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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              <s xml:id="echoid-s7504" xml:space="preserve">
                <pb o="46" file="0344" n="362" rhead="LA SCIENCE DES INGENIEURS,"/>
              nus de l’angle droit eſt à celui de 45 degrés, ainſi on dira ſi 100000
                <lb/>
              donnent 70710, que donneront 4095 liv. </s>
              <s xml:id="echoid-s7505" xml:space="preserve">péſanteur du Pont pour
                <lb/>
              celle des poids, que l’on trouvera de 2895 liv. </s>
              <s xml:id="echoid-s7506" xml:space="preserve">dont la moitié qui eſt
                <lb/>
              1447, ſerala péſanteur que doit avoir chaque poids; </s>
              <s xml:id="echoid-s7507" xml:space="preserve">mais comme
                <lb/>
              pour avoir égard au frotement, il vaut mieux les faire plus péſans
                <lb/>
              que trop légers, á cauſe qu’on ne peut pas les augmenter, au lieu
                <lb/>
              qu’il n’y a point d’inconvenient de ſurcharger le Pont s’il ſe trouvoit
                <lb/>
              au-deſſous de l’équilibre, il eſt à propos, en faveur de toutes ces
                <lb/>
              conſidérations, d’augmenter chaque poids de 100 liv. </s>
              <s xml:id="echoid-s7508" xml:space="preserve">c’eſt-à-dire de
                <lb/>
              lesfaire de 1547 liv. </s>
              <s xml:id="echoid-s7509" xml:space="preserve">au lieu de 1447. </s>
              <s xml:id="echoid-s7510" xml:space="preserve">Je n’ai pas dit que les poids de
                <lb/>
              baſcule devoient être cilindriques; </s>
              <s xml:id="echoid-s7511" xml:space="preserve">car l’on s’imagine bien qu’on ne
                <lb/>
              peut leur donner une figure qui convienne mieux pour rouler faci-
                <lb/>
              lement le long des couliſſes: </s>
              <s xml:id="echoid-s7512" xml:space="preserve">il s’agit donc de ſavoir qu’elle ſera la
                <lb/>
              valeur de l’axe de ces cilindres, ou celle du diamêtre de leur baſe,
                <lb/>
              qui eſt la même choſe; </s>
              <s xml:id="echoid-s7513" xml:space="preserve">car je ſupoſe ces deux lignes égales, afin
                <lb/>
              que les poids ayent moins de volume.</s>
              <s xml:id="echoid-s7514" xml:space="preserve"/>
            </p>
            <p>
              <s xml:id="echoid-s7515" xml:space="preserve">Sachant qu’un pied cube de fer péſe 580 liv. </s>
              <s xml:id="echoid-s7516" xml:space="preserve">commençons par
                <lb/>
              chercher quel eſt la péſanteur du cilindre qui ſeroit inſcrit dans un
                <lb/>
              pied cube: </s>
              <s xml:id="echoid-s7517" xml:space="preserve">pour cela, il faut remarquer que ces deux ſolides, ayant
                <lb/>
              la même hauteur, ſeront en même rai
                <unsure/>
              ſ
                <unsure/>
              on que leur baſe, par con-
                <lb/>
              ſéquent comme le quarré du diamêtre d’un cercle eſt à la ſuperficie
                <lb/>
              du même cercle, ou ſi l’on veut comme 14 eſt à 11; </s>
              <s xml:id="echoid-s7518" xml:space="preserve">il faut donc
                <lb/>
              dire, comme 14 eſt à 11, ainſi 580 péſanteur d’un pied cube defer,
                <lb/>
              eſt à celle du cilindre inſcrit, qu’on trouvera d’environ 456 liv.</s>
              <s xml:id="echoid-s7519" xml:space="preserve"/>
            </p>
            <p>
              <s xml:id="echoid-s7520" xml:space="preserve">Les cilindres ſemblables étant dans la raiſon des cubes de leur
                <lb/>
              axe, on pourra dire ſi un cilindre de 456. </s>
              <s xml:id="echoid-s7521" xml:space="preserve">liv. </s>
              <s xml:id="echoid-s7522" xml:space="preserve">dont le diamêtre de la
                <lb/>
              baſe & </s>
              <s xml:id="echoid-s7523" xml:space="preserve">l’axe ſont chacun d’un pied, donne 1728 pouces pour le
                <lb/>
              cube de ſon axe; </s>
              <s xml:id="echoid-s7524" xml:space="preserve">combien donnera 1547 liv. </s>
              <s xml:id="echoid-s7525" xml:space="preserve">péſanteur d’un autre
                <lb/>
              cilindre ſemblable au précédent pour le cube de ſon axe, on trou-
                <lb/>
              vera 5862 pouces, dont extrayant la racine cube, elle ſera de 18
                <lb/>
              pouces qui eſt la valeur de l’axe que l’on demande; </s>
              <s xml:id="echoid-s7526" xml:space="preserve">il n’y a donc
                <lb/>
              pas de difficulté à avoir les poids de baſcule dans la juſte proportion
                <lb/>
              qui leur convient, puiſqu’on n’a qu’à demander aux Forges où l’on
                <lb/>
              coule le fer, deux poids péſants chacun 1547 liv. </s>
              <s xml:id="echoid-s7527" xml:space="preserve">dès qu’on leur
                <lb/>
              donnera pour baſe un cercle de 18 pouces de diamêtre, & </s>
              <s xml:id="echoid-s7528" xml:space="preserve">pour axe
                <lb/>
              une ligne égale à ce diamêtre.</s>
              <s xml:id="echoid-s7529" xml:space="preserve"/>
            </p>
            <p>
              <s xml:id="echoid-s7530" xml:space="preserve">J’ajoûterai que ces poids doiventêtre percés dans le milieu par un
                <lb/>
              trou d’un pouce en quarré, afin qu’on puiſſe y paſſer un eſſieu qui ſer-
                <lb/>
              ve à entretenir la chape qui doit en faciliter le mouvement le long
                <lb/>
              des couliſſes. </s>
              <s xml:id="echoid-s7531" xml:space="preserve">Cette chape eſt figurée ſur la planche où elle accom-
                <lb/>
              pagne le poids qui eſt déſigné par la Lettre V: </s>
              <s xml:id="echoid-s7532" xml:space="preserve">ſi je dis qu’il faut faire </s>
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