Alberti, Leone Battista
,
Architecture
,
1755
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the Plain upon which it is to be drawn, which
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is what we are here to conſider, may be effect
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ed in the following Manner. </
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<
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>Let ſuch a Num
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ber of Poles be laid along, and of ſuch a
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Strength and Thickneſs as may be ſufficient
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for the Weight; let them be ſound, even,
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ſmooth, and cloſe joined to one another: Be
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tween the Bottom of the Weight and this Plain
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which it is to ſlide upon, there ſhould be ſome
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thing to make the Way more ſlippery; and
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this may be either Soap, or Tallow, or Lees of
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Oil, or perhaps Slime. </
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<
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>There is another Way
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of making the Weight ſlip along, which is by
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underlaying it croſs-ways with Rollers: But
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theſe, though you have a ſufficient Number of
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them, are very hard to be kept even to their
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proper Lines and exact Direction; which it is
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abſolutely neceſſary they ſhould be, and that
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they ſhould all do Duty equally and at once,
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or elſe they will run together in Confuſion,
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and carry the Weight to one Side And if you
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have but few of them, being continually load
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ed, they will either be ſplit or flatted, and ſo
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be rendered uſeleſs; or elſe that ſingle Line
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with which they touch the Plain underneath,
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or that other with which they touch the
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Weight that is laid upon them, will ſtick faſt
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with their ſharp Points and be immoveable
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A Cylinder or Roller is a Body conſiſting of a
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Number of Circles joined together; and the
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Mathematicians ſay that a Circle can never
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touch a right Line in more than one Point;
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for which Reaſon I call the ſingle Line which
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is preſſed by the Weight, the Point of the Rol
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ler. </
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>The only Way to provide againſt this In
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convenience, is to have the Roller made of the
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ſtrongeſt and ſoundeſt Stuff, and exactly ac
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cording to Rule and Proportion.</
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<
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>CHAP. VII.</
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Of Wheels, Pins, Leavers, Pullies, their Parts, Sizes and Figures.
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<
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>But as there are ſeveral other Things, be
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ſides thoſe already mentioned, which are
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neceſſary for our Purpoſe, ſuch as Wheels, Pul
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lies, Skrews and Leavers, we ſhall here treat of
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them more diſtinctly. </
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<
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>Wheels in a great Mea
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ſure are the ſame as Rollers, as they always
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preſs down perpendicularly upon one Point:
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But there is this Difference between them,
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namely, that Rollers are more expeditious,
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Wheels being hindered by the Friction of their
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Pins or Axis. </
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<
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>The Parts of a Wheel are three:
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The large outer Circle, the Pin or Axis in the
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Middle, and the Hole or Circle into which the
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Pin is let. </
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<
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>This Circle ſome perhaps would
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rather call the Pole; but becauſe in ſome Ma
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chines it ſtands ſtill, and in others moves about,
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we rather deſire Leave to call it the Axicle.
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<
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>If the Wheel turns upon a very thick Axis, it
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will go very hard; if upon too thin a one, it
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will not ſupport its Load; if the outer Circle
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of the Wheel be too ſmall, the ſame Inconve
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nience will happen that we obſerved of the
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Roller, that is, it will ſtick in the Plain; if it
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be too large, it will go along tottering from
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Side to Side, and it will never be ready or
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handy at turning one way or the other. </
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<
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>If the
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Axicle or Circle in which the Axis turns, be
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too large, it will grind its Way out; if it be
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too narrow, it will hardly be able to turn. </
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<
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>Be
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tween the Axis and the Circle in which it turns,
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there ſhould be ſomewhat to lubricate: Be
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cauſe one of theſe is to be conſidered as the
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Plain, and the other as the Bottom or Keel of
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the Weights. </
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<
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>Rollers and Wheels ſhould be
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made of Elm or Holm-Oak: The Axis of
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Holly or the Cornel-tree, or indeed rather of
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Iron: The Circle for the Wheel to turn in, is
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made beſt of Braſs with one third of Tin. </
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<
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>Pul
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lies are little Wheels. </
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<
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>Leavers are of the Na
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ture of the Radii or Spokes of a Wheel. </
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<
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>But
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every Thing of this Sort, whether large Wheels
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which Men turn about by walking within
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them, or Cranes or Skrews, or any other En
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gine, working either by Leavers or Pullies; the
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Principles, I ſay, of all theſe are deduced from
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the Balance. </
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<
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>They tell us, that
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Mercury
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was
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believed to be a God chiefly upon this Ac
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count, that without the leaſt Geſture with his
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Hand, he could make his Meaning perfectly
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clear and plain by his Words. </
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<
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>This, though
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I am a little fearful of ſucceeding in it, I ſhall
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here endeavour to do to the utmoſt of my
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Power: For my Deſign is to ſpeak of theſe
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Things not like a Mathematician, but like a
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Workman; and to ſay no more than is abſo
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lutely neceſſary. </
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<
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>For the clearer underſtand
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ing therefore of this Matter, I will ſuppoſe that
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you have in your Hand, a Dart. </
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<
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>In this Dart I
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