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

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            <s xml:id="echoid-s362" xml:space="preserve">VIII. </s>
            <s xml:id="echoid-s363" xml:space="preserve">1. </s>
            <s xml:id="echoid-s364" xml:space="preserve">Radii lucis (hoc eſt lucidi tranſitûs aut impulſùs quales de-
              <lb/>
            ſcripſimus tramites) in eodem exiſtentes ſimilari medio directi ſunt.
              <lb/>
            </s>
            <s xml:id="echoid-s365" xml:space="preserve">Hoc è dictis abunde patet. </s>
            <s xml:id="echoid-s366" xml:space="preserve">Quin indè Corollarii vice deducitur radios
              <lb/>
            quoad rem ipſam, Phyſicéque loquendo figurà priſmaticos eſſe, vel
              <lb/>
            cylindricos. </s>
            <s xml:id="echoid-s367" xml:space="preserve">Nempe corpuſculum illud quodpiam in lucidi ſuperficie
              <lb/>
            poſitum, à quo radius originem ſuam ducit, dum à primò ſuo loco ceu
              <lb/>
            baſe defertur aut totâ ſuâ ſuperficie contiguum ſibi corpus rectà propel-
              <lb/>
            lit, figuræ ſuæ (vel impulſi ſaltem corporis figuræ) congruum deſig-
              <lb/>
            nat, ſuper hac vel illa baſe conſtitutum, ſolidum longum, exile, teres,
              <lb/>
            quale cylindrus, aut priſma. </s>
            <s xml:id="echoid-s368" xml:space="preserve">Proinde quando Mathematicè rem tra-
              <lb/>
            ctamus, iſtos radios pro rectis lineis habere poſſumus; </s>
            <s xml:id="echoid-s369" xml:space="preserve">tum quia reve-
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            ra ſunt adeo tenues & </s>
            <s xml:id="echoid-s370" xml:space="preserve">recti; </s>
            <s xml:id="echoid-s371" xml:space="preserve">tum quia plerumque pro cylindricis ejuſ-
              <lb/>
            modi ſeu priſmaticis figuris ipſarum axes ità ſumi poſſunt, ut nihil indè
              <lb/>
            ratiocinio Mathematico derogetur.</s>
            <s xml:id="echoid-s372" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s373" xml:space="preserve">IX. </s>
            <s xml:id="echoid-s374" xml:space="preserve">2. </s>
            <s xml:id="echoid-s375" xml:space="preserve">Ab omni corporis lucidi (vel illuſtrati) puncto ad quodvis
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            medii (non obſtaculis interciſi) punctum lucis aliquis radius dirigitur.
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            </s>
            <s xml:id="echoid-s376" xml:space="preserve">Hæc apud Opticos tritiſſima ſuppoſitio quò vel intelligi vel admitti
              <lb/>
            poſſit, omninò duplicem limitationem exigere videtur, è ſupra dictis
              <lb/>
            utramque deducibilem. </s>
            <s xml:id="echoid-s377" xml:space="preserve">Unam, ut omnis puncti nomine nedum non
              <lb/>
            præciſè punctum quodcunque Mathematicum, ac nec omnem particu-
              <lb/>
            lam concipiamus realem & </s>
            <s xml:id="echoid-s378" xml:space="preserve">Phyſicam; </s>
            <s xml:id="echoid-s379" xml:space="preserve">verùm ſaltem admodum exi-
              <lb/>
            guam, qualíque ferme minorem vel animo deſignare nequeamus; </s>
            <s xml:id="echoid-s380" xml:space="preserve">al-
              <lb/>
            teram ut non in unoquoque ſtrictè dicto temporis inſtanti, nec in omni
              <lb/>
            reali temporis portiuncula cogitemus hoc contingere, ſed ut nullum
              <lb/>
            temporis intervallum ſentiri poſſit ità curtum, aut momentaneum, quin
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            intra ipſum à quavis lucidi deſignabili parte deſignatam ad medii partem
              <lb/>
            radius aliquis exporrigatur. </s>
            <s xml:id="echoid-s381" xml:space="preserve">Enimverò cùm radiorum iſtæ quas aſ-
              <lb/>
            ſignavimus radices, lucidum componentia corpuſcula, ſint illorum,
              <lb/>
            quorum nos utcunque quantitates ſenſu vel animo pertingere valemus,
              <lb/>
            corporum reſpectu tanquam infinitè parva, nec non infinità quaſi per-
              <lb/>
            nicitate donata, non difficilè concipi poteſt in omni deſignabili, vel
              <lb/>
            imaginabili lucentis ſpatiolo prorſus innumerabilem eorum multitudi-
              <lb/>
            tudinem exiſtere, quorum fere ſingula diverſas in plagas tendunt; </s>
            <s xml:id="echoid-s382" xml:space="preserve">ut
              <lb/>
            nulla ſit deſignabilis plaga, quam non una quæpiam appetat, aliquam
              <lb/>
            ſaltem, utlibèt imperceptibilis & </s>
            <s xml:id="echoid-s383" xml:space="preserve">anguſti, temporis moram interpo-
              <lb/>
            nendo. </s>
            <s xml:id="echoid-s384" xml:space="preserve">In eo ſiquidem tempuſculo lucidi partes ſingulas innumera
              <lb/>
            ſucceſſivè talia corpuſcula ſubingrediuntur juxta deſerúntque, de qui-
              <lb/>
            bus mirum fuerit ni quoddam unum ad deſignatum medii ſpatium ten-
              <lb/>
            dat, ſibi tranſmittendo meatuum aliquem (quos & </s>
            <s xml:id="echoid-s385" xml:space="preserve">pari ratione </s>
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