MECH 
file top of the (u&ion-pipe muft be opened by the elafti- 
city of the air in this pipe, and the air muft expand into 
the barrel; and, being no longer a balance for the atmo- 
fphere, the water in the ciftern muft be forced into the 
fuftion-pipe, and rile in it to a certain height. When 
the plunger defcends, it muft drive the water through the 
Valve N (for the valve M will immediately (hut), and 
along with it moft of the air which had come into the 
barrel. And, as this air occupied the upper part of the 
barrel, part of it will remain when the plunger has reached 
the bottom ; but a ftroke or two will expel it all, and 
then every fucceeding ftroke of the defcending pifton will 
drive the water along the rifing-pipe, and every afcent of 
the plunger will be followed by the water from the ciftern. 
The advantage propofed by this form of piftcn is, that it 
may be more accurately made and polilhed than the infide 
of a working-barrel; and it is of much eafier repair. Yet 
we do not find that it is much ufed, although an invention 
of the 17th century (we think by fir Samuel Morland), 
and much praifed by the writers on thefe fubjects. 
It is eafy to fee that the fucking-pump may be varied 
in the fame way. Suppofe this plunger to be open both 
at top and bottom, but the bottom filled with a valve 
opening upward. When this is puftied to the bottom 
of the barrel, the air which it tends to comprefs lifts the 
valve (the lateral pipe FIKLH being taken away and 
'the paflage ftnst up), and efcapes through the plunger. 
When it is drawn up, it makes the fame rarefaflion as 
the (olid-plunger, becaufe the valve at O (huts, and the 
water will come up from the ciftern as in the former cafe. 
If the plunger be now thruft down again, the valve M 
(huts, the valve O is forced open, and the plunger is filled 
with water. This will be lifted by it during its next 
afcent; and, when it is pufhed down again, the water 
which filled it muft now be pufhed out, and will flow 
over its fides into the ciftern at the head of the barrel. 
Inftead of making the valve at the bottom of the pifton, 
it may be made at the top ; but this difpolition is much 
inferior, becaufe it cannot rarefy the air in the barrel 
one half. This is evident; for the capacity of the barrel 
and plunger together cannot be twice the capacity of the 
barrel. 
It may be made after a ftill different form, as reprefented 
in fig. 67. Here the fuftion-pipe, CO, comes up through 
a cifiern K M N L, deeper or longer than the intended 
ftroke of the pillon, and has a valve C at top. The pif¬ 
ton, or what acts in lieu of it, is a tube AHGB,, open at 
both ends, and of a diameter fomewhat larger than that 
of the fuction-pipe. The interval between them is filled 
up at HG by a ring or belt of foft leather, which is faf- 
tened to the outer tube, and moves up and down with it, 
Aiding along the fmoothly -poliflied furface of the fndtion- 
pipe w ith very little friction. There is a valve I on the 
top of this pifton, opening upwards. Water is poured 
into the outer ciftern. The outer cylinder or pifton being 
drawn up from the bottom, there is a great rarefaction 
of the air which was between them, and the atntofphere 
prefles the water up through the fuclion-pipe to a certain 
height; for the valve I keeps (hut by the prelfure of the 
atmofphere and its own weight. Pufhing down the pif¬ 
ton cauies the air, which had expanded from the fuClion- 
pipe into the piftcn, to efcape through the valve I; draw¬ 
ing it up a fecond time, allows the atmofphere to prefs 
more water into the fuftion-pipe, to fill it, and alfo part 
of the pifton. When this is pufhed down again, the wa¬ 
ter which had come through the valve C is then forced 
out through the valve I into the ciftern KMNL; and 
now the whole is full of water. When, therefore, the 
pifton is drawn up, the water follows, and fills it, if not 
33 feet above the water in the cifiern. When is pufhed 
down again, the water which filled the pifton is all thrown 
out into the ciftern; and after this it delivers its full 
contents of water every ftroke. The water in the ciftern 
K MN L effectually prevents the entry of any air between 
the twp pipes-; fo that a very moderate compreffion of 
Vob. XIV. No. xojo. 
A N I C ft. ' 749 
the belt of foft leather at the mouth of the pifton-cylinder 
is fuflicient to make all perfectly tight. 
It might be made differently. The ring of leather 
might be faltened round the top of the inner cylinder at 
DE, and Aide on the infide of the pifton-cylinder; but 
the firft form is moft eafily executed. Mufchenbroek has 
given a figure of this pump in his large Syftem of Natu¬ 
ral Philofophy, and fpeaks very highly of its performance. 
But we do not fee any advantage which it poffeffes over 
the common fucking-pump. He indeed fays that it is 
without fridion, and makes no mention of the ring of 
leather between the two cylinders. Such a pump will 
raife water extremely well to a fmall height ; and it feerr.s 
to have been a model only which he had examined : but, 
if the fuflion-pipe is long, it will by no means do without 
the leather; for, on drawing up the pifton, the water of 
the upper ciftern will rife between the pipes, and fill the 
pifton, and none will come up through the fuftion-pipe. 
We may take this opportunity of obferving, that the 
many ingenious contrivances of pumps without jriEiion are 
of little importance in great works; becaufe the friftion 
which is completely fuflicient to prevent all efcape of wa¬ 
ter in a well-conftrutted pump is but a very trifling part 
of the whole force. In the great pumps which are ufed 
in mines, and are worked by a fleam-engine, it is very 
ufual to make the piftons and valves without any leather 
whatever. The working-barrel is bored truly cylindrical, 
and the pifton is made of metal of a fize that will jail: pafs 
along it without (ticking. When this is drawn up with the 
velocity competent to a properly-loaded machine, the 
quantity of water which efcapes round the pifton is infig- 
nificant. The pifton is made without leathers, not to 
avoid friClion, which is alfo infignificant in fuch works ; 
but to avoid the neceflity of frequently drawing it up for 
repairs through fuch a length of pipes. 
If a pump abfolutely without friClion be wanted, the 
following feems preferable for fimplicity and performance 
to any we have (een, when made ufe of in proper fitua- 
tions. Let N O (fig. 68.) be the furface of the water in 
the pit, and K the place of delivery. The pit muft be as 
deep in water as from K to N O. A BC D is a wooden 
trunk, round or fquare, open at both ends, and having a. 
valve P at the bottom. The top of this trunk muft be 
on a level with K, and has a fmall ciftern E A D F. It 
alfo communicates laterally with a riling pipe G H K, fur- 
nilhed with a valve at H opening upwards. LM is a beam 
of timber fo fitted to the trunk as to fill it without flick¬ 
ing, and is of at le-aft equal length. It hangs by a chain 
from a working beam, and is loaded on the top with 
weights exceeding that of the column of water which it 
difplaces. Now, fuppofe this beam allowed to defcend 
from the pofition in which it is drawn in the figure; the 
water muft rife all around it, in the crevice which is be¬ 
tween it and the trunk, and alfo in the rifing pipe; be¬ 
caufe the valve P (huts, and FI opens; lb that, when the 
plunger has got to the bottom, the water will (land at the 
level of K. When the plunger is again drawn up to the 
top by the action of the moving power, the water finks 
again in the trunk, but not in the rifing-pipe, becaufe it 
is flopped by the valve H. Then, allowing the plunger 
to defcend again, the water muff again rife in the trunk 
to the level of K, and it muft now flow out at K} and 
the quantity dilcharged will be equal to the part of the 
beam below the furface of the pit-water, deduCling the 
quantity which fills the fmall (pace between the beam 
and the trunk. This quantity may be reduced alntoft to 
nothing; for, if the infide of the trunk and the outfide 
of the beam be made tapering, the beam may be let down 
till they exaCtiy fit; and, as this may be done in fquare- 
work, a good workman can make it exceedingly accurate. 
But, in this cafe, the lower half of the beam and trunk 
muft not taper; and this part of the trunk muft be of 
fuflicient width round the beam to allow free paffage into 
the rifing-pipe; or, which is better, the rifing-pipe muft 
branch off from the bottom of the trunk, A difcharge 
9, E may 
