Bélidor, Bernard Forest de, La science des ingenieurs dans la conduite des travaux de fortification et d' architecture civile

Table of Notes

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            <p>
              <s xml:id="echoid-s2989" xml:space="preserve">
                <pb o="44" file="0152" n="155" rhead="LA SCIENCE DES INGENIEURS,"/>
              points C & </s>
              <s xml:id="echoid-s2990" xml:space="preserve">D, il lui ſera indifferent que tous les couplets ſoient
                <lb/>
              unis ou non, qu’on augmente leur péſanteur, ou qu’on la laiſſe
                <lb/>
              comme elle étoit en premier lieu: </s>
              <s xml:id="echoid-s2991" xml:space="preserve">on pourroit même ſuſpendre des
                <lb/>
              poids égaux au bas de chacun, ſans que cela cauſât aucun change-
                <lb/>
              ment à la courbe CFD.</s>
              <s xml:id="echoid-s2992" xml:space="preserve"/>
            </p>
            <p>
              <s xml:id="echoid-s2993" xml:space="preserve">Prevenu de cela, on ſçait qu’on ne dérange rien dans l’équilibre
                <lb/>
              des puiſſances en changeant ſeulement leur direction en ſens con-
                <lb/>
              traire: </s>
              <s xml:id="echoid-s2994" xml:space="preserve">ainſi dans la ſupoſition que tous les couplets ſont unis à ne
                <lb/>
              pouvoir ſe déranger de la figure curviligne qu’ils compoſent tous
                <lb/>
              enſemble, ſi l’on fait tourner la chaine CFD ſur la ligne CD comme
                <lb/>
                <note position="left" xlink:label="note-0152-01" xlink:href="note-0152-01a" xml:space="preserve">
                  <emph style="sc">Fig</emph>
                . 8.</note>
              ſur un axe pour prendre la ſituation opoſée, mais toûjours verti-
                <lb/>
              cale CFD, tous les couplets, gardant entr’euxla même ſituation qu’ils
                <lb/>
              avoient auparavant, tendront au centre de la terre ſelon les mêmes
                <lb/>
              lignes de direction; </s>
              <s xml:id="echoid-s2995" xml:space="preserve">& </s>
              <s xml:id="echoid-s2996" xml:space="preserve">ſoit qu’on augmente leur péſanteur ou non,
                <lb/>
              pourvû que cette augmentation ſoit la même, ils ſe maintiendront
                <lb/>
              toûjours en équilibre, & </s>
              <s xml:id="echoid-s2997" xml:space="preserve">ils ne feront pas plus d’effort pour tomber
                <lb/>
              que s’ils n’étoient point entretenus par quelque cauſe qui les em-
                <lb/>
              pêche de ſe déranger.</s>
              <s xml:id="echoid-s2998" xml:space="preserve"/>
            </p>
            <p>
              <s xml:id="echoid-s2999" xml:space="preserve">Supoſant preſentement que la courbe CFD repreſente l’intradoſe
                <lb/>
              d’une Voûte ABC, qui ſoit par-tout d’une égale épaiſſeur, & </s>
              <s xml:id="echoid-s3000" xml:space="preserve">qu’à
                <lb/>
              la place des couplets on imagine des Vouſſoirs fort petits qui ayent
                <lb/>
              la même péſanteur & </s>
              <s xml:id="echoid-s3001" xml:space="preserve">dont les lignes de directions tirées de leur
                <lb/>
              centre de gravité ſeront les mêmes que celles des couplets, ces
                <lb/>
                <note position="left" xlink:label="note-0152-02" xlink:href="note-0152-02a" xml:space="preserve">
                  <emph style="sc">Fig</emph>
                . 5.</note>
              vouſſoirs demeureront en équilibre ainſique l’étoient ces couplets,
                <lb/>
              deſorte que s’ils ſont bien unis les uns contre les autres par un ci-
                <lb/>
              ment qui les réduiſe tous à ne faire qu’un ſeul corps, ils compo-
                <lb/>
              ſeront enſemble la Voûte ABC, dont toutes les parties ſeront en
                <lb/>
              équilibre.</s>
              <s xml:id="echoid-s3002" xml:space="preserve"/>
            </p>
            <p>
              <s xml:id="echoid-s3003" xml:space="preserve">Si l’on vouloit faire uſage de cette courbe, je crois qu’on ſeroit
                <lb/>
              obligé de raprocher ſes deux entrêmités G & </s>
              <s xml:id="echoid-s3004" xml:space="preserve">H, afin qu’elles ſoient
                <lb/>
              diſpoſées comme EA & </s>
              <s xml:id="echoid-s3005" xml:space="preserve">FC, & </s>
              <s xml:id="echoid-s3006" xml:space="preserve">non pas comme EG & </s>
              <s xml:id="echoid-s3007" xml:space="preserve">FH, qui ne
                <lb/>
              conviendroit pas dans l’execution, à cauſe que la naiſſance de la
                <lb/>
              Voûte feroit un Farret avec le pié-droit, ce qui choqueroit la vûë,
                <lb/>
              il eſt bon de profiter de ce que la théorie peut enſeigner; </s>
              <s xml:id="echoid-s3008" xml:space="preserve">mais
                <lb/>
              quand il s’agit de la pratique, on peut ſans ſcrupule ne le pas
                <lb/>
              ſuivre exactement pour raporter les choſes à l’uſage. </s>
              <s xml:id="echoid-s3009" xml:space="preserve">On trouvera
                <lb/>
              dans le ſecond tome de l’Analiſe du R. </s>
              <s xml:id="echoid-s3010" xml:space="preserve">P. </s>
              <s xml:id="echoid-s3011" xml:space="preserve">Reyneau l’équation de
                <lb/>
              la chainette & </s>
              <s xml:id="echoid-s3012" xml:space="preserve">la maniere de la tracer, c’eſt pourquoi je n’en parle
                <lb/>
              point ici.</s>
              <s xml:id="echoid-s3013" xml:space="preserve"/>
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