Gravesande, Willem Jacob 's
,
An essay on perspective
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on PERSPECTIVE.
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the Eye, and above it, when the ſaid Plane is in-
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clined towards the Objects. </
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xml:space
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that F f of Fig. </
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<
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qual to R S, and the Line Tt, Fig. </
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be here a Part of the Line Z C continued, and
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made equal to R S.</
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">III. When the Perſpective Plane is Parallel or
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Horizontal.</
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. V.</
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cal Plane into Perſpective.</
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">Draw the Line C F at Pleaſure, in which aſ-
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ſume the Point I, and make I H and I G, equal
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to the Eye’s Diſtance from the perſpective
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Plane: </
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">Moreover, make I C, and I F equal to
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the Eye’s Diſtance from the Geometrical Plane,
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or at the leaſt, let I G and I H, be to I F and I C,
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as the Eye’s Diſtance from the perſpective Plane,
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is to its Diſtance from the Geometrical Plane.
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</
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">This being done, raiſe two Perpendiculars to
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the Line C F, in the Points G and H, and take
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two Rulers, each of which has two equal Threads
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ſo faſten’d to them, that the Diſtance P Q, and
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N M be equal: </
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">Then about F and C as Centers,
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with the Semidiameters M N or P Q, deſcribe
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two Arcs cutting the Perpendiculars raiſed at the
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Points G and H, in the Points C and D, and fix
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the Extremities of the two Threads of one Ruler,
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in the Points C and D, and the Threads of the
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other, in the Points F and E.</
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.</
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Point of the given Figures. </
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