Gravesande, Willem Jacob 's
,
An essay on perspective
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on PERSPECTIVE.
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take the Part 2 s, equal to the Height of the Eye
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above the Point 2, which is in the Baſe of the
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Column; </
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<
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xml:space
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">likewiſe aſſume s a in the ſaid Line
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equal to S A of the precedent Figure, and from the
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Point a draw to a s the indefinite Perpendicular
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a Y. </
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<
s
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xml:space
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">Theſe General Preparations being made,
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take at Pleaſure the ſmall equal Parts 6 i and 69
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in the Line s a; </
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<
s
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echoid-s1181
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xml:space
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">draw the Lines i h and 9 m Pa-
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rallel to 63 z, and from the Point h draw the Line
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h 3 4, thro’ the Center 3 of the Semicircle h m;
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</
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<
s
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echoid-s1182
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xml:space
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">aſſume a 5 in a Y equal to i 4, and draw the Line
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5 s cutting i b in g, and 9 m in q. </
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<
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xml:space
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">And, (in Figure
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32.) </
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s
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xml:space
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">about the Point A, as a Center, with the
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Radius i h or 9 m, which are equal, deſcribe the
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Circle F L M H, cutting the Arc B A C in the
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Points D and E; </
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>
<
s
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echoid-s1185
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xml:space
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">then draw the Line D E cut-
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ting the Line A S in I; </
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<
s
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echoid-s1186
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xml:space
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">aſſume I G equal to i g,
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and I Q equal to 9 q; </
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<
s
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echoid-s1187
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xml:space
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preserve
">and thro’ the Points Q and
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G, draw F H and L M, parallel to the Line E D,
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cutting the Circle D M E F in the Points L,
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M, F, and H. </
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<
s
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echoid-s1188
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xml:space
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preserve
">Now if the Repreſentations of Four
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Points, whereof L M F and H, are the Seats, and
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the two firſt of which is equal to 29, and of the
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two others 2 i, be found*; </
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<
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xml:space
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">the Repreſentation
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of the ſaid four Points will be ſo many Points of
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Appearance ſought. </
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<
s
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xml:space
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">And by drawing two other
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Lines, as i h and 9 m, and proceeding as be-
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fore, the Repreſentation of ſo many more Points
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will be had.</
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>
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<
s
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xml:space
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">Note, Becauſe a part of the Torus is hid by
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<
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">Fig. 32.</
note
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the Column, therefore to avoid uſeleſs Operations,
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a Circle muſt be deſcribed about the Center A,
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with the Radius 36, cutting the Arc B C A in
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the Points T and O, and the Lines STY and SOZ
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muſt be drawn; </
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<
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xml:space
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">then all the Points as F and H,
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falling between the Lines TY and O Z are uſeleſs,
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and L and M not coming under this Obſervation
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muſt only be uſed; </
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<
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xml:space
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">Note alſo, that there is no
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neceſſity to determine Geometrically </
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