346 RAILWAY CONSTRUCTION. 



opening D, of large diameter. The electrical and mechanical 

 locking apparatus is placed at the curved slot, and until the 

 locking-bolt, which stands across the passage of the curved slot, 

 be lifted by the joint operations of the signalmen and their 

 instruments at both ends of the section, no staff can be with- 

 drawn. When the instruments are standing in their normal 

 position of "staffs in," the signalmen can arrange between them 

 to withdraw a staff say either from the NORTH cabin instru- 

 ment or from the SOUTH cabin instrument of the section, but 

 only from one of them; and the act of taking out that staff 

 automatically locks both instruments, and prevents the possi- 

 bility of taking out any other staff from either instrument until 

 the staff already removed is restored and inserted in one or 

 other of the instruments. From the above description it will 

 be seen that the electric train- staff instrument provides for the 

 safe working of two or more trains proceeding, one at a time, 

 in the same direction over a section of single line, each one being 

 supplied with a train-staff, which must be handed over at the 

 end of a section before another staff can be issued for a following 

 train. Should the train-staffs accumulate in one instrument, 

 in consequence of more trains running in one direction than 

 another, a re-distribution of staffs is effected by the authorized 

 persons according to fixed regulations. 



In the diagram sketch, Fig. 517, a piece of single line is 

 shown divided into sections or blocks, with loops or passing- 

 places at the stations. At the station E a train-staff taken out 

 of the instrument F serves for the section up to the instrument 

 L at the station H ; and on the train-staff is a key which will 

 open the detached locks on the points of the small intermediate 

 station, G, as described in Fig. 507, in connection with the 

 working of detached locks. At the station H the engine-driver 

 receives another staff from the instrument M, which takes him 

 to the instrument N at station K, and in like manner on this 

 staff is a key which will open the detached lock on the colliery 

 siding points at I. At stations H and K are shown loops, or 

 short pieces of double line, with platform to enable an UP train 

 to cross or pass a DOWN train. The distance apart of the electric 

 train-staff stations will depend greatly upon the number of the 

 trains, and for a frequent train-service it may be necessary to 

 have the instruments at every station, whether large or small. 

 The electric train-staff is of great advantage in the working of 



