RACK RAILWAYS. 91 



applied to the rack mechanism, the adhesion brakes being in that 

 case insufficient in themselves. Usually there are brake discs on 

 the shaft of the pinion mechanism, by means of which the pinions 

 may be completely locked, and there is an auxiliary loose pinion 

 with brake discs on the trailing axle. The last serves merely for 

 stopping the train, in case of any accident to the driving pinions 

 or their gear. The braking on down gradients is done by using 

 the steam cylinders as air compressors, there being special pro- 

 visions for this purpose. On the Nilgiri line the engines are 

 furnished with the Chatelier brake on both rack and adhesion 

 cylinders. All stock, both passenger and goods, are fitted with 

 the vacuum automatic brake acting on all six engine wheels and 

 all eight wheels of each vehicle. The rack pinions are also power- 

 fully braked. The trains are worked down the descent almost 

 entirely by the Chatelier brake, the driver keeping one hand on 

 that, and the other on the handle of the vacuum. Thus in an 

 instant, he can apply the former on the engine and the latter 

 throughout the whole length of the train. 



A similar system is in use on the Mount Lyell 3 ft. 6 in. rack 

 line in Tasmania. 



In the Strub system, the form of the central rack with smooth 

 high vertical sides, allows of the employment of a scissors shape 

 grip brake, which is worked by hand from the vehicle fitted with 

 it, gripping the rack bar itself, and it forms an effective addition 

 to the other brakes used. 



For bridges under the railway, arches instead of girders are 

 preferable, as otherwise the action of the pinions on the racks 

 would tend to cause the whole superstructure to creep downwards. 

 When girders are used, heavy abutments must be built on the 

 lower end of the bridge bearing against the end of the girders. 

 To guard against creep in the road generally, anchoring stop posts 

 butting against the down side of sleeper at intervals are some- 

 times required to be driven. However, in the Nilgiri line, the 

 deep fish plates butting against the sleepers, seem to be sufficient. 



