Gravesande, Willem Jacob 's
,
An essay on perspective
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on PERSPECTIVE.
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being produced, will meet each other in the
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Horizontal Line.</
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xml:space
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the Perſpective Plane is conſider’d as being
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inclined.</
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<
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I.</
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Geometrical Plane.</
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<
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">Let X be the Vertical Plane; </
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Line, S the Station Point, and H the Interſecti-
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on of the Station Line and Baſe Line. </
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s
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draw the Vertical Line H V through the Point H,
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making an Angle with S I, equal to the Angle
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of Inclination of the perſpective Plane; </
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raiſe the Perpendicular I O to S I, in the Sta-
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tion Point S, equal to the Height of the Eye;
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</
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">and through the Extremity of the ſaid Perpen-
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dicular, draw the principal Ray O V, paral-
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lel to S I, and cutting H V in the Point of
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Sight V.</
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<
s
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">Now it is evident, that O V determines the
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Length of the principal Ray, and H V the Di-
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ſtance from the Baſe Line to the Horizontal
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Line; </
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<
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">and ſince the Demonſtration of the
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Problems in the aforegoing Chapters regarding
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the Geometrical Plane, have alſo Relation to
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the perſpective Plane being inclined, the ſaid
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Problems may be here uſed; </
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xml:space
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">and conſequently,
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this inclined perſpective Plane is reduced to a
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Perpendicular one, view’d by an Eye, whoſe
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Height is H V, and Diſtance O V.</
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