Alberti, Leone Battista
,
Architecture
,
1755
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<
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>CHAP. VIII.</
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Of the Skrew and its Circles or Worm, and in what Manner great Weights
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are either drawn, carried or puſhed along.
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<
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>We have already treated of Wheels, Pul
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lies and Leavers; we are now to pro
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ceed to the Skrew. </
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<
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>A Skrew conſiſts of a
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Number of Circles like Rings, which take up
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on themſelves the Burthen of the Weight. </
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<
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>If
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theſe Rings were entire, and not broken in
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ſuch a Manner, that the End of one of them is
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the Beginning of the other; it is certain the
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Weight which they ſupport, though it might
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be moved about, would neither go upwards nor
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downwards, but evenly round upon an equal
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Plain according to the Direction of the Rings:
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The Weight therefore is forced to ſlide either
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upwards or downwards along the Slope of the
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Rings, which act herein after the Manner of
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the Leaver. </
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<
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>Again, if theſe Rings or this Worm
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be of a ſmall Circumference, or be cut in too
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near to the Center of the Skrew, the Weight
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will then be moved by ſhorter Leavers and
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with a ſmaller Force. </
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<
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>I will not here omit one
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Thing which I did not think to have menti
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oned in this Place: Namely, that if you could
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ſo order it that the Bottom or Keel of any
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Weight which you would move might (as far
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as could be done by the Art and Skill of the
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Workman) be made no broader than a Point,
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and be moved in ſuch a Manner upon a firm
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and ſolid Plain as not in the leaſt to cut into
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it, I would engage you ſhould move
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Archi
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medes's
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Ship, or effect any thing elſe of this
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Nature whatſoever. </
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<
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>But of theſe Matters we
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ſhall treat in another Place. </
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<
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>Each of theſe
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Forces in particular, of which we have already
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ſpoken, are of great Power for the moving of
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any Weight; but when they are all joined to
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gether, they are vaſtly ſtronger. </
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<
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>In
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Germany
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you every where ſee the Youth ſporting upon
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the Ice with a ſort of wooden Pattens with a
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very fine thin Bottom of Steel, in which with
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a very ſmall Strain they ſlip over the Ice with
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ſo much Swiftneſs, that the quickeſt flying
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Bird can hardly out-go them. </
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<
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>But as all Weights
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are either drawn, or puſhed along, or carried,
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we may diſtinguiſh them thus: That they are
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drawn by Ropes; puſhed along by Leavers;
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and carried by Wheels, Rollers and the like:
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And how all theſe Powers may be made uſe of
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at the ſame Time, is manifeſt. </
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<
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>But in all theſe
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Methods, there muſt of Neceſſity be ſome one
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Thing, which ſtanding firm and immoveable
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itſelf, may ſerve to move the Weight in Queſ
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tion. </
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>
<
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>If this Weight is to be drawn, there muſt
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be ſome greater Weight, to which you may
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faſten the Inſtruments you are to employ; and
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if no ſuch Weight can be had, fix a ſtrong iron
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Stake of the Length of three Cubits, deep in
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to the Ground which muſt be rammed down
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tight all about it, or well ſtrengthened with
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Piles laid croſs-ways: And then faſten the
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Ropes of your Pullies or Cranes to the Head
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of the Stake which ſtands up out of the Ground.
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</
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<
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>If the Ground be ſandy, lay long Poles all the
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Way for the Weight to ſlide upon, and at the
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Head of theſe Poles faſten your Inſtruments to
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a good ſtrong Stake. </
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>
<
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>I will take Notice of
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one Thing which the Unexperienced will never
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allow, till they underſtand the Matter thorough
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ly; which is, that along a Plain it is more con
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venient to draw two Weights than one; and
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this is done in the following Manner: Having
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moved the firſt Weight to the End of the
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Timbers laid for it to ſlide upon, fix it there
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with Wedges in ſuch a Manner that nothing
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can ſtir it, and then faſten or tie to it the En
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gines, or Inſtruments with which you are to
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draw your other Weight; and thus the move
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able Weight will be overcome and drawn along
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the ſame Plain by the other Weight, which is
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no more than equal to it, but only that it is
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fixed. </
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<
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>If the Weight is to be drawn up on high,
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we may very conveniently make uſe of one
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ſingle Pole, or rather of the Maſt of a Ship;
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but it muſt be very ſtout and ſtrong. </
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>
<
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>This
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Maſt we muſt ſet upright, faſtening the Foot
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of it to a Stake, or fixing it ſtrong in any other
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Manner that you pleaſe. </
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>
<
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>To the upper End of
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it we muſt faſten no leſs than three Ropes, one
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on the right Side, another on the leſt, and the
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other running down directly even with the
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Maſt. </
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<
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>Then at ſome Diſtance from the Foot
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of the Maſt fix your Capſtern and Pullies in
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the Ground, and putting this laſt Rope through
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the Pullies, let it run through them ſo as to
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draw the Head of the Maſt a little downwards,
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