Ibn-al-Haitam, al-Hasan Ibn-al-Hasan; Witelo; Risner, Friedrich, Opticae thesavrvs Alhazeni Arabis libri septem, nunc primùm editi. Eivsdem liber De Crepvscvlis & Nubium ascensionibus. Item Vitellonis Thuvringopoloni Libri X. Omnes instaurati, figuris illustrati & aucti, adiectis etiam in Alhazenum commentarijs, a Federico Risnero, 1572

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            <s xml:id="echoid-s17478" xml:space="preserve">
              <pb o="250" file="0256" n="256" rhead="ALHAZEN"/>
            tem ſtili ſuper extremitatem diametri circuli medij, & ponat uiſum ſuum ſuper ſuperius foramen,
              <lb/>
            & intueatur oram inſtrumenti:</s>
            <s xml:id="echoid-s17479" xml:space="preserve"> tunc uidebit extremitatem ſtili.</s>
            <s xml:id="echoid-s17480" xml:space="preserve"> Et ſi mouerit extremitatem ſtili,
              <lb/>
            & extraxerit illam à puncto, quod eſt extremitas diametri medij circuli, non uidebit extremitatem
              <lb/>
            ſtili.</s>
            <s xml:id="echoid-s17481" xml:space="preserve"> Ex quo patet, quòd extremitatem ſtili comprehendit rectè.</s>
            <s xml:id="echoid-s17482" xml:space="preserve"> Nam duo centra foraminum, &
              <lb/>
            extremitas diametri circuli medij ſunt in eadem linea recta:</s>
            <s xml:id="echoid-s17483" xml:space="preserve"> & experimentator non comprehen-
              <lb/>
            dit extremitatem ſtili in hoc ſitu, cum extremitas ſtili non fuerit ſuper extremitatem diametri.</s>
            <s xml:id="echoid-s17484" xml:space="preserve"> Et
              <lb/>
            ſi euulſerit uitrum, & poſuerit ipſum è contrario, ſcilicet ut ponat conuexum uitri ex parte duo-
              <lb/>
            rum foraminum, & differentiam eius communem ſuper primum locum, & expertus fuerit extre-
              <lb/>
            mitatem ſtili:</s>
            <s xml:id="echoid-s17485" xml:space="preserve"> etiam uidebit illam, cum fuerit in extremitate diametri circuli medij:</s>
            <s xml:id="echoid-s17486" xml:space="preserve"> ideo in hoc ſi-
              <lb/>
            tu etiam linea, quæ tranſit per centra duorum foraminum, ex cuius uerticatione comprehendit
              <lb/>
            uiſus extremitatem ſtili:</s>
            <s xml:id="echoid-s17487" xml:space="preserve"> erit perpendicularis ſuper ſuperficiem uitri æqualem, & ſuperficiem eius
              <lb/>
            conuexam.</s>
            <s xml:id="echoid-s17488" xml:space="preserve"> Deinde oportet experimentatorem euellere uitrum, & extrahere à centro laminæ li-
              <lb/>
            neam rectam in ſuperficie laminæ, quæ contineat cum diametro laminæ, ſuper cuius extremitates
              <lb/>
            ſunt duæ lineæ perpendiculares in ora inſtrumenti, angulum obtuſum:</s>
            <s xml:id="echoid-s17489" xml:space="preserve"> & extrahat illam, donec
              <lb/>
            perueniat ad oram inſtrumenti:</s>
            <s xml:id="echoid-s17490" xml:space="preserve"> deinde extrahat à centro laminæ lineam in ſuperficie laminæ,
              <lb/>
            quæ contineat cum prima linea angulum rectum:</s>
            <s xml:id="echoid-s17491" xml:space="preserve"> & protrahat illam in utramque partem:</s>
            <s xml:id="echoid-s17492" xml:space="preserve"> tunc
              <lb/>
            hæc linea continebit cum diametro laminæ angulum acutum:</s>
            <s xml:id="echoid-s17493" xml:space="preserve"> & diameter laminæ erit obliqua ſu-
              <lb/>
            per hanc lineam.</s>
            <s xml:id="echoid-s17494" xml:space="preserve"> Deinde ſuperponat uitrum laminæ, & ponat differentiam eius communem ſu-
              <lb/>
            per lineam, quam ultimò ſignauit in ſuperficie laminæ, & ponat ſuperficiem uitri æqualem ex par-
              <lb/>
            te duorum foraminum, & ponat medium differentiæ communis ſuper centrum laminæ.</s>
            <s xml:id="echoid-s17495" xml:space="preserve"> Sic ergo
              <lb/>
            erit centrum uitri ſuper centrum circuli medij, ut prius declaratum eſt:</s>
            <s xml:id="echoid-s17496" xml:space="preserve"> & linea, quæ tranſit per cen
              <lb/>
            tra duorum foraminum, tranſibit per centrum uitri.</s>
            <s xml:id="echoid-s17497" xml:space="preserve"> Et hæc linea erit obliqua ſuper ſuperficiem ui-
              <lb/>
            tri æqualem:</s>
            <s xml:id="echoid-s17498" xml:space="preserve"> nam diameter laminæ illi æquidiſtans, eſt obliqua ſuper differentiam communem,
              <lb/>
            quæ eſt in uitro.</s>
            <s xml:id="echoid-s17499" xml:space="preserve"> Et hæc linea erit perpendicularis ſuper ſuperficiem uitri conuexam, [ut oſten-
              <lb/>
            ſum eſt 25 n 4] quia tranſit per centrum eius.</s>
            <s xml:id="echoid-s17500" xml:space="preserve"> Deinde extrahat experimentator ab extremita-
              <lb/>
            te lineæ, quam primò ſignauit in lamina, lineam perpendicularem in ora inſtrumenti:</s>
            <s xml:id="echoid-s17501" xml:space="preserve"> & ducat il-
              <lb/>
            lam ad circumferentiam circuli medij:</s>
            <s xml:id="echoid-s17502" xml:space="preserve"> & ſint hæ lineæ nigræ.</s>
            <s xml:id="echoid-s17503" xml:space="preserve"> Erit ergo linea cum ab illo puncto
              <lb/>
            extracta fuerit ad centrum circuli medij, quod eſt centrum uitri, perpendicularis ſuper ſuperficiem
              <lb/>
            uitri æqualem, & ſuper ſuperficiem uitri ſphæricam.</s>
            <s xml:id="echoid-s17504" xml:space="preserve"> Super ſuperficiem autem uitri æqualem eſt
              <lb/>
            perpendicularis, [per 8 p 11] quia eſt æquidiſtans primæ lineæ ſignatæ in lamina ſuper differen-
              <lb/>
            tiam communem, quæ eſt in uitro:</s>
            <s xml:id="echoid-s17505" xml:space="preserve"> ſuper ſphæricam uerò [per 25 n 4] quia tranſit per centrum e-
              <lb/>
            ius.</s>
            <s xml:id="echoid-s17506" xml:space="preserve"> Punctum ergo, ad quod peruenit linea extracta in ora inſtrumenti, quod eſt ſuper circumferen-
              <lb/>
            tiam circuli medij, eſt caſus, in quem cadit perpendicularis, exiens à centro uitri ſuper ſuperficiem
              <lb/>
            uitri planam.</s>
            <s xml:id="echoid-s17507" xml:space="preserve"> Deinde oportet experimentatorem ponere inſtrumentum in uas, & ponere extremi-
              <lb/>
            tatem ſtili in puncto, quod eſt extremitas diametri circuli medij, & ponat experimentator ſuum ui
              <lb/>
            ſum ſuper ſuperius foramen, & intueatur oram inſtrumenti:</s>
            <s xml:id="echoid-s17508" xml:space="preserve"> tunc non uidebit extremitatem ſtili:</s>
            <s xml:id="echoid-s17509" xml:space="preserve">
              <lb/>
            deinde moueat ſtilum ad partem contrariam illi, in qua eſt caſus perpendicularis:</s>
            <s xml:id="echoid-s17510" xml:space="preserve"> & tunc etiam nõ
              <lb/>
            uidebit extremitatem ſtili:</s>
            <s xml:id="echoid-s17511" xml:space="preserve"> deinde moueat ſtilum ad partem illam, in qua eſt caſus perpendicula-
              <lb/>
            ris, & per circumferentiam circuli medij:</s>
            <s xml:id="echoid-s17512" xml:space="preserve"> tunc enim, ſi motus fuerit ſuauis, uidebit extremitatem
              <lb/>
            ſtili in ſuo loco, in quo apparuit.</s>
            <s xml:id="echoid-s17513" xml:space="preserve"> Deinde præcipiat alicui cooperire centrum uitri tenui & ſubtili li-
              <lb/>
            gno:</s>
            <s xml:id="echoid-s17514" xml:space="preserve"> & tunc non uidebit extremitatem ſtili:</s>
            <s xml:id="echoid-s17515" xml:space="preserve"> & ſi abſtulerit coopertorium, uidebit ipſum.</s>
            <s xml:id="echoid-s17516" xml:space="preserve"> Ex hac
              <lb/>
            ergo experimentatione patet, quòd cum uiſus comprehendit extremitatem ſtili, eſt ſecundum re-
              <lb/>
            fractionem:</s>
            <s xml:id="echoid-s17517" xml:space="preserve"> & quòd refractio eſt à centro uitri:</s>
            <s xml:id="echoid-s17518" xml:space="preserve"> & quòd forma refracta eſt in ſuperficie circuli me-
              <lb/>
            dij, quæ eſt perpendicularis ſuper ſuperficiem uitri æqualem, apud quam fit refractio ad perpendi-
              <lb/>
            cularem, ut prius declaratum eſt [5 n.</s>
            <s xml:id="echoid-s17519" xml:space="preserve">] Et ſi experimentator aſpexerit locum extremitatis ſtili:</s>
            <s xml:id="echoid-s17520" xml:space="preserve"> in-
              <lb/>
            ueniet ipſum inter caſum perpendicularis & extremitatem diametri circuli medij, quæ tranſit per
              <lb/>
            centra duorum foraminum.</s>
            <s xml:id="echoid-s17521" xml:space="preserve"> Linea ergo, quæ exit ab extremitate ſtili ad centrum uitri, cum exten-
              <lb/>
            ſa fuerit rectè in aere:</s>
            <s xml:id="echoid-s17522" xml:space="preserve"> perpendicularis exiens à centro uitri ſuper ſuperficiem uitri æqualem, erit
              <lb/>
            media inter perpendicularem & lineam, quæ tranſit per centra duorum foraminum.</s>
            <s xml:id="echoid-s17523" xml:space="preserve"> Et forma ex-
              <lb/>
            tremitatis ſtili, quæ extenſa eſt ab extremitate ſtili ad centrum uitri, extenſa eſt ſuper hanc lineam,
              <lb/>
            & extenſa eſt in rectitudine eius ad centrum uitri.</s>
            <s xml:id="echoid-s17524" xml:space="preserve"> Hæc enim linea eſt perpendicularis ſuper ſuper-
              <lb/>
            ficiem uitri ſphæricam, quæ eſt ex parte extremitatis.</s>
            <s xml:id="echoid-s17525" xml:space="preserve"> Deinde cum hæc forma fuerit refracta ſuper
              <lb/>
            lineam, quæ tranſit per centra duorum foraminum:</s>
            <s xml:id="echoid-s17526" xml:space="preserve"> lineæ radiales, quæ exeunt in hoc ſitu à uiſu,
              <lb/>
            non perueniunt ad uitrum, præter lineam, quæ tranſit per centra duorum foraminum:</s>
            <s xml:id="echoid-s17527" xml:space="preserve"> calamus e-
              <lb/>
            nim, qui extenditur inter duo foramina, ſecat omnem in eam à uiſu exeuntem ad uitrum, præter-
              <lb/>
            quam lineam, quę tranſit per centra duorum foraminum.</s>
            <s xml:id="echoid-s17528" xml:space="preserve"> Viſus autem non comprehendit for-
              <lb/>
            mas, niſi ex uerticationibus harum linearum tantùm:</s>
            <s xml:id="echoid-s17529" xml:space="preserve"> ergo formæ non extenduntur niſi rectè:</s>
            <s xml:id="echoid-s17530" xml:space="preserve"> er-
              <lb/>
            go uiſus non comprehendit hanc formam, niſi ex uerticatione huius lineę perpendicularis.</s>
            <s xml:id="echoid-s17531" xml:space="preserve"> Er-
              <lb/>
            go quę extenditur rectè in aere, eſt perpendicularis ſuper ſuperficiem aeris contingentis ſuperfi-
              <lb/>
            ciem uitri ęqualem.</s>
            <s xml:id="echoid-s17532" xml:space="preserve"> Ergo hęc refractio erit ad partem contrariam parti perpendicularis, exeuntis
              <lb/>
            à loco refractionis ſuper ſuperficiem aeris.</s>
            <s xml:id="echoid-s17533" xml:space="preserve"> Nam linea, quę tranſit per centra duorum foraminum,
              <lb/>
            magis diſtat à perpendiculari, quę extenditur in aere, quàm linea, quę exit ab extremitate ſti-
              <lb/>
            li ad centrum uitri, quę extenditur in aere.</s>
            <s xml:id="echoid-s17534" xml:space="preserve"> Et hęc forma exit à uitro, & refringitur in aere:</s>
            <s xml:id="echoid-s17535" xml:space="preserve"> &
              <lb/>
            aer eſt ſubtilior uitro.</s>
            <s xml:id="echoid-s17536" xml:space="preserve"> Ethoc modo fiet refractio formę de aqua ad aerem.</s>
            <s xml:id="echoid-s17537" xml:space="preserve"> Viſus enim compre-
              <lb/>
            </s>
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