RlVEtl. 
When the acquifed velocity is quite 
spent, through the many obstacles, so 
tiiat the current becomes horizontal, there 
will then nothing remain to propagate 
the motion, and continue the stream, but 
the depth, or the perpendicular pressure 
of the water, w'hich is always propor- 
tional to the depth. And this resource in- 
creases, as the occasion for it increases ; 
for in proportion as the water loses of the 
velocity acquired by the descent, it rises 
and increases in its depth. 
It appears from the laws of motion, per- 
taining to bodies moved on inclined planes, 
that when water flows freely upon an in- 
clined bed, it acquires a velocity, which is 
always as the square root of the quantity of 
descent of the bed. But in an horizontal 
bed, opened by sluices or otherwise, at one 
or both ends, the water flows out by its 
gravity alone. 
The greatest velocity of a river is about 
the middle of its depth and breadth, or that 
point which is the furthest possible from the 
surface of the water, and Horn the bottom 
and sides of the bed or channel. Whereas, 
on the contrary, the least velocity of the 
water is at the bottom and sides of the bed, 
because there the resistance arising from 
friction is the greatest, which is communi- 
cated to the other parts of the section of 
the river inversely as the distances fiom 
the bottom and sides. To find whether 
the water of a river, almost horizontal, 
flows by means of the velocity acquired in 
its descent, or by the pressure of its depth, 
set up an obstacle perpendicular to it ; then 
if the water rise and swell immediately 
against the obstacle, it runs by virtue of its 
fall ; but if it first stop a little while, in vir- 
tue of its pressure. 
Rivers, according to this author, almost 
always make their own beds. If the bot- 
tom have originally been a large declivity, 
the water, hence falling with a great force, 
will have swept away the most elevated 
parts of the soil, and carrying them lower 
down, will gradually render the bottom 
more nearly horizontal. 
The water, having made its bed horizon- 
tal, becomes so itself, and consequently 
rakes with the less force against the bot- 
tom, till at length that force becomes only 
equal to the resistance of the bottom, which 
is now arrived at a state of permanency, 
at least for a considerable time ; and the 
longer according to the quality of the soil, 
clay and chalk resisting longer than sand or 
mud. 
On the other hand, the vvater is contb 
nually wearing away the brims of its chan- 
nel, and this with the more force, as, by 
the direction of its stream, it impinges more 
directly against them, By this means it 
has a continual tendency to render them 
parallel to its own course. At the same 
time that it has thus rectified its, edges, it 
has widened its own bed, and thence be- 
coming less deep, it loses part of its force 
and pressure : this it continues to do till 
there is an equilibrium between the force 
of the water and the resistance of its banks, 
and then they will remain without further 
change. And it appears, by experience, 
that these equilibriums ar« all real, as we 
find that rivers only deepen and widen to a 
certain pitch. 
The union of two rivers into one makes 
the whole flow’ the swifter, because, instead 
of the friction of four shores, they have only 
two to overcome, and one bottom instead 
of two ; also the stream, being further dis- 
tant from the banks, goes on with the less 
interruption, besides, that a greater quan- 
tity of water, moving with a greater velo- 
city, digs deeper in the bed, and of course 
retrenches of its former width. Hence also 
it is, that rivers, by being united, take up 
less space on the surface of the earth, and 
are more advantageous to low grounds, 
which drain their superfluous moisture into 
them, and have also less occasion for dykes 
to prevent their overflowing. 
A very good and simple method of mea- 
suring the velocity of the current of a river, 
or canal, is the following. Take a cylin- 
drical piece of dry light wood, and of a 
length something less than the depth of the 
water in the river ; about one end of it let 
there be suspended as many small weights, 
as may keep the cylinder in ft vertical or 
upright position, with its head just above 
water. To the centre of this end fix a 
small straight rod, precisely in the direction 
of the cylinder’s .axis ; to the end that, 
when the instrument is suspended in the 
water, the deviations of the rod from a per- 
pendicularity to the surface of it, may indi- 
cate which end of the cylinder goes fore- 
most, by which may be discovered the dif- 
ferent velocities of the water at different 
depths ; for when the rod inclines forward, 
according to the direction of the current, 
it is a proof that the surface of the water 
has the greatest velocity ; but when it re- 
clines backward, it shows that the swiftest 
current is at the bottom ; and when it re- 
mains perpendicular, it is a sign that the 
