34 RAILWAY CONSTRUCTION. 



Where the traffic is moderate, it may be sufficient to have 

 block-telegraph instruments at each of the stations, but with 

 a very frequent train service it will be found necessary to 

 divide the line into shorter sections, and erect signal-cabins and 

 block-telegraph instruments at intermediate points between 

 stations. 



The code of bell or gong signals is extended to include 

 various matters in connection with the train-working. For 

 example, when a DOWN train is passing cabin B at full speed, the 

 signalman may observe that there is something wrong a carriage 

 or waggon on fire, a tail-lamp missing, or other irregularity. It 

 is too late to stop the train with his own signals, but by means 

 of his bell or gong he can call upon the signalman in cabin 

 C to stop and examine the train, and the DOWN distant and 

 home signals at C can be raised to danger before the train 

 reaches the cabin at C. 



In every block-telegraph signal-cabin there is a train-book 

 in which the signalman has to write down the time and descrip- 

 tion of every arriving or passing train, and, as this book lies 

 before him, he has a complete record of the train-working, with 

 the particulars of the exact times when the line clear signals 

 were given, and also when the train arrived or passed his signal- 

 cabin. 



To guard against the possibility of a signalman inadvertently 

 giving line clear, or allowing another train to pass his cabin 

 before the previous train had reached the signal-cabin in advance, 

 some railways have adopted the lock and block system. By 

 this arrangement the starting signal at any cabin is electrically 

 and mechanically locked from the cabin in advance, and can 

 only be released or lowered by the action of the outgoing train 

 itself when passing over a treadle or other appliance connected 

 with the rails of the running-line at the signal-cabin in advance. 

 This method practically gives the train the complete control of 

 the section ; and any signalman attempting, in error, to lower his 

 starting signal would find it to remain fixed to danger and 

 immovable, until released by the arrival of the train at the 

 advance cabin. 



Train-staff for Single Line. When there is only a single line 

 of railway for both an UP and DOWN train-service, very de6nite 

 precautions must be adopted to prevent the meeting or collision 

 of trains travelling in opposite directions. Where the piece of 



