3H RAILWAY CONSTRUCTION. 



is only necessary to light the lamps to put the signals in complete 

 condition for night-working. For some years, when the traffic 

 was small, with trains at low speeds and at considerable intervals, 

 one double-arm semaphore signal-post at a station was made to 

 serve for all purposes ; but as the train service became more 

 frequent and more rapid, it was found that another semaphore 

 or tall post signal, was necessary to give warning to the engine- 

 driver some distance back before reaching the station or home 

 signal. More particularly was this necessary at those stations 

 where it was not intended that every train should stop. This 

 new signal, called the distant signal, very soon came into 

 general use. It was placed at distances varying from 400 to 

 800 yards away back from the station or home signal, and was 

 worked by a long strained wire extending from the distant 

 signal to a ground-lever placed near the home signal, the levers 

 for these distant signals and home signals being thus near 

 together and under the control of one man. More recently it 

 was found necessary to introduce another important wire- worked 

 signal called a starting signal, which is placed at the outgoing 

 or departure end of the passenger platforms, lines, or station 

 sidings, to prevent any train or engine starting or proceeding on 

 its journey until such starting signal is lowered to indicate that 

 the line is clear. 



These simple, independent, hand-worked semaphore signals 

 did good service for many years, but being independent and in 

 no way physically connected with one another at junctions, or 

 stations, or with the switches they were intended to control, it 

 was quite possible for mistakes to arise where everything 

 depended upon the accuracy and prompt decision of the signal- 

 man. The possibility that such mistakes could occur, and the 

 certainty that they actually did occur, and too often with most 

 disastrous results, led gradually to the grouping and interlocking 

 of a large number of signal levers and switch levers together in 

 one signal cabin. The advantages of the concentrating and 

 interlocking of signals and switches are twofold. In the first 

 place, one man in the signal cabin can work and control the 

 levers for a large number of switches and signals, where formerly 

 several men were required to be located at various places in the 

 station-yard; but the second, and by far the most important 

 advantage, is that with proper interlocking arrangements it is 

 practically impossible to give conflicting signals. 



