Alberti, Leone Battista, Architecture, 1755

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            <p type="main">
              <s>
                <pb xlink:href="003/01/139.jpg" pagenum="121"/>
              the Plain upon which it is to be drawn, which
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              is what we are here to conſider, may be effect­
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              ed in the following Manner. </s>
              <s>Let ſuch a Num­
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              ber of Poles be laid along, and of ſuch a
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              Strength and Thickneſs as may be ſufficient
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              for the Weight; let them be ſound, even,
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              ſmooth, and cloſe joined to one another: Be­
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              tween the Bottom of the Weight and this Plain
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              which it is to ſlide upon, there ſhould be ſome­
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              thing to make the Way more ſlippery; and
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              this may be either Soap, or Tallow, or Lees of
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              Oil, or perhaps Slime. </s>
              <s>There is another Way
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              of making the Weight ſlip along, which is by
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              underlaying it croſs-ways with Rollers: But
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              theſe, though you have a ſufficient Number of
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              them, are very hard to be kept even to their
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              proper Lines and exact Direction; which it is
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              abſolutely neceſſary they ſhould be, and that
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              they ſhould all do Duty equally and at once,
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              or elſe they will run together in Confuſion,
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              and carry the Weight to one Side And if you
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              have but few of them, being continually load­
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              ed, they will either be ſplit or flatted, and ſo
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              be rendered uſeleſs; or elſe that ſingle Line
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              with which they touch the Plain underneath,
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              or that other with which they touch the
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              Weight that is laid upon them, will ſtick faſt
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              with their ſharp Points and be immoveable
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              A Cylinder or Roller is a Body conſiſting of a
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              Number of Circles joined together; and the
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              Mathematicians ſay that a Circle can never
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              touch a right Line in more than one Point;
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              for which Reaſon I call the ſingle Line which
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              is preſſed by the Weight, the Point of the Rol­
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              ler. </s>
              <s>The only Way to provide againſt this In­
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              convenience, is to have the Roller made of the
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              ſtrongeſt and ſoundeſt Stuff, and exactly ac­
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              cording to Rule and Proportion.</s>
            </p>
            <p type="head">
              <s>CHAP. VII.</s>
            </p>
            <p type="head">
              <s>
                <emph type="italics"/>
              Of Wheels, Pins, Leavers, Pullies, their Parts, Sizes and Figures.
                <emph.end type="italics"/>
              </s>
            </p>
            <p type="main">
              <s>But as there are ſeveral other Things, be­
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              ſides thoſe already mentioned, which are
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              neceſſary for our Purpoſe, ſuch as Wheels, Pul­
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              lies, Skrews and Leavers, we ſhall here treat of
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              them more diſtinctly. </s>
              <s>Wheels in a great Mea­
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              ſure are the ſame as Rollers, as they always
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              preſs down perpendicularly upon one Point:
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              But there is this Difference between them,
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              namely, that Rollers are more expeditious,
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              Wheels being hindered by the Friction of their
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              Pins or Axis. </s>
              <s>The Parts of a Wheel are three:
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              The large outer Circle, the Pin or Axis in the
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              Middle, and the Hole or Circle into which the
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              Pin is let. </s>
              <s>This Circle ſome perhaps would
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              rather call the Pole; but becauſe in ſome Ma­
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              chines it ſtands ſtill, and in others moves about,
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              we rather deſire Leave to call it the Axicle.
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              </s>
              <s>If the Wheel turns upon a very thick Axis, it
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              will go very hard; if upon too thin a one, it
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              will not ſupport its Load; if the outer Circle
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              of the Wheel be too ſmall, the ſame Inconve­
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              nience will happen that we obſerved of the
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              Roller, that is, it will ſtick in the Plain; if it
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              be too large, it will go along tottering from
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              Side to Side, and it will never be ready or
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              handy at turning one way or the other. </s>
              <s>If the
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              Axicle or Circle in which the Axis turns, be
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              too large, it will grind its Way out; if it be
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              too narrow, it will hardly be able to turn. </s>
              <s>Be­
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              tween the Axis and the Circle in which it turns,
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              there ſhould be ſomewhat to lubricate: Be­
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              cauſe one of theſe is to be conſidered as the
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              Plain, and the other as the Bottom or Keel of
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              the Weights. </s>
              <s>Rollers and Wheels ſhould be
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              made of Elm or Holm-Oak: The Axis of
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              Holly or the Cornel-tree, or indeed rather of
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              Iron: The Circle for the Wheel to turn in, is
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              made beſt of Braſs with one third of Tin. </s>
              <s>Pul­
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              lies are little Wheels. </s>
              <s>Leavers are of the Na­
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              ture of the Radii or Spokes of a Wheel. </s>
              <s>But
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              every Thing of this Sort, whether large Wheels
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              which Men turn about by walking within
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              them, or Cranes or Skrews, or any other En­
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              gine, working either by Leavers or Pullies; the
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              Principles, I ſay, of all theſe are deduced from
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              the Balance. </s>
              <s>They tell us, that
                <emph type="italics"/>
              Mercury
                <emph.end type="italics"/>
              was
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              believed to be a God chiefly upon this Ac­
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              count, that without the leaſt Geſture with his
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              Hand, he could make his Meaning perfectly
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              clear and plain by his Words. </s>
              <s>This, though
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              I am a little fearful of ſucceeding in it, I ſhall
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              here endeavour to do to the utmoſt of my
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              Power: For my Deſign is to ſpeak of theſe
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              Things not like a Mathematician, but like a
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              Workman; and to ſay no more than is abſo­
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                <arrow.to.target n="marg12"/>
                <lb/>
              lutely neceſſary. </s>
              <s>For the clearer underſtand­
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              ing therefore of this Matter, I will ſuppoſe that
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              you have in your Hand, a Dart. </s>
              <s>In this Dart I
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              </s>
            </p>
          </chap>
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