328 RAILWAY CONSTRUCTION. 



there are shunting signals for the movement and marshalling of 

 trains setting-back signals in connection with the making up 

 of passenger trains ; taking on or off passenger carriages ; or 

 moving out empty passenger carriages ; and many other special 

 signals which become necessary for the working of a large and 

 complicated train service. 



The above simple diagrams will explain some of the principal 

 requirements to be kept in view when working out signalling 

 arrangements. Where the lines and sidings are very numerous, 

 as at important junctions and large terminal stations, the signal- 

 ling becomes very intricate, and may require three or four 

 cabins, slotted together in such manner that the necessary 

 co-acting may be insured for the proper controlling of the main- 

 line signals. Many of these signal-cabins contain a large 

 number of levers, some of them having as many as a hundred, 

 and a few of them two hundred and forty levers, or more, all of 

 them so carefully arranged that no conflicting signal can be 

 given. Not only has much skill to be exercised in the accurate 

 adjustment of the interlocking machinery, but much study must 

 be devoted to determine the exact duty of every lever, for the 

 locking or releasing of other levers. 



Signal-cabins may be built of stone, brick, or wood. They 

 should be roomy, well ventilated, and have abundance of light. 

 Every signal- cabin should be placed in the position from which 

 the signalman can obtain the best view of the signals and points 

 under his charge. The height of the cabin floor will depend 

 upon any obstacles that may intervene between the cabin and 

 the signals, such as over-line bridges, station roofs, buildings, or 

 other obstructions. Sometimes the floor has to be kept as low 

 as five feet above rail-level, to secure a line of sight under the 

 over-line bridges; and in others the floor has to be raised 

 twenty, or even thirty feet above rail-level. 



Figs. 500, 501, and 502 show plan, transverse section, and 

 elevation of a signal-cabin suitable for a small roadside station. 

 The lower story and chimney-stack are of brick, and the upper 

 story of wood, with slated roof. There is room for an inter- 

 locking frame of twenty or twenty-five levers, and space at the 

 end of the cabin for the block-telegraph instruments, or electric 

 train-staff instruments. The roof- work is open up to the slate- 

 boards, to obtain as much air capacity as possible. In the 

 transverse section a winch for working mechanical gates is 



