A 1 11 A 
copper or boiler, there are two holes sepa- 
rated 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 constant 
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 substan- 
tial iron doors, and to lay a copper or leaden 
pipe, of sufficient size, from the hold into 
the ash-place, and thus to supply a draught 
of air for feeding the fire ; a constant dis- 
charge of air from the hold will be thus ob- 
tained, and fresh air will be supplied down 
the hatches, and by such other communi- 
cations 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 sup- 
ply 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. 
Am-trunk, a simple contrivance by Dr. 
Hales, for preventing the stagnation of pu- 
trid effluvia, and purifying the air in jails 
and close rooms ; which consists of a square 
trunk open at both ends, one of which is 
fixed in the ceiling, and the other is ex- 
tended to a considerable height above the 
roof. The noxious effluvia, ascending 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 pro- 
portionable, in order to promote the ascent 
of the vapour. As the pressure of fluids, 
and consequently of the air, corresponds to 
their perpendicular altitude, the longer these 
trunks are, so much the greater will be the 
difference between columns of air pressing 
at the bottom and .at the top ; and of course 
so much the greater will be their effect. See 
Ventilator. 
Air -vessel, in hydraulics, is a name given 
to those metalline cylinders, which are 
placed between the two forcing-pumps in 
AIR 
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 contained in it will be com- 
pressed by the water, in proportion to the 
quantity admitted, and by its spring force 
the water into a pipe, which will discharge 
a constant and equal stream ; whereas in the 
common squirting engine the stream is dis- 
continued between the several strokes. 
Other water-engines are furnished with ves- 
sels of this kind. 
Air -vessels, in botany, are certain ca- 
nals, or ducts, whereby a kind of absorp - 
tion and respiration is effected in vegetable 
bodies. 
Air-vessels have been distinguished from 
sap-vessels; the former being supposed to 
correspond to the trachea and lungs of ani- 
mals ; the latter to their lacteals and blood- 
vessels. 
Dr. Grew, in an inquiry into the motion 
and cause of the air in vegetables, shews, 
that it enters them various ways, not only 
by the trunk, leaves, and other parts above 
ground, but at the root. For the recep- 
tion, as well as expulsion of the air, the 
pores are so very large in the trunks of 
some plants, as in the better sort of thick 
walking-canes, that they are visible to a 
good eye without a glass ; but with a glass 
the cane seems as if it were stuck full of 
large pin-holes, resembling the pores of the 
skin in the ends of the fingers and ball of 
the hand. In the leaves of the pine, through 
a glass, they make an elegant shew, stand- 
ing almost exactly in rank and file through- 
out the length of the leaves. But though 
the air enters in partly at the trunk, and 
also at other parts, especially in some plants, 
yet its chief admission is at the root : much 
as in animals, some, part of the air may con- 
tinually pass into the body and blood by the 
pores of the skin ; but the chief draught is 
at the mouth. If the chief entrance of the 
air were at the trunk, before it could be 
mixed with the sap in the root it must de- 
scend ; and so move not only contrary to its 
own nature, but in a contrary course to the 
sap : whereas, by its reception at the root, 
and its transition from thence, it has a more 
natural and easy motion of ascent. The 
same fact is farther deduced from the fine- 
ness and smallness of the diametral aper- 
tures in the trunk, in comparison of those 
in the root, which nature has plainly de- 
signed for the separation of the air from the 
sap, after they are both together received 
into them. 
Air-vessels are found in the leaves of all 
