Air-brake, a brake operated by air pressure, usually applied to brake, simultaneously, all the wheels of a moving train. In the Westinghouse type, by means of an ingenious 'triple valve' carried one on each carriage, the train pipe is made to serve the dual purpose of supply and control. An air-pump on the engine compresses air into the main receiver, from which it flows through a reducing valve into the train pipe. The pressure, acting on the under side of the triple valve, moves the valve to its extreme
position, thereby opening a passage to an auxiliary receiver on the carriage and also putting the brake cylinder into communication with the atmosphere. A spring in the brake cylinder keeps the brakes in the 'off' position.
To apply the brakes, the pressure is lowered in the train pipe. The air pressure in the auxiliary receiver reverses the triple valve, thus admitting air to the brake cylinder and closing the outlet to atmosphere.
To remove the brakes, air from the main receiver is passed into the train pipe, and the triple valve is restored to the 'off' position. See Traction.—Bibliography: W. W. Wood, Westinghouse Air-brake; R. H. Blackhall, Air-brake Catechism.
Air-cells, cavities in the cellular tissue of the stems and leaves of plants which contain air only, the juices of the plants being contained in separate vessels. They are largest and most numerous in aquatic plants, as in the Vallisneria spirālis and the Victoria regia, the gigantic leaves of which latter are buoyed up on the surface of the water by their means.—The minute cells in the lungs of animals are also called air-cells. There are also air-cells in the bodies of birds. They are connected with the respiratory system, and are situated in the cavity of the thorax and abdomen, and sometimes extend into the bones. They are most fully developed in birds of powerful and rapid flight, such as the albatross.
Aird, Thomas, a Scottish poet and miscellaneous writer, friend of Professor Wilson, De Quincey, and Carlyle, long editor of a newspaper in Dumfries; born 1802, died 1876. He wrote The Devil's Dream on Mount Aksbeck; The Old Bachelor, &c.
Airdrie, a municipal and parliamentary burgh of Scotland, in Lanarkshire, near the Monkland Canal, 11 miles east of Glasgow, in the centre of a rich mining district, with a large cotton-mill, foundries and machine shops, breweries, &c., and collieries and ironworks in its vicinity. Pop. 24,160.
Air-engine, an engine in which air heated, and so expanded, or compressed air is used as the motive power. A great many engines of the former kind have been invented, some of which have been found to work pretty well where no great power is required. They may be said to be essentially similar in construction to the steam-engine, though of course the expansibility of air by heat is small compared with the expansion that takes place when water is converted into steam. Engines working by compressed air have been found very useful in mining, tunnelling, &c., and the compressed air may be conveyed to its destination by means of pipes. In such cases the waste air serves for ventilation and for reducing the oppressive heat.
Aire (ār), a river of England, W. Riding of Yorkshire, rising to the south-east of Penyghent and flowing in a south-easterly direction to join the Ouse above Goole, having passed through Leeds on its way; length, 70 miles. It is navigable up to Leeds, and forms an important portion of the Aire and Calder Navigation system, which connects Goole, Hull, &c., with Liverpool. The Calder enters the Aire at Castleford. The district specially known as Airedale is the valley of the Aire above Leeds.—A large breed of terrier, of which there are several varieties, is known as the Airedale terrier, a strongly-built animal, rather long in the legs, with a hard, close coat.
Aire, a river of France, in the Argonne region, a tributary of the Aisne.