Gravesande, Willem Jacob 's, An essay on perspective

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          <pb o="102" file="0178" n="207" rhead="An ESSAY"/>
          <p style="it">
            <s xml:id="echoid-s2247" xml:space="preserve">The firſt of theſe Machines is undoubtedly much
              <lb/>
            preferable to the other; </s>
            <s xml:id="echoid-s2248" xml:space="preserve">becauſe it is firmer, and
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            renders the Work eaſier and exacter; </s>
            <s xml:id="echoid-s2249" xml:space="preserve">and Prints may
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            be eaſier repreſented in it, than in the other. </s>
            <s xml:id="echoid-s2250" xml:space="preserve">Add to
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            all this, that with a ſmall Alteration it may be made
              <lb/>
            capable of a few Uſes, which are peculiar to
              <lb/>
            the ſecond Machine; </s>
            <s xml:id="echoid-s2251" xml:space="preserve">yet ſince this latter one is
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            much ſimpler, of a much leſs Price, and is eaſier to
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            be carry’d from Place to Place, I thought it conveni-
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            ent to lay down alſo its Deſcription in this ſmall
              <lb/>
            Tract.</s>
            <s xml:id="echoid-s2252" xml:space="preserve"/>
          </p>
          <p style="it">
            <s xml:id="echoid-s2253" xml:space="preserve">I ſhall not here take up the Reader’s Time in enu-
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            merating the Advantages accruing to Painters from
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            Machines of this Nature: </s>
            <s xml:id="echoid-s2254" xml:space="preserve">But only add, that they
              <lb/>
            are of great Uſe for reducing or leſſening ſeveral ſe-
              <lb/>
            parate Objects in the ſame Picture; </s>
            <s xml:id="echoid-s2255" xml:space="preserve">which therefore
              <lb/>
            may be copy’d after Nature in the moſt perfect man-
              <lb/>
            ner poſſible. </s>
            <s xml:id="echoid-s2256" xml:space="preserve">It is very difficult to give ſeveral Objects
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            their true Bigneſs in a Picture, and to diſpoſe them
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            ſo as to have the ſame Point of Sight; </s>
            <s xml:id="echoid-s2257" xml:space="preserve">but this is
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            done extremely eaſy by means of Machines; </s>
            <s xml:id="echoid-s2258" xml:space="preserve">for the
              <lb/>
            Point of Sight in them will be the ſame always, as
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            long as the Convex Glaſs has the ſame Diſpoſition,
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            and the Bigneſs of the Repreſentations of Objects in
              <lb/>
            the Machines, do depend upon the Objects Diſtances
              <lb/>
            from them.</s>
            <s xml:id="echoid-s2259" xml:space="preserve"/>
          </p>
          <p style="it">
            <s xml:id="echoid-s2260" xml:space="preserve">This Invention, by Induſtry, may be certainly im-
              <lb/>
            prov’d, and the following Obſervations will be not a
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            little conducing thereto. </s>
            <s xml:id="echoid-s2261" xml:space="preserve">1. </s>
            <s xml:id="echoid-s2262" xml:space="preserve">You muſt uſe but one
              <lb/>
            Convex Glaſs; </s>
            <s xml:id="echoid-s2263" xml:space="preserve">for when there are two or more, the
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            true Repreſentations of Objects will be loſt; </s>
            <s xml:id="echoid-s2264" xml:space="preserve">which is
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            an Inconveniency one is alſo ſubject to, when a Con-
              <lb/>
            cave Glaſs is any ways us’d in the Conſtruction of the
              <lb/>
            Machine. </s>
            <s xml:id="echoid-s2265" xml:space="preserve">2. </s>
            <s xml:id="echoid-s2266" xml:space="preserve">When more than two Mirrours or Look-
              <lb/>
            ing glaſſes are us’d, the Rays, after having ſuffer’d a
              <lb/>
            triple Reflection, are ſo weaken’d, that the Objects
              <lb/>
            will not be well repreſented: </s>
            <s xml:id="echoid-s2267" xml:space="preserve">And even when but two
              <lb/>
            Mirrours are us’d, they muſt be well poliſh’d 3. </s>
            <s xml:id="echoid-s2268" xml:space="preserve"/>
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