CHAPTER V.
Signals and Interlocking.
An attempt will now be made to give some idea of the elaborate system of signalling the trains, which, in conjunction with the use of the electric telegraph, alone enables the traffic of a great railway to be carried on with safety and despatch, and which has grown up from the rudest beginnings side by side with the growth of the railway system itself.
There is, of course, a very obvious and primary necessity, on any railway, for some visible indication by means of which the drivers of the trains may be warned when they may proceed, and when they must come to a stand, and shortly after the opening of the Stockton and Darlington, which was the earliest railway constructed, one of the station masters is said to have adopted the simple expedient of placing a lighted candle in the window of the station-house when it was necessary for a train to stop. From this rude beginning to the complicated system of signals and interlocking which may be seen, for example, at Clapham Junction or Waterloo is a very long step in advance, and it has, of course, only been achieved by a gradual process of evolution. Thus when the Liverpool and Manchester Railway was first opened in 1830, the only arrangement made for signalling the trains was a flag by day or a
