Brake, Or Break, an instrument for retarding or arresting by friction the motion of wheels. When applied to a hoisting reel, it consists of a flexible band of iron bent around a wheel; one end of the band is made fast to the frame of the reel, and the other end is attached to the small arm of a lever, the whole being so arranged that a slight pull on a rope attached to the long arm of the lever tightens the iron band on the rim of the wheel, which is arrested by the consequent friction. A carriage brake in its primitive form consists of a beam placed crosswise under the frame of the vehicle, and supporting two curved blocks of wood, one at each end, which may be firmly pressed against the periphery of the wheels. The brake was formerly an instrument of little importance, and prior to 1835 only one patent for a brake was granted in the United States. Since the adoption of high speed upon railroads the subject of brakes has become one of great interest. There are two kinds used on railroad carriages, the ordinary brake for stopping the train at stations, and the safety brake, which may be applied instantaneously to the wheels of all the carriages on a train for the purpose of bringing it to a sudden halt.

The ordinary car brake consists of a friction block, a lever, a chain and rod for moving the lever, and a windlass upon the platform of the car. The general plan and principle of action are represented in fig. 1, where a is the wheel turned by the brakeman, s the shaft around which the chain c is wound, forming the windlass, which by the action of simple levers draws the friction blocks b b, fig. 2, against the periphery of the wheel. The application may be made in various ways. - Of the safety brakes there are several, but they may all be divided into three kinds: the first, in which the power is derived from a coiled spring; a second, in which it is derived from compressed air contained in a cylinder; and a third, in which electro-magnetism is the motive power. All these brakes employ the same friction block and leverage, which is connected with the windlass ordinarily turned by the brakeman. What is known as the Creamer brake, which is extensively used in the United States, employs a spiral spring as the motive power. This spring is coiled in a drum, which is placed upon the platform of the car, and through the drum passes the shaft, which is turned by the brakeman.

The general arrangement is represented in fig. 3, in which d is the drum containing the spring, s the shaft, and c the chain (corresponding to s and c in fig. 1).' The spring is wound up by means of a special attachment to the shaft turned by the brake-man, which can be connected or disconnected at pleasure. A cord, r, is attached by one end to the rope which passes through the train, and by the other to the lever I, which on being pulled by the cord liberates the spring, causing it to exert its force through the chain and lever upon the friction block, drawing it against the wheel. - The compressed air brake used in the United States is known as the Westinghouse air brake, and is made at Pittsburgh, Penn. Under each carriage there is placed a cylinder, fig. 4, 18 or 20 inches in length and about 8 inches in diameter, which is connected by metallic pipes and india-rubber tubing with a reservoir of compressed air attached to the engine, and which by a force pump receives a pressure of about 60 lbs. to the square inch. When the engineer wishes to bring the train to a sudden stop, he opens a valve leading from the air chamber to the various cylinders under the carriages. The air rushes through the tubes, and, pressing upon the piston heads, moves them.

By a connection with the piston rods the friction blocks are forced against the wheels simultaneously throughout the whole train. - An electric brake, devised by M. Achard of Paris, is described in President Barnard's " Report of the Paris Exposition of 1867," but it does not possess the practical advantages of either the Creamer or the Westinghouse brake.

Fig. l.

Fig. 2.

Fig. 3.