in Physics. See Atmosphere, Meteorology, and Pneumatics.

in Painting, &c., denotes the manner and verisimilitude of action; or it is that which expresses the disposition of the agent. It is sometimes also used in a synonymous sense with gesture or attitude.

in Music. See Music.

Air-Gun, a pneumatic machine for propelling bullets, &c., with great violence. See Pneumatics.

Air-Jacket, a sort of jacket formerly made of leather, in which were several bags or bladders, composed of the same material, communicating with each other. These were filled with air through a leather tube having a brass stop-cock accurately ground at the extremity, by which means the air blown in through the tube was confined in the bladders. The jacket is now superseded by a tubular belt of cloth, made air-tight by a solution of caoutchouc in naphtha, buckled round the breast, by the help of which the person is supported in the water, without making the efforts used in swimming.

Air-Pipes. See Ventilators.

Air-Pump, a machine by which the air contained in a proper vessel may be exhausted or drawn out. See Pneumatics.

Air-Shafts, among Miners, denote holes or shafts descending from the open air to meet the adits and furnish fresh air. The damps, deficiency, and impurity of air which occur when adits are wrought 30 or 40 fathoms long, make it necessary to sink air-shafts, in order to give the air liberty to play through the whole work, and thus discharge vitiated air, and furnish good air for respiration: the expense of which shafts, on account of their great depths, hardness of the rock, drawing of water, &c., sometimes equals, nay, exceeds, the ordinary charge of the whole adit.

Air-Threads, or Air Gossamer, a name given to the long filaments so frequently seen in autumn floating about in the air.

These threads are the work of spiders, especially of that species called the aranea obtestrix, which, having mounted to the summit of a bush or tree, darts from its tail several of these threads, till one is produced capable of supporting the creature in the air. On this it mounts in quest of prey, and frequently rises to a very considerable height.

Air-Vessels are spiral ducts in the leaves, &c. of plants, supposed to be analogous to the lungs of animals, in supplying the different parts of a plant with air.