Alberti, Leone Battista, Architecture, 1755

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          <chap>
            <p type="main">
              <s>
                <pb xlink:href="003/01/308.jpg" pagenum="228"/>
              former was of a more convenient Depth: For
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              it is not ſo much a great Plenty as a good Depth
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              of Water that is neceſſary for Navigation.
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              </s>
              <s>Though a handſome Breadth is very conveni­
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              ent too, becauſe by that means the Streams
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              comes ſlower againſt the Banks. </s>
              <s>A River
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              that has not a ſound Bottom, will ſcarce
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              have ſtrong Banks; and ſcarce any Bottom
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              can be called ſound, which has not ſuch a
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              Strength as we have formerly required in the
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              Foundations of Buildings, namely, to be ſo ſolid
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              as in a Manner to defy even Tools of Iron.
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              </s>
              <s>Thus the Bottom will be uncertain if the Banks
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              are chalky, or if the River runs along a flat
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              Plain, or if the Soil is covered with looſe round
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              Stones. </s>
              <s>When the Banks of a River are un­
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              firm, its Channel will be ſtopt up with Shelves,
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              Ruins, broken Trunks of Trees, and ſoft
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              Stones. </s>
              <s>The weakeſt Sides of all, and the moſt
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              variable, are thoſe thrown up by ſome ſudden
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              Inundation. </s>
              <s>From this Weakneſs of the Sides
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              follows what is ſaid of the
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              Meander
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              and the
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                <emph type="italics"/>
              Euphrates,
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              the former of which we are told,
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              uſed eaſily to cut through his ſoft Banks and
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              be daily running into new Windings, and the
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                <emph type="italics"/>
              Euphrates
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              on the other Hand was continually
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              ſtopping up the Canals, through which he was
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              conveyed, with the Ruins of his Shore. </s>
              <s>Theſe
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              Defects in the natural Banks the Ancients uſed
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              to remedy with artificial ones; the Rules for
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              which are much the ſame with thoſe for
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              other Kinds of Structures; for we are to con­
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              ſider well with what Lines we erect it, and with
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              what Kind of Work. </s>
              <s>If the artificial Bank is
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              built in a parallel Line with the Current of the
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              River, the Force of the Stream will never bear
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              againſt it: But if it is built ſo as to ſtand
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              againſt the Current, if it is not very ſtrong it
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              will be overthrown by it; or if it be too low
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              the Water will overflow it. </s>
              <s>If ſuch a Bank be
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              not overthrown, it will be continually growing
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              higher and higher at the Bottom, becauſe there
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              every Thing which the Stream brings along
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              with it will ſtop, till at laſt having made a Hill
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              againſt it which it can remove no further, it
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              will be apt to turn its Courſe another Way. </s>
              <s>If
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              the Force of the Water throws down the Bank,
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              then it will have thoſe Effects natural to it,
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              which we obſerved before, by filling all the
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              Hollows, driving out the Air, and ſweeping
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              away every Thing that it meets in its Paſſage:
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              But ſtill leaving behind it by Degrees as it
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              ſlackens the Violence of its own Courſe, ſuch
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              heavy Things as are not eaſily carried far.
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              </s>
              <s>Thus in the Mouth of the Breach which the
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              River makes in its Banks, the Inundation will
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              leave a Shelf of coarſe Sand of a conſiderable
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              Height; but as it goes further it will only co­
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              ver the Ground with a ſmall Slime. </s>
              <s>If the
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              River does not immediately break down its
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              Bank, but only overflows the Top of it,
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              the Violence with which it falls upon the
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              Ground on the other Side of it will waſh away
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              the Earth, till by Degrees it undermines and
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              brings down the whole Bank itſelf. </s>
              <s>If the Cur­
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              rent neither is parallel with the Bank, nor ſets
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              againſt it directly, but only ſtrikes it oblique­
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              ly, it will bear no leſs, in Proportion to the
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              Angle of its Obliquity, againſt the Sides to
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              which it is thrown off, than againſt that which
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              it meets with firſt. </s>
              <s>And indeed this Flexion
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              will give it ſomewhat of the Nature of a Bank
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              that fronts the Current directly; ſo that it will
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              be liable to the very ſame Injuries as the latter.
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              </s>
              <s>Thus the Bank will be waſhed away ſo much
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              the ſooner, as the Eddies of the Water will be
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              more vehement and furious, foaming, and in a
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              Manner boiling with Violence: For theſe
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              Whirls and Eddies in a River ſeem to have
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              ſomewhat of the Nature and Force of a Screw,
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              which no Strength or Solidity can long reſiſt.
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              </s>
              <s>We may obſerve as well under Stone Bridges,
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              how deep the Channel is dug by the Fall of the
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              Water; as in thoſe Part of the River where after
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              having been ſome Time confined within nar­
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              rower Banks, it finds a broader Channel to ex­
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              tend itſelf in, with what Fury it breaks out,
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              rowling into Variety of Eddies, and tearing
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              away every Thing that it meets with, either
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              from the Banks or from the Bottom. </s>
              <s>I dare
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              venture to affirm, that
                <emph type="italics"/>
              Hadrian
                <emph.end type="italics"/>
              's Bridge at
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                <emph type="italics"/>
              Rome,
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              is one of the ſtouteſt Pieces of Work
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              that perhaps ever was performed; and yet the
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              Fury of the Water has ſo decay'd it, that I
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              dread its Deſtruction: For the Land-floods
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              every Year load its Piers with Boughs and
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              Trunks of Trees which they bring down
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              along with them, and in a great Meaſure ſtop
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              up the Arches. </s>
              <s>This makes the Water riſe ſtill
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              higher, and then it falls down percipitately in­
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              to wild Eddies, which undermine the Back of
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              the Piers and endanger the whole Structure.
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              </s>
              <s>Thus much of the Banks: Let us now ſay
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              ſomething of the Bottom of the River.
                <emph type="italics"/>
              He­
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              rodotus
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              relates, that
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              Nitocris,
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              King of the
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              Aſſy­
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              rians,
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              ſlackened the Courſe of the River
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              Eu­
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              phrates
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              near
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              Meſopotamia,
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              which before was
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              too impetuous, by making its Channel wind
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              about more than it uſed to do. </s>
              <s>It is alſo rea­
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              ſonable to ſuppoſe that the Water which has </s>
            </p>
          </chap>
        </body>
      </text>
    </archimedes>
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