TRANSACTIONS OF SECTION G. 519 



France showed that the pressure commenced to be brought on in one second at the 

 farthest carriage, and was fully one in two and a half seconds from the time of first 

 moving the brake lever. 



The importance of simultaneous action of the brakes in every part of a train 

 arises from the fact that the train is not a rigid mass, but is made up of separate 

 vehicles connected by means of spring draw-bars and buffers. The length of the 

 train can thus be modified to a certain extent by the degree of compression of 

 these springs. In a recent experiment on the North-Eastern Railway the train 

 consisted of twenty-four carriages, and the whole extent to which the buffers could 

 be compressed amounted to 35 feet. A train travelling at sixty miles an hour 

 moves at 88 feet in a second. If the brakes act on the front part of the train 

 before they affect the hind part the speed of the front carriages may be diminished 

 by 10 to 15 feet in a second, whilst the hind part moves on with undiminished 

 speed ; thus the hind part may press against the front part with a force of from 10 

 to 15 foot-tons for every ton weight of the hind vehicles. The buffer springs 

 would be compressed by this force and remain so till the brakes acted equally on 

 all the wheels, when a reaction of the buffer springs would take place ; this reaction 

 creates the violent jerks often felt with continuous brakes, and occasionally results 

 in fractures of couplings and draw-bars. In a perfect brake the application would 

 be instantaneous, and simultaneous on all the wheels of a train. 



It is beyond the scope of this paper to enter fully into the merits of different 

 kinds of brakes, but it may be convenient to sum up what seem to be the require- 

 ments of a perfect brake. 



1. It should be fitted to act upon each wheel of the engine, tender, and every 

 other vehicle in a train of any length. The brake-blocks, when out of action, 

 must be kept a certain distance away from the wheels, in order to prevent any 

 liability to drag against the wheels; and this distance, after being once adjusted, 

 gradually increases by the wear of the blocks, and often exceeds three-quarters of 

 an inch ; while the springing of the brake-gear under great strain also adds to the 

 extent of movement required in the brake force before the blocks are fully applied. 

 Hence the brake-gear should be so adjusted as to be capable of moving the brake- 

 blocks instantaneously through a space of one inch. 



2. However brought into action, it should be capable of exerting upon the 

 blocks of each pair of wheels, within two seconds, a force of twice, or at the very 

 least one-and-three-quarter times, the load on those wheels. 



3. The brake-block pressure acting on each wheel should be regulated so that 

 the friction between the brake-block and the wheel may always be limited so as 

 not to exceed the adhesion between the wheel and the rail ; by which means it will 

 produce the maximum effect at each moment of its application. 



4. The brake-block pressure should be capable of being applied by engine-driver 

 or by guards. 



5. The engine, tender, and vehicles should each carry its own store of brake- 

 power, which should be independent of the brake-power on any other vehicle. 



6. The brake-block pressure should be automatically applied to every vehicle 

 by the separation of the train into two or more parts, and it should also be applied 

 by the act of the wheels of any carriage leaving the rails. 



7. The brake-block pressure should be automatically applied by such failure of 

 the connections or appliances as would render it afterwards incapable of application 

 until the failure had been remedied. 



8. The brake-block pressure should be capable of application with any degree 

 of force up to the maximum, and it should be capable of continued action on 

 inclines, or of repeated applications at short intervals at junctions and stations. 



In addition to these requirements, the questions of cost, durability, convenience 

 in operation, and other essential points, will of course come under consideration. 



The experiments which have been here described were made on trains travelling 

 under conditions which were necessarily continually varying, both in respect of the 

 condition of the rails and other matters ; and they therefore contained many 

 elements beyond the reach of calculation. It is hoped that some opportunity may 

 arise, ere long, for resuming experiments on friction at high velocities under 



