Firtt, the communication with the higher cittern is open¬ 
ed, which, being at the bottom two feet under tine level 
of the water in the lock, is filled to the depth of one foot, 
the water in the lock descending one foot aifo at the fame 
time ; that communication is then Unit, and the commu¬ 
nication between the lock and the fecond cittern is open¬ 
ed.; one foot more of the water then paffes into that cif- 
tern front the lock, and fills it; the opening is then flint : 
the fame is done with the third, fourth, fifth, fixth, fe- 
venth, eighth, ninth, and tenth, ciHerns, one by one, until 
they are all filled ; and, when the tenth or lowernioft cif- 
tern is filled, tiiere remains but two feet depth of water 
in the lock. The communication between the lock and 
the lower part of the canal is then opened, and the laft 
two feet depth of water is emptied into the lower part of 
the canal. By this means it is evident that, inftead of 
twelve feet depth of water being let def'cend into the low¬ 
er part of the canal, there is ot iy two feet depth that de- 
fcends, or i-6th of the w.hoie ; therefore, inttead of 4320 
cubic feet being' ttfed, there are only 720 cubic feet nfed : 
the remainder of the water in the citterns being ufed as 
follows : When another boat is to mount, the flu ices be¬ 
ing then (hut, and the boat in the lock, the tenth or low- 
oermoft cittern is emptied into the lock, which it fills one 
foot ; the communication being then fhut, the next lowed 
cittern, or the ninth, is emptied into the lock, which is 
thereby filled another foot; and Co, in like manner, all the 
other citterns are emptied one after another, until the high¬ 
er cittern being' emptied, which fills the tenth foot of water 
in the lock, there remains but two feet of water to fill, 
'which is done from the upper part of the canal, by open¬ 
ing the higher (luice to pafs the boat ; by that means the 
fame quantity of water descends from the upper part of 
the canal into the lock, that in the other cafe defcended 
from the lock into the lower part of the canal; fo that, in 
both cafes, the fame quantity of water is faved, that is, 
iive-fixths of what would be necelfary were there no cif- 
terns. Suppofe again that, upon the fame canal, and im¬ 
mediately after the twelve feet lock, it would be advan¬ 
tageous to conftrudt one of eighteen feet; then, in order 
not to life any greater quantity of water, it will be necef- 
lary to have fixreen citterns, upon different levels, com¬ 
municating with the lock in tlie fame manner. Should 
again a lock of only fix feet be wanted, after that of eigh¬ 
teen, then it will only be neceffary to have four citterns 
upon different levels, as fhewn at fig. 4 in the fame Plate, 
and fo of any other, height of a lock. The rule is this: 
For finding the number and lize of the citterns, each cif- 
tern being the fame in fuperficies with the lock, its depth 
mutt be fitch as to contain ohe half the quantity of water 
meant to be ufed in the patting of one boat. 7 'he depth 
of the lock, divided by the depth neceffary for fuch a 
cittern, will give, in”all cafes, the whole number of cif- 
terns, and two more; dedttft the number two, therefore, 
from tire number which you find by dividing the depth of 
the lock by the depth of one cittern, and you have always 
the number of citterns required; which are to be placed 
upon different levels, according to the ride already given. 
The above is the principle and manner of ufing the lock, 
for faving water in canals, and'for enabling engineers to 
confiruct locks of different depths upon the fame canal, 
without ufing more water for the deep locks than for the 
/hallow ones. With regard to the manner of difpofing 
the citterns, the citxumttances of the ground, the decli¬ 
vity, &c. will be the betr guide for the'engiheer. in put¬ 
ting this method in practice, to Cave expence, as there can 
never be. any great preffure of water in any of the citterns, 
I propefe to make the bottom.of clay, and to furrotuid 
them with brick or hewn frone. As to flic lock iifelf, it 
is confl-rufcted in the ufual manner, except for the com¬ 
munications with the citterns; and, as it is 'neceffary to 
avoid any accidents, from tliefe communications being left 
open when they ought npt- fo to be',, there may be two 
valves upon each.; the-one to fhut when preffed upon by 
the water in the lock, and the other to fhut when preffed 
A L. 
upon by the water in the cittern, which will be the cafe 
alternately, as-the water is higher in the one, or in the 
other ; fo that there will never be any communication, ex¬ 
cept v. hen the valves are opened intentionally to let the 
water pafs.” 
Some improvements to this method were publilhed in 
October, 1794, by Mr. Pitt, furveyor to the Wyrley and 
Ellington Canal Company, which we have exemplified at 
fig. 5, in. the preceding Plate, as follows : A, the chamber 
of the lock; B the upper, C the lower, canal: at D is 
promoted a culvert, or round arch, through, the lower part 
of the fide wall: this culvert being confhufted within the 
water will not be liable to blow. E F, walls or piers, of 
the fame materials with tire lock-walls, with openings 
through their upper part, to conrrnunicate with the fide- 
ponds G, If, I ; in each of thefe openings are to be fixed, 
and clofely fitted, two Hiding valves, the inner one folid, 
the outer one with an opening and folid bottom; thefe 
valves to be conftruded fo as to be drawn with a winch or 
windlafs, in the fame manner with the gate-valves, 
To explain the effeft of thefe fide-ponds, imagine the 
whole full of the lock to be nine feet, and the fide-ponds 
each to occupy a fi.ace, in proportion to the fuperficies of 
the infide of the lock, as thirteen to two-; then the pond, 
G mutt be conttrndted with its bottom two feet fix inches 
he low tiie top water of the upper pond ; PI mutt be two 
feet two inches lower than G ; and I, two feet two inches 
lower than H ; the effect will be as follows: The lock 
being filled for the boat patting down, the boat inclofed, 
and gate fliur, the inner valve at 1 is to be drawn, when 
twenty-fix inches deptli of the upper water within the 
lock will immediately rufh through the open part of the 
outer valve into the pond G, which will contain it in a 
depth of four inches; and it will be retained thereby the 
folid bottom of the valve ; the inner valves at 2 and 3 are 
to be immediately and fucceffively drawn, each with the 
fame effebt: then, the lower gate-valve being drawn, the 
boat paffes, into the lower canal in tiie ufual way, with the 
lofs only of two feet fix inches of water. When the lock 
again wants filling, the outer valves are to be drawn fuc- 
ceilively, bin in tiie retrograde order of 3, 2, 1 ; by which 
means fix feet fix inches of water will be returned into 
the lock, and two feet fix inches only .wanted from the 
upper canal; thus of the lock of water is faved, and 
only expended. - 
But, to prevent delay, perhaps a more (imple conttruc- 
tion, though attended with fomewhat lefs faving, may be 
preferable; in which cafe, a fingle (ide-pond, four times 
the fuperficies of the infide of the lock, its bottom five 
feet below the fop water of the upper canal, will produce 
the following effect: the inner valve being drawn, four 
feet of the upper water will immediately rufh through the 
opening of the outer valve into the (ide-pond, (which will 
contain it in a depth of one foot,) and be retained there by 
the folid bottom of the: outer valve ; then, the boat hav¬ 
ing palled in the ufual way, the (ide-pond .will fill four feet 
of the bottom of tiie lock. In-this cafe, in which the de¬ 
lay will be very trifling, if properly conttructed, 5-91115 
of the water is expended,, and 4.-91113 faved. in order to 
render the delay as little as pofiible,- it isabfolutely necef¬ 
fary to bellow the greatett attention to tiie following par¬ 
ticulars. Firtt, that the centre of tiie lock, and the centre 
of the fide-pond, be near each other. Secondly, that the 
funnel of communication, between' tiie lock and the fide- 
pond, be as fhort and as roomy as pofiible. Thirdly, that 
the valves be of good fize ; with due attention to which 
particulars, it is not doubted but more than one-third of 
tiie water may be faved, with left man a minute’s delay 
in each paffage, and ar a vow trifling additional expeiice. 
Another advantageous effect will be produced, by con-, 
firu&ing the floed'-wear.t of the canals to difeharge thern- 
felves into the fide- pond ; by winch means the fide-pond; 
will- become a refervoir to the lock; and tliedpck may of¬ 
ten be filled from it, without drawing a fingle (imp of wa¬ 
ter from tiifH upper canal. Are the lidci ponds inay be. 
wholly 
