Gravesande, Willem Jacob 's
,
An essay on perspective
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on PERSPECTIVE.
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Sight to the Horizontal Line, equal in Length
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to the principal Ray; </
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Perpendicular will be the Point ſought.</
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<
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">If nothing is determin’d, the Place of the Eye
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may be taken at pleaſure in the Horizontal
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Plane.</
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<
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III.</
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precedent Method, about the Eye O, as a Cen-
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ter; </
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">deſcribe the Arc of a Circle I H, touching
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the Horizontal Line.</
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<
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.</
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">About the given Point A, as a Center, de-
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ſcribe the Arc of a Circle L C, touching the Baſe
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Line: </
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touching the two Circles L C and H I; </
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Point a, the Interſection of the ſaid two Lines,
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will be the Appearance ſought.</
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<
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.</
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">To demonſtrate this, draw the Line A B
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perpendicular to the Baſe Line; </
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cular to the Horizontal Line; </
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perpendicular to the Tangent H C. </
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Perpendiculars will cut the Lines to which they
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are perpendicular, in the Points wherein theſe
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laſt touch the Circle L B C, or H V I. </
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wiſe draw the Line A E from the given Point
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A, to the Point E, wherein the Line H C cuts
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the Baſe Line. </
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Eye O to the Point D, wherein the ſaid Line
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HC cuts the Horizontal Line.</
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