M E C H . 
this as much as poffible, the outer cylinder terminates in . 
a fort of cup or difli, and the inner cylinder ftiould be 
tapered at top. 
This machine is exceedingly ingenious and refined ; 
and there is no doubt but its performance will ex¬ 
ceed that of any other pump which raifes the water to 
the fame height, becaufe fridtion is completely avoided, 
and there can be no want of tightnefs of the pifton. But 
this is all its advantage; and,from what has been obferved, 
it is but trifling. The expenfe would be enormous; for, 
with whatever care the cylinders are made, the interval 
between the inner and outer cylinders mult contain a very 
great quantity of mercury. The middle cylinder mult be 
made of iron plate, and mult be without a Team, for the 
mercury would diffolve every folder. For fuch reafons, 
it lus never come into general ufe. But it would have 
been unpardonable to have omitted the defcription of an 
invention which is fo original and ingenious; and there 
are fome occalions where it may be of great ufe, as in 
nice experiments for illuftrating the theory of hydraulics: 
it would give the finelt piftons for meafuring the preffures 
of water in pipes, &c. 
The following pump without fridtion may be con- 
flrudted in a variety of ways by any common carpenter, 
without the afliflance of the pump-maker or plumber, and 
will be very efreftive for railing a great quantity of water 
to fmall heights, as in draining marfnes, marl-pits, quar¬ 
ries, &c. or even for the fervice of a houfe. ABCD 
(fig. 71.) is a fquare trunk of carpenter’s work open at 
both ends, and having a little ciltern and fpout at top. 
Near the bottom there is a partition made of board, per¬ 
forated with a hole E, and covered with a clack, ffjf 
reprel'ents a long cylindrical bag or pudding, made or lea¬ 
ther or of double canvas, with a fold of thin leather, fuch 
as (heeplkin, between the canvas bags. This is firmly 
nailed to the board E, with foft leather between. The 
upper end of this bag is fixed on a round board, having 
a hole and valve F. This board may be turned in the 
lathe with a groove round its edge, and the bag fattened 
to it by a cord bound tight round it. The fork of the 
pifton-rod FG is firmly fixed into this board; tli-e bag is 
kept diltended by a number of wooden hoops or rings of 
ft long wire ff, ff, ff, &c. put into it at a few inches 
diftance from each other. It will be proper to conneft 
thefe hoops, before putting them in, by three or four 
cords from top to bottom, which will keep them at their 
proper diltances. Thus will the bag have the form of a 
barber’s bellows-pow.ter-puft'. The diftance between the 
hoops fhould be about twice the breadth of the rim of the 
wooden ring to which the upper valve and pifton-rod are 
fixed. Now let this trunk be immerfed in the water. It 
is evident that, if the bag be ft'retched from the comprefled 
form which its own weight will give it by drawing up the 
pifton-rod, its capacity will be enlarged, the valve F will 
be (hut by its own weight, the air in the bag will be rare¬ 
fied, and the atmofphere will prefs the water into the 
bag. When the rod is thruft down again, this water will 
come out by the valve F, and rill part of the trunk. A 
repetition of the operation will have a firnilar effeft; the 
trunk will be filled, and the water will at laft bedii'charged 
by the fpout. 
Here is a pump without friftion, and perfeftly tight ; 
for the leather between the folds of canvas renders the 
bag impervious both to air and water; and the canvas has 
very confiderable ftrength. We know from experience, 
that a bag of fix inches diameter, made of fail-cloth N° 3. 
-with a fheepfkin between, will bear a column of 15 feet 
of water, and ftand fix hours’ work per day for a month 
without failure; and that the pump is confiderably fupe- 
rior in effeft to a common pump of the fame dimenfions. 
We mu ft only obferve, that the length of the bag mult 
be three times the intended length of the ftroke; fo that, 
when the pifton-rod is in its higheft pofition, the angles 
or ridges of the bag may be pretty acute. If the bag be 
3«ore ftretched than this, the forge which mult be exerted 
. N I C S. 751 
by the labourer becomes much greater than the weight 
of the column of water which lie is railing. If the pump 
be laid aflope, which is very ufual in thefe occafional and 
hafty drawings, it is neceffary to make a guide for the 
pifton-rod within the trunk, that the bag .may play up 
and down without rubbing on the rides, which would 
quickly wear it out. 
The experienced reader will fee that this pump is very 
like that of Gofiet and De la Deuille, deferibed by Belidor 
and moll writers on hydraulics. It would be (till more 
like it, if the bag were on the under fide of the partition 
E, and the valve placed farther down the trunk. But 
we think the prefent form greatly preferable in point of 
ftrength. When in the other fituation, the column of 
water lifted by the pillon tends to burjl the bag, and this 
with a great force, as the intelligent reader well knows ; 
but, in the form recommended here, the bag is commjfcd , 
and the (train on each part may be made much lefs than 
that which tends to burlt a bag of fix inches diameter. 
The nearer the rings are placed to each other, the fmaller 
will the (train be. The fame bag-pifton may be employed 
for a forcing-pump, by placing it below the partition, 
and inverting the valve; and it will then be equally 
ltrong, becaufe the reliftance in this cafe too will aft by 
comprellion. 
Another improvement of the common pump has been 
made by Mr. Todd, of Hull. This invention in fome par¬ 
ticulars bears, a relemblance to the ordinary one, but he 
has contrived to double its powers by the following means : 
Having prepared the pifton-cylinder, which may be twelve 
feet high, he cuts from the bottom thereof about three 
feet ; at the end of the great cylinder he places an atmo- 
fpheric-valve, and to the top of the fmall cylinder a ferv- 
ing-valve. In the bottom of the fmall cylinder, which 
contains the ferving-valve, is inferted an oblong elliptical 
curved tube, of equal calibre with the principal cylinder, 
and the other end is again inferted in the top of the great 
cylinder. This tube is divided in-the fame manner as the 
fir It cylinder, with atmofpheric and ferving valves, exaftly 
parallel with the valves of the firft cylinder. The pump, 
thus having double valves, produces double effefts, which 
effects may be ftill further increafed by extending the di¬ 
menfions. The cylinder is ferewed for fervice on a male 
tube-ferew, which projects from the fide of a refervoir or 
water-ciftern, and is worked by hand. The pifton-plunger 
is wprked by a toothed fegment-wheel, firnilar to the prin¬ 
ciple of the one ufed in working the chain-pumps of (hips 
belonging to the royal navy ; and the wheel receives its 
motion from a hand-winch, which is confiderably accele¬ 
rated by a fly-wheel of variable dimenfions, at the oppo- 
fite end. This pump, in addition to its increafed powers, 
poffeffes another very great and prominent advantage. By 
('crewing to it the long leather tube and fire-pipe of the 
common engine, it is in a lew minutes converted into an 
effeftive fire-engine. Hence, whoever poffeffes one may 
be (aid to have a convenient domeftic apparatus againtt 
fire. Three men can work it; one to turn the winch, 
another to direct the fire-pipe, and a third to (upply the 
water. 
Double, triple, or quadruple, pumps, admit of great 
variety in their conftruftion, to fuit different purpofes. 
Tne beft colleftion of thele with which we are acquainted, 
is to be-found in Leupold’s Theatrum Mackinarum Hydrau- 
licarum: fome of thefe are very Angular and ingenious, 
and have particular advantages to l’uit iocal circumftances, 
and give them a preference. 
A fimple method of working two pumps at once, by 
means of a balance, is exhibited in Plate XXIV. where 
A B, fig. 72. is the balance, having a large iron ball at 
each end, placed in equilibrium on the two fpindles CG, 
(fee fig. 73.) The perlon who works the pump (lands 011 
two boards I, I, nailed to two crofs-pieces fattened to the 
axis of the machine, and fupports himfelf by a crofs-bar 
D d joined to the two parts D, E. At the diftance of ten 
inches on each fide of the axis are ihlpended the iron rods 
M, N, 
