RAILWAY CONSTRUCTION. 32$ 



locking frame of the signal-cabin. Four distinct sets of trains 

 have to be dealt with at this class of junction, and the inter- 

 locking must be so arranged that when the signals are lowered 

 for the advance of any one train, no conflicting signals can be 

 given to any other train. 



Assuming a train approaching from A, which has to continue 

 on the main line past B on towards C, then the levers in the 

 signal-cabin must first be pulled over to set the points 9 and 

 bolt-lock 8 in proper position for the main line ; and this opera- 

 tion will release the levers which have to be pulled over to 

 lower the signals 5, 4, and 6, but at the same time will lock, 

 and prevent the pulling over of the levers or lowering of the 

 signals 2 and 1 for a train from A to B and D, or of the signals 

 14 and 15 for a train from D to B and A. The levers will, 

 .however, be free to pull over for setting the points 12 and 

 lowering the signals 16, 17, and 13 for a train on the main line 

 from C to B and A. 



In a similar manner, assuming a train approaching from D, 

 which has to continue up to the main line at B and on towards 

 A, then the lever in the cabin must first be pulled over to set 

 the trailing points 12 in proper position ; and this operation will 

 release the levers which have to be pulled over to lower the 

 signals 14 and 15, but at the same time will lock, and prevent 

 the pulling over of the levers or lowering of the signals 5 and 4 

 for a train from A to B and C, or of the signals 16 and 17 for 

 a train from C to B and A. The levers will, however, be free 

 to pull over for setting the points 9 and bolt-lock 8 and 

 lowering the signals 2 and 1 for the passage of a train on to the 

 branch line from A to B and D. 



For a train from C to B and A, the levers 12, 16, 17, and 13 

 would be required, and these would lock levers 14 and 15, and 

 prevent the approach of any train from D to B, but they would 

 leave free the levers necessary either for a train from A to B 

 and C, or for a train from A to B and D, but only one of them 

 at a time, the setting of the one series locking the other series. 



A train from A to B and D would require the proper setting 

 of the points 9, bolt-lock 8, and signals 2, 1, and 3 ; and these 

 would lock 5 and 4, but would leave free the levers necessary 

 either for a train from C to B and A, or for a train from D to 

 B and A, but only one of them at a time. 



The cross-over road from the UP to DOWN main line, near the 



