A Mechanical Installation.

A central site, if possible overlooking the whole interlocked area, is selected for the signal cabin. Within this area, which generally comprises the running roads and those points giving access to the running roads from sidings, goods yard, engine sheds, etc., all crossovers, points, and facing point locks are connected by rodding to their levers in the signal cabin.

Signals and shunting signals are also connected to their respective cabin levers by a stranded steel wire. Trap points may have

Interlocking Machine, Electric Pneumatic Signalling, Dunedin.

page 32 separate levers or be worked in conjunction with nearby points. Trap points are always indicated on the ground by square targets which turn with the points and not separately connected to the interlocking machine. This machine where possible, is so placed in the cabin that the signalman faces the yard as he works, having No. 1 lever on his left.

The main line signal levers are placed at the ends of the machine, those on the signalman's left controlling the trains moving from left to right.

Points, points lock, and shunting signal levers are so grouped in the centre of the machine as to eliminate unnecessary walking for the operator. The machine (or frame) consists of these levers, their undergear to connect with points and signals, and the locking plate.

Though the lever handles in the top story-all gaily arrayed in paint and polished metal-make the braver show, the most important part of the work is performed on the ground floor.

In the lower story are the cranks and wires connecting the machine to the outside system. Also close under the upper floor is placed the locking plate, which is the brain of the machine.-(To be continued.)