_Answer._ What is called, after its inventor, the Westinghouse atmospheric brake is now used more than any other. Next to this, Smith’s vacuum brake is used most. Besides these two, Creamer’s, Ward’s, Loughridge’s and Henderson’s systems of brakes are used to a limited extent. The two first are, however, the only ones which have come into sufficiently extensive use as yet to justify us in describing them here. QUESTION 443. _How does the Westinghouse brake act and how is it constructed?_ _Answer._ As its name indicates, the medium employed for transmitting the power for operating the brakes is atmospheric air. [Illustration: Fig. 223. Scale ¹⁄₂ in. = 1 foot.] This is compressed to any required density by a steam pump which is located between the driving-wheels, or in any other convenient place on the locomotive. This pump is shown in section in fig. 223 and consists of two cylinders, the upper one, _A_, the steam cylinder, the piston of which is connected by its rod with the piston in the lower cylinder, _B_. This latter is operated by the steam piston, and at each stroke a quantity of air, equal to the space swept through by the lower piston, is compressed and thus forced into a cylindrical reservoir, which is usually placed under the foot-board of the locomotive, in which it is stored for use at any time when the brakes are to be applied. The air and steam cylinders are supplied with suitable valves for admitting and releasing the air and steam. From this reservoir it is conducted back under the tender and cars by pipes, which are connected together between the engine and tender and between the cars by India rubber hose. Two pieces of hose are attached to the engine and also to each end of the tender and cars, so that in case one piece should break the others will act. Each of these pieces is united or coupled to the corresponding piece opposite to it by a peculiar coupling made for the purpose, so that they can be quickly disconnected if the cars, engine or tender are uncoupled.