MECHANICS, 
'more is loft, becnuTe Of the frlfHon of the machine, and 
the power expended in working its parts; we (hould, 
therefore, afcertain the quantity of water that can be 
railed in a given time by the force of one or more men, 
without deductions for friction ; and, when a (hip’s or 
other pump is to be conlidered, if its produce comes near 
to this ftandard, we (hould be fatisfied as to its perform¬ 
ance, and look for improvements in the conveniences of 
its conftruiftion. 
Defaguliers, in the fecond volume of his Experimental 
Philofophy, has taken much pains to find out an average 
of the quantity of water which can be raifed in a given 
time by any number of men ; and this will ferve to guide 
us in thefe purfuits, and to enable us to value the preten- 
fions of projectors in the art of railing water. He found, 
that the mean ftrength of a man, when applied to the belt 
kind of pump that had been in his time in ufe, amounts 
to no more than the railing of one hogfhead of water in a 
minute to the height of ten feet. Mr. Smeaton fays, he 
made a variety of machines, and many obfervations of this 
kind, but never found the value of men’s ftrength at a 
medium quite equal to what is fet down by Defaguliers, 
unlefs they are fuppofed to work in hafte or diltrefs for a 
few minutes. 
The improvements which are defirable in pumps for a 
(hip’s ufe, are, ift, that as little power as poffible Ihould be 
loft in friction anti refiftance of the water palling through 
the valves and pipes ; 2dly, that no water be loIt by leak¬ 
age, and that the pump be not liable to choke up by chips 
or other extraneous matters getting into the pump ; 3<Jly, 
it (hould not be obliged to raile its water to a greater 
height than is neceflary for it to run off, namely, to the 
load-water line of a (hip; laftly, that it Ihould be lo 
adapted, that the united efforts of a great number of men 
can be applied, without any of them working to a difad- 
vantage. The pum'ps which are at prefent in ufe in the 
navy are of two kinds, the chain-pump and the hand-pump ; 
the chief dependence of pumping the ftiip, in emergency, 
being placed upon the former, the latter being ufed in 
ordinary occafions, to clear the hold from that trifling 
leakage which would injure the cargo, though it purs the 
(hip in no danger. Englilh (hips o< war carry four chair.- 
pumps and three hand-pumps, all being fixed in the lame 
well, which alfo includes the main-malt. One of the 
hand-pumps is called the wafh-deck pump, beinguled to 
raife water from a ciitern in the hold to the upper deck, 
for w a filing the (hip ; but, in emergency, it afiifts to pump 
til? (hip. 
The chain-pump is reprefented on Plate XXV. It con- 
fifts of a chain M TKG, (fig. 82.) about thirty feet long, 
carrying a number of fiat piltons M, N, O, P, Q, which 
are made to revolve in the barrels A B CD and G H, by 
driving the wheel F. When the flat piltons are at the 
lower part of the barrel T, they are immerfed in the water 
RR ; and, as they rife in the barrel G H, they bring up 
the water along with them into the refervoir M G, from 
which it is conveyed by the fpout S. The teeth of the 
wheel F are fo contrived as to receive one-half of the flat 
piltons, and let them fold in : and fometimes another wheel 
like F is fixed at the bottom D. The diltance of the pif- 
tons from the fide of the barrel is about half an inch ; bur, 
as the machine is generally worked with great velocity, 
the afcending piftons bring along with them into the re¬ 
fervoir as much water as fills the cavity G H. Sometimes 
chain-pumps are conftrutfted without the barrels A B C D 
and G H. In this cale, tiie flat piftons are converted into 
buckets connected with a chain, which dip in the water 
with their mouths downwards, and convey it to the refer¬ 
voir. The buckets are moved by hexagonal axles, and the 
dilfance between each is nearly equal to the depth of the 
huckets. Chain-pumps are frequently in an inclined po- 
fition; and in this pqfirion they raife the greateft quantity 
of water when the diftance of the flat piftons is equal to 
their breadth, and when the inclination of the barrelsTs 
about 24° 21k 
753 
The hair-rope machine, invented by the fieur Vera, 
operates on the fame principle as the chain-pump. In- 
ltead of a chain of piltons moving round the wheel F, a 
hair-rope is fubltituted. The part of the rope at T that 
is loweft always dips in the water, which, adhering to the 
rope, is raifed along with it. When the rope reaches the 
top at G and M, it pafles through two (mall tubes, which* 
being fixed in the bottom of the refervoir, prevent the water 
from returning into the well. Another form of Vera’s 
pump is fliown at fig 83. where A and B are three hair- 
ropes palling over the pulleys b and d, each of which had 
three grooves. The lower pulley b> is immerfed in the 
water, and is kept therein by a weight fufpended from ir, 
Thefe pulleys are turned round with great rapidity'by 
means of two multiplying wheels, one of which is feen at G. 
By turning the pulleys, the cords revolve alfo with great 
rapidity, and the afcending fides carry up a confiderable 
quantity of water, which they difcharge with violence into 
the refervoir H, from whence it is conveyed into any ccn= 
venient place by the pipe K L. The ropes Ihould not be 
more than an inch afunder. 
The chain-pump now in ufe in the navy is of a very 
improved conltruHion, compared with the original chain- 
pumps. It was introduced by Mr. Cole, under the di¬ 
rection of captain Bentinck. The chain of this machine 
is Ample, and not much expofedto damage. It is exactly 
limilarto that of the fire-engine, and appears to have been 
firlt applied to the pump by Mr. Mylne to exhaud the 
water from the cailfons at Blacklriars-bridge. It has 
thence been transferred tothe marine by Capt. Bentinck, 
after having received fome material additions to anfwer 
that fervice. The links of the chain are each formed of 
two long plates of iron, with a hole at each end, and 
fixed together by two bolts, ferving as pins for the joints. 
The buckets or faucers fixed upon it are two circular 
plates of brafs, with a piece of leather between them. 
The fprocket-wheels for the chain are formed in the fame 
manner as the trundles ufed in mills, by two : ron wheels 
fixed at eight inches diftance upon the axle, and united 
by feveral round iron bolts, forming a reft for the chain ; 
and its links have hooks, which are taken by thefe bolts; 
and thus the chain is fecured upon the wheel, to prevent 
it from jerking back, when charged with a column of 
water. This pump was a great improvement upon the 
old chain-pumps, ufed in (hips before, in which the 
chain was of too complicated a fabric, and the fprocket- 
wheels tiled to work it were deficient, in wanting fours 
contrivance to prevent the chain from Aiding or jerking 
back upon the furface of the wheel, which frequently 
happened when the buckets were charged with a conii- 
derable weight of water, or when the pumps were vio¬ 
lently worked. The links were too ih-ort, and the awk¬ 
ward manner in which they were conneffed expoftd tliein 
to a great friefion in palling round the wheels; hence 
they were fometimes apt to break, or burit afunder, in 
very dangerous fituations, when it was extremely diffi¬ 
cult or impracticable to repair the chain. Mr. Cole’s 
pump isfo conftrucied, that the chain may be eafily taken 
up and repaired, when broken, or choaked with ballaft ; 
and it difcharges a much greater quantity of water with 
an inferior number of men, as appeared from a trial of 
this machine with the old chain-pump on-board the Sea- 
ford frigate; where it was found that its effedls, when 
compared with the latter, were as follows : The new 
pump with four men raifed one ton of water in 4.3f fe- 
conds, while the old pump required feven men to raife 
the fame quantity of water in 76 feconds. In this expe¬ 
riment, the chain of the new pump vv.v purpofeiy broken, 
and dropped into the well, and afterwards taken up anti 
repaired, and fet to work again in two minutes and a half 5,. 
then the lower wheel of the pump was taken up, to (how 
how readily it might be cleared and refitted for aftion, 
after being choaked with fand or gravel, which could be 
performed in four or five minutes. Thefe are advantages 
which, with a feaman, have a lupeiior confederation to 
5- thaS-, 
