Bion, Nicolas, Traité de la construction et principaux usages des instruments de mathématique, 1723
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        <div xml:id="echoid-div217" type="section" level="1" n="83">
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            <s xml:id="echoid-s1872" xml:space="preserve">
              <pb o="55" file="069" n="69" rhead="DU COMPAS DE PROPORTION. Liv. II. Chap. II."/>
            degrez propoſez; </s>
            <s xml:id="echoid-s1873" xml:space="preserve">ouvrez enſuite le compas de proportion de ſorte
              <lb/>
            que cette diſtance s'accorde aux deux nombres 60 marquez de part
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            & </s>
            <s xml:id="echoid-s1874" xml:space="preserve">d'autre ſur la ligne de cordes, ellcs feront l'angle requis.</s>
            <s xml:id="echoid-s1875" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s1876" xml:space="preserve">Si, par exemple, vous voulez qu'elles faſſent un angle de 40 de-
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            grez, comme en la figure 9 de la planche 7, prenez la diſtance du
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            centre au nombre 40, & </s>
            <s xml:id="echoid-s1877" xml:space="preserve">la portez à l'ouverture de 60 à 60. </s>
            <s xml:id="echoid-s1878" xml:space="preserve">Si vous
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            voulez un angle droit, prenez la diſtance du centre à 90 degrez, & </s>
            <s xml:id="echoid-s1879" xml:space="preserve">
              <lb/>
            la portez pareillement à l'ouverture de 60 à 60, & </s>
            <s xml:id="echoid-s1880" xml:space="preserve">ainſi des autres.</s>
            <s xml:id="echoid-s1881" xml:space="preserve"/>
          </p>
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        <div xml:id="echoid-div218" type="section" level="1" n="84">
          <head xml:id="echoid-head136" xml:space="preserve">USAGE II.
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          Le compas de proportion étant ouvert, trouver les degrez
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          de ſon ouverture.</head>
          <p>
            <s xml:id="echoid-s1882" xml:space="preserve">PRenez l'ouverture de 60 degrez, & </s>
            <s xml:id="echoid-s1883" xml:space="preserve">la portez le long de la ligne
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            des cordes depuis le centre, le nombre où elle ſe terminera,
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            marquera les degrez de ſon ouverture.</s>
            <s xml:id="echoid-s1884" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s1885" xml:space="preserve">C'eſt ſur la ligne des cordes que l'on place quelquefois des pinu-
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            les pour meſurer un angle ſur la terre, ou poury en faire un d'autant
              <lb/>
            de degrez que l'on veut, en ajoûtant un genoüil au compas de pro-
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            portion, & </s>
            <s xml:id="echoid-s1886" xml:space="preserve">le plaçant ſur un pied, pour l'élever à la hauteur de
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            l'œil, en pratiquant ce que nous venons de dire en ces deux ufages;
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            </s>
            <s xml:id="echoid-s1887" xml:space="preserve">mais nous eſtimons qu'il eſt plus aiſé de ſe ſervir d'un demi cercle
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            diviſé pour faire ces ſortes d'operations.</s>
            <s xml:id="echoid-s1888" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div219" type="section" level="1" n="85">
          <head xml:id="echoid-head137" xml:space="preserve">USAGE III.
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          Sur une ligne droite donnée faire un angle rectiligne d'aut ant
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          de degrez qu'on voudra.</head>
          <p>
            <s xml:id="echoid-s1889" xml:space="preserve">DEcrivez ſur la ligne donnée un arc de cercle ayant pour centre
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            le point auquel vous voulez faire l'angle, portez le rayon du-
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            dit arc à l'ouverture de la corde de 60 degrez; </s>
            <s xml:id="echoid-s1890" xml:space="preserve">lecompas de propor-
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            tion demeurant ainſi ouvert, prenez l'ouverture de la corde du
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            nombre des degrez propoſez, & </s>
            <s xml:id="echoid-s1891" xml:space="preserve">la portez depuis la ligne ſur l'arc
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            que vous avez décrit; </s>
            <s xml:id="echoid-s1892" xml:space="preserve">tirez enfin une ligne droite du centre par l'ex-
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            tremité de cet arc, pour former l'angle requis.</s>
            <s xml:id="echoid-s1893" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s1894" xml:space="preserve">Soit propoſé pour exemple de faire à l'extremité B de la ligne AB,
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              <note position="right" xlink:label="note-069-01" xlink:href="note-069-01a" xml:space="preserve">Fig. 10.</note>
            un angle de 40 degrez; </s>
            <s xml:id="echoid-s1895" xml:space="preserve">ayant fait dudit point B un arc de cercle à
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            diſcretion, portez-en le rayon toûjours à l'ouverture de la corde de
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            60 degrez, parce que le rayon d'un cercle eſt toûjours égal à la cor-
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            de de 60 degrez du même cercle; </s>
            <s xml:id="echoid-s1896" xml:space="preserve">prenez enſuite l'ouverture de la
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            corde de 40 degrez, & </s>
            <s xml:id="echoid-s1897" xml:space="preserve">la portez ſur l'arc de cercle CD; </s>
            <s xml:id="echoid-s1898" xml:space="preserve">enfin tirant
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            la droit du pointe B par lepoint D, vousaurez fait un angle de 40
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            degrez, figure 10.</s>
            <s xml:id="echoid-s1899" xml:space="preserve"/>
          </p>
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