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

Table of Notes

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        <div xml:id="echoid-div574" type="section" level="1" n="284">
          <pb o="274" file="290" n="290" rhead="CONSTRUCT. ET USAGES DES INSTRUMENS"/>
          <p>
            <s xml:id="echoid-s8626" xml:space="preserve">Il eſt abſolument néceſſaire que la ligne droite CD, qui repreſen-
              <lb/>
            te l'horiſon, ſoit parfaitement de niveau, aſin d'y pouvoir commen-
              <lb/>
            cer la diviſion du cercle. </s>
            <s xml:id="echoid-s8627" xml:space="preserve">Pour l'examiner il ſaut obſerver par les fen-
              <lb/>
            tes ou les petits trous des pinules FG, qui ſont attachées vers les ex-
              <lb/>
            trémitez de l'alidade qui tourne librement par le moyen d'un clou
              <lb/>
            à tête autour du centre E. </s>
            <s xml:id="echoid-s8628" xml:space="preserve">Il faut, dis-je, obſerver un même objet
              <lb/>
            éloigné, en mettant l'œil à l'une deſdites pinules; </s>
            <s xml:id="echoid-s8629" xml:space="preserve">après avoir tour-
              <lb/>
            né l'Aſtrolabe ſile même objet ſe voit toutes les 2 fois ſans changer
              <lb/>
            l'alidade, c'eſt une marque que la ligne de foi convient avec l'hori-
              <lb/>
            ſon. </s>
            <s xml:id="echoid-s8630" xml:space="preserve">Mais ſi pour voir une ſeconde fois le même objet il faut mou-
              <lb/>
            voir l'alidade, c'eſt-à-dire, la hauſſer ou baiſſer, le point milieu en-
              <lb/>
            tre ces 2 poſitions marquera la vraie ligne horiſontale, paſſant par
              <lb/>
            le centre de l'inſtrument; </s>
            <s xml:id="echoid-s8631" xml:space="preserve">ce qu'il ſera bon de veriſier par pluſieurs
              <lb/>
            obſervations réiterées avant que de commencer la diviſion qui ſe
              <lb/>
            fera de la maniere que nous avons expliqué ci-devant.</s>
            <s xml:id="echoid-s8632" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div576" type="section" level="1" n="285">
          <head xml:id="echoid-head413" style="it" xml:space="preserve">Vſage de l'Aſtrolabe.</head>
          <p>
            <s xml:id="echoid-s8633" xml:space="preserve">P Our obſerver la hauteur des Aſtres ſur l'horiſon, & </s>
            <s xml:id="echoid-s8634" xml:space="preserve">leur diſtan-
              <lb/>
            ce du Zénith qui en eſt le complément.</s>
            <s xml:id="echoid-s8635" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s8636" xml:space="preserve">Pour cet effet on ſuſpend l'Aſtrolabe par ſon anneau & </s>
            <s xml:id="echoid-s8637" xml:space="preserve">on tour-
              <lb/>
            ne ſon côtévers l'Aſtre, en hauſſant un des bouts de l'alidade F, juſ-
              <lb/>
            qu'à ce que le raïon de l'Aſtre paſſe par les 2 pinules FG; </s>
            <s xml:id="echoid-s8638" xml:space="preserve">alors l'a-
              <lb/>
            lidade marquera par ſes extremitez, autour du cercle diviſé, la hau-
              <lb/>
            teur de l'Aſtre H, depuis C juſqu'en F, compris entre le raïon hori-
              <lb/>
            ſontal EC, & </s>
            <s xml:id="echoid-s8639" xml:space="preserve">le raïon de l'Aſtre EF, parce que cet inſtrument dans
              <lb/>
            cette ſituation repreſente un vertical. </s>
            <s xml:id="echoid-s8640" xml:space="preserve">La diviſion AG ou ou AF mar-
              <lb/>
            quera la diſtance de l'Aſtre au Zénith.</s>
            <s xml:id="echoid-s8641" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div577" type="section" level="1" n="286">
          <head xml:id="echoid-head414" style="it" xml:space="preserve">Conſtruction de l'Anneau.</head>
          <p>
            <s xml:id="echoid-s8642" xml:space="preserve">C Ette ſigure repreſente un anneau ou cercle de cuivre. </s>
            <s xml:id="echoid-s8643" xml:space="preserve">Il ſe ſait
              <lb/>
              <note position="left" xlink:label="note-290-01" xlink:href="note-290-01a" xml:space="preserve">XIX.
                <lb/>
              Planche.
                <lb/>
              Fig. 5.</note>
            de 8 à 10 pouces de diametre; </s>
            <s xml:id="echoid-s8644" xml:space="preserve">il eſt néceſſaire qu'il ſoit d'une
              <lb/>
            bonne épaiſſeur, aſin qu'étant plus peſant il conſerve mieux ſa ſitua-
              <lb/>
            tion perpendiculaire; </s>
            <s xml:id="echoid-s8645" xml:space="preserve">la diviſion ſe marque dans ſa ſurface concave.
              <lb/>
            </s>
            <s xml:id="echoid-s8646" xml:space="preserve">Il y a un petit trou en C, qui traverſe l'anneau parallelement à ſon
              <lb/>
            plan. </s>
            <s xml:id="echoid-s8647" xml:space="preserve">Ce trou eſt éloigné de 45 d. </s>
            <s xml:id="echoid-s8648" xml:space="preserve">du point de ſuſpenſion B, & </s>
            <s xml:id="echoid-s8649" xml:space="preserve">il eſt
              <lb/>
            le centre d'un quart de cercle DE, diviſé en 90 d. </s>
            <s xml:id="echoid-s8650" xml:space="preserve">Un de ſes raïons
              <lb/>
            CE eſt parallele au diametre vertical BH, point de ſuſpenſion; </s>
            <s xml:id="echoid-s8651" xml:space="preserve">& </s>
            <s xml:id="echoid-s8652" xml:space="preserve">
              <lb/>
            l'autre raïon horiſontal eſt perpendiculaire au même diametre.</s>
            <s xml:id="echoid-s8653" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s8654" xml:space="preserve">Nous ne diſons rien ici de la préciſion avec laquelle on doit avoir
              <lb/>
            ce diametre. </s>
            <s xml:id="echoid-s8655" xml:space="preserve">L'habileté de l'Ouvrier y ſuppléera ſacilement. </s>
            <s xml:id="echoid-s8656" xml:space="preserve">Enſuite
              <lb/>
            </s>
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