Gravesande, Willem Jacob 's
,
An essay on perspective
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[81] Fig. 77.R V T o
Page: 233
[82] Fig. 78.Z Z Y C M L I E A H D X G F B S Q P N 4 3 2
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An ESSAY
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B and C, which will be the two moſt extreme
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ones that can be ſeen.</
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<
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style
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">To do this another Way.</
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xml:space
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">If the upper Face of the Cylinder or Priſm
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">Fig. 26,
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27.</
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be otherwiſe requir’d to be found, the ſame Things
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being given as in the foregoing Method, we draw
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the Line P Q in the perſpective Plane, parallel
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to the Baſe Line, whoſe Diſtance therefrom we
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make equal to the Height of the Priſm or Cy-
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linder, whoſe Perſpective is requir’d. </
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change its Geometrical Plane, ſo that the Baſe
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Line coincides with P Q, and that in this Tran-
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ſpoſition a Perpendicular to the Baſe Line coin-
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cides with this ſame Perpendicular continued to-
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wards P Q. </
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">Finally we find the Perſpective of the Baſe of the Priſm or Cylinder, thus changed
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in Situation by uſing P Q for a Baſe Line, and
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the ſaid Perſpective is the Repreſentation of their
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upper Faces.</
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<
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.</
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">If we ſuppoſe the Plane of the upper Surface
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of the Priſm to be continued, it will meet the
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Perſpective Plane in P Q; </
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">and the upper Face
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in this Plane continued, will have the ſame
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Situation in Reſpect to P Q, as the Baſe hath
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on the Geometrical Plane with Regard to the
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Baſe Line. </
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">If then the ſaid continued Plane be
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conceived to lye on the perſpective Plane, the
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upper Faces of the Priſm or Cylinder, will be
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as the Baſes changed in the Manner aforeſaid;
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</
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">therefore the Appearance of the ſaid Baſes
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changed, will be that of the upper Surfaces.</
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<
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tranſpoſe Figures, and when the Height of </
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