•ther cans* whatever.” The celebrated 
Wolfe in his hydraulics assures that “ it 
is a constant and universal practice, for ac- 
celerating the current of waters, to deepen 
"the bed, and at the same time to render it 
narrower.” 
When the velocity which a river has ac- 
quired by the elevation of its springs and 
the impulse of the back water, is at last to- 
tally destroyed by the different causes of 
resistance becoming exactly equal to, or 
greater than, the first, the bed and current at 
the same time being horizontal, nothing else 
remains to propagate the motion, except the 
sole perpendicular compression of the upper 
waters upon the lower,, which is always in a 
direct ratio of their depth. But this neces- 
sary resource, this remaining cause of motion 
in rivers, augments in proportion as all the 
others diminish, and as the want of it in- 
creases; for as the waters of rivers in ex- 
tensive plains lose the acceleration of motion 
acquired in their descent, from their springs, 
their quantity accumulates in the same bed 
by the junction of several streams together, 
and their depth increases in consequence. 
This junction and successive accumulation 
ot many streams in the same bed, which we 
§ee universally in a greater or lesser degree 
in all rivers throughout the known world, 
, and which is so absolutely necessary to the 
motion of their waters, can only be attributed, 
says Signor Guglielmini, to the infinite wis- 
dom of the supreme Author of Nature. 
The velocities of flowing waters is very 
far from being in proportion to the quantity 
of declivity in their bed. If it was a river 
whose declivitv is uniform and double to that 
of another, it ought only to run with. double 
the swiftness when compared to it ; but in 
; effect it is found to have a much greater, and 
its rapidity, instead of being only double, 
will be Iriple, quadruple, and sometimes 
i even more ; for its velocity depends much 
more on the quantity and depth of the water, 
and on the compression of the upper waters 
on the lower, than on the declivity of the 
bed. Consequently, whenever the bed of a 
river or canal is to be dug, the declivity 
must not be distributed equally throughout 
the whole length ; but, to give a swifter cur- 
rent to the water, the declivity must be 
much greater in the beginning of its course 
than towards the end where it disembogues 
Itself, and where the decli vity must be almost 
insensible, as we see is the case in all natural 
rivers; for when they approach near the sea, 
their declivity is little or nothing ; yet they 
flow with a rapidity which is so much greater, 
as they contain a greater volume of water ; 
so that in great livers, although a large ex- 
tent of their bed next the sea should be abso- 
lutely horizontal, and without any declivity 
at all, yet their waters do not cease to flow, 
and to, flow even with great rapidity, both 
from the impulsion of the back-waters, and 
from the compression of the upper waters 
upon the lower in the same section. 
Whoever is well acquainted with the prin- 
ciples of the higher geometry, will easily 
perceive that it would be no difficult matter 
so to dig the bed of a canal or river, that the 
velocity of the current should be every where 
equal. It would be only giving it in the form 
of a curve along which a moving body should 
recede from a given point, and describe 
spaces every where proportional to the times, 
allowance being made for the quantity of 
effect of the compression of the upper waters 
upon the lower. This curve is what is called 
the horizontal isochronic, being the ’flattest 
of an infinity of others which would equally 
answer the "problem where fluids were not 
concerned. 
All obstacles whatever in the bed of a 
l iver or canal, such as rocks, trunks of trees, 
banks of sand and mud, &c. must necessari- 
ly hinder proportionablv the free running off 
of the water ; for it is evident, that the waters 
so far back from these obstacles, until the 
horizontal level of the bottom of the bed 
becomes higher than the top of the obstacles, 
must be entirely kept up and hindered from 
running off in proportion. Now as the 
waters "must continue to come down from 
their sources, if their free running off is hin- 
dered by any obstacles whatever, their rela- 
tive height back from them must necessarily 
be increased until their elevation, combined 
with the velocity of their current proceeding 
from it, is arrived to such a pitch at the point 
where the obstacles exist, as to counterba- 
lance the quantity of opposition or impedi- 
ment proceeding thence, which frequently 
does not happen until all the lower parts of 
the country round about are laid under 
water. 
Now it is certain from all experience, that 
the beds of rivers and canals in general are 
subject to some or others of the obstacles 
above-mentioned. If rocks or trees do not 
bar their channels, at least the quantity of 
sand, earth, and mud, which their streams 
never fail to bring down, particularly in 
floods, and which are unequally deposited 
according to the various windings and de- 
grees of swiftness in the current, must un- 
avoidably, in course of time, fill up, in part, 
different places in the channel, and hinder the 
free running off of the back-waters. This is 
certainlv the case, more or less, in all rivers, 
and in all canals of long standing, as is no- 
torious to all those well acquainted with 
them. Hence, if these accidents are not 
carefully and with a constant attention pre- 
vented, inundations occur which sometimes 
lay waste whole districts, and ruin the finest 
tracts of ground, by covering them with 
sand ; hence rivers become unnavigable, and 
canals useless for the purposes for which they 
were constructed. Canals, in particular, as 
their waters for the most part remain stagnant 
in them, are still more liable than rivers to 
have their beds fill up by the subsiding of 
mud, and that especially for some distance 
above their sluices ; insomuch, that if con- 
tinual care is not taken to prevent it, or re- 
medy it as often as it happens, they will soon 
become incapable of receiving and passing 
the same vessels as formerly. Nay, the 
very sluices themselves, if the floors of their 
bottoms are not of a depth conformable to 
the bed of the canal, will produce the same 
accidents as those we have been speaking o'l ; 
for if they are placed too low, they will be 
continually filling up with sand or mud; if 
too high, "they have the same effect as banks 
or bars in the bed of a river, that is, they 
hinder all the back-waters under their level 
from running off, and soon fill up the bed 
to that height by the subsiding of mud. 
This effect is much accelerated by the shut- 
ting of the lower sluices, which makes a great 
volume of water flow back to those next 
4 F 2 
above them, till the whole is filled and be- 
come stagnant. Now it is evident, that this 
stale of tilings must contribute far more'lo 
the subsidency of mud, and all other matters 
brought down by the waters in canals, than 
can be the case in rivers whose currents con- 
stantly flow. 
The waters of all rivers and canals are 
from time to time muddy ; their streams, 
particularly during rains and floods, carry 
along with them earth and other substances 
which subside in those places where their 
currents are the least, by which their beds 
are continually raised ; so that the successive 
increase of inundations in rivers, and of un- 
fitness for navigation in canals, when they 
are neglected and left to themselves, is a na- 
tural and necessary consequence of the state 
of things, which no intelligent person can be 
at a loss to account for ; and yet whole coup- 
tries remain in this habitual state of negli- 
gence, to their very great detriment. 
Having thus shown the principal accidents 
which rivers and canals are liable to, with the 
causes of them, our author proceeds to point 
out the most efficacious methods of prevent- 
ing them, or at least of diminishing their ef- 
fects. They flow immediately from the 
principles laid down in his essay, and do not 
need many words to make them completely 
understood. A work of this kind, he ob- 
serves, if it is properly conducted, must be 
begun at the lower end of the river or canal : 
that is, at that end where their waters are 
discharged into the sea, or where they fall 
into some other greater river or canal, 
whence their waters are carried off without 
further hindrance. If it is a river whose 
bed, by being filled up with sand, mud, or 
other obstacles, and by being otherwise be- 
come irregular in its course, is often subject 
to its inundations, and incapable of internal 
navigation, the point, from which the work 
must be begun and directed throughout all 
the rest of the channel, is from the lowest 
water-mark of spring-tides on the shore at the 
month of the river, or even something be- 
low it, if it can be done; though this part 
will soon fill up again by the sand, mud, Nr, 
which the tides cease not to roll in. 
If it is a canal whose bed is to be dug 
anew, or one already made, which is to be 
cleaned and deepened from the, sea-shore or 
some large river back into the country, and 
where no declivity is to be lost, as is the case 
in all flat countries ; tire work must be be- 
gun, and the depth of the whole channel di- 
rected, from tire lower water-mark of spring- 
tides, if tire mouth is to the sea, or from 
such a depth in the channel of the river, 
if the canal falls into one, that there maybe 
such a communication of water from the ca- 
nal to the river, in all situations of the cur- 
rent, as may let boats freely pass from one 
to the other. This, of course, must also 
direct the depth of the tloor of the last sluice 
towards the mouth of the canal, be it to the 
sea or into a river. If the bottom or floor 
of a sluice already constructed is too .low, 
it will soon till up with sand or mud, and 
hinder the gates from opening, unless it is 
continually cleaned out : if, on the contrary, 
this floor is too high, and in a canal whose 
natural declivity is too little for the free cur- 
rent of the water, as is generally the case 
in Holland and Flanders, all depth of the 
