BRAKE, a contrivance to stop motion by friction, applied mainly to car wheels and hoisting apparatus. Originally it was a flexible iron band so placed that it might be drawn tightly around most of the outer surface of the revolving wheel, the friction gradually slackeniug the motion. In carriages curved blocks of wood were used, and pressed against the tire by a lever worked with the hand or the foot. Modern invention has given us systems of brakes that may be instantly applied to every wheel in a train of cars. For the Creamer brake, once somewhat in favor, a powerful spiral spring was the power applied. This spring was coiled in a drain through which a shaft passes, and was set free by the brakeman, or all the brakes on a train could be set free by one act of the engineer. The Westinghouse air-brake Is now very generally used in America. Each carriage has beneath its floor a cylinder and piston which may he operated by compressed air; the piston acts on suitable levers and rods to set the brakes against the wheels, the brakes also connected with the ordinary braking mechanism at the platform of the cars. Compressed air is conveyed to the cylinders
by tubes leading from a reservoir at the locomotive, and this reservoir is filled by a special engine which is independent of the ordinary motive mechanism. The special engine acts automatically, starting when the pressure of air in the reservoir is below a fixed standard, and stopping when the pressure reaches another fixed standard. The engine-driver communicates the compressed air to the cylinders by the simple act of turning a valve-handle through one fourth of a circumference; the brakes are instantly set" with great force throughout the train. A different system uses a vacuum, and the pistons beneath the cars are acted on by atmospheric pressure, when the cylinders are in communication with the vacuous reservoir. The Westinghouse and the other air brakes serve to place the train very fully under the control of the engine-driver; per mitting the stoppage of trains from high speed in a very short space.