MECHANICS. 
750 
may be made from tlie ciftern EADF, fo that as little 
water as pollible may defcend along the trunk when the 
pifton is raifed. 
One great excellence of this pump is, that it is perfectly 
free from all the deficiencies which in common pumps re- 
fult from want of being air-tight. Another is, that the 
quantity of water raifed is precifely equal to the power 
expended ; for any want of accuracy in the work, while 
it occafions a diminution of the quantity of water dif- 
charged, makes an equal diminution in the weight which 
is neceffary for pufhing down the plunger. We have feen 
a machine confiding of two fuch pumps fufpended from 
the arms of a long beam, the upper fide of which was 
formed into a walk with a rail on each fide. A man flood 
on one end till it got to the bottom, and then walked fo- 
berly up to the other end, the inclination being about 
twenty-five degrees at firft, but gradually diminifhed as 
he went along, and changed the load of the beam. By 
this mean? he made the other end go to the bottom, and 
fo on alternately, with the eafieft of all exertions, and 
what we are molt fitted for by our flrufture. With this 
machine, a very feeble old man, weighing no pounds, 
raifed 7 cubic feet of water 115 feet high in a minute, and 
continued working eight hours every day. A flout young 
man, weighing nearly 135 pounds, raifed 8£ to the fame 
height; and, when he carried 30 pounds conveniently 
flung about him, he raifed 9J feet to this height, work¬ 
ing ten hours a-day without fatiguing himfelf. This ex¬ 
ceeds Defaguliers’s maximum of a hoglhead of water 10 
feet high in a minute, in the proportion of 9 to 7 nearly. 
It is limited, to very moderate heights; hut in fuch fitua- 
tions it is very eft'eflual. It was the contrivance of an 
untaught labouring man, poffefled of uncommon mecha¬ 
nical genius. 
The molt ingenious contrivance of a pump without 
friftion is that of Mr. Halkins, defcribed by Dd'aguliers, 
and called by him the Quichfilver-Pump. Its conflruftion 
mid mode of operation are pretty complicated; but the 
following defcription will, we hope, render it fufficiently 
plain. Let ilmk (fig. 69.) be a cylindrical iron pipe, 
about fix feet long, open at top. Let eghf be another 
cylinder, connected with it at the bottom, and of fmaller 
diameter. It may either be folid, or, if hollow, it mult 
be dole at top. Let acdb be a third iron cylinder, of an 
intermediate diameter, fo that it may move up and down 
between the other two without touching either, but with 
as little interval as pofiible. Let this middle cylinder 
communicate, by means of the bent pipe A B, with the 
upright pipe FE, having valves C and D (both opening 
upwards) adjoining to the pipe of communication. Sup- 
pofe the outer cylinder fufpended by chains from the end 
of a working-beam ; and let mercury be poured into the 
interval between the three cylinders till it fills the fpace 
to op, about | of their height. Alfo fuppofe that the 
lower end of the pipe FE is immerfed into a ciftern of 
water, and that the valve D is lefs than 33 feet above the 
fnrface of this water. Now fuppofe a perforation made 
fomewhere in the pipe A B, and a communication made 
with an air-pump. When the air-pump is worked, the 
air contained in C E, in A B, and in the fpace between 
the inner and middle cylinders, is rarefied, and is ab- 
ftrafted by the air-pump; for the valve D immediately 
fliuts. The preflure of the atmolphere will caufe the wa¬ 
ter to rife in the pipe C E, and will caufe the mercury to 
fife between the inner and middle cylinders, and fink be¬ 
tween the outer and middle cylinders. Let us fuppofe 
mercury twelve times heavier than water : then, for every 
foot that the water rifes in EC, the level between the 
outfide and infide mercury will vary an inch, and, if we 
fuppofe DE to be 30 feet, then, if we can rarefy the air 
lb as to raife the water to D, the outfide mercury will 
be deprefled to qr, and the infide mercury will have rifen 
to st, sq and tr being about 30 inches. In this flate of 
things, tile water will run over by the pipe B A, and every 
thing will remain nearly in this pofition. The columns 
of water and mercury balance each other, and balance 
the preflure of the atmofphere. While things are in this 
flate of equilibrium, if we allow the cylinders to defcend 
a little, the water will rife in the pipe FE, which we may 
now confider as a fu&ion-pipe; for by this motion the 
capacity of the whole is enlarged, and therefore the pref- 
fure of the atmofphere will ft ill keep it full, and the litua- 
tion of the mercury will again be fuch that all lhall be irj 
equilibrio. It will be a Jittle lower in the infide fpace, 
and higher on the outfide. 
Taking this view of things, we fee clearly how the wa¬ 
ter is fupported by the atmofphere at a very confiderable 
height. The apparatus is analogous to a fiphon which 
has one leg filled with water and the other with mercury. 
But it was not neceffary to employ an air-pump to fill it. 
Suppofe it again empty, and all the valves fhut by their 
own weight. Let the cylinders defcend a little. The 
capacity of the fpaces below the valve D is enlarged, and 
therefore the included air is rarefied, and fome of the air 
in the pipe CE mult diffufe itfelf into the fpace quitted 
by the inner cylinder. Therefore the atmofphere will 
prefs fome water up the pipe FE, and fome mercury into 
the inner fpace between the cylinders. When the cylin¬ 
ders are raifed again, the air which came from the pipe 
CE would return into it again, but is prevented by the 
valve C. Railing the cylinders to their former height 
would comprefs this air; it therefore lifts the valve D, 
and efcapes. Another depreflion of the cylinders will 
have a fimilar effect. The water will rife higher in F C, 
and the mercury in the inner fpace ; and then, after re¬ 
peated ftrokes, the water will pafs the valve C, and fill 
the whole apparatus, as the air-pump had caufed it to do 
before. 
The pofition of the cylinders, when things are in thi$ 
fituation, is reprefented at fig. 70. the outer and inner 
cylinders in their loweft pofition having defcended about 
30 inches. The mercury in the outer fpace ftands at qr, 
a little above the middle of the cylinders, and the mer¬ 
cury in the inner fpace is near the top, t s, of the inner 
cylinder. Now, let the cylinders be drawn up. The wa¬ 
ter above the mercury cannot get back again through the 
valve C, fig. 69. which fliuts by its own weight. We 
therefore attempt to comprefs it; but the mercury yields, 
and defcends in the inner fpace, and rifes in the outer, 
till both are quickly on a level, about the height v v, 
fig. 70. If we continue to raife the cylinders, the com- 
preflion forces out more mercury, and it now ftands lower 
in the inner than in the outer fpace. But, that there may 
be fomething to balance this inequality of the mercurial 
columns, the water goes through the valve D, fig. 69. and 
the equilibrium is reftored when the height of the water 
in the pipe E D above the furface of the internal mercury 
is twelve times the difference of the mercurial columns, 
(on the former fuppofition of fpecific gravity.) If the 
quantity of water is fuch as to rife two feet in the pipe 
ED, the mercury in the outer fpace will be two inches 
higher than that in the inner fpace. Another depreflion 
of the cylinders will again enlarge the fpace within the 
apparatus, the mercury will, take the pofition of fig. 69. 
and more water will come in. Raifing the cylinders will 
fend this water four feet up the pipe ED, and the mer¬ 
cury will be four inches higher in the inner than in the 
outer fpace. Repeating this operation, the water will be 
raifed ltill higher in DE; and this will go on till the 
mercury in the outer fpace reaches the top of the cylin¬ 
der; and this is the limit of the performance. The di- 
men fi.ons with which we fet out will enable the machine 
to raife the water about 30 feet in the pipe ED; which, 
added to the 30 feet of CF, makes the whole height 
above the pit-water 60 feet. By making the cylinders 
longer, we increafe the height of F D. This machine 
mult be worked with great attention, and but (lowly ; 
for, at the beginning of the forcing-ltroke, the mercury 
very rapidly links in the inner fpace, and rifes in the 
outer, and fo may dalh out and be loft. To prevent 
3 this- 
