Gravesande, Willem Jacob 's
,
An essay on perspective
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An ESSAY
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Rulers, keeping all the Threads tight, ſo that
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the two Threads fix’d in the Points C and F,
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croſs each other in the Point A; </
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xml:space
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Point a, wherein the two other Threads croſs
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each other, is the Perſpective ſought. </
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xml:space
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this Manner may the Repreſentations of any
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Number of Points be ſound.</
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<
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Triangle C A F: </
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formed for finding the Repreſentations of diffe-
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rent Points, have the ſame Baſes D E and C F,
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which are between themſelves, as the Eye’s Di-
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ſtance from the perſpective Plane, to its Diſtance
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from the Geometrical Plane; </
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<
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tices form ſimilar Figures, whoſe correſpondent
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Lines are in the ſame Proportion; </
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conſequently , are the Appearances ſought.</
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P E, and M D of one Colour, and the two
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Threads Q F, and C N of another.</
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. VI.</
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of Lines, equal and perpendicular to the Geometri-
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cal Plane.</
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<
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with the ſame Letters in the precedent Figure,
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as alſo let P Q and M N be the Rulers: </
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over, let B be the Point, wherein a </
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