Caverni, Raffaello, Storia del metodo sperimentale in Italia, 1891-1900

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              <s>
                <pb xlink:href="020/01/413.jpg" pagenum="394"/>
              ex utraque parte convexorum. </s>
              <s>Is enim ad alios usus inutilis satis videtur,
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              nec interest convexitates istorum duorum ocularium contiguas esse ut
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              sic D⫏, vel oppositas ⫏D ut sic, aut hoc modo, quod aliis praefertur, dispo­
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              sitas ⫏⫏: nullis enim tollitur obsolute iris. </s>
              <s>Si aliunde emanet hoc, est ab
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              incidentia nimis obliqua radiorum in superficiem refringen­
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              tem ” (MSS. Gal. </s>
              <s>Disc., T. CXXXVI, c. </s>
              <s>19). </s>
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              <s>Ma non era ancora dell'Huyghens pubblicata la Diottrica,
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                <figure id="id.020.01.413.1.jpg" xlink:href="020/01/413/1.jpg" number="37"/>
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              <s>Figura 29.
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              nella quale si riserbava a dar quella teoria dell'acromatismo,
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              di che aveva fatto già l'applicazione alle lenti del suo Tele­
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              scopio. </s>
              <s>Nella proposizìone LIV di quel celebre Trattato, uscito
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              postumo nel 1703 come sappiamo, dop'aver l'Autore descritto
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              l'andamento dei raggi refratti ne'Telescopi di quattro lenti,
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              così soggiunge, per sodisfare co'principii diottrici a coloro,
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              i quali non intendevano il segreto effetto del suo oculare
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              composto: “ Mirum videtur in hoc Telescopio colores iridis
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              oriri plurium ocularium refractione, non magis quam cum una
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              ocularis adhibetur. </s>
              <s>Sed ratio haec est quod lens QR (fig. </s>
              <s>29)
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              corrigit et aufert colores quas lens KL produxit. </s>
              <s>Idem enim
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              accidit radio OKRN, per superficies inclinatas ad K ac deinde
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              ad R transeunti, ac si per cuneos binos contrarie positos SS, TT (fig. </s>
              <s>30)
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              transiret parallelis lateribus qui colore non inficitur non magis quam si per
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              laminam vitream incederet ” (Lugd. </s>
              <s>Batav. </s>
              <s>1703, pag. </s>
              <s>195, 96).
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                <figure id="id.020.01.413.2.jpg" xlink:href="020/01/413/2.jpg" number="38"/>
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            </p>
            <p type="caption">
              <s>Figura 30.</s>
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              <s>Aveva senza dubbio ragione il Petit a dire che a que­
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              sto modo
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              nullis tollitur absolute iris,
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              ma, a riuscire al
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              tanto desiderato effetto, aveva pure l'Huyghens aperta così
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              e raddirizzata la via agli ottici futuri. </s>
              <s>Il Newton poi dimo­
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              strò che non bastava comporre insieme due mezzi rifran­
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              genti della stessa natura, ma che bisognava fossero di na­
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              tura alquanto diversa e propose di accoppiare insieme lenti
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              cristalline con lenti ripiene d'acqua. </s>
              <s>“ Si perspicillorum
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              vitra obiectiva ex vitris duobus sphaerice figuratis et aquam
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              inter se claudentibus constentur, fieri potest ut a refractionibus aquae er­
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              rores refractionum quae fiunt in vitrorum superficiebus extremis satis ac­
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              curate corrigantur ” (Principia Philos. </s>
              <s>T. I, Genevae 1739, pag. </s>
              <s>547). L'Eu­
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              lero ridusse a calcolo, di quelle lenti di varia rifrangibilità, lo spessore e la
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              forma, e il Dollond, componendo insieme i due cunei ugeniani sopra de­
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              scritti, di due cristalli di vario poter dispersivo, riuscì finalmente a risol­
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              vere il problema. </s>
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              <s>
                <emph type="center"/>
              VI.
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              </s>
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            <p type="main">
              <s>Non senza una giusta ragione, ripensando l'Huyghens alla numerosa se­
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              quela, che ebbero gli esempi galileiani, si compiaceva seco stesso di essere
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              stato il primo, nel numero de'costruttori del Telescopio, a farsi, dopo Ga-</s>
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