Salusbury, Thomas
,
Mathematical collections and translations (Tome I)
,
1667
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the ſaid Cylinder the Helical Line deſcribed by the Line AEFGH,
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which we vulgarly call the Wale of the Screw, which was produ
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ced by the Line A C. </
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<
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>And in this manner is the Inſtrument made,
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which is by the Greeks called
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and by us a Screw; which
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winding about
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cometh to work
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and inſinu
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ate with its
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Wales under
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the Weight, and
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with facility rai
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ſeth it. </
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>And we
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having demon
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ſtrated, That up
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on [
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or along
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]
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the elevated Plane the Force hath the ſame proportion to the
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Weight, that the perpendicular Altitude of the ſaid Plane hath to
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its Length; ſo, ſuppoſing that the Force in the Screw A B C D is
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multiplied according to the proportion by which the Length of the
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whole Wale exceedeth the Altitude C B, from hence we come
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to know that making the Screw with its Helix's more thick or cloſe
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together, it becometh ſo much the more forceable, as being begot
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by a Plane leſs elevated, and whoſe Length regards its own Per
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pendicular Altitude with greater proportion. </
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>But we will not
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omit to advertiſe you, that deſiring to find the Force of a propo
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ſed Screw, it will not be needful that we meaſure the Length of
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all its Wales, and the Altitude of the whole Cylinder, but it
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will be enough if we ſhall but examine how many times the Di
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ſtance betwixt two ſingle and Contiguous terms do enter into one
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ſole Turn of the ſame Wale, as for example, how many times
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the Diſtance AF is contained in the Length of the Turn AEF:
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For this is the ſame proportion that the Altitude CB hath to all
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the Wale.</
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Levar in capo
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ſignfieth to lift
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on high by force</
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*
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in La
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tine
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Cocblea,
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any
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Screw winding
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like the Shell of
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a Snail.</
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>If all that be underſtood which we have hitherto ſpoken touch
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ing the Nature of this Inſtrument, I do not doubt in the leaſt but
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that all the other circumſtances may without difficulty be compre
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hended: as for inſtance, that inſteed of making the Weight to
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mount upon the Screw if one accommodates its Nut with
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the Helix incavated or made hollow, into which the Male Screw
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that is the Wale entring, & then being turned round it raiſeth and
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lifteth up the Nut or Male Screw together with the Weight which
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was hanged thereat. </
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<
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>Laſtly, we are not to paſs over that Conſidera
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tion with ſilence which at the beginning hath been ſaid to be neceſ
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ſary for us to have in all Mechanick Inſtruments, to wit, That
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what is gained in Force by their aſſiſtance, is loſt again in Time, </
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