Gravesande, Willem Jacob 's
,
An essay on perspective
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this Appearance paſſes thro’ that of the Point
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L, it will be a Part of C X. </
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xml:space
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">But becauſe that
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Line, drawn from the Point L, paſſes thro’ the
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propos’d Point; </
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">the Repreſentation of the ſaid
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Point is alſo in C X; </
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Interſection of C X, and T X.</
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<
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">If the Point T ſhould be at too great a
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Diſtance; </
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<
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">or if T B X, or C X, ſhould too ob-
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liquely cut each other; </
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<
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">the perſpective Plane
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muſt then be ſuppos’d to be reduc’d to a
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pendicular, or upright one; </
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<
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tation of a Point, above the Geometrical Plane,
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(whoſe Seat is L, and Height M E) muſt be
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found .</
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<
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III.</
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cular to the Geometrical Plane`.</
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<
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">The Appearance of the Extremity of the Per-
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<
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pendicular muſt be found , in conſidering
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ſaid Extremity as a Point above the Geometri-
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cal Plane, by the Height of the propos’d Perpendi-
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cular: </
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">Then if a Line be drawn from the Point
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D, to the Point of Sight; </
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<
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">its Interſection
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T X, will give the Appearance a of the Seat of
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the Perpendicular propos’d.</
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<
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">Note, When there is a Neceſſity of having re-
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courſe to the Remarks of the foregoing Problem,
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in order to find the Point X; </
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<
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may be found, in drawing A S and D V, and
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afterwards joining the Points B and X by a
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Line. </
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