Gravesande, Willem Jacob 's, An essay on perspective

Table of Notes

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            nearly equal to the Height of the Top of the
              <lb/>
            Machine above the Table: </s>
            <s xml:id="echoid-s2371" xml:space="preserve">Then we open the
              <lb/>
            Aperture N at the Back-part of the Box upon the
              <lb/>
            Machine; </s>
            <s xml:id="echoid-s2372" xml:space="preserve">and incline the Mirrour L, ſo as to make
              <lb/>
            an Angle of 45 deg. </s>
            <s xml:id="echoid-s2373" xml:space="preserve">with the Horizon, when Ob-
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            jects are to be repreſented for the perpendicular
              <lb/>
            Picture. </s>
            <s xml:id="echoid-s2374" xml:space="preserve">Then, if the Mirrour H be taken away,
              <lb/>
            as alſo the Board F, together with the two Ru-
              <lb/>
            lers D E and D E, we ſhall perceive the Repre-
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            ſentation upon the Sheet of Paper on the Table
              <lb/>
            A, of all Objects, whoſe Rays falling upon the
              <lb/>
            Looking-glaſs L, can be thereby reflected upon
              <lb/>
            the Convex Glaſs; </s>
            <s xml:id="echoid-s2375" xml:space="preserve">which Convex Glaſs muſt be
              <lb/>
            rais’d or lower’d, by means of the Screw about
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            the Cylinder carrying it, until the ſaid Objects
              <lb/>
            appear entirely diſtinct.</s>
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            <s xml:id="echoid-s2377" xml:space="preserve">16. </s>
            <s xml:id="echoid-s2378" xml:space="preserve">When the ſame Objects are requir’d to be
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            repreſented for the inclin’d Picture, the Looking-
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            glaſs L muſt have half the Inclination we would
              <lb/>
            give to the Picture.</s>
            <s xml:id="echoid-s2379" xml:space="preserve"/>
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            <s xml:id="echoid-s2380" xml:space="preserve">17. </s>
            <s xml:id="echoid-s2381" xml:space="preserve">When the ſaid Objects are to be repreſent-
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            ed upon the Picture being parallel, the Aperture
              <lb/>
            N muſt be ſhut, and the Door B open’d; </s>
            <s xml:id="echoid-s2382" xml:space="preserve">then
              <lb/>
            the Mirrour H muſt be rais’d to the Top of the
              <lb/>
            Box, in putting it in a Situation parallel to the
              <lb/>
            Horizon. </s>
            <s xml:id="echoid-s2383" xml:space="preserve">This Diſpoſition of the Machine may
              <lb/>
            ferve when one is upon a Balcony, or ſome
              <lb/>
            other high Place; </s>
            <s xml:id="echoid-s2384" xml:space="preserve">to deſign a Parterre under-
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            neath.</s>
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            <s xml:id="echoid-s2386" xml:space="preserve">18. </s>
            <s xml:id="echoid-s2387" xml:space="preserve">If we have a mind to deſign a Statue
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            ſtanding in a Place ſomething elevated, and it is
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            requir’d to be ſo repreſented, as to be painted
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            againſt a Cieling; </s>
            <s xml:id="echoid-s2388" xml:space="preserve">the Back-ſide of the Machine
              <lb/>
            muſt be turned towards the Statue, and the Box
              <lb/>
            X ſo turned, that the Door B may face the Sta-
              <lb/>
            tue; </s>
            <s xml:id="echoid-s2389" xml:space="preserve">then, the Door being open’d, the Looking-
              <lb/>
            glaſs L muſt be placed vertically, with its po-
              <lb/>
            liſh’d Side towards the Statue; </s>
            <s xml:id="echoid-s2390" xml:space="preserve">and the Box </s>
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