Huygens, Christiaan, Christiani Hugenii opera varia; Bd. 2: Opera geometrica. Opera astronomica. Varia de optica
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        <div xml:id="echoid-div142" type="section" level="1" n="61">
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            <s xml:id="echoid-s2726" xml:space="preserve">
              <pb file="0130" n="139" rhead="PRÆFATIO AD LECTOREM."/>
            lum hinc fructum colliges.</s>
            <s xml:id="echoid-s2727" xml:space="preserve"/>
          </p>
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        <div xml:id="echoid-div143" type="section" level="1" n="62">
          <head xml:id="echoid-head93" xml:space="preserve">DEFINITIONES.</head>
          <p>
            <s xml:id="echoid-s2728" xml:space="preserve">1 Si in circulo, ellipſe vel hyperbola ducantur è centro
              <lb/>
            in ejus perimetrum duæ rectæ, appellamus planum
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            ab illis rectis & </s>
            <s xml:id="echoid-s2729" xml:space="preserve">perimetri ſegmento comprehenſum,
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            ſectorem.</s>
            <s xml:id="echoid-s2730" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s2731" xml:space="preserve">2 Si perimetri ſegmentum inter illas rectas comprehenſum à
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            rectis quotcumque ſubtendatur, ita ut triangula rectili-
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            nea (quorum communis vertex eſt ſectionis centrum & </s>
            <s xml:id="echoid-s2732" xml:space="preserve">
              <lb/>
            baſes rectæ ſubtendentes) ſint æqualia; </s>
            <s xml:id="echoid-s2733" xml:space="preserve">vocamus rectili-
              <lb/>
            neum illud ab iſtis triangulis conflatum, polygonum re-
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            gulare inſcriptum, ſi ſectio conica fuerit circulus vel el-
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            lipſis; </s>
            <s xml:id="echoid-s2734" xml:space="preserve">quod ſi fuerit hyperbola, vocamus illud rectili-
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            neum polygonum regulare circumſcriptum.</s>
            <s xml:id="echoid-s2735" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s2736" xml:space="preserve">3 Si perimetri ſegmentum inter illas rectas comprehenſum à
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            rectis quotcunque tangatur & </s>
            <s xml:id="echoid-s2737" xml:space="preserve">à tactibus ad ſectionis cen-
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            trum ducantur rectæ; </s>
            <s xml:id="echoid-s2738" xml:space="preserve">ſi inquam omnia trapezia, a tan-
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            gentibus proximis & </s>
            <s xml:id="echoid-s2739" xml:space="preserve">rectis ad centrum comprehenſa, fue-
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            rint æqualia; </s>
            <s xml:id="echoid-s2740" xml:space="preserve">appello rectilineum ab illis conflatum, poly-
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            gonum regulare circumſcriptum, ſi ſectio conica ſit elli-
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            pſis vel circulus, & </s>
            <s xml:id="echoid-s2741" xml:space="preserve">polygonum regulare inſcriptum ſi
              <lb/>
            fuerit hyperbola.</s>
            <s xml:id="echoid-s2742" xml:space="preserve"/>
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          <p>
            <s xml:id="echoid-s2743" xml:space="preserve">4 Si omnes anguli (excepto illo ad ſectionis centrum) po-
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            lygoni regularis à ſubtendentibus comprehenſi </s>
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