Alberti, Leone Battista, Architecture, 1755

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          <chap>
            <pb xlink:href="003/01/145.jpg" pagenum="123"/>
            <p type="head">
              <s>CHAP. VIII.</s>
            </p>
            <p type="head">
              <s>
                <emph type="italics"/>
              Of the Skrew and its Circles or Worm, and in what Manner great Weights
                <lb/>
              are either drawn, carried or puſhed along.
                <emph.end type="italics"/>
              </s>
            </p>
            <p type="main">
              <s>We have already treated of Wheels, Pul­
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              lies and Leavers; we are now to pro­
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              ceed to the Skrew. </s>
              <s>A Skrew conſiſts of a
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              Number of Circles like Rings, which take up­
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              on themſelves the Burthen of the Weight. </s>
              <s>If
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              theſe Rings were entire, and not broken in
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              ſuch a Manner, that the End of one of them is
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              the Beginning of the other; it is certain the
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              Weight which they ſupport, though it might
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              be moved about, would neither go upwards nor
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              downwards, but evenly round upon an equal
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              Plain according to the Direction of the Rings:
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              The Weight therefore is forced to ſlide either
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              upwards or downwards along the Slope of the
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              Rings, which act herein after the Manner of
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              the Leaver. </s>
              <s>Again, if theſe Rings or this Worm
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              be of a ſmall Circumference, or be cut in too
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              near to the Center of the Skrew, the Weight
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              will then be moved by ſhorter Leavers and
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              with a ſmaller Force. </s>
              <s>I will not here omit one
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              Thing which I did not think to have menti­
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              oned in this Place: Namely, that if you could
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              ſo order it that the Bottom or Keel of any
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              Weight which you would move might (as far
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              as could be done by the Art and Skill of the
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              Workman) be made no broader than a Point,
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              and be moved in ſuch a Manner upon a firm
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              and ſolid Plain as not in the leaſt to cut into
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              it, I would engage you ſhould move
                <emph type="italics"/>
              Archi­
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              medes's
                <emph.end type="italics"/>
              Ship, or effect any thing elſe of this
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              Nature whatſoever. </s>
              <s>But of theſe Matters we
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              ſhall treat in another Place. </s>
              <s>Each of theſe
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              Forces in particular, of which we have already
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              ſpoken, are of great Power for the moving of
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              any Weight; but when they are all joined to­
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              gether, they are vaſtly ſtronger. </s>
              <s>In
                <emph type="italics"/>
              Germany
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                <lb/>
              you every where ſee the Youth ſporting upon
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              the Ice with a ſort of wooden Pattens with a
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              very fine thin Bottom of Steel, in which with
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              a very ſmall Strain they ſlip over the Ice with
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              ſo much Swiftneſs, that the quickeſt flying
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              Bird can hardly out-go them. </s>
              <s>But as all Weights
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              are either drawn, or puſhed along, or carried,
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              we may diſtinguiſh them thus: That they are
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              drawn by Ropes; puſhed along by Leavers;
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              and carried by Wheels, Rollers and the like:
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              And how all theſe Powers may be made uſe of
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                <arrow.to.target n="marg13"/>
                <lb/>
              at the ſame Time, is manifeſt. </s>
              <s>But in all theſe
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              Methods, there muſt of Neceſſity be ſome one
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              Thing, which ſtanding firm and immoveable
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              itſelf, may ſerve to move the Weight in Queſ­
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              tion. </s>
              <s>If this Weight is to be drawn, there muſt
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              be ſome greater Weight, to which you may
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              faſten the Inſtruments you are to employ; and
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              if no ſuch Weight can be had, fix a ſtrong iron
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              Stake of the Length of three Cubits, deep in­
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              to the Ground which muſt be rammed down
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              tight all about it, or well ſtrengthened with
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              Piles laid croſs-ways: And then faſten the
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              Ropes of your Pullies or Cranes to the Head
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              of the Stake which ſtands up out of the Ground.
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              </s>
              <s>If the Ground be ſandy, lay long Poles all the
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              Way for the Weight to ſlide upon, and at the
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              Head of theſe Poles faſten your Inſtruments to
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              a good ſtrong Stake. </s>
              <s>I will take Notice of
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              one Thing which the Unexperienced will never
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              allow, till they underſtand the Matter thorough­
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              ly; which is, that along a Plain it is more con­
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              venient to draw two Weights than one; and
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              this is done in the following Manner: Having
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              moved the firſt Weight to the End of the
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              Timbers laid for it to ſlide upon, fix it there
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              with Wedges in ſuch a Manner that nothing
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              can ſtir it, and then faſten or tie to it the En­
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              gines, or Inſtruments with which you are to
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              draw your other Weight; and thus the move­
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              able Weight will be overcome and drawn along
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              the ſame Plain by the other Weight, which is
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              no more than equal to it, but only that it is
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              fixed. </s>
              <s>If the Weight is to be drawn up on high,
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              we may very conveniently make uſe of one
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              ſingle Pole, or rather of the Maſt of a Ship;
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              but it muſt be very ſtout and ſtrong. </s>
              <s>This
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              Maſt we muſt ſet upright, faſtening the Foot
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              of it to a Stake, or fixing it ſtrong in any other
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              Manner that you pleaſe. </s>
              <s>To the upper End of
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              it we muſt faſten no leſs than three Ropes, one
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              on the right Side, another on the leſt, and the
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              other running down directly even with the
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              Maſt. </s>
              <s>Then at ſome Diſtance from the Foot
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              of the Maſt fix your Capſtern and Pullies in
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              the Ground, and putting this laſt Rope through
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              the Pullies, let it run through them ſo as to
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              draw the Head of the Maſt a little downwards,
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              </s>
            </p>
          </chap>
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