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

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            <pb xlink:href="068/01/063.jpg" pagenum="49"/>
            <p type="head">
              <s>ANNOTATION.</s>
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              <s>Here it is to be noted, that the River it ſelf may have ſundry
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              and divers heights, in ſeveral parts of its Chanel, by reaſon of
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              the various velocities of the water, and its meaſures; as hath
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              been demonſtrated in the firſt book.</s>
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            <p type="head">
              <s>SUPPOSITION I.</s>
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              <s>It is ſuppoſed, that the Rivers equal in breadth, and quick
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              height, that have the ſame inclination of bed or bottom, ought
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              alſo to have equal velocities, the accidental impediments being
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              removed that are diſperſed throughout the courſe of the water,
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              and abſtracting alſo from the external windes, which may velo­
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              citate, and retard the courſe of the water of the River.</s>
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            <p type="head">
              <s>SUPPOSITION II.</s>
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            <p type="main">
              <s>Let us ſuppoſe alſo, that if there be two Rivers that are in
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              their beds of equal length, and of the ſame inclination, but of
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              quick heights unequal, they ought to move with like velocity,
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              according to the ſenſe explained in the ſecond definition.</s>
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              <s>SUPPOSITION III.</s>
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              <s>Becauſe it will often be requiſite to meaſure the time exactly
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              in the following Problems, we take that to be an excellent
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              way to meaſure the time, which was ſhewed me many years ſince
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              by
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              Signore Galilæo Galilæi,
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              which is as followeth.</s>
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              <s>A ſtring is to be taken three Roman feet long, to the end of
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              which a Bullet of Lead is to be hanged, of about two or three
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              ounces; and holding it by the other end, the Plummet is to be
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              removed from its perpendicularity a Palm, more or leſs, and then
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              let go, which will make many ſwings to and again, paſſing and
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              repaſſing the Perpendicular, before that it ſtay in the ſame: Now
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              it being required to meaſure the time that is ſpent in any what­
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              ſoever operation, thoſe vibrations are to be numbred, that are
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              made whilſt the work laſteth; and they ſhall be ſo many ſecond
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              minutes of an hour, if ſo be, that the ſtring be three Roman feet
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              long, but in ſhorter ſtrings, the vibrations are more frequent, and
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              in longer, leſs frequent; and all this ſtill followeth, whether the
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              Plummet be little or much removed from its Perpendicularity, or
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              whether the weight of the Lead be greater or leſſer.</s>
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              <s>Theſe things being pre-ſuppoſed, we will lay down ſome fa­</s>
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          </chap>
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