[18] Only the "drum" type of armature is treated here.
[19] This refers to continuous-current dynamos only.
[20] The Robertson.
Chapter X.
RAILWAY BRAKES.
The Vacuum Automatic brake—The Westinghouse air-brake.
In the early days of the railway, the pulling up of a train necessitated the shutting off of steam while the stopping-place was still a great distance away. The train gradually lost its velocity, the process being hastened to a comparatively small degree by the screw-down brakes on the engine and guard's van. The goods train of to-day in many cases still observes this practice, long obsolete in passenger traffic.
An advance was made when a chain, running along the entire length of the train, was arranged so as to pull on subsidiary chains branching off under each carriage and operating levers connected with brake blocks pressing on every pair of wheels. The guard strained the main chain by means of a wheel gear in his van. This system was, however, radically defective, since, if any one branch chain was shorter than the rest, it alone would get the strain. Furthermore, it is obvious that the snapping of the main chain would render the whole arrangement powerless. Accordingly, brakes operated by steam were tried. Under every carriage was placed a cylinder, in connection with a main steam-pipe running under the train. When the engineer wished to apply the brakes, he turned high-pressure steam into the train pipe, and the steam, passing into the brake cylinders, drove out in each a piston operating the brake gear. Unfortunately, the steam, during its passage along the pipe, was condensed, and in cold weather failed to reach the rear carriages. Water formed in the pipes, and this was liable to freeze. If the train parted accidentally, the apparatus of course broke down.