Gravesande, Willem Jacob 's
,
An essay on perspective
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An ESSAY on
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out the Camera Obſcura, is ſimilar to that which
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they form, after having paſſed through the Glaſs:
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</
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<
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">Therefore the Rays which fall upon the Paper in
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the Camera Obſcura, likewiſe give the true Re-
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preſentation of the Objects thereon. </
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<
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to be demouſtrated.</
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<
s
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">Theſe Objects appear inverted, becauſe the
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Rays croſs each other in paſſing through the Glaſs;
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</
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<
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">thoſe coming from above going below, &</
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<
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II.</
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<
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upon a plain Mirrour or Speculum, before they fall
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upon a Convex Glaſs, no-wiſe deforms the Repreſen-
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tation of Objects.</
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<
s
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<
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Rays in the ſame Order as it receives them.</
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<
s
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">Now to ſhew the Uſe that may be drawn from
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the Camera Obſcura in Deſigning, I ſhall here lay
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down the Deſcription and Uſe of Two Machines,
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which I uſe for this End.</
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<
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">The Deſcription of the Firſt Machine.</
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<
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<
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xml:space
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Chair, (ſuch as People are carried in) the back Part
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of the Top is rounded, and its Foreſide P Q ſwells
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out in the middle: </
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<
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<
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the Machine, the Side whereof oppoſite to the
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Door, is ſuppoſed to be raiſed up, that ſo its In-
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ſide may be ſeen.</
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<
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ble, and turns upon two Iron-pins, going into
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the Wood of the Fore-ſide of the Machine, and is
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ſuſtain’d by two ſmall Chains, that ſo the ſaid
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Table may be lifted up; </
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