20 
A I R 
in its immenfe expanfe. Telefcopes of the belt fort be¬ 
came ufelefs, and I began to be apprehenfive for the death 
of the little animals, on account of the feverity of the 
cold. They defcended however about two hours after, 
quite fafe and well, in the town of Delitzfch, three miles 
from Leiplick. I went to claim them, and found them 
again over the town in the air with the parachute.” 
Mr. Blanchard’s fhirty-fecond afcenfion was made at 
Brunfwick, in the month of Auguft 1788, in which he was 
much aflifted by means of his wings. 
In regard to philofophical obfervations, derived from 
the new fubjedt of air-balloons, there have been very few 
made; the novelty of the difcovery, and of the profpedt 
enjoyed from the car of an aerofhitic machine, have com¬ 
monly diftradted the attention of the aeronauts; not to 
remark that many of the adventurers were inadequate to 
the pitrpofe of making improvements in philofophy, be¬ 
ing moftly influenced either by pecuniary motives, or the 
vanity of adding their names to the lift of aerial travellers. 
The agreeable ftillnefs and tranquillity experienced aloft 
in the atmofphere, have been matter of general obferva- 
tion. Some machines have afcended to a great height, as 
far, it has been faid, as two miles; and they have com¬ 
monly pafled through fogs and clouds, above which they 
ttave enjoyed the clear light and heat of the fun, whillt 
the earth beneath was actually covered by denfe clouds, 
which poured down abundance of rain. In afcending ve¬ 
ry high, the aeronauts have often experienced a pain in 
their ears, arifing, it is fuppofed, from the internal air be¬ 
ing not of the fame denfity as the air without; but the pain 
ufually went off in a ftiort time: and it feems that this ef- 
fedt is fifnilar to what is experienced by perfons who de- 
fcend by a diving-bell to conliderable depths in the fea. 
The late unfortunate Mr. Spalding, the celebrated diver, 
fpoke of this eftedt with a marked and philofophical ac¬ 
curacy : after defcending two or three fathoms below the 
furface, he began to feel a pain in his ears, which gra¬ 
dually increafed to a very great degree if the defcent was 
too quick; his method was therefore to defcend llowly, 
and to make a ftop for fome minutes at the depth of five 
fathom, which is nearly equal to the prellure of the at¬ 
mofphere, and where confequently the air in his bell was 
of double the denlity of common air at the furface ; after 
refting here awhile, his ears, as he exprefled it, gave a 
crack, and he was fuddenly relieved of the pain. He then 
defcended five fathoms more, with the fame fymptoms, 
and the fame eftedt: and fo on continually, from one five 
fathoms to another, defcending leifurely, and flopping a 
little at each ftage, to give time for his conllitution to 
adapt itfelf to the degree of condenfation of the air; af¬ 
ter which he felt no more inconvenience, till he came to 
afcend again, which was performed with the fame caution 
and circumftances. One experiment is recorded, in which 
the air of a high region, being brought down, and exami¬ 
ned by means of nitrous air, was found to be purer than 
the air below. The temperature of the upper regions 
too, it has been found, is much colder than that of the 
air near the earth; the thermometer, in fome aeroftatic 
machines, having defcended many degrees below the free¬ 
zing point of water, while it was confiderably higher than 
that degree at the earth’s furface. 
A ir-b ladder, f. Any cuticle or veficle filled with air. 
—The pulmonary artery and vein pafs along the furfaces 
of thefe air-bladders , in an infinite number of ramifica¬ 
tions. Arbutknot .—The bladder in fifties, by the contrac¬ 
tion and dilatation of which, they vary the properties of 
their weight to that of their bulk, and rife or fall.—Tho’ 
tire air-bladder in fifties feems neceflary for fwimming, yet 
fome are fo formed as to fwim without it. Cudworlk. 
Air-built, adj. Built in the air, without any folid 
foundation: 
Hence the fool’s paradife, the ftatefman’s fcheme, 
The air-built caftle, and the golden dream, 
The maid’s romantic wifli, the chemift’s flame, 
And poet’s vifton of eternal fame. Pope, 
A I R 
Air-drawn, adj. Drawn or painted in air-i a word 
not ufed. 
AIRER,yi He that expofes to the air. 
AIR-GUN, /. in pneumatics, is a machine for propel¬ 
ling bullets with great violence, by the foie means of con- 
denfed air. The firft account we meet with of an air-gun, 
is in the Elemens d'Artillerie of David Rivaut, who was 
preceptor to Louis XIII. of France. He aferibes the in¬ 
vention to one Marin, a burgher of Lifieux, who prefented 
one to Henry IV. 
To conftrudt a machine of this kind, it is only neceflary 
to take a firong veffel of any fort, into which the air is to 
be thrown or condenfed by means of a fyringe, or other- 
wife, the more the better; then a valve is fuddenly opened, 
which lets the air efcapeby a fmall tube in which a bullet 
is placed, and which is thus violently forced out before 
the air. It is evident then that the eftedt is produced by vir¬ 
tue of the elaftic property of the air; the force of which 
is diredtly proportional to its condenfation ; and therefore 
the greater quantity that can be forced into the engine, the 
greater will be the effedt. Now this eff'edt will beexadtly 
fimilar to that of a gun charged with powder, and there¬ 
fore we can eafily form a comparifon between them : for 
inflamed gunpowder is nothing more than very condenfed 
elaftic air; fo that the two forces are exadtly fimiliar. 
Now it is ftiewn by Mr. Robins, in his New Principles of 
Gunnery, that the fluid of inflamed gun-powder, has, at 
the firft moment, a force of elafticity equal to about 1000 
times that of common air; and therefore it is neceflary 
that air fhould be condenfed 1000 times more than in its 
natural ftate, to produce the fame eftedt as gun-powder. 
But then it is to be conlidered, that the velocities with 
which equal balls are impelled, are diredtly proportional 
to the fquare roots of the forces; fo that, if the air in an 
air-gun be condenfed only ten times, then the velocity it 
will projedt a ball with, will be, by that rule, one-tenth of 
that arifing from gun-powder; and, if the air were con¬ 
denfed twenty times, it would communicate a velocity of 
one-feventh of that of gun-powder. But in reality the 
air-gun flioots its ball with a much greater proportion of 
velocity than as above, and for this reafon, that as the re- 
fervoir, or magazine of condenfed air, is commonly very 
large in proportion to the tube which contains.the ball, 
its denfity is very little altered by expanding through that 
narrow tube, and confequently the ball is urged all the 
way by nearly the fame uniform force as at the firft in- 
ftant; whereas the elaftic fluid arifing from inflamed gun¬ 
powder is but very fmall in proportion to the tube or 
barrel of the gun, occupying at firft: indeed but a very 
fmall portion of it next the but-end: and therefore by 
dilating into a comparatively large fpace, as it urges the 
ball along the barrel, its elaftic force is proportionally 
weakened, and it adts always lefs and lefs on the ball in 
the tube. From which caufe it happens, that air, con¬ 
denfed into a good large machine only ten times, will fhoot 
its ball with a velocity hut little inferior to that given by 
the gun-powder. And if the valve of communication be 
fuddenly Unit again by a fpring, after opening it to let 
fome air efcape, then the fame colledtion of it may ferve 
to impel many balls, one after the other. 
In all cafes in which a confiderable force is required, and 
confequently a great condenfation of air, it will be requi- 
fite to have the condenfing fyringe of a fmall bore, per¬ 
haps not more than half an inch in diameter: otherwife 
the force to produce the compreflion will become fo great, 
that the operator cannot werk the machine; for, as the 
prefliire againft every fquare inch is about fifteen pounds, 
and againft every circular inch about twelve pounds, if 
the fyringe be one inch in diameter, when one atmofphere 
is injected, there will be a reliftance of twelve pounds 
againft the pilton; when two, of twenty-four pounds; and, 
when ten are.injedted, there will be a force of 120 pounds 
to overcome; whereas ten atmofplieres adt againft the 
half-inch pifton, whofe area is but one-quarter of the for¬ 
mer, with one-quarter of tho force only, namely, thirty 
pounds-;. 
