Alberti, Leone Battista
,
Architecture
,
1755
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they are not deſigned to ſupport the Weight
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of a vaulted Roof, but only a flat one of Sum
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mers and Rafters. </
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<
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>Let their Thickneſs there
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fore be only one twentieth Part of their Height,
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and let their Height be only once the Breadth
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of the Front and an Half, and never more. </
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<
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>At
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the Angles of the Iſles come out Pilaſters from
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the Naked of the Wall, running parallel with,
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and on a Line with, the Columns, not leſs than
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twice, nor more than three Times the Thick
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neſs of the Wall. </
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<
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>Others, ſtill more to ſtrength
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en the Building, make ſuch a Pilaſter in the
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Middle of the Row of Columns, in Breadth
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three of the Diameters of one the Columns, or
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at moſt four. </
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<
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>The Columns themſelves too
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muſt never have the ſame Solidity as thoſe
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uſed in Temples; and therefore, if we make
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our Colonades with an Architrave over it, we
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may obſerve the following Rules. </
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>If the Co
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lumns are to be
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Corinthian,
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ſubſtract a twelfth
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Part from their Diameter; if
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Ionic,
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a tenth;
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if
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Doric,
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a ninth. </
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>As for the Compoſition of
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the other Members, the Capitals, Architrave,
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Freze, Cornice, and the like, you may proceed
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in the ſame Manner as in Temples.</
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*</
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†</
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⤡</
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<
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>CHAP. XV.</
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Of Colonades both with Architraves and with Arches; what Sort of Columns
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are to be uſed in Baſiliques, and what Cornices, and where they are to be
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placed; of the Height and Wedth of Windows and their Gratings; of the
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Roofs and Doors of Baſiliques, and their Ornaments.
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<
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>Columns that are to have Arches over
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them, ought by rights to be ſquare; for
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if they were round, the Work would not be
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true, becauſe the Heads of the Arches would
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not lie plum upon the Solid of the Column
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underneath; but as much as their Squares ex
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ceeded a Circle, ſo much of them would hang
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over the Void. </
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>To remedy this Defect, the
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beſt ancient Maſters placed over the Capitals
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of their Columns another Abacus or Plinth, in
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Thickneſs ſometimes one fourth and ſometimes
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one fiſth Part of the Diameter of the Column;
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the upper Part of this Plinth, which went off
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with a Cima-recta, was equal to the greateſt
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Breadth of the Top of the Capital, and its Pro
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jecture was equal to its Height, ſo that by this
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means the Heads and Angles of the Arches had
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a ſuller and firmer Seat. </
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<
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>Colonades with
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Arches, as well as thoſe with Architraves, are
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various, ſome being thinner ſet, others cloſer,
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and ſo on. </
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<
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>In the cloſer Sort the Height of
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the Void muſt be three Times and an half the
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Breadth of the Aperture; in the thin Set, the
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Height muſt be once the Breadth and two
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thirds; in the leſs thin, the Height muſt be
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twice the Breadth; in the cloſeſt of all, the
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Breadth muſt be one third of the Height. </
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<
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>We
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have formerly obſerved, that an Arch is no
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thing elſe but a Beam bent. </
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<
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>We may there
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fore give the ſame Ornaments to Arches as to
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Architraves, according to the different Sorts of
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Columns over which they are turned; beſides
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which, if we would have our Structure very
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rich, over the Heads of our Arches we may
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run an Architrave, Freze, and Cornice in a
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ſtraight Line, with the ſame Proportions as we
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ſhould make them over Columns that ſhould
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reach to that Height. </
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<
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>But as the Baſilique is
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ſometimes encompaſſed only with one ſingle
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Iſle, and at other Times with two, the Place of
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the Cornice over the Columns and Arches muſt
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vary accordingly. </
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<
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>In thoſe which are encom
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paſſed only with one ſingle Portico, having di
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vided the Height of your Wall into nine Parts,
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the Cornice muſt go only to five; or if you
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divide it into ſeven, to four. </
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<
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>But in thoſe
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which are to have double Iſles, the Cornice
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muſt be placed at one third of the Height of
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the Wall at leaſt, and at never more than three
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eighths. </
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<
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>We may alſo over the firſt Cornice,
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as well for the greater Ornament as for real
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Uſe, place other Columns, and eſpecially Pi
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laſters, directly plum over the Centers of the
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Columns which are below them. </
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<
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>And this
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indeed is of great Service, as it maintains the
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Strength and Firmneſs of the Ribs of the Work,
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and adds Majeſty to it, and at the ſame Time
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takes off much from the Weight and Expence
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of the Wall; and over this upper Colonade
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too we make a regular Entablature, according
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to the Order of the Columns. </
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<
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>In Baſiliques
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with double Side Iſles, we may raiſe three Rows
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of Columns in this Manner one above another;
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but in others we ſhould make but two. </
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<
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>Where </
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