Castelli, Benedetto, Of the mensuration of running waters, 1661

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              <s>
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              the ſame water in paſſing under the Bridge, in our caſe meeteth
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              with eight of the ſame impediments, bearing, and thruſting upon
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              two ſides of each Arch (to omit the impediment of the bottom,
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              for that it is the ſame in the River, and under the Bridge) from
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              which inadvertency ſometimes follow very great diſorders, as
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              quotidian practice ſhews us.</s>
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            <p type="head">
              <s>APPENDIX IX.</s>
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              <s>It is alſo worthy to conſider the great and admirable benefit
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              that thoſe fields receive, which are wont to drink up the Rain­
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              water with difficulty, through the height of the water in the
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              principal Ditches; in which caſe the careful Husbandman cutteth
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              away the reeds and ruſhes in the Ditches, through which the
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              waters paſs; whereupon may be preſently ſeen, ſo ſoon as the
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              reeds and ruſhes are cut, a notable Ebb in the level of the water
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              in the Ditches; inſomuch that ſometimes it is obſerved, that the
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              water is abated after the ſaid cutting a third and more, of what it
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              was before the cutting. </s>
              <s>The which effect ſeemingly might de­
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              pend on this, That, before thoſe weeds took up room in the
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              Ditch, and for that cauſe the water kept a higher level, and the
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              ſaid Plants being afterwards cut and removed, the water came to
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              abate, poſſeſſing the place that before was occupied by the
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              weeds: Which opinion, though probable, and at firſt ſight ſa­
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              tisfactory, is nevertheleſs inſufficient to give the total reaſon of
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              that notable abatement which hath been ſpoken of: But it is ne­
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              ceſſary to have recourſe to our confideration of the velocity in
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              the courſe of the water, the chiefeſt and true cauſe of the vari­
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              ation of the meaſure of the ſame Running-Water; for, that
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              multitudes of reeds, weeds, and plants diſperſed through the cur­
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              rent of the Ditch, do chance notably to retard the courſe of the
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              water, and therefore the meaſure of the water increaſeth; and
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              thoſe impediments removed, the ſame water gaineth velocity,
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              and therefore decreaſeth in meaſure, and conſequently in
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              height.</s>
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              <s>And perhaps this point well underſtood, may be of great
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              profit to the fields adjacent to the
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              Pontine
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              Fens, and I doubt not
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              but if the River
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              Ninfa,
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              and the other principal Brooks of thoſe
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              Territories were kept well cleanſed from weeds, their waters
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              would be at a lower level, and conſequently the drains of the
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              fields would run into them more readily; it being alwayes to be
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              held for undoubted, that the meaſure of the water before the
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              cleanſing, hath the ſame proportion to the meaſure after clean­
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              ſing, that the velocity after the cleanſing hath to the velocity
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              before the cleanſing: An dbecauſe thoſe weeds being cleanſed </s>
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