CANAL. 
over the flioal. From this fi-mple contrivance originated 
the invention of locks, wiiich have (nice cor.ftituted the 
mairi-fpriog of inland navigation. 
A lock is a kind of baton, placed lengthufife in a, river 
or canal, lined with wails of mafonry on each fide, and 
terminated by two gates, placed where there is a cafcade 
or natural fall'of water ; and fo conftru£»ed, that, the ba- 
fon'being filled with water by an upper fiuice to th.e level 
of the waters above, a veflcl'may a feend. through the up¬ 
per gate; or, the wafer in tlie lock being reduced to the 
level of the water at the bottom of tlie cafcade, the vef¬ 
fel may defeend through the lower gate ; for, when the 
waters are brought to a level on either fide, tire gate on 
that "fide may be eafily opened. But, as the lower gate is 
(trained in proportion to the depth of water "fit fupports, 
when the perpendicular height of the water exceeds 15 or 
16 feet, more locks than one are requifite. Thus, if the 
fall be 17 feet, two leeks are erected, each having feet 
fall; and', if the fall be 26 feet, three locks are employed, 
each having eight feet eight inches fall. Tlie fide-walls 
of a lock ought to be very-strong. Where the natural 
foundation is bad, they mu fa be founded on piles, and 
platforms of wood ; they lhnul-i likevyife Hope outwards, 
in .order to refill the prelfiffe of she earth from.behind. 
To illuftrate this, let fig. 1, in the annexed Plate, re- 
prefent the feet ion of an open lock, with the veffel about 
to enter; and fig. 2, the feclion of a lock, full of water, 
and the veffel raifed to a level' with the water in the fupe- 
rior canal; GH a difl’ipft pafiage for letting water run 
from the fifperior canal into the lock; K F, another paf- 
fage, for water to.pa'fs from the lock to the inferior canal.' 
X and Y reprefent the flood-gages, each of which con- 
fids of two leaves, refiing by their edges upon each other, 
fo as to form an obtufe angle, the better to refid the pref- 
fure of the water. The firil gate prevents the water of tlie 
fuperior canal from falling into the lock, and the fecond 
Units up and fudains the water in the lock. Thefe flood¬ 
gates have each a tong lever A, 13 , C, D, by which they are 
made to open. Thefe gates fiiould be. made very tight 
and clofe, that as little water as poffibl c n'»a y be waded. 
Through the pafiage; GH, which defeends obliquely, by 
opening the fiuice G, the water is Set down from the fupe¬ 
rior canal into the lock, where it is flopped and retained by 
the gate C when fnut, till the water in the lock comes to he 
on a level with th.e water in the fuperior canal, as repre- 
fented in fig 2. When, on tlie other hand, the water con¬ 
tained by the lock is to be let out, the pafiage G H mud be 
fhut, by letting down the fiuice G ; the gate D mud be 
alfo fhut, and the pafiage K F opened by raifmg the fiuice 
K. A free pafiage being thus given to the water, it de¬ 
feends through K F into the inferior canal, until the wa¬ 
ter in the lock is on a level with the water in the inferior 
canal, as reprefented in fig. 1. Now, let it be required to 
raife.a vefi'e! from the inferior to the fuperior canal; if the 
lock happens to be full of water, as at fig. 2, the fiuice G 
mud be fhut, and alfo tlie gate D, and the fiuice K opened, 
fo that the water in the lock may run out, till it is on a level 
with the water in the inferior canal. Then the leaves of 
the gate C arc to be opened by tlie levers, which is eafily 
performed, tlie whiter on each fide of the gate being in 
equiiibrio : the veffel then fails into the lockl After this 
tlie gate C and the fiuice K are to be fhut, and the fiuice 
G opened, in order to fill the lock, till the water in the 
lock, and confequently the veffel, be upon a level with 
the water in the fuperior canal. The gate D is then open¬ 
ed, and the veffel paffes into the upper.canal, ff it be re¬ 
quired to make a veffel defeend into the inferior canal, no¬ 
thing more is neceffary than to reverfe the order of thefe 
operations; the whole depending on the power of water 
to raife or fink heavy bodies, when floating upon its fur- 
face. Infiead of the paffages G H and KF, fmall Unices 
are now made in the lock-gates, which are more Ample, 
and can be opened and-flint with equal eafe and facility. 
Mr. James Playfair, of Ruffell-place, St. Pancras, Lon¬ 
don, has fuggefled a method of conftnMting locks on a 
Vol. III. No. 156. 
new principle, whereby the vaft quantify of-water'11 nially 
expended in the a (cent and ’-deferent" of veffds,. isin a'great 
meafure faved. This .contrivance^ howfever, Teems only 
of value on 'thefe 'canals--where -a fcarcity of water pre¬ 
vails; particular!® as it is attended with much greater de r 
lay in pa fling boats, than is experienced by the common 
locks. This invention is i'ecurcd by letters patent, bear¬ 
ing date July 5, 1791, wherein the’ method is deferibed as 
follows : “ I, the laid James Playfair, do declare, that rhe 
nature and principle of this manner of faving water con- 
fift in letting the water, which has ferved to raife or fall 
a boat or barge from die lock, pafs into refers-oirs or cif- 
terns, whofe apertures of communication with the lock 
are upon different levels, and which may be placed or con- 
ftfitcfed at the fide of tides of the lock with, which they 
communicate, cr in any other contiguous fituation that 
circuinfiances may render eligible ; whic h apertures may 
be opened and fhut at pleafure, fo that the’.water’ may pafs 
from the lock to each feferveir of the canal,"dr f* wremh 
refer voir to the lock, in the following manner’: 1 die. wa¬ 
ter which fills the lock, when a boat is to afcer.d or de¬ 
feend, in (lead of being pa fled immediately into the lower 
part of the canal, is let pafs info thefe ciItems or refer- 
voirs, upon different levels; then, their communications 
with the lock being flint, they remain full until another 
veffel is wanted to pafs; then again tlie ciftefns are emp¬ 
tied into the lock, which is thereby nearly filled, fo that 
only the remainder which is not filled is fupplied from the 
higher part of the canal. Each of thefe ci item's untie 
have aagjurface not lefs than that of the lock, and muff: con¬ 
tain half as much water as is meant to be expended for the 
pacing of each veffel. The ciftern tlie moll elevated is 
placed twice its own depth, (meafuring by the aperture, o-r 
communicating opening of the ciflerns) under the level 
of the writer in the higher part of the canal. The fecond 
ciftern is placed once its own depth under the firfr, and fo 
on are the others, to the 1 owe ft; which lafl is placed once 
its own depth above the level of the water in the lower 
part of the canal. The apertures of the intermediate 
ciflerns, whatever their number may be, mu ft all be equal¬ 
ly divided into different levels; the furface of the water 
in the one being always on tlie level of the bottom of the 
aperture of the ciftern which is immediately above. As 
an example of the manner and rule for conft’rucling thefe 
ciflerns, which it is my defire to render as clear as poffi- 
ble, fuppofe that a lock is to be coiiftrudled twelve feet 
deep, that is, that the veffel may afeend or defeend twelve 
feet in palling. Suppofe the lock lixty feet long, and fix 
feet wide, the,quantity of water required to fill the lock, 
and to pafs a boat, is 4320 cubic feet ; and fuppofe that, 
in calculating the quantity of water that can be procured 
for fupplying the canal, after allowing for warte, it is. 
found (according to the number of boats that may be-ex- 
pedled to pafs) that there will not be above loo cubic feet 
for each, then it will be neceffary to lave 5-6U1S of the 
whole quantity that in the common cafe would be r.eceffa- 
ry ; to do which ten ciflerns mufi be made, (the mode of 
placing which is expreffed in the preceding Plate, fig. 3,) 
each of w hich ciflerns mufi be one foot deep, or deeper at 
pleafure, and each mull have a -furface of 360 feet fquare, 
equal to the furface of the lock. Tlie bottom of the 
aperture of the lowed ciftern mufi be placed one foot 
above the level of the water in the lower part‘of the ca¬ 
nal, or eleven feet under the level of the high water ; the 
fecond ciftdrn mud be two feet above the level of the low 
water; the third three feet, and fo on of the others; the 
bottom of tiie tenth or uppermoft ciftern being ten feet 
above the low wafer, and two feet lower than tlie high 
water ; and, as each ciftern mufi be twelve inches hi depth, 
the furface of the water in the higher ciftern will be one 
foot under the level of the water in the upper part of the 
canal. The ciflerns being thus conftrufled, when the lock 
is full, and tlie boat to be let down, tiie communications 
between the lock and the ciflerns, which until then have 
all been (hut, are to be opened in the following manner: 
i O Firft, 
