Alberti, Leone Battista, Architecture, 1755

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            <p type="main">
              <s>
                <pb xlink:href="003/01/074.jpg" pagenum="58"/>
              with their Backs againſt each other, joining
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              perpendicularly. </s>
              <s>The third Stone which is
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              laid upon theſe ſecond ones, muſt be ſet
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              by the Plum-lines, as we directed in raiſing
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              the Wall, with even Joinings, ſo that they
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              may ſerve both the Arches, and be a Binding
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              to both their Wedges. </s>
              <s>Let the Lines of the
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              Joinings of all the Stones in the Arch point
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              exactly to the Centre of that Arch.</s>
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            <p type="main">
              <s>THE moſt skillful Workmen always make
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              the Key-ſtone of one ſingle Piece, very large
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              and ſtrong; and if the Breadth of the Top is
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              ſo great, that no one Stone will ſuffice, it will
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              then be no longer only an Arch, but a vaul­
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              ted Roof.</s>
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            <p type="head">
              <s>CHAP. XIV.</s>
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              <s>
                <emph type="italics"/>
              Of the ſeveral Sorts of Vaults, and wherein they differ; of what Lines they
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              are compoſed, and the Method of letting them ſettle.
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              </s>
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            <p type="main">
              <s>There are ſeveral Sorts of Vaults; ſo
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              that it is our Buſineſs here to enquire
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              wherein they differ, and of what Lines they
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              are compoſed; in doing of which, I ſhall be
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              obliged to invent new Names, to make myſelf
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              clear and perſpicuous, which is what I have
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              principally ſtudied in theſe Books. </s>
              <s>I know
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                <emph type="italics"/>
              Ennius
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              the Poet calls the Arch of the Heavens
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              the mighty Vaults; and
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              Servius
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              calls all Vaults
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              made like the Keel of a Ship, Caverns: But I
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              claim this Liberty; that whatever in this Work,
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              is expreſſed aptly, clearly, and properly, ſhall
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              be allowed to be expreſſed right. </s>
              <s>The differ­
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              ent Sorts of Vaults are theſe, the plain Vault,
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              the Camerated, or mixed Vault, and the he­
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              miſpherical Vault, or Cupola; beſides thoſe
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              others which partake of the Kind of ſome of
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              theſe. </s>
              <s>The Cupola in its Nature is never
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              placed but upon Walls that riſe from a cir­
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              cular Platform: The Camerated are proper for
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              a ſquare one; the plain Vaults are made over
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              any quadrangular Platform, whether long or
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              ſhort, as we ſee in all ſubterraneous Porticoes.
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              </s>
              <s>Thoſe Vaults too which are like a Hill bored
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              through, we alſo call plain Vaults; the plain
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              Vault therefore, is like a Number of Arches
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              join'd together Sideways; or like a bent Beam
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              extended out in Breadth, ſo as to make a Kind
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              of a Wall turn'd with a Sweep over our
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              Heads for a Covering. </s>
              <s>But if ſuch a Vault
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              as this, running from North to South, hap­
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              pens to be croſs'd by another which runs from
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              Eaſt to Weſt, and interſects it with equal
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              Lines meeting at the Angles like crooked
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              Horns, this will make a Vault of the Camer­
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              ated Sort. </s>
              <s>But if a great Number of equal
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              Arches meet at the Top exactly in the Centre,
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              they conſtitute a Vault like the Sky, which
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              therefore we call the Hemiſpherical, or com­
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              pleat Cupola. </s>
              <s>The Vaults made of Part of
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              theſe, are as follows: If Nature with an even
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              and perpendicular Section, were to divide the
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              Hemiſphere of the Heavens in two Parts, from
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              Eaſt to Weſt, it would make two Vaults,
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              which would be proper Coverings for any
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              ſemi-circular Building. </s>
              <s>But if from the Angle
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              at the Eaſt, to that at the South, and from the
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              South to the Weſt, thence to the North, and
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              ſo back again to the Eaſt, if Nature were to
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              break and interrupt this Hemiſphere by ſo
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              many Arches turn'd from Angle to Angle,
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              ſhe would then leave a Vault in the Middle,
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              which for its Reſemblance to a ſwelling Sail,
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              we will venture to call a Velar Cupola. </s>
              <s>But
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              that Vault which conſiſts of a Number of
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              plain Vaults meeting in a Point at Top, we
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              ſhall call an Angular Cupola.</s>
            </p>
            <p type="main">
              <s>IN the Conſtruction of Vaults, we muſt
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              obſerve the ſame Rules as in that of the Walls,
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              carrying on the Ribs of the Wall clear up to
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              the Summit of the Vault; and according to
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              the Method preſcribed for the Former, obſerv­
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              ing the ſame Proportions and Diſtances: From
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              Rib to Rib, we muſt draw Ligatures croſſways,
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              and the Interſpaces we muſt fill up with Stuf­
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              fing. </s>
              <s>But the Difference between the Work­
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              ing of a Vault and a Wall, lies in this; that
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              in the Wall the Courſes of Stone are laid even
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              and perpendicular by the Square and Plum­
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              line; whereas, in the Vault the Courſes are
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              laid by a curve Line, and the Joints all point
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              to the Centre of their Arch.</s>
            </p>
            <p type="main">
              <s>THE Ancients hardly ever made their Ribs
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              of any but burnt Bricks, and thoſe generally
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              about two Foot long, and adviſe to fill up the
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              Interſpaces of our Vaults with the lighteſt
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              Stone, that they might not oppreſs the Wall
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              with too great a Weight. </s>
              <s>But I have obſerved
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              that ſome have not always thought themſelves
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              obliged to make continued ſolid Ribs, but in
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              their ſtead, have at certain Diſtances, ſet Bricks
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              lying Sideways, with their Heads jointing into </s>
            </p>
          </chap>
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