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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on PERSPECTIVE.
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Point A parallel to the Baſe Line, and made e-
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qual to B C. </
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<
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xml:space
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">Now if from the Extremities of
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the ſaid Line A L, Perpendiculars are let fall,
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meeting the Baſe Line in the Points P and M,
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and from theſe Points, Lines are drawn to the
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Point of Sight V; </
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<
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xml:space
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">then a N will likewiſe be
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the Perſpective of A L; </
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<
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xml:space
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">and ſince P M is equal
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to D E, a N will be likewiſe equal to G H, and
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conſequently a N will be likewiſe equal to a I,
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which is equal to G H.</
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<
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II.</
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<
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">The ſame Things being given, as in the
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precedent Method, about the Point A, as a
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">Fig. 23.</
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Center, and with the Radius B C, deſcribe the
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Arc of a Circle L M, and draw the Line O L
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from the Eye touching it; </
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<
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">then about a, (which
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is the Repreſentation of A) as a Center deſcribe
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the Circular Arc G I touching the Line L O,
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and cutting another Line drawn through a Per-
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pendicular to the Baſe Line in the Point I: </
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ſay the Point I is the Extremity of the Repre-
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ſentation ſought.</
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<
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.</
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<
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<
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">To prove this, let fall the Perpendiculars A L
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and a G upon the Line O L, which will meet
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the ſaid Line in the Points wherein it touches
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the circular Arcs M L and G I.</
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<
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">Alſo aſſume D E in the Baſe Line equal to B C
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or A L, and draw the Line D F; </
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draw a H parallel to the Baſe Line.</
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<
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xml:space
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">Now let us conſider the Figure X, which re-
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preſents a Plane paſſing through the Eye and
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the Point A of the foregoing Figure, wherein
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O f here, repreſents O F there; </
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