Alberti, Leone Battista
,
Architecture
,
1755
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with their Backs againſt each other, joining
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perpendicularly. </
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<
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>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. </
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>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.</
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>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.</
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<
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>CHAP. XIV.</
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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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>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. </
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<
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>I know
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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. </
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<
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>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. </
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>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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<
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>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. </
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<
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>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. </
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>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. </
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<
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>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. </
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<
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>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. </
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<
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>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.</
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<
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>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. </
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>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.</
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<
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>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. </
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<
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>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 </
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