Many different devices have been used to apply the brake-shoes to the wheels, and various sources of power. Hand-power brakes have been used, worked by levers, or by screws, or by winding a chain on a staff; or, in still other forms, springs wound up by hand are released and apply the brakes by their pressure. The momentum of the train has been employed to wind up chains by the rotation of the axles. This is the principle of the chain-brake, very much used in England. This same source of power has been utilized by causing the drawheads, when thrust in as the cars run together, to wind up the brake-chains. Hydraulic pressure has been used in cylinders under the cars; and finally air, either under pressure or acting against a vacuum, has been found to be the most useful of all means of operating train-brakes. Early forms of hand-brakes are seen in the illustrations of some old English cars. The coach shows a hand-brake operated by a screw and system of levers. By turning a crank the guard puts in operation the system of levers which apply the brake with great force; but the operation is slow. The common hand-brake of the United States is too well known to need illustration. With this brake a chain is wound around the foot of a staff, and the pull of this chain is transmitted by a rod to the brake-levers. This apparatus is simple, and when a train is manned by a sufficient number of smart brakemen it is capable of doing good service. This simple form of hand-brake will probably be used in freight-car service until it is replaced by air-brakes, and the various forms of chain and momentum brakes do not appear likely to be much more used in the future than they have been in the past. Therefore, no further space will be given to them.