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AIR COMPRESSOR. York, 1902); for a somewhat more technical discussion of the production and use of compressed air, F. Richards, Compressed Air (New York, 1895). The most comprehensive descriptive treatise on compressed air in English is Hiscox, Compressed Air and Its Applications (New York, 1901).

AIR CUSHION, ki.is.li'nn. A mattress or cushion composed of a bag or sack of air-tight fabric, which can he inflated, and which possesses many advantages of comfort, cleanliness, and portability. Airbeds were known as early as the beginning of the eighteenth century, but, being made of leather, were expensive, and it was only after the invention of air-tight or rub- ber cloth that they could be constructed at a moderate cost. An air-bed consists of a sack in the form of a mattress, which may be divided into a number of compartments, each airtight, or, as is more usual at present, it may have a single compartment with the walls tied to each other to preserve its shape when inflated. The bed is supplied with a valve, or valves, through which the air is blown in by a bellows or an air- pump. They are especially valuable in many cases of sickness, and for use by camping parties. Air-inflated pillows are made to go with the mat- tresses. The air-cushion is another contrivance of the same kind, the layer of rubber being se- curely pasted or cemented to a layer of strong cloth, the cloth giving strength and the rubber impenetrability, and the whole sack covered with ticking. The chief drawback to these contri- vances is their liability to being spoiled by a rent or a puncture.

AIRD, ard, (1802-76). A Scottish poet of considerable talent. He was born at Bowden, in Roxburghshire, was educated at the University of Edinburgh, and gained the friendship of many distinguished men, especially John Wilson, who always spoke of him in very high terms. In 1835 he became editor of The Dumfries Herald, a new journal, started on conservative principles, an office which he filled till 1864. His works are not so well known as they deserve to be, from their intrinsic merit. In spite of very warm praise from Carlyle and others, they have failed to secure a large measure of public approbation. The Devil's Dream is perhaps an exception to the rest, for it is both well known and admired. There is something almost Dantesque in the stern, intense, and sublime literalness of the conception. Whether the scenes are on a large scale, as in The Devil's Dream, or minute, as in The Summers Day, there is the same clear, vigorous, and picturesque word-painting. In 1827 Aird published Religious Characteristics, a piece of exalted prose-poetry; in 1845, The Old Bachelor, a volume of tales and sketches; in 1848, a collected edition of his poems, a second edition of which appeared in 1856, and in 1852 he edited the select poems of David Macbeth Moir (the "Delta" of Blackwood's), prefixing a memoir. See his life and poems, edited by J. Wallace (1878).

AIRD'RIE (Gadhel. Smooth Height; from aird, height). A flourishing town in Lanarkshire, Scotland, 11 miles east of Glasgow (Map: Scotland, D 4). The highroad between Edinburgh and Glasgow intersecting it forms its principal street. It has risen rapidly, was incorporated in 1821, and is now one of the most flourishing inland towns in Scotland. Little more than a century ago it consisted of a solitary farmhouse or two. but the abundance of iron and coal found in the vicinity has given its industries an immense impetus. There are also cotton weaving establishments and paper mills. Pop., 1891, municipal borough, 19,135; 1901, 22,288.

AIRE, ar, or AIRE-SUR-L'ADOUR, ar'- sur'la'door'. A town of the department of Landes, France, picturesquely situated on the slope of a hill on the left bank of the Adour, 112 miles south of Bordeaux (Map: France, F 8). It has been the seat of a bishopric since the fifth century, and its cathedral of St. Wolfram is a fine example of flamboyant Gothic, begun by Cardinal Georges Antoine, under Louis XII., but afterward completed in a mean and paltry style. Aire has also a college and a library. Its industries are not considerable, hut its tanyards and hat factories give employment to most of its inhabitants. Pop., 1896, 2434; 1901, 2247.

AIRE, or AIRE-SUR-LA-LYS, fir'si.ir-U-k-s'. A town of the department of Pas-de-Calais, France, on the Lys and at the junction of three canals, 30 miles southeast from Calais. The town is fortified and well built, but its situation is low and marshy. Its chief buildings are the handsome Gothic church of St. Peter, dating from the fifteenth century, the Hôtel du Baillage or Corps de Garde of the sixteenth century, the Hôtel de Ville, and extensive barracks. It has various domestic manufactures and a trade in agricultural products. Pop.. 1901, 8458.

AIREDALE TER'RIER, ar'dSl. See.

AIR EN'GINE. See and.

AIR GUN. An instrument somewhat resembling a sporting rifle, designed to discharge darts or bullets by the elastic force of compressed air. As ordinarily made, an air gun consists essentially of an air chamber or reservoir, usually located in the stock; of a condensing syringe for pumping air into the reservoir, and of a valve operated by a trigger, which admits the compressed air from the reservoir to the barrel behind the bullet. In some weapons of this sort a pressure of as much as 500 pounds is secured in the reservoir. Usually only a portion of the air in the reservoir is used for a single shot, and, therefore, a number of shots may be fired without recharging the reservoir simply by releasing the pull on the trigger immediately and thus closing the valve between the reservoir and barrel after a small portion of the air has escaped. This permits repeating air guns to be made similar in the mechanism for inserting the bullets to repeating firearms. Obviously, the pressure in the reservoir decreases with each discharge of air, and, therefore, each succeeding bullet is discharged with less force than the preceding one. At best. the force with which a bullet is discharged from an air gun is much less than is given by gunpowder. Sometimes air guns are made in the form of canes or walking sticks, which, like sword canes, are carried for purposes of personal defense in sudden emergencies. The range of an air gun of the ordinary kind is from 180 to 250 feet. The air gun was known in France over two centuries ago, and the ancients were acquainted with a device by which air acted on the short arm of a lever, the longer