394 Defcription of a Ventilator 
tin, or other cheap metal; its internal diameter being ten 
inches, and its length three feet; having a crutch- handled 
pifton to work with, and an iron parr viz. a hollow in- 
verted cone, two feet long, to condenfe the air, and increafe 
its power in its paffage downwards. This cylinder fhould be 
riveted or ferewed, by means of an iron collar or ftraps, ta 
the deck it paffes through, both above and below, as at aa; 
and fhould be farther fecured by fome hold-faft near 2, to 
keep it fteady in working. 
Fig. 2. is a bottom of wood, four inches and a half thick, 
with z a projecting rim at its bafe, for the metal cylinder to 
reft on, when cemented and {crewed to the wood. The centre 
of this bottom is excavated, for the reception of the crown 
of the nofle. In the fame figure the nofle is reprefented with 
its crown like a bowl-difh, to condenfe the air oradually, 
without refiftance, in its advance to the more contracted bafe 
of the inverted cone, z. ¢. the top or entrance of the nofle. 
About two-thirds down this nofle may be fixed a male ferew, 
as cc, for the purpofe hereafter mentioned. 
N.B. The forcing-pump fhould be cafed in wood: to 
protect it from outward bruifés, which would prevent the 
working of the pifton, and ruin its effects. The leather 
round the embolus fhould be greafed when ufed. 
Fig. 3. is acrutch-handle, faftened to the embolus A by 
its iron legs B, B. A isa cylinder of wood, cafed with lea- 
ther, fo as to fit well, but glide fmoothly in the metal cylin- 
der; having an opening as large as its ftrength will permit, 
for the free accefs of atmofpheric air. C is a valve, well 
leathered on its top, and, yielding downwards to the preffure: 
of the air when the pifton is raifed up. D is a crofs bar of 
iron, to confine the valve, fo that it may clofe inflantly om 
the return of the pifton downwards. 
Fig. 4. is a tin pipe or tube, of lefs than four inches dia- 
meter, and of fuch length as, when fixed to the bafe of the 
cylinder, Fig. 1, fhall admit the nofle d, Fig. 2, to within 
half an maa of the valve E, at the bottom of the wooden 
cylinder F, in Fig. 4; which valve E will then yield to the 
preflure of air condenfed in its paffage through the. nofle, 
and deliver it into the pipes below. This valve muft be well 
leathered 
