Gravesande, Willem Jacob 's, Physices elementa mathematica, experimentis confirmata sive introductio ad philosophiam Newtonianam; Tom. 1

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        <div xml:id="echoid-div2307" type="section" level="1" n="574">
          <p>
            <s xml:id="echoid-s15358" xml:space="preserve">
              <pb o="92" file="0606" n="669" rhead="PHYSICES ELEMENTA"/>
            perimenti 4, hujus capitis, illuminentur, trans priſma viſa,
              <lb/>
            diſtinctis limitibus terminantur.</s>
            <s xml:id="echoid-s15359" xml:space="preserve"/>
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        <div xml:id="echoid-div2308" type="section" level="1" n="575">
          <head xml:id="echoid-head755" xml:space="preserve">CAPUT XXI.</head>
          <head xml:id="echoid-head756" style="it" xml:space="preserve">De Iride.</head>
          <p>
            <s xml:id="echoid-s15360" xml:space="preserve">PEractis quæ radios, quibus corpora illuminantur, ſpe-
              <lb/>
            ctant, antequam hanc materiam miſſam faciamus, expli-
              <lb/>
            candum eſt phænomenon, nimium notabile & </s>
            <s xml:id="echoid-s15361" xml:space="preserve">vulgare ut
              <lb/>
            ſilentio prætereatur.</s>
            <s xml:id="echoid-s15362" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s15363" xml:space="preserve">Arcus cæleſtis, aut Iris, à nemine ſæpiſſimè non fuit ob-
              <lb/>
            ſervatus; </s>
            <s xml:id="echoid-s15364" xml:space="preserve">quibuſdam præmiſſis, explicandum erit unde oria-
              <lb/>
            tur</s>
          </p>
          <p>
            <s xml:id="echoid-s15365" xml:space="preserve">Detur medium denſius, rariori circumdatum, circulo BD
              <lb/>
              <note position="left" xlink:label="note-0606-01" xlink:href="note-0606-01a" xml:space="preserve">875.</note>
            FH terminatum. </s>
            <s xml:id="echoid-s15366" xml:space="preserve">Incidant in illud radii homogenei paralle-
              <lb/>
              <note position="left" xlink:label="note-0606-02" xlink:href="note-0606-02a" xml:space="preserve">
                <emph style="sc">TAB. XVIII</emph>
              .
                <lb/>
              fig. 1.</note>
            li inter ſe, quorum unus eſt AB; </s>
            <s xml:id="echoid-s15367" xml:space="preserve">ducatur ſemidiameter
              <lb/>
            CB continuata ad N; </s>
            <s xml:id="echoid-s15368" xml:space="preserve">perpendicularis eſt hæc ad ſuperfi-
              <lb/>
            ciem media dirimentem; </s>
            <s xml:id="echoid-s15369" xml:space="preserve">ABN eſt ergo angulus inciden-
              <lb/>
            tiæ hic æqualis eſt angulo oppoſito ad verticem CBL, cu-
              <lb/>
            jus ſinus eſt CL, per centrum ad BL perpendicularis; </s>
            <s xml:id="echoid-s15370" xml:space="preserve">re-
              <lb/>
            fringitur radius ad perpendicularem , eſtque angulus
              <note symbol="*" position="left" xlink:label="note-0606-03" xlink:href="note-0606-03a" xml:space="preserve">624.</note>
            fractionis CBM, cujus ſinus eſt CM, à C ad BD perpen-
              <lb/>
            dicularis: </s>
            <s xml:id="echoid-s15371" xml:space="preserve">pro ſingulis radiis, ut AB, datur eadem ratio in-
              <lb/>
            ter lineas, ut CL & </s>
            <s xml:id="echoid-s15372" xml:space="preserve">CM . </s>
            <s xml:id="echoid-s15373" xml:space="preserve">Radius BD pro parte in
              <note symbol="*" position="left" xlink:label="note-0606-04" xlink:href="note-0606-04a" xml:space="preserve">639.</note>
            dium rarius penetrat juxta DE, pro parte reflectitur per
              <lb/>
            DF; </s>
            <s xml:id="echoid-s15374" xml:space="preserve">efficitque angulum reflectionis CDF æqualem angulo
              <lb/>
            incidentiæ BDC; </s>
            <s xml:id="echoid-s15375" xml:space="preserve">unde BD & </s>
            <s xml:id="echoid-s15376" xml:space="preserve">DF æquales ſunt. </s>
            <s xml:id="echoid-s15377" xml:space="preserve">
              <note symbol="*" position="left" xlink:label="note-0606-05" xlink:href="note-0606-05a" xml:space="preserve">805.</note>
            dius DF pro parte etiam ex denſiori medio exit per FG,
              <lb/>
            pro parte reflectitur per FH; </s>
            <s xml:id="echoid-s15378" xml:space="preserve">qui eodem modo pro parte
              <lb/>
            exit per HI, & </s>
            <s xml:id="echoid-s15379" xml:space="preserve">pro parte reflectitur: </s>
            <s xml:id="echoid-s15380" xml:space="preserve">hanc autem refle-
              <lb/>
            ctionem, ulterioresque reflectiones & </s>
            <s xml:id="echoid-s15381" xml:space="preserve">refractiones non
              <lb/>
            conſideramus; </s>
            <s xml:id="echoid-s15382" xml:space="preserve">nimium debiles ſunt, propter varias quas lu-
              <lb/>
            men paſſum eſt diviſiones.</s>
            <s xml:id="echoid-s15383" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s15384" xml:space="preserve">Radius FG, qui poſt unicam reflectionem medium den-
              <lb/>
            ſius exit, cum radio incidente AB format angulum GPA,
              <lb/>
            qui variat in diverſis radiis incidentibus; </s>
            <s xml:id="echoid-s15385" xml:space="preserve">Ideò, licèt hi paral-
              <lb/>
            leli fuerint, diſperguntur, poſt unicam reflectionem exeuntes,
              <lb/>
              <note position="left" xlink:label="note-0606-06" xlink:href="note-0606-06a" xml:space="preserve">
                <emph style="sc">TAB. XVIII</emph>
              .
                <lb/>
              fig. 2.</note>
            ut ex inſpectione figuræ patet.</s>
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