Cardano, Girolamo, De subtilitate, 1663

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              Cùm autem circulus interior proximior
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              ſit obſcuritati, cæruleus videtur: medius,
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              qui luminoſior eſt, viridis: exterior, qui &
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              maximus, ampliori luce illuſtratus, croceus
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              eſt. </s>
              <s id="s.002959">Purpureus verò atque xanthus, non
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              principales ſunt colores: ſed cum varietate
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              luminis ex altero in alterum colorem ſit
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              tranſitus, coëuntibus terminis neceſſe eſt
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              in in medio, velut etiam in picturis, te­
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              nuiter colores alios apparere. </s>
              <s id="s.002960">Eſt autem
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              centrum Solis & oculi, & iridis in vna li­
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              nea. </s>
              <s id="s.002961">Sic enim ex caua nebula perpendicu­
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              lares radij reflectuntur: & quanquam ne­
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              bula ipſa non ſit rotunda, ſoli tamen ra­
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              dij, qui ex parte rotunda reflectuntur, quia
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              ſoli perpendiculares ſunt, Solis imaginem
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              referunt: quæ quia debilis eſt, & debili­
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              ter reflectitur, colorum ſpeciem repræſen­
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              tat: nam lux cùm debilis redditur, in
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              ſplendidum colorem tranſit: quæ ſi ma­
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              gis debilitetur, in colores nigro propin­
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              quiores mutatur: pòſt ſi plus etiam, ad
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              colores ſine luce peruenit: demùm ad ni­
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              grum vbi minimum eſt de luce, vltimo
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              cùm deficit, tranſit in tenebras. </s>
              <s id="s.002962">Igitur
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              cùm ad centrum ex ſola rotunda, cauá­
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              que parte radij reflectantur, & ſi nubes
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              non caua ſit, & plures guttæ antè, reli­
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              qua quidem tota nubes conſpicitur, ſed à
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              caua, rotundáque reflexio fit perpendicula­
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              ris, quæ iridem, id eſt, Solem repræſen­
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              tat, non aliter, quam ex aquæ guttis vi­
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              debis, colores ſcilicet varios atque ſplen­
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              didos. </s>
              <s id="s.002963">Cùm igitur Sol eſt in finitore, &
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              oculus ( vt dixi ) in recta linea cum centro
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              iridis, centrum iridis in finitore, neceſſa­
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              riò, erit, quare tunc ad vnguem iris ſub ſe­
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              micirculi forma apparebit: nam reliqua
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              medietas neceſſariò tota eſt ſub finitore,
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              ſi centrum in illo eſt. </s>
              <s id="s.002964">Cùm verò Sol al­
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              tior extiterit, manifeſtum eſt, quod li­
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              nea ducta à Solis centro per oculum infrà
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              finitorem cadet: igitur tunc centrum iridis
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              erit ſub finitore: & quò Sol extiterit al­
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              tior, linea ducta à Sole per oculum hu­
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              milior erit, quare & centrum iridis, quod
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              in hac linea eſt. </s>
              <s id="s.002965">Itáque quantò cen­
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              trum iridis magis erit ſub finitore, eò ſu­
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              perioris ſemicirculi pars maior abſconde­
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              tur ab oculis noſtris: quare quantò altior
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              Sol, eò minorem portionem vnius circu­
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              li iridem eſſe neceſſe eſt. </s>
              <s id="s.002966">Liquet autem ex
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              his, tum quòd iridis pars media abſque ne­
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              bula eſt, tum quòd ſub terra latitet, iri
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              dem nihil eſſe: nam non ex centro nebulæ
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              radij reflectuntur, ſed centrum ſolum ima­
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              ginatione conſtat. </s>
              <s id="s.002967">Quòd etiam vna tantùm
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              videri poſſit, haud dubium eſt. </s>
              <s id="s.002968">Nam cùm
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              oculus in linea ſit, quæ à Sole procedit ad
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              centrum nebulæ, nulla alia, niſi idem ha­
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              beat centrum iris videri poterit. </s>
              <s id="s.002969">Sed nec
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              ſub eodem centro, quoniam ex Sole refle­
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              xio fieri nequit: nam oculus habet ratio­
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              nem centri cauitatis: non quia ſit centrum,
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              ſed quia ex duobus punctis in eadem linea,
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              quæ à centro eſt, duæ lineæ ad eadem pun­
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              cta ſub æquis angulis reflecti non poſſunt.
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              Relinquitur igitur, vt ex prima alia refle­
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              ctatur, quare ſecundam maiorem prima eſſe
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              neceſſe eſt, & debiliorem multò: itaque ex
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              ſecunda tertiam oriri eſt impoſſibile. </s>
              <s id="s.002970">Quia
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              igitur ex prima reflexa ſecunda oritur, ne­
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              ceſſe eſt, vt lineæ ſeu radij circuli prioris
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              iridis interiores, cùm maiorem angulum
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              faciant, longiùs reſiliant, exteriores pro­
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              piùs: quare cir coeruleus erit exterior circulus
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              ſecundæ iridis, medius viridis, vt primi ex­
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              terior croceus, contraria ad vnguem prio­
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              ri ratione. </s>
              <s id="s.002971">Planum etiam ex his eſſe exiſti­
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              mo, quòd cùm Sol eſt in meridie iuxta æſti­
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              uum ſolſtitium ſemicirculi maximam habet
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              altitudinem: quò fit, vt centrum iridis ſe­
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              midiametro totius circuli eius ſit infra fini­
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              torem viſus, quare iris non videbitur: ſed
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              cùm iuxta autumni æquinoctium, & per
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              totam hyemem, & poſt æquinoctium ver­
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              num videbitur, ſed eò minor, quò ( vt di­
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              ctum eſt
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              )
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              ſolſtitio æſtiuo, & meridie ma­
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              gis appropinquabit. </s>
              <s id="s.002972">Cur autem dum iris
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              modica eſt, & parùm à finitore eleuatur, eò
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              maioris circuli pars eſſe videtur? </s>
              <s id="s.002973">Cauſa eſt,
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              quòd oculus magis diſtare iridem, quò
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              humilior eſſe iudicat: quoniam diſtantiam
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              intelligit, vt de aſtris diximus. </s>
              <s id="s.002974">Sed cùm
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              diſtare verticem iridis plus iudicat, latio­
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              rem etiam exiſtimat, velut etiam dixi, de
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              Sole, & Luna orientibus, at angulus maior
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              circuli maiorem illum eſſe oſtendit, quod
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              facilè quiſque intelligit, cùm minorem cir­
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              culum maiori ita inſcribit, vt ſe tangant:
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              apparet enim maiorem in circumambiente
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              linea eſſe latiorem: ea de cauſa minor por­
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              tio iridis, maioris circuli pars eſſe videtur.
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              Sed non ſolùm irides ex nebulis, verum ex
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              remis dum agitantur in mari lucis reflexio­
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              ne, à guttis aquæ fiunt: & hyeme auſtro
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              ſtante circa lucernas, maximè ab his, qui
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              oculos habent humidos: & à guttis inſper­
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              ſis parieti, dum à Sole illuminantur, in obſ­
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              curo oculo è directo reſpiciente: omnium
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              enim vna eſt cauſa, vt rectè refert Ariſto­
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              teles. </s>
              <s id="s.002975">Sed Pareliæ, Virgæ, & Corona, quam
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              nos circa Solem vidimus, Halonem vo­
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              cant, coloris cauſam eandem habent, quam
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              diximus: verùm, Pareliæ & ipſæ ſolum ex
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              reflexione ad oculum fiunt, nulla prorſus in
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              nubibus imagine: atque ideò ex guttilis
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              tunc nubes conſtat. </s>
              <s id="s.002976">Iris & igitur Pareliæ
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              plerumque pluuias nunciant leues, quia gut­
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              tulæ ex aqua ſunt & diuiſæ, radiuſque Solis
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              penetrat. </s>
              <s id="s.002977">Corona autem ſubſtantiam habet
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              quippe quæ fit ex reflexione Solis, aut Lu­
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              næ, aut ſyderis alterius, tanquam ex cen­
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              tro à nube denſa in circuitum, rotunda fi­
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              gura. </s>
              <s id="s.002978">Itaque non oculus eas fingit vt iridem
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              & Parelias, ſed factas videt, & in nubibus
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              conſiſtentes. </s>
              <s id="s.002979">Velut etiamſi cryſtallum, tri­
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              gonum, ſeu priſma, vel hexagonam Soli
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              expoſueris, in aduerſo pariete colores non
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              fictos, ſed veros iridis videbis: & ſimiliter
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              ſub vaſe vitreo pleno atque Soli, vel etiam
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              lumini claro expoſi to, eoſdem conſpicere
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              licet. </s>
              <s id="s.002980">Sed ficti erunt, ſi cryſtallum inſpicias
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              aut vitrum: nam quales tu vides, & vbi
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              vides Sole præſente, ſocius non omninò
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              videbit: aut diſſimiles, aut non eodem lo­
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              co, quia veræ non ſunt, ſed ab oculi aſpe­
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              ctus ratione tantum proficiſcuntur. </s>
              <s id="s.002981">Quò fit </s>
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