Barrow, Isaac, Lectiones opticae & geometricae : in quibus phaenomenon opticorum genuinae rationes investigantur, ac exponuntur: et generalia curvarum linearum symptomata declarantur
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            <emph style="sc">Lect</emph>
          . IV.</head>
          <p>
            <s xml:id="echoid-s1424" xml:space="preserve">I. </s>
            <s xml:id="echoid-s1425" xml:space="preserve">AD ea jam accedimus quæ radiis obveniunt ad planam ſuperfici-
              <lb/>
            em, vel ad rectam lineam, refractis. </s>
            <s xml:id="echoid-s1426" xml:space="preserve">Quod argumentum eo
              <lb/>
            diligentiùs proſequemur, quia nondum pro merito ſuo videtur ſatis ex-
              <lb/>
            cultum; </s>
            <s xml:id="echoid-s1427" xml:space="preserve">ut & </s>
            <s xml:id="echoid-s1428" xml:space="preserve">quoniam in eo tractando methodum præſtituemus no-
              <lb/>
            bis, & </s>
            <s xml:id="echoid-s1429" xml:space="preserve">quaſi normam in ſequentibus obſervandam. </s>
            <s xml:id="echoid-s1430" xml:space="preserve">Ad rem.</s>
            <s xml:id="echoid-s1431" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s1432" xml:space="preserve">II. </s>
            <s xml:id="echoid-s1433" xml:space="preserve">Parallelorum rectæ lineæ (EF) incidentium radiorum (AB,
              <lb/>
              <note position="right" xlink:label="note-0049-01" xlink:href="note-0049-01a" xml:space="preserve">Fig. 31.</note>
            MN) refracti (B _a_, N μ) ſunt etiam ſibi paralleli. </s>
            <s xml:id="echoid-s1434" xml:space="preserve">Nam quoniam
              <lb/>
            AB, MN ſunt, ex hypotheſi, paralleli, erunt anguli ABE, MNE
              <lb/>
            pares. </s>
            <s xml:id="echoid-s1435" xml:space="preserve">Itaque refractos habent angulos pares; </s>
            <s xml:id="echoid-s1436" xml:space="preserve">horúmque comple-
              <lb/>
            menta (ſcilicet anguli _a_ BF, μ NF) æquantur, quare liquet refractos
              <lb/>
            B _a_, N μ ſibi parallelos eſſe.</s>
            <s xml:id="echoid-s1437" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s1438" xml:space="preserve">III. </s>
            <s xml:id="echoid-s1439" xml:space="preserve">Hinc infinitè diſtantis, hoc eſt parallelos radios emittentis (in-
              <lb/>
            finitam ad ſenſum diſtantiam intelligo, qualis eſt quoad hoc ſtellæ cu-
              <lb/>
            juſpiam) puncti locus apparens, aut imago per hujuſmodi reſractio-
              <lb/>
            nem eſſecta infinitè quoque diſtat; </s>
            <s xml:id="echoid-s1440" xml:space="preserve">quippe cùm hæc etiam per radios
              <lb/>
            parallelos adſpectetur. </s>
            <s xml:id="echoid-s1441" xml:space="preserve">Itaque ſitus ejus reſpectu visûs ubivis poſiti fa-
              <lb/>
            cilè determinatur. </s>
            <s xml:id="echoid-s1442" xml:space="preserve">Sit oculi puta centrum O; </s>
            <s xml:id="echoid-s1443" xml:space="preserve">& </s>
            <s xml:id="echoid-s1444" xml:space="preserve">A punctum radians
              <lb/>
            immenſè diſſitum; </s>
            <s xml:id="echoid-s1445" xml:space="preserve">connexáque AO refringentem EF ſecet in G;
              <lb/>
            </s>
            <s xml:id="echoid-s1446" xml:space="preserve">ſitque radii AG reſractus G _a_;</s>
            <s xml:id="echoid-s1447" xml:space="preserve">; per O verò ducatur OBZ ad _a_ G
              <lb/>
              <note position="right" xlink:label="note-0049-02" xlink:href="note-0049-02a" xml:space="preserve">Fig. 32.</note>
            parallela; </s>
            <s xml:id="echoid-s1448" xml:space="preserve">in hac ad infinitum protenſa (velut ad Z) apparebit pun-
              <lb/>
            ctum A. </s>
            <s xml:id="echoid-s1449" xml:space="preserve">Cùm enim radii AG, AB ſint (ad ſenſum) paralleli, eti-
              <lb/>
            am ipſorum refracti erunt paralleli. </s>
            <s xml:id="echoid-s1450" xml:space="preserve">Quare cùm G _a_ ſit refractus ipſius
              <lb/>
            AG, erit BO, ad G _a_ parallela, etiam radii AB refractus. </s>
            <s xml:id="echoid-s1451" xml:space="preserve">Ergò
              <lb/>
            punctum A in recta OB protenſa apparebit. </s>
            <s xml:id="echoid-s1452" xml:space="preserve">Quoad hujuſmodi radi-
              <lb/>
            ationem nil ſuccurrit aliud; </s>
            <s xml:id="echoid-s1453" xml:space="preserve">itaque de propinquo radiantis puncti ſym-
              <lb/>
            ptomata contemplemur.</s>
            <s xml:id="echoid-s1454" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s1455" xml:space="preserve">IV. </s>
            <s xml:id="echoid-s1456" xml:space="preserve">Sit recta AB rectæ refringenti EF perpendicularis; </s>
            <s xml:id="echoid-s1457" xml:space="preserve">in qua
              <lb/>
              <note position="right" xlink:label="note-0049-03" xlink:href="note-0049-03a" xml:space="preserve">Fig. 33.</note>
            ſit punctum radians A, ab EF haud ad ſenſum longè remotum; </s>
            <s xml:id="echoid-s1458" xml:space="preserve">ab </s>
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