Alberti, Leone Battista
,
Architecture
,
1755
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that the Buildings there did not joyn one to
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ano her.
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Plato,
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on the contrary, is ſo far from
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approving of thoſe Separations, that he would
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have the Houſes all cloſe contiguous, and
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that the joyning together of their Walls ſhould
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make a Wall to the City.</
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<
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>CHAP. VI.</
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Of Bridges both of Wood and Stone, their proper Situation, their Peers,
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Arches, Angles, Feet, Key-ſtones, Cramps, Pavements, and Slopes.
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<
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>The Bridge, no doubt, is a main Part
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of the Street; nor is every Part of the
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City proper for a Bridge; for beſides that it
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is inconvenient to place it in a remote Corner
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of the Town, where it can be of Uſe but to
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few, and that it ought to be in the very Heart
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of the City, to lie at hand for every body; it
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ought certainly to be contrived in a Place
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where it may eaſily be erected, and without
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too great an Expence, and where it is likely
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to be the moſt durable. </
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<
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>We ſhould therefore
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chuſe a Ford where the Water is not too deep;
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where the Shore is not too ſteep; which is
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not uncertain and moveable, but conſtant
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and laſting. </
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<
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>We ſhould avoid all Whirl
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pools, Eddies, Gulphs, and the like Inconve
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niences common in bad Rivers. </
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<
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>We ſhould
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alſo moſt carefully avoid all Elbows, where the
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Water takes a Turn; for very many Reaſons;
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the Banks in ſuch Places being very liable to
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be broken, as we ſee by Experience, and be
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cauſe Pieces of Timber, Trunks of Trees, and
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the like, brought down from the Country by
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Storms and Floods, cannot ſwim down ſuch
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Elbows in a ſtrait Line, but turn aſlant, meet
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and hinder one another, and lodging againſt
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the Piles grow into a great Heap, which ſtops
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up the Arches, and with the additional
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Weight of the Water at length quite breaks
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them down.</
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<
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>OF Bridges, ſome are of Stone, others of
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Wood. </
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<
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>We ſhall ſpeak firſt of thoſe which
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are of Wood, as the moſt eaſy of Execution;
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next we ſhall treat of thoſe which are built of
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Stone. </
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<
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>Both ought to be as ſtrong as poſſible;
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that therefore which is built of Wood, muſt
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be fortified with a good Quantity of the
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ſtrongeſt Timbers. </
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<
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>We cannot give a better
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Example of this Sort of Bridges than that built
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by
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fulius Cæſar,
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which he gives us a Deſcrip
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tion of himſelf, as follows: He faſtened to
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gether two Timbers, leaving a Diſtance be
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tween them of two Foot; their Length was
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proportioned to the Depth of the River, and
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they were a Foot and an half thick, and cut
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ſharp at the Ends. </
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<
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>Theſe he let down into
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the River with Cranes, and drove them well in
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with a Sort of Rammers, not perpendicularly
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down like Piles, but ſlanting upwards, and
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giving Way according to the Current of the
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River. </
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<
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>Then, oppoſite to theſe, he drove in
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two others, faſtened together in the ſame Man
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ner, with a Diſtance between them at Bottom
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of forty Foot, ſlanting contrary to the Force
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and Current of the Stream. </
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<
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>When theſe were
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thus fixed, he laid acroſs from one to the other,
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Beams of the Thickneſs of two Foot, which
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was the Diſtance left between the Timbers
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drove down; and faſtened theſe Beams at the
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End, each with two Braces, which being
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bound round and faſtened of oppoſite Sides,
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the Strength of the whole Work was ſo great
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and of ſuch a Nature, that the greatcr the
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Force of Water was which bore againſt it,
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the cloſer and firmer the Beams united. </
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<
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>Over
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theſe other Beams were laid acroſs and faſtened
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to them, and a Floor, as we may call it, made
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over them with Poles and Hurdles. </
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<
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>At the
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ſame Time, in the lower Part of the River,
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below the Bridge, other Timbers, or ſloping
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Piles, were driven down, which being faſtened
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to the reſt of the Structure, ſhould be a Kind
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of Buttreſs to reſiſt the Force of the Stream;
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and other Piles were alſo driven in at a ſmall
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Diſtance above the Bridge, and ſtanding ſome
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what above the Water, that if the Enemy
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ſhould ſend Trunks of Trees, or Veſſels, down
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the Stream, in order to break the Bridge, thoſe
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Piles might receive and intercept their Vio
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lence, and prevent their doing any Prejudice
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to the Work. </
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<
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>All this we learn from
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Cæſar.
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Nor is it foreign to our Purpoſe to take Notice
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of what is practiced at
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Verona,
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where they
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pave their wooden Bridges with Bars of Iron,
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eſpecially where the Wheels of Carts and Wag
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gons are to paſs. </
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<
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>It remains now that we
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