distant signal is essentially a warning signal, as contrasted with the “ home ” and “ starting ” signals, which must not be passed when at danger. The interlocking gear of a signal box is so arranged that a distant cannot be cleared until its home and starting signals have been cleared also. An engine-driver, on seeing a “ distant ” against him, would continue his course, merely reducing speed and preparing to stop his train at the home signal. By day a Fig. 26.—VIEW OF REAR PART OF LOCOMOTIVE, SHOWING CONTACT SHOE AND BATTERY FOR OPERATING WHISTLE; “ distant ” is distinguishable by the “ fish- tail ” notch cut in the end of the arm ; but at night the same colour indication is given by all signals, so that a driver may mistake a distant for a stop signal, or vice versa. In a dense fog signals become obscured, and special detonating fog-signals, laid on the line by men detailed for the purpose, are necessary. In order to overcome the difficulties arising from darkness and fog, a new device has been tried on the Great Western Railway. Its essential features are—(1) It gives the driver a positive distant signal indication, which cannot be disregarded; (2) it is equally Fig. 27.—CAB INDICATOR, WHISTLE, AND BELL.