344 RAILWAY CONSTRUCTION. 



was required at the opposite end of the section, thus causing 

 much confusion and delay. The ordinary electric telegraph 

 could have been utilized to assist in regulating these train 

 movements, but it was felt that a mere telegraph message was 

 not sufficient to ensure positive safety, and that something 

 more tangible was required in the shape of a staff, or token, 

 without which no train should be allowed to travel on a single 

 line of railway. To meet this requirement, the electric train- 

 tablet, and the electric train-staff instruments have been 

 invented, each of them being so arranged that upon any one 

 section, or pair of instruments, a tablet or train-staff may be 

 taken out from the instrument at either end of the section, but 

 when once taken out, no other tablet or train-staff can be with- 

 drawn from either instrument until the first has been delivered 

 and placed again in one or other of the two instruments. 



Figs. 514, 515, and 516 are sketches of an electric train-staff 

 instrument which has been very largely adopted on single lines, 

 both at home and abroad. 



In a similar manner to the block-telegraph instruments for 

 double line, the electric train-staff instruments have each a bell 

 or gong by which the adjacent signalmen can communicate 

 their calls and answers in accordance with a regulation code. 

 In the signal-cabins of the intermediate stations two instruments 

 are required, one for the staffs belonging to the section to the 

 left of the cabin, and the other for the staffs of the section to 

 the right. At a terminal station only one instrument is required. 



The head of the instrument contains the electrical and 

 mechanical locking apparatus which controls the withdrawal of 

 a train-staff, or is acted upon by its insertion. The circular 

 name-plates and pointers, together with the galvanometer in the 

 centre, serve as indicators to guide the signalmen, in carrying 

 out the various operations. The staffs usually consist of thin 

 steel tubes, solid at the ends, with metal rings fixed upon them, 

 as shown in the sketch, the number and position of the rings 

 varying according to the section or pair of staff stations to which 

 they belong ; this difference in the rings effectually preventing 

 the possibility of one set of staffs being used or inserted in 

 either of the instruments of the adjoining sections. The staffs 

 rest normally in the long vertical slot A, with the rings fitting 

 in vertical grooves, which prevent the removal of any staff 

 except by passing it along the curved slot BC, and out by the 



