Barrow, Isaac, Lectiones opticae & geometricae : in quibus phaenomenon opticorum genuinae rationes investigantur, ac exponuntur: et generalia curvarum linearum symptomata declarantur

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          <p>
            <s xml:id="echoid-s436" xml:space="preserve">
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            dios diverſo medio obliquè incidentes, velut experimur, inflecti; </s>
            <s xml:id="echoid-s437" xml:space="preserve">ſal-
              <lb/>
            tem eò ſpectantia lucis præcipua ſymptomata, tribus porrò ſubjiciendis
              <lb/>
            hypotheſibus comprehenſa, vix aliâ ratione commodius explicari.</s>
            <s xml:id="echoid-s438" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s439" xml:space="preserve">XI. </s>
            <s xml:id="echoid-s440" xml:space="preserve">4. </s>
            <s xml:id="echoid-s441" xml:space="preserve">Omnis radii lucidi inflectio (hoc ſubinde generali nomine,
              <lb/>
            compendii cauſà, tam r@fractionem, quàm reflectionem complector)
              <lb/>
            fit in ſuperficie ad medii inflectentis ſuperficiem perpendiculari, ſeu
              <lb/>
            recta. </s>
            <s xml:id="echoid-s442" xml:space="preserve">Hujuſce ſuppoſitionis haud ullam facilè ſatìs commodam & </s>
            <s xml:id="echoid-s443" xml:space="preserve">
              <lb/>
            claram rationem reperias apud Opticos; </s>
            <s xml:id="echoid-s444" xml:space="preserve">petitione principii, vel in-
              <lb/>
            comprehenſibili quâdam obſcuritate laborat quicquid fermè eò ſpectans
              <lb/>
            afferunt; </s>
            <s xml:id="echoid-s445" xml:space="preserve">neque valdè miror radium lucis ſemper ut rectam concipien-
              <lb/>
            tibus individuam lineam id eis accidiſſe; </s>
            <s xml:id="echoid-s446" xml:space="preserve">quo poſito vix probam ullam
              <lb/>
            ejuſce rei cauſam aſſignari poſſe credo. </s>
            <s xml:id="echoid-s447" xml:space="preserve">Cadat enim radius linearis
              <lb/>
            A B in ſpeculi (inſtantiæ gratiâ) plani ſuperficiem ad punctum B; </s>
            <s xml:id="echoid-s448" xml:space="preserve">per
              <lb/>
              <note position="left" xlink:label="note-0028-01" xlink:href="note-0028-01a" xml:space="preserve">Fig. 2.</note>
            quod utcunque ducantur duæ rectæ C D, E F; </s>
            <s xml:id="echoid-s449" xml:space="preserve">cùm igitur rectæ A B,
              <lb/>
            C D ſint in uno quodam plano, quidni reflectio radii peragatur in iſto
              <lb/>
            plano? </s>
            <s xml:id="echoid-s450" xml:space="preserve">Simili ratione quoniam rectæ A B, E F ſunt in uno plano,
              <lb/>
            quidni radius in hoc etiam reflectionem patiatur? </s>
            <s xml:id="echoid-s451" xml:space="preserve">eodémque planè
              <lb/>
            modo quìd obſtat quo minùs in ſingulis omnibus, hoc eſt infinitis
              <lb/>
            planis, ſpeculi ſuperficiem ſecantibus, & </s>
            <s xml:id="echoid-s452" xml:space="preserve">per rectam A B ceu com-
              <lb/>
            munem ſectionem traductis perficiatur reſlectio, idémque proinde ra-
              <lb/>
            dius unus in partes undique cunctas reflexus diſpergatur? </s>
            <s xml:id="echoid-s453" xml:space="preserve">cur hoc fieri
              <lb/>
            non poſſit, utique non capio. </s>
            <s xml:id="echoid-s454" xml:space="preserve">Quod reſpondetur enim, poſito plano
              <lb/>
            A B C ad ſpeculi ſuperficiem recto magis illud planum, quam cætera
              <lb/>
            quævis ſpeculi ſuperficiei contrarium eſſe, proindè reſiſtentiam in
              <lb/>
            eo maximam contingere, proptereáque radium in eo potiſſimùm in-
              <lb/>
            flecti, parùm ſatisfacit; </s>
            <s xml:id="echoid-s455" xml:space="preserve">quoniam, ut ſuperiùs inſinuatum, extra
              <lb/>
            punctum ipſum B, cui radius impingit, alia nulla ſpecularis ſuperficici
              <lb/>
            pars meritò venit conſideranda quid enim (ut hoc adjiciam prædictis)
              <lb/>
            an in univerſam quà longè latéque diſtenditur, ipſius ſpeculi ſuperfi-
              <lb/>
            ciem agit hic linearis radius, & </s>
            <s xml:id="echoid-s456" xml:space="preserve">ab ea viciſſim patitur; </s>
            <s xml:id="echoid-s457" xml:space="preserve">an in ejus deſi-
              <lb/>
            nitam aliquam partem agit, patitúrque ab hac? </s>
            <s xml:id="echoid-s458" xml:space="preserve">quis in totam agere,
              <lb/>
            vel à tota pati concedet? </s>
            <s xml:id="echoid-s459" xml:space="preserve">Et cur id uni parti deputandum præ aliis?
              <lb/>
            </s>
            <s xml:id="echoid-s460" xml:space="preserve">ubi terminus figetur? </s>
            <s xml:id="echoid-s461" xml:space="preserve">quouſque procedet operatio? </s>
            <s xml:id="echoid-s462" xml:space="preserve">quinimò potiùs,
              <lb/>
            quia radii per rectam A B procurrentis impulſui tantùm id ſpeculi quod
              <lb/>
            eſt in recta A B verſus G protracta reſiſtit, ideò pulſus in ipſam A B
              <lb/>
            rejicietur; </s>
            <s xml:id="echoid-s463" xml:space="preserve">Et nulla ſuccurrit cauſa ſontica, propter quam aliorſum
              <lb/>
            deflectat; </s>
            <s xml:id="echoid-s464" xml:space="preserve">nihil datur, quod ejus tendentiam aliò determinet. </s>
            <s xml:id="echoid-s465" xml:space="preserve">Igitur
              <lb/>
            ut aliis, quæ puto variæ aſſignantur, hujus effecti cauſis excutiendis
              <lb/>
            abſtineam, indè genuinam ejuſce rationem (ut & </s>
            <s xml:id="echoid-s466" xml:space="preserve">generatim </s>
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