Gravesande, Willem Jacob 's
,
An essay on perspective
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An ESSAY
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<
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<
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xml:space
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">In ſome ſeparate Place, draw the Lines C E
<
lb
/>
and C P, making an Angle with each other
<
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equal to the Angle of Inclination of the given
<
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Line; </
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<
s
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xml:space
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">and in one of theſe Lines, aſſume C E
<
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equal to the given Line, and let fall the Perpen-
<
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/>
dicular E P, from the Point E upon the other
<
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Line. </
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<
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">Then aſſume A B, in the Direction of
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the propos’d Line, equal to C P; </
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<
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xml:space
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ving found a, the Perſpective of A, and the
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Point T , the Perſpective of a Point
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xml:space
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">50.</
note
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above B, the Height of P E; </
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<
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xml:space
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">join the Points a
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and T by a right Line; </
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<
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xml:space
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ance will be had.</
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<
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">If from the Extremity of the inclin’d Line, a
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Perpendicular be let fall upon the Geometrical
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Plane, the ſaid Perpendicular will meet this
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Plane in the Point B, and will be equal to P E;
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</
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<
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">as is evident by the Conſtruction of the Figure
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C P E. </
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<
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">But the Point T is the Repreſentation
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of the Extremity of this Perpendicular; </
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<
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xml:space
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therefore it is alſo the Extremity of the inclin’d
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Line. </
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<
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">Which was to be demonſtrated.</
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<
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">There are ſome Caſes of this Propoſition, that
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may be ſhorten’d. </
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<
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ral Lines of this Kind parallel between them-
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ſelves, and whoſe accidental Point can be
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found : </
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xml:space
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">When an inclin’d Line is
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position
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xlink:label
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xlink:href
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">68.</
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>
rallel to the perſpective Plane. </
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>
<
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