43$ iWE cavallo's Defer if t ion of 
CK coil tains the valve at E, which lets the air pafs upwards 
but prevents its return, and which is fo contrived as that, when 
the pifton is drawn quite to the top of the barrel, the leaf! pof- 
iible quantity of air fhould he left into the barrel. The parts 
which form this valve are fhewn feparately in fig. 3. where 
1,3 is a brafs piece that lcrews into a proper cavity made for 
its reception in the piece CE, and which is hollow, except its 
lower part, where it confifts of a thin lamina perforated with 
a fmall hole 3. Into the hollow of the laft mentioned part is 
ferewed the other perforated piece 2,4, having a flip of oil-filk 
ftretched over its lower part 4, and tied round a fmall inden- 
ture or groove made on its lower part. This flip of oil-filk 
anfwers better than a piece of bladder or leather : it juft covers 
the hole 3, and is about four times broader than the diameter 
of the hole. 
It will be eafily conceived, that when the air is forced through 
the hole 3, it will lift up the flip of oil-filk, andpaffingby the- 
.fides of it, and alfo through the large perforation of the piece 
2,4, will go upwards, &c. ; but can by no means return back- 
wards, fince any prefl'ure, that the air makes on the upper part 
of the. oil lilk, will only flop the paflage more effectually. 
A valve much like this is in the pifton, the parts of which are 
Ihewn feparately in fig. 4. u is a perforated brafs piece ferewed 
to the cylindrical handle or axis GG, which is alfo perforated 
with a fhort and bent hole. The piece at is ferewed into the 
part u , and contains a valve, viz. a fmall piece 6 with a flip of 
oil-filk tied round its groove yy, which flip of oil-filk bears 
again ft the hole 5. The piece x ferewing into the other piece 
z/, fattens the round leathers which, about thirty in number, 
form the flopping part of the pifton, and rub with their edges 
againft the cavity of the barrel. This is a very ufeful improve- 
ment, 
