226 AIR 
expence of which (hafts, in regard to their val? depths, 
hardnefs of the rock, drawing of water, &c. fometimes 
equals, nay exceeds, the ordinary charge of the whole 
adit. Sir Robert Murray defcribes a method, ufed in the 
coal-mines at Liege, of working mines without air-fhafts. 
When the miners at Mendip have funk a groove, they 
will not be at the charge of an air-fit aft till they come at- 
ore ; and for the fupply of air have boxes of elm exactly 
doled, of about fix inches In the clear, by which they 
carry it dow n about twenty fathoms. They cut a trench 
af a little diltance from the top of the groove, covering it 
with turf and rods difpofed to receive the pipe, which 
they contrive to come in Tideways to their groove, four 
feet from the top ; which carries down the air to a great 
depth. When they come at ore, and need an air-lhalt, 
they, fink it four or five fathoms difiant, according to the 
convenience of the breadth, and of the fame fafhion with 
the groove, to draw as well ore as air. 
Air-threads, in natural hiflory, a name given to the 
long filaments, fo frequently feen in autumn floating about 
in the air. Thefe threads are the work of fpiders, efpe- 
cially of that fpecies called the long-legged field-fpider; 
which, having mounted to the fuuimit of abufhor tree, 
darts from its tail feveral of thefe threads, till one is pro¬ 
duced capable of fupporting the creature in the air: on 
tills it mounts in queft of prey, and frequently rifes to a 
Very conliderable height. See Aranea. 
Air-trunk, is a contrivance by Dr. Hales to prevent 
the (lagnation of putrid effluvia in gaols, and other places ^ 
where' a great number of people are crowded together in 
a fmall fpace. It confifts of a long fquare trunk open at 
both ends ; one of which is inferted into the deling of 
the room, the air of which is required to be kept pure; 
and the other extends a good way beyond the roof. Thro’ 
this trunk a continued circulation is carried on: and the 
realon is, that the putrid effluvia which do fo much mif- 
chief when collected, being much lighter than the pure 
Atmofphere, arife to the top of the room ; and, if they 
there find a vent, will continually go out through it. 
Thefe effluvia arife in very conliderable quantity, being 
calculated by the late Dr. Keil at no lefs than thirty-nine 
ounces from one man in twenty-four hours. 
Thefe trunks were firff made trial of by Mr. Yeoman, 
over the Houfe of Commons, where they were nine inches 
wide within; and over the court of King’s Bench in Well- 
minfter-hall, w here they were fix inches wide. They are 
fometimes made wider, and fometimes narrower: but the 
wider they are the longer they ought to be, more effefili¬ 
ally to promote the afcent of the vapour. The reafon 
why vapours of this kind afcend more fwiftly through a 
long trunk than a fhort one, is, that the pretfure of fluids 
is always according to their different depth, without regard 
to the diameter of their bafis, or of the veflel which con¬ 
tains them ; and, upon this principle, a gallon of water 
maybe made to fplit aftrongcafk. See Hydrostatics. 
When the column of putrid effluvia is long and narrow, 
the difference between the column of atmofphere’prefling 
on the upper end of the trunk, and that v hich preffes on 
the lower end, is much greater than if the column of pu¬ 
trid effluvia was fhort and wide; and, confequently, the 
afcent is much fw'ifter. One pan of a (ingle pair of fcales, 
which was two inches in diameter, being held within one 
of thefe trunks over the Houfe of Commons, the force of 
the afcending air made it rife fo as to require four grains 
to reftore the equilibrium, and this when there w r as no 
perfon in the houfe ; but, when it was full, no lefs than 
twelve grains Were requisite to reftore the equilibrium ; 
which clearly ftiews that thefe trunks muff be of real and 
very great efficacy. 
Air-vessel, in hydraulics, is a veflel of air within 
fome water-engines, which being comprefled, by forcing 
in a conliderable quantity of water, by its uniform fpring, 
forces it out at the pipe in a conflant uninterrupted ftream, 
to a great height. 
Air-veffel too, in the improved fire-engines, isametal- 
A I R 
lie cylinder, placed between the two forcing-pumps, by 
the adlion of whole piftons the wat^r is forced into this 
veflel, through two pipes, w ith valves; then the air, pre- 
vioufly contained in it, is comprelfed by the water, in 
proportion to the quantity admitted, and this air, by its 
fpring, forces the water through a pipe by a conflant and 
equal ftream ; whereas, in the common fquirting engine, 
the ftream is difeontinued between the feveral ftrokes. See 
Hydraulics. 
Air-vessels, in botany, are fpiral duels in the leaves, 
&c. of plants, fuppofed to be analagous to the lungs of 
animals, in fupplying the different parts of a plant with 
air. 
AIRY, adj. [from airy aeriuSj Lat.] Compofed of air. 
Relating to the air ; belonging to the air.—There are fifti¬ 
es that have wings, that are no flrangers to the airy region. 
Boyle. —High in air. Open to the free air. Light as air: 
thin ; unfubftantial; without folidity.—I hold ambition 
of fo airy and light a quality, that it is but a fhadow’s Iha- 
dow. Shakcfpeare. —Wanting reality; having no Heady 
foundation in truth or nature; vain; trifling.—I have 
found a complaint concerning the fcarcity of money, which 
occasioned many airy propolitions for the remedy of it. 
Temple. —Fluttering; loofe; as if to catch the air; full of 
levity.—By the name of ladies, he means all young per- 
fons, (lender, finely fliaped, airy, and delicate: fuch as are 
nymphs and Naiads. Dryden. —Gay; Uprightly: full of 
mirth; vivacious; lively; fpirited; light of heart.—He 
that is merry and airy at (liore when he fees a did temped 
on the fea, or dances when God thunders from heaven, 
regards not when God fpeaks to all the world. Taylor. 
AIR,/ in mythology, was adored by the Heathens un¬ 
der the names of Jupiter and Juno; the former repre- 
fenting the fuperior and finer part of the atmofphere, and 
the latter the inferior and grofler part. The augurs alfo 
drew prefages from the clouds, thunder, lightning, &rc. 
Air, in painting, &c. denotes the manner and very life 
of action; or it is that which ex preffes the difpofition of 
the agent. It is fometimes alfo ufed in a fynonymous fenfe 
with gefture or attitude. 
Air, in mufic, is taken in different fenfes. It is fome¬ 
times contrafted-with harmony; and, in this fenfe, it is fy¬ 
nonymous with melody in general. Its proper meaning is, 
A tune which is fet to words, or to fhort pieces of poetry 
that are called fongs. In operas, we give the name of air 
to fuch pieces of mufic as are formed with meafures and 
cadences, to diftinguifh it from the recitative ; and, in ge¬ 
neral, every piece of mufic is called an air, which is form¬ 
ed for the voice, or even for inflruments, and adapted to 
ftanzas, whether it forms a wliole in itfelf, or whether it 
can be detached from any whole of which it forms a part, 
and be executed alone. If the fubjecl admits of harmo¬ 
ny, and is fet in parts, the air is, according to their num¬ 
ber, denominated a duett, a trio, a quartetto, &c. ~ We need 
not follow Roufleau, and the other philologifts, in their 
endeavours to inveftigafe the etymon of the word air. Its 
derivation, though found and afeertained, would contri¬ 
bute little to illuflrate its meaning in that remote fenfe, to 
which, through a long continuance of time, and the vari¬ 
ous viciflitudes of language, it has now paffed. The cu¬ 
rious may confult the fame article in the 'Didlionnaire dc 
Muftque, by M. Roufleau. 
In modern mufic. there are feveral different kinds of 
airs, each of which agrees to a certain kind of dancing, 
and from thefe dances the airs themfelves take their fpeci- 
fic names. The airs of our operas, are, if we may die 
permitted the expreflion, the canvafs or fubflratuni upon 
which are painted all the pidlures of imitative mufic; me¬ 
lody is the defign, and harmony the colouring; every pic- 
turefque objefl feledted from the mofl beautiful parts of 
nature, every reflefled fentiment of the human heart, are 
the models which the artiff imitates; whatever gains at¬ 
tention, whatever interefts the foul, whatever charms the 
ear, or caufes emotion-in the heart, thefe are the objedls 
of his imitation. 'See Imitation. An air which delights 
the 
