Alberti, Leone Battista
,
Architecture
,
1755
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each other, like the Teeth of a Comb; as a Man
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locks his right Hand Fingers into his left; and
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the Interſpaces they filled up with any common
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Stone, and eſpecially with Pumice Stone, which
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is univerſally agreed to be the propereſt of all,
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for the ſtuffing Work of Vaults. </
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<
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>In building
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either Arches or Vaults, we muſt make uſe of
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Centres. </
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<
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>Theſe are a Kind of Frames made
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with the Sweep of an Arch of any rough Boards
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juſt clapt together for a ſhort Service, and
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covered either with Hurdles, Ruſhes, or any
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ſuch common Stuff, in order to ſupport the
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Work till it is ſettled and hardened. </
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<
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>Yet there
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is one ſort of Vault which ſtands in no Need
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of theſe Machines, and that is the
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perfect
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Cupola;
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becauſe it is compoſed not only of
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Arches, but alſo, in a Manner, of Cornices.
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<
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>And who can conceive the innumerable Liga
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tures that there are in theſe, which all wedge
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together, and interſect one another both with
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equal and unequal Angles? </
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<
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>So that in whatſo
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ever Part of the whole Cupola you lay a Stone,
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or a Brick, you may be ſaid at the ſame time
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to have laid a Key-ſtone to an infinite Number,
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both of Arches, and Cornices. </
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<
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>And when
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theſe Cornices, or Arches are thus built one
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upon the other, if the Work were inclined to
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ruinate, where ſhould it begin, when the Joints
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of every Stone are directed to one Centre with
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equal Force and preſſure? </
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<
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>Some of the Ancients
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truſted ſo much to the Firmneſs of this Sort of
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Structure, that they only made plain Cornices
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of Brick at ſtated Diſtances, and filled up the
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Interſpaces with Rubble. </
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<
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>But I think, thoſe
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acted much more prudently, who in raiſing
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this Sort of Cupola, uſed the ſame Methods as
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in Walling, to cramp and faſten the under
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Cornices to the next above, and the Arches
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too in ſeveral Places, eſpecially if they had not
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plenty of Pit Sand to make very good Cement,
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or if the Building was expoſed to South Winds,
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or Blaſts from the Sea. </
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<
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>You may likewiſe
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turn the Angular Cupolas without a Centre,
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if you make a perfect one in the Middle of the
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Thickneſs of the Work. </
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<
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>But here you will
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have particular Occaſion for Ligatures to faſten
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the weaker Parts of the outer one tightly to
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the ſtronger Parts of that within. </
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<
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>Yet it will
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be neceſſary when you have laid one or two
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Rows of Stone to make little light Stays, or
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Catchers jutting out, on which, when thoſe
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Rows are ſettled, you may ſet juſt Frame-work
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enough to ſupport the next Courſes above, to
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the Height of a few Feet, till they are ſufficiently
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hardened; and then you may remove theſe
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Frames, or Supports, higher and higher to
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the other Courſes till you have finiſh'd the
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whole Work. </
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<
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>The other Vaults, both plain and
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mixed, or camerated, muſt needs be turn'd
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upon Centres. </
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<
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>But I would have the firſt
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Courſes, and the Heads of their Arches be
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placed upon very ſtrong Seats; nor can I ap
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prove the Method of thoſe who carry the
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Wall clear up firſt, only leaving ſome Mould
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ings, or Corbels, upon which, after a Time,
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they turn their Arches; which muſt be a very
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infirm and periſhable Sort of Work. </
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<
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>The
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true Way is to turn the Arch immediately,
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and equally with the Courſes of the Wall
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which is to ſupport it, that the Work may
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have the ſtrongeſt Ligatures that is poſſible,
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and grow in a Manner all of one Piece. </
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<
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>The
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Vacuities which are left between the Back of
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the Sweep of the Arch, and the Upright of
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the Wall it is turn'd from, call'd by Work
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men, the
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Hips
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of the Arch, ſhould be fill'd
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up, not with Dirt, or old Rubbiſh, but rather
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with ſtrong ordinary Work, frequently knit
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and jointed into the Wall.</
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<
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>I AM pleaſed with thoſe who, to avoid over
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burthening the Arch, have ſtuffed up theſe
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Vacuities with earthen Pots, turn'd with their
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Mouths downwards, that they might not con
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tain any wet, if it ſhould gather there, and
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over theſe thrown in Fragments of Stone not
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heavy, but perfecty ſound. </
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<
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>Laſtly, in all Man
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ner of Vaults, let them be of what Kind they
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will, we ought to imitate Nature, who, when
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ſhe has knit the Bones, faſtens the Fleſh with
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Nerves, interweaving it every where with Li
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gatures running in Breadth, Length, Height
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and circularly. </
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<
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>This artful Contexture is what
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we ought to imitate in the joining of Stones
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in Vaults. </
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<
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>Theſe Things being compleated,
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the next, and laſt Buſineſs is to cover them
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over; a Work of the greateſt Conſequence in
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Building, and no leſs difficult than neceſſary;
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in effecting, and compleating of which, the
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utmoſt Care and Study has been over and over
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employed. </
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<
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>Of this we are to treat; but firſt,
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it will be proper to mention ſomething neceſ
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ſary to be obſerved in working of Vaults; for
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different Methods are to be taken in the Exe
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cution of different Sorts: Thoſe which are
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turn'd upon Centres muſt be finiſh'd out of
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hand, without Intermiſſion; but thoſe which
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are wrought without Centres muſt be diſcon
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tinued, and left to ſettle Courſe by Courſe,
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left new Work being added to the firſt before
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it is dry, ſhould ruin the Whole. </
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<
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>As to thoſe
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