1former was of a more convenient Depth: For
it is not ſo much a great Plenty as a good Depth
of Water that is neceſſary for Navigation.
Though a handſome Breadth is very conveni
ent too, becauſe by that means the Streams
comes ſlower againſt the Banks. A River
that has not a ſound Bottom, will ſcarce
have ſtrong Banks; and ſcarce any Bottom
can be called ſound, which has not ſuch a
Strength as we have formerly required in the
Foundations of Buildings, namely, to be ſo ſolid
as in a Manner to defy even Tools of Iron.
Thus the Bottom will be uncertain if the Banks
are chalky, or if the River runs along a flat
Plain, or if the Soil is covered with looſe round
Stones. When the Banks of a River are un
firm, its Channel will be ſtopt up with Shelves,
Ruins, broken Trunks of Trees, and ſoft
Stones. The weakeſt Sides of all, and the moſt
variable, are thoſe thrown up by ſome ſudden
Inundation. From this Weakneſs of the Sides
follows what is ſaid of the Meander and the
Euphrates, the former of which we are told,
uſed eaſily to cut through his ſoft Banks and
be daily running into new Windings, and the
Euphrates on the other Hand was continually
ſtopping up the Canals, through which he was
conveyed, with the Ruins of his Shore. Theſe
Defects in the natural Banks the Ancients uſed
to remedy with artificial ones; the Rules for
which are much the ſame with thoſe for
other Kinds of Structures; for we are to con
ſider well with what Lines we erect it, and with
what Kind of Work. If the artificial Bank is
built in a parallel Line with the Current of the
River, the Force of the Stream will never bear
againſt it: But if it is built ſo as to ſtand
againſt the Current, if it is not very ſtrong it
will be overthrown by it; or if it be too low
the Water will overflow it. If ſuch a Bank be
not overthrown, it will be continually growing
higher and higher at the Bottom, becauſe there
every Thing which the Stream brings along
with it will ſtop, till at laſt having made a Hill
againſt it which it can remove no further, it
will be apt to turn its Courſe another Way. If
the Force of the Water throws down the Bank,
then it will have thoſe Effects natural to it,
which we obſerved before, by filling all the
Hollows, driving out the Air, and ſweeping
away every Thing that it meets in its Paſſage:
But ſtill leaving behind it by Degrees as it
ſlackens the Violence of its own Courſe, ſuch
heavy Things as are not eaſily carried far.
Thus in the Mouth of the Breach which the
River makes in its Banks, the Inundation will
leave a Shelf of coarſe Sand of a conſiderable
Height; but as it goes further it will only co
ver the Ground with a ſmall Slime. If the
River does not immediately break down its
Bank, but only overflows the Top of it,
the Violence with which it falls upon the
Ground on the other Side of it will waſh away
the Earth, till by Degrees it undermines and
brings down the whole Bank itſelf. If the Cur
rent neither is parallel with the Bank, nor ſets
againſt it directly, but only ſtrikes it oblique
ly, it will bear no leſs, in Proportion to the
Angle of its Obliquity, againſt the Sides to
which it is thrown off, than againſt that which
it meets with firſt. And indeed this Flexion
will give it ſomewhat of the Nature of a Bank
that fronts the Current directly; ſo that it will
be liable to the very ſame Injuries as the latter.
Thus the Bank will be waſhed away ſo much
the ſooner, as the Eddies of the Water will be
more vehement and furious, foaming, and in a
Manner boiling with Violence: For theſe
Whirls and Eddies in a River ſeem to have
ſomewhat of the Nature and Force of a Screw,
which no Strength or Solidity can long reſiſt.
We may obſerve as well under Stone Bridges,
how deep the Channel is dug by the Fall of the
Water; as in thoſe Part of the River where after
having been ſome Time confined within nar
rower Banks, it finds a broader Channel to ex
tend itſelf in, with what Fury it breaks out,
rowling into Variety of Eddies, and tearing
away every Thing that it meets with, either
from the Banks or from the Bottom. I dare
venture to affirm, that Hadrian's Bridge at
Rome, is one of the ſtouteſt Pieces of Work
that perhaps ever was performed; and yet the
Fury of the Water has ſo decay'd it, that I
dread its Deſtruction: For the Land-floods
every Year load its Piers with Boughs and
Trunks of Trees which they bring down
along with them, and in a great Meaſure ſtop
up the Arches. This makes the Water riſe ſtill
higher, and then it falls down percipitately in
to wild Eddies, which undermine the Back of
the Piers and endanger the whole Structure.
Thus much of the Banks: Let us now ſay
ſomething of the Bottom of the River. He
rodotus relates, that Nitocris, King of the Aſſy
rians, ſlackened the Courſe of the River Eu
phrates near Meſopotamia, which before was
too impetuous, by making its Channel wind
about more than it uſed to do. It is alſo rea
ſonable to ſuppoſe that the Water which has
it is not ſo much a great Plenty as a good Depth
of Water that is neceſſary for Navigation.
Though a handſome Breadth is very conveni
ent too, becauſe by that means the Streams
comes ſlower againſt the Banks. A River
that has not a ſound Bottom, will ſcarce
have ſtrong Banks; and ſcarce any Bottom
can be called ſound, which has not ſuch a
Strength as we have formerly required in the
Foundations of Buildings, namely, to be ſo ſolid
as in a Manner to defy even Tools of Iron.
Thus the Bottom will be uncertain if the Banks
are chalky, or if the River runs along a flat
Plain, or if the Soil is covered with looſe round
Stones. When the Banks of a River are un
firm, its Channel will be ſtopt up with Shelves,
Ruins, broken Trunks of Trees, and ſoft
Stones. The weakeſt Sides of all, and the moſt
variable, are thoſe thrown up by ſome ſudden
Inundation. From this Weakneſs of the Sides
follows what is ſaid of the Meander and the
Euphrates, the former of which we are told,
uſed eaſily to cut through his ſoft Banks and
be daily running into new Windings, and the
Euphrates on the other Hand was continually
ſtopping up the Canals, through which he was
conveyed, with the Ruins of his Shore. Theſe
Defects in the natural Banks the Ancients uſed
to remedy with artificial ones; the Rules for
which are much the ſame with thoſe for
other Kinds of Structures; for we are to con
ſider well with what Lines we erect it, and with
what Kind of Work. If the artificial Bank is
built in a parallel Line with the Current of the
River, the Force of the Stream will never bear
againſt it: But if it is built ſo as to ſtand
againſt the Current, if it is not very ſtrong it
will be overthrown by it; or if it be too low
the Water will overflow it. If ſuch a Bank be
not overthrown, it will be continually growing
higher and higher at the Bottom, becauſe there
every Thing which the Stream brings along
with it will ſtop, till at laſt having made a Hill
againſt it which it can remove no further, it
will be apt to turn its Courſe another Way. If
the Force of the Water throws down the Bank,
then it will have thoſe Effects natural to it,
which we obſerved before, by filling all the
Hollows, driving out the Air, and ſweeping
away every Thing that it meets in its Paſſage:
But ſtill leaving behind it by Degrees as it
ſlackens the Violence of its own Courſe, ſuch
heavy Things as are not eaſily carried far.
Thus in the Mouth of the Breach which the
River makes in its Banks, the Inundation will
leave a Shelf of coarſe Sand of a conſiderable
Height; but as it goes further it will only co
ver the Ground with a ſmall Slime. If the
River does not immediately break down its
Bank, but only overflows the Top of it,
the Violence with which it falls upon the
Ground on the other Side of it will waſh away
the Earth, till by Degrees it undermines and
brings down the whole Bank itſelf. If the Cur
rent neither is parallel with the Bank, nor ſets
againſt it directly, but only ſtrikes it oblique
ly, it will bear no leſs, in Proportion to the
Angle of its Obliquity, againſt the Sides to
which it is thrown off, than againſt that which
it meets with firſt. And indeed this Flexion
will give it ſomewhat of the Nature of a Bank
that fronts the Current directly; ſo that it will
be liable to the very ſame Injuries as the latter.
Thus the Bank will be waſhed away ſo much
the ſooner, as the Eddies of the Water will be
more vehement and furious, foaming, and in a
Manner boiling with Violence: For theſe
Whirls and Eddies in a River ſeem to have
ſomewhat of the Nature and Force of a Screw,
which no Strength or Solidity can long reſiſt.
We may obſerve as well under Stone Bridges,
how deep the Channel is dug by the Fall of the
Water; as in thoſe Part of the River where after
having been ſome Time confined within nar
rower Banks, it finds a broader Channel to ex
tend itſelf in, with what Fury it breaks out,
rowling into Variety of Eddies, and tearing
away every Thing that it meets with, either
from the Banks or from the Bottom. I dare
venture to affirm, that Hadrian's Bridge at
Rome, is one of the ſtouteſt Pieces of Work
that perhaps ever was performed; and yet the
Fury of the Water has ſo decay'd it, that I
dread its Deſtruction: For the Land-floods
every Year load its Piers with Boughs and
Trunks of Trees which they bring down
along with them, and in a great Meaſure ſtop
up the Arches. This makes the Water riſe ſtill
higher, and then it falls down percipitately in
to wild Eddies, which undermine the Back of
the Piers and endanger the whole Structure.
Thus much of the Banks: Let us now ſay
ſomething of the Bottom of the River. He
rodotus relates, that Nitocris, King of the Aſſy
rians, ſlackened the Courſe of the River Eu
phrates near Meſopotamia, which before was
too impetuous, by making its Channel wind
about more than it uſed to do. It is alſo rea
ſonable to ſuppoſe that the Water which has
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