Gravesande, Willem Jacob 's
,
An essay on perspective
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preſentations being join’d, will give the Perſpe-
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ctive ſought. </
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ing the Chords thro’a Point, whoſe Repreſenta-
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tion is known.</
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<
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<
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xml:space
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xml:space
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">Fig. 16.</
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the Center P of the Circle, whoſe Perſpective is
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ſought, let fall the Perpendicular P F upon the ſaid
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Line G I, which biſect in the Point R. </
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<
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as a Center, and with the Radius R P, deſcribe an
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Arc of a Circle M P N, cutting the given Circle in
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the Points M and N. </
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<
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">Now, if the Perſpective of
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L H and N M be found, the two Conjugate Dia-
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meters of an Ellipſis, which is the Repreſentation of
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the given Circle, will be bad. </
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<
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be drawn by ſome one of the Methods laid down by
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thoſe who have treated of Conick Sections.</
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<
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Truth of this. </
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<
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">of the great
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Latin Treatiſe of Conic Sections, written by M. </
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<
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la Hire; </
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<
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apply’d. </
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<
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the Points M and N to the Point F, will touch the
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Circle in the ſaid Points M and N. </
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viſual Rays, going from the Eye towards all the Parts
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of the Circumference of the Circle, form a Cone,
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3. </
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of a Cone, made by the perſpective Plane. </
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That the Line G I ought to be conceiv’d, as being
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the Interſection of the Geometrical Plane, and a
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Plane paſſing thro’ the Eye parallel to the perſpective
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Plane.</
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