AIH 



AIR, a thin elastic fluid, surrounding- 

 tile globe of the earth. It iscompounded 

 principally of two gasses, viz. oxygen and 

 azote, together with a variety of other 

 substances, suspended or dissolved there- 

 in. The mechanical and chemical effects 

 of this extensive fluid mass are discussed 

 under various heads of science. See AT- 

 JNIOSPHERE, CHEMISTRY, and the articles 

 thence referred to. 



AIR, in music, generally speaking 1 , is 

 any melody, the passages of which are so 

 constructed as to lie within the province 

 of vocal expression, or which, when sung 

 or played, forms that connected chain of 

 sounds which we call tune. The strict 

 import of the word is confined to vocal 

 music, and signifies a composition writ- 

 ten for a single voice, and applied to 

 words. 



AiR-gvm, a machine for exploding balls 

 by means of condensed air. 



Authors describe two kinds of this ma- 

 chine, viz. the common one, and what is 

 called the magazine air-gun. See PXEU- 



-HATICS. 



AiR-pipes, a contrivance invented by 

 Mr. Sutton, a brewer of London, for clear- 

 ing the holds of ships, and other close 

 places, of their foul air. The principle 

 upon which this contrivance is founded is 

 well known. It is no other than the rare- 

 fying power of heat, which, by causing a 

 diminution of the density of the air in one 

 place, allows that which is in contact with 

 it to rush in, and to be succeeded by a 

 constant supply from remoter parts, till 

 the air becomes every where equally elas- 

 tic. If a tube then, be laid in the well- 

 hold, or any other part of a ship, and the 

 upperpart of this tube be sufficiently heat- 

 ed to rarefy the impending column of air, 

 the equilibrium will be maintained by the 

 putrid air from the bottom of the tube, 

 which, being thus drawn out, will be suc- 

 ceeded by a supply of fresh air from the 

 other parts of the ship; and by continuing 

 the operation, the air will be changed in 

 all parts of the ship. Upon this principle, 

 Mr. Sutton proposed to purify the bad air 

 of a ship by means of the fire used for the 

 coppers, or boiling places, with which 

 every ship is provided. Under every such 

 copper or boiler there are two holes, se- 

 parated by a grate, one for the fire and 

 the other for the ashes ; and there is also 

 a flue, communicating with the fire place, 

 for the discharge of the smoke. The fire, 

 after it is lighted, is preserved by the con- 

 stant draught of air through these two 

 holes and the flue ; and if the two holes 

 are closed, the fire is extinguished. But 





when these are closed, if another hole, 

 communicating with any other airy place, 

 and also with the fire, be opened, the fire 

 will of course continue to burn. In order 

 to clear the holds of the ships of the bad 

 air, Mr. Sutton proposed to close the two 

 holes above mentioned, viz. the fire-place 

 and ash-place, with substantial iron doors, 

 and to lay a copper or leaden pipe, of suf- 

 ficient size, from the hold into the ash- 

 place, and thus to supply a draught of air 

 for feeding the fire ; a constant discharge 

 of air from the hold will be thus obtained, 

 and fresh air will be supplied down the 

 hatches, and by such other communica- 

 tions as are open into the hold. If other 

 pipes are connected with this principal 

 pipe, communicating either with the 

 wells or lower decks, the air that serves 

 to feed the fire will be drawn from such 

 places. 



AiR-shafts, among miners, -are holes 

 made from the open air to meet the adits, 

 and supply them with fresh air. 



These, when the adits are long, or ex- 

 ceeding thirty or forty fathoms, become 

 highly necessary, as well to give vent to 

 the damps and noxious vapours, as to let 

 in fresh air. 



AiR-Zr?mfc, a simple contrivance by Dr. 

 Hales, for preventing the stagnation of 

 putrid effluvia, and purifying the air in 

 jails and close rooms ; which consists of 

 a square trunk, open at both ends, one of 

 which isfixedin the ceiling, and the other 

 is extended to a considerable height 

 above the roof. The noxious effluvia, as- 

 cending to the top of the room> escape by 

 this trunk. Some of these have been 

 nine, and others six, inches in the clear ; 

 but, whatever be their diameter, their 

 length should be proportional, in order 

 to promote the ascent of the vapour. As 

 the pressure of fluids, and consequently 

 of the air, corresponds to their perpendi- 

 cular altitude, the longer these trunks 

 are, so much the greater will be the dif- 

 ference between columns of air pressing 

 at the bottom and at the top ; and of 

 course so much the greater wilt be their 

 effect. See VENTILATOR. 



Am-vesset, in hydraulics, is a name 

 given to those metalline cylinders, which 

 are placed between the two forcing- 

 pumps in the improved fire-engines. The 

 water is injected by the action of the 

 pistons through two pipes, with valves, 

 into this vessel : the air previously com- 

 tained in it will be compressed by the 

 water, in proportion to the quantity ad- 

 mitted, and by its spring force the water 

 into a pipe, which will discharge a con- 



