M ECHANI'CS, 
7 50 
M, N, to which the piftons are attached. The workman, 
by bearing alternately on the right and left foot, puts the 
balance in motion. The piitons P, O, are alternately ele¬ 
vated and deprefled; and the water railed in the barrel of 
each is driven into the pipe H H, in which it is elevated 
toa height proportional to the diameter of the valves and 
the power of the balance. In order to make the ofcilla- 
tions of the balance equal, and prevent it from acquiring 
too great a velocity, iron fprings, F, G, are fixed to the 
upright polls, which limit the length of its ofcillations. 
The filver medal and twenty guineas were voted by the 
Society of Arts, in 1814, to Mr. Peter Hedderwick, of 
Lower Eaft Smithfield, for a double-pifton pump, yielding 
double the tifual quantity of water from the lame bore. 
The following communication was received from him : 
“ In the pumps with double piftons hitherto made, the 
pifton-rods have been attached to one fide of the p.iftons, 
thereby giving an unequalpull upon the piftons ; whereas, 
in this pump, they are attached to the centre of the pifton, 
the lower piiton-rod palling through the centre of the up¬ 
per pifton. The method of doing this is more particularly 
fhown in figs. 74 and 75. In fig. 74, KKDD is part of 
the pifton-rod of the upper pifton, with two branches D D, 
jointed at D D to the pifton FF. G G is part of the pif¬ 
ton-rod of the lower pifton, palling through the crols- 
bar FF, which is attached to the top of the upper pifton ; 
E E, is another crofs-bar, by which the pifton-rod G G 
pafl'es. The jointed pifton, as here fhown, is neceffnry 
only in large pumps. In fmaller ones, the joint D, and 
the bar E fc, may be difpenfed with; and thus the pifton- 
rod may be all in one piece, faftened to the top of the 
pifton-box at F F, the pliancy of the rods rendering the 
joint at D needlefs. Fig. 75 reprefer.ts the top of the 
pifton, with the crofs-bar F F, through which the lower 
pifton-rod G G, fig. 74, pall'es at I. The two valves are 
formed of one piece of leather in the ufual manner, which 
is confined under the bar or crofs-piece FF, and is 
ftrengthened by having two plates of iron rivetted upon it, 
one on each valve, the valves being what are ufually termed 
butterfly-valves. The principle will appear from the 
manner of working the pump, as follows: In fig. 76, 
ABCDH is a handle or bent lever upon one fide, and 
M NL K I a fimilarone on the other fide, of the pump, by 
which the power is communicated to the piftons ; the le¬ 
ver ABCDH is moveable round the fulcrum or centre D, 
and the lever M N L KI round the centre K ; the extre¬ 
mities I and H are connefled by a bar I H, fo that, when 
the end of the one lever A B is deprefled, the other M N is 
railed ; the ftraight parts C D and L K of the levers are 
continued to E and O, beyond their centres of motion 
D and K, fo as to be as nearly over the centre of the bore 
of the pump ns poftible, but free of each other in the opera¬ 
tion of working. By this connexion, when the handle A B 
is deprefled, the handle MN is raifed. The pifton G is 
deprefled, and the other pifton F raifed. This motion 
being reciprocally continued, gives a double advantage in 
lifting the water; for, when the one handle is pulled 
down, the pifton attached to that handle is railed ; and, 
when the fame handle is raifed up, the pifton belonging 
to the oppofite.handle is alio railed.” 
The following are the remarks of the fociety, after 
making lome experiments with the model prefented to 
them by the inventor.—From the conltruction of this 
pump with two piftons, it appeared evident that the pump- 
barrel would raife twice as much water in the lame time 
as two others of equal bore with one pifton each ; a be¬ 
nefit of lufficient importance in many cafes of accidents 
at fra; but, upon a comparative trial before the com¬ 
mittee ot mechanics, it turned out, that the pump with 
two piftons actually raifed twice and a half as much water, 
as another pump, with one piiton only, which was con¬ 
nected with it fo as to make equal ftrokss therewith, did 
in th fame time, a difference in favour of the pump with 
two piftons to remarkably great, as to occafion doubts 
in the minds of the committee, whether the piftons or 
bore of the double-plfton pump might not have been more 
accurately formed than in that with a fingle pifton. On 
this account, they lliifted the piftons from the one barrel 
to the other ; but, on repeating the experiment, the refult 
was the fame as before ; a convincing proof that the ex¬ 
periment was a fair one; and in faff, the difference in the 
eff’edl of the two pumps can be perfectly well accounted 
for, by the confideration that, in the pump with a fingle 
piiton, the water, after being put into motion by the ac¬ 
tion of the pump, is fuddenly flopped by the change of 
motion during the defeent of the pifton, and has to be 
again put into motion at every ftroke of the pump, to the 
great hindrance of the regular difeharge of the water; 
whereas, in the pump with two piftons, the flow from it 
is nearly continual during its aftion, the one pifton con- 
ftantly afcendi.-ig vyhillt the other is defending, and the 
momentum of the water continuing its af'cent during the 
change of motion in the piftons, and thus producing the 
very great difference in favour of the performance of the 
pump with two piftons. Neither does this pump ever re¬ 
quire double the force that is applied to one with a fingle 
pifton, to work it, it being much eafier to continue a 
motion when commenced than to renew it perpetually 
when interrupted, as it is in the pumps with one pifton only. 
A triple-pump, from Bockler’s Tkeatrum Machinarum, is 
fhown at fig. 77. The nature of the machinery by which 
this pump is worked, will be fufficiently obvious after an 
infpeftion of the figure. The horizontal wheei C, and Its 
fliaft A, are turned by the capftan-bars B ; this wheei 
drives the pinion D, on the axle of which is the equaliz¬ 
ing fly E, and the crank F; the rotatory motion of the 
crank alternately raifes and depreffes the bar G, with the 
lever H turning on a roller and pivots, and thus works the 
pump I; at the fame time the connefting rods K move in 
like manner the lever M, and work the pump O ; and the 
rods L move the lever N, and work the pump P. If the 
levers H, M, N, are net. fo contrived that the extremities 
of each lhall move through equal (paces, the bores of 1,0, 
and P, mult be made in the inverl’e ratio of tliofe (paces, 
otherwife one or other of the refervoirs may be drawn dry ; 
a defeat that fliould be carefully guarded againft. 
A gentleman at Moy, near Armagh, has laid before the 
Dublin Society, a defeription of a machine for working 
eight pumps, of any length, of eight inches in the bore 
and 18 inches plunge, and to ftrike between 30 and 40 
flrokes a-minute each pump, with the labour of one man 
only. The pumps can be fet fo clofe that they will take 
up lefs room than other kind of pumps, and will raife more 
water on-board fhips, or on land, than can be raifed in 
the fame time by any chain-pump, which requires 70 men 
to work it 011-board a man-of-war ; and will alfo raife more 
water than any fteam-engine can do in the fame time. 
Pumps for draining mines are worked by horfes, or 
water, but more than either by the fteam-engine, which, 
had it produced no other advantage than the facilities it 
offers in mining, would have been of more real value than 
any philofophical difeovery ever made. The pumps for 
this purpole are generally fucking-pumps of the common 
conltruftion, made of caft-iron, except that they have an 
opening at the lower part of the barrel, to give accefs to 
the valve or bucket when they require repair or renewal 
of the leathers ; and this is clofed by a door or lid, faf¬ 
tened on with ferews. The pump-rod is fufpended by 
chains from the arched end of a lever fituated over the 
pit, and put in motion by the pifton of the fteam-engine 
adfing at the oppofite end, or by a crank turned from a 
horfe-wheel or water-wheei. When the depth is conil- 
derable, the pit is divided into twm or three lifts, and as 
many different pumps ufed; the loweft to raife the water 
from the bottom of the mine into a ciltero at the firft lift, 
in which the fecond pump lfands, and railes the water to 
a (econd ciliern, from which the third or upper pump 
raifes it to the furface, or to the level or fubterranean paf- 
fage, at which it can run off to home lower land than that 
on which the engine is etecled. The rods of the three 
pumps 
