330 RAILWAY CONSTRUCTION. 



shown at the end of the interlocking frame. There is a liberal 

 amount of glass, and two or three sliding windows, which the 

 signalman can open to enable him to speak to the engine-drivers 

 or others during shunting operations. The lower story of the 

 cabin can be utilized for trimming lamps and keeping a small 

 supply of coals and other stores. When working after dark the 

 lamps in the cabins should be well protected by shades, to 

 prevent the lights being seen by engine-drivers, and mistaken 

 for signals. 



Interlocking. There are several systems of interlocking, each 

 of them varying considerably in the form and mode of appli- 

 cation, but all of them having the same general object of 

 securing or releasing the necessary levers for each combination 

 of signalling movements. A brief description of one of the 

 systems will explain the order in which the movements have to 

 be made, and the security which can be obtained by the locking. 



Figs. 503, 504, and 505, are sketches illustrating one of the 

 types of wedge and tappet interlocking. Each lever works on 

 a fulcrum or pinion as at A, and has a lower arm B for lifting 

 the rods leading off to points or signals, and an arm C to carry 

 a counterweight when necessary. Cast-iron braces D are 

 placed at convenient distances between the series of levers to 

 carry the top frame E on which the lever floor casing F is bolted. 

 This casing is continuous from end to end of the locking frame, 

 with the exception of the narrow openings through which the 

 levers travel when moving backwards or forwards. The sleeve- 

 block G, resting in the depressed portions of the arc, retains the 

 lever in position. When taking hold of the main lever L, the 

 signalman's hand draws the small side lever M, close to the main 

 lever, and raises the sleeve-block G sufficiently high to pass over 

 the top of arc F, the lever L can then be pulled or pushed 

 over, and the block G will fall into the depression at the end of 

 the stroke when the hand is removed. N is a tappet or thin 

 flat bar attached to the main lever, and which works backwards 

 or forwards between the wedges in the wedge frame 0. The 

 wedges move horizontally between guide pieces, and work either 

 singly or are connected by the lower slide bars to other wedges 

 some distance away on the frame according to the position of 

 the levers which have to stand or move in unison for the releas- 

 ing or locking. A strong cover is placed over the wedge frame 

 to keep out the dirt. 



