Bion, Nicolas, Traité de la construction et principaux usages des instruments de mathématique, 1723

Table of Notes

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            <s xml:id="echoid-s5135" xml:space="preserve">
              <pb o="159" file="173" n="173" rhead="POUR LEVER LES PLANS. Liv. IV. Ch. VI."/>
            les raïons viſuels des 2 lunetes étant l'une ſur l'autre ſont d'accord,
              <lb/>
            & </s>
            <s xml:id="echoid-s5136" xml:space="preserve">pour les faire convenir on avance ou recule le petie chaſſis qui
              <lb/>
            porte les filets par le moyen des vis. </s>
            <s xml:id="echoid-s5137" xml:space="preserve">La largeur depuis le centre des
              <lb/>
            lunetes juſqu'aux échancrures de l'alidade eſt ordinairement de 5
              <lb/>
            degrez, ce qui fait que la diviſion avance d'autant de degrez plus
              <lb/>
            d'un côté que de l'autre, comme la figure le montre.</s>
            <s xml:id="echoid-s5138" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s5139" xml:space="preserve">Les lunetes ſont à 2 ou à 4 verres, & </s>
            <s xml:id="echoid-s5140" xml:space="preserve">ont toutes une ſoye très-
              <lb/>
            fine tenduëau foyer du verre objectif, pour ſervir de pinule.</s>
            <s xml:id="echoid-s5141" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s5142" xml:space="preserve">Les lunetes à 4 verres font voir les objets dans leur veritable ſitua-
              <lb/>
            tion; </s>
            <s xml:id="echoid-s5143" xml:space="preserve">mais celles des 2 verres les renverſent en ſorte que ce qui eſt à
              <lb/>
            doit paroît à gauche, & </s>
            <s xml:id="echoid-s5144" xml:space="preserve">ce qui eſt en haut paroît en bas; </s>
            <s xml:id="echoid-s5145" xml:space="preserve">mais cela
              <lb/>
            n'ôte pas la juſteſſe de l'operation, parce qu'elles donnent toûjours
              <lb/>
            le point de direction.</s>
            <s xml:id="echoid-s5146" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s5147" xml:space="preserve">Ces lunetes ſont faites de tuïaux de cuivre ſoudez & </s>
            <s xml:id="echoid-s5148" xml:space="preserve">tournez en
              <lb/>
            forme cylindrique, comme on voit par la figure D, qui repreſente u-
              <lb/>
            nelunete détachée. </s>
            <s xml:id="echoid-s5149" xml:space="preserve">Le verre oculaire, qui eſt celui dont on aproche
              <lb/>
            l'œil pour regarder les objets, eſt au bout marqué 1. </s>
            <s xml:id="echoid-s5150" xml:space="preserve">On le poſe dans
              <lb/>
            un autre petit tuïau qui eſt à part, auſſi marqué 1, que l'on avance
              <lb/>
            ou recule dans le tuïau de la lunete ſelon les difſerentes vûës. </s>
            <s xml:id="echoid-s5151" xml:space="preserve">Ce pe-
              <lb/>
            tit tuïau porte auſſi quelquefois au foyer du verre la ſoye fine qui
              <lb/>
            ſert de pinule; </s>
            <s xml:id="echoid-s5152" xml:space="preserve">mais pour le mieux cette ſoie eſt attachée ſur une peti-
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            te piece de cuivre, qu'on voit auſſi à part, ſur laquelle on trace bien
              <lb/>
            juſte un trait quarré marqué 2, ſur lequel on poſe cesſoies. </s>
            <s xml:id="echoid-s5153" xml:space="preserve">On place
              <lb/>
            cette piece dans un rainure faite dans un petit chaſſis de cuivre ſou-
              <lb/>
            dé au tuïau de la lunete à l'endroit marqué. </s>
            <s xml:id="echoid-s5154" xml:space="preserve">2. </s>
            <s xml:id="echoid-s5155" xml:space="preserve">La petite vis marquée
              <lb/>
            5, eſt faite pour avancer ou reculer la petite piece qui porte les ſoyes.
              <lb/>
            </s>
            <s xml:id="echoid-s5156" xml:space="preserve">Le verre objectif eſt placé à l'autre bout de la lunete du côté de l'ob-
              <lb/>
            jet que l'on veut voir. </s>
            <s xml:id="echoid-s5157" xml:space="preserve">Il eſt auſſi placé dans un petittuïau marqué
              <lb/>
            3, & </s>
            <s xml:id="echoid-s5158" xml:space="preserve">qui entre à force dans le canal de la lunete, afin que ce verre ne
              <lb/>
            change pas facilement de place quand la lunete eſt ajuſtée. </s>
            <s xml:id="echoid-s5159" xml:space="preserve">Ces ver-
              <lb/>
            res ſont convexes, ce qui rend leur milieu plus épais que leurs bords. </s>
            <s xml:id="echoid-s5160" xml:space="preserve">
              <lb/>
            Mais l'oculaire doit avoir plus de convexité que l'objectif, afin que
              <lb/>
            les objets paroiſſent plus grands qu'à la vûë ſimple.</s>
            <s xml:id="echoid-s5161" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s5162" xml:space="preserve">On appelle le foyer d'un verre convexe l'endroit où les raïons qui
              <lb/>
            viennent d'un objet lumineux ou coloré, lequel eſt dans une diſtan-
              <lb/>
            ce fort éloignée, vont ſe réunir après avoir paſſé au-delà du verre;
              <lb/>
            </s>
            <s xml:id="echoid-s5163" xml:space="preserve">c'eſt pourquoi la peinture des objets qui ſont oppoſez au verre, ſe re-
              <lb/>
            preſente très-diſtinctement dans cet endroit. </s>
            <s xml:id="echoid-s5164" xml:space="preserve">Par exemple, le point
              <lb/>
            L, à l'extremite du côte de la figure H, eſt le foyer du verre S, à cau-
              <lb/>
            ſe que c'eſt le point où les raions, qui entrent par l'autre bout N du
              <lb/>
            </s>
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