tin improved Air-Pump, &c. 439 
Ment, fines the common way of ufingtwo leathers turned over 
corks is both troublefome to make, and feldom fits exactly. 
The piece K fattened to the lower end of the barrel is per- 
forated with a hole, the direction of which is clearly teen 111 
the figure, and which communicates with the perforation of 
the round piece L, which is fere'wed to K with a leather be- 
tween. The perforation therefore of K communicates with 
the cavity of the brafs tube RS, this being foldered to L. The 
part oi the piece K, which projects within the barrel, is fmal- 
ler in diameter than the cavity of the barrel, and the inter- 
vening ipace is exactly fitted by the moveable ring 8,8, the two 
parts of which are ferewed together, holding fall: between, the 
edge of a piece of dil-filk, which firetches over the upper part 
of the piece K* and covers its aperture, A vertical view of the 
above-mentioned oil-filk, with five holes in it, is fhewn in 
fig. 6. 
It appears from this defeription* that the air can pafs through 
the valve from without to within the barrel, but not vice verfa. 
It will be alfo eafily conceived, that the air can pafs from the 
cavity of the tube R through the perforation of the pieces L 
and K, within the cavity of the barrel, only when the faid air 
has elafticity, or force enough to pufh up the oil-filk. Now the 
principal improvement in this machine is, to lift up the oil-filk 
by a power applied externally, when the weakened elafticity of 
the air within the cavity of the tube R, &c. is not capable of 
doing it by itfelf, and here follows the defeription of this me- 
dian ifm. 
The double ring 8, 8, which holds the oil-filk, is faftenedto 
two fteel wires 9, 9, which are fhewn in fig. 5. ; this figure 
being a fedion of the lower part of the pump through a plane 
perpendicular to the plane of the fe£tion, fig. 1. Thofe wires 
Vol. LXXIII. M m m pafs 
