The continuous brake which to-day prevails all over the world, is the automatic air-brake. In the United States much the largest part of the rolling stock used in passenger service is equipped with the Westinghouse automatic brake. A few roads peculiarly situated use the Eames vacuum-brake. That brake is used on the elevated roads of New York, and on the Brooklyn bridge roads. The Westinghouse brake is also largely used in England, on the Continent of Europe, in India, Australia, and South America. In the United States it is being rapidly applied to freight cars also. This brake, therefore, being the highest development of the automatic air-brake, and the one most widely used, will be briefly described, as best representing the most approved type of the most important of all safety appliances. The general diagram which is given on pages 196-97 shows all of the principal parts as applied to a locomotive, a tender, and a passenger car. The diagram is reduced from one prepared by Mr. M. N. Forney for a new edition of his "Catechism of the Locomotive." In the plan view are shown very clearly the hand-wheels, the chains, the rods, and the levers by which the brake is applied by hand. In passenger service the hand-wheels are rarely used, but they are retained for convenience in switching cars in the yard, and for those rare emergencies in which the air-brakes fail. Under the middle of the car the ordinary pull-rod of the old hand-brake is cut and two levers are inserted. One lever is connected with the brake-cylinder, and the other with the piston which slides in that cylinder. When air is admitted to the cylinder the piston is driven out, and the brakes are applied exactly as they would be were the chains wound up by turning the hand-wheels. Compressed air is supplied to the cylinder from the reservoir near it, in which pressure is maintained at from 70 to 80 pounds per square inch by a pump placed on one side of the locomotive. The pump fills the main reservoir on the engine, and also the car-reservoirs, by means of the train-pipe which extends under all the cars. When the brakes are off there is a full pressure of air in all of the car-reservoirs and train-pipes. It is a _reduction_ of the pressure in the train-pipes which causes the brakes to be applied. [Illustration: Plan and Elevation of Air-brake Apparatus.--Reservoirs and piping in solid black; brake gear shaded.]