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

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              <s>
                <pb xlink:href="020/01/612.jpg" pagenum="55"/>
              sane mutatio nulla alia est, quam inclinatio seu accesio seu refugium lucis
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              veluti ad arcem, et ad id quod potest ipsam roborare ac proinde tueri et
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              conservare. </s>
              <s>Haec autem arx est radius seu linea perpendicularis, quae uti
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              dictum est quocumque progrediatur robustissima et irrefracta progreditur. </s>
              <s>
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              Contra accidit cum lux e denso in rarius diaphanum permeat. </s>
              <s>Siquidem,
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              cum inveniat minorem diaphani resistentiam merito a perpendiculari rece­
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              dit, tamquam eius auxilio non amplius pro sui conservatione indigens ” (Ve­
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              netiis 1600, pag. </s>
              <s>70). </s>
            </p>
            <p type="main">
              <s>A rimproverar la scienza scesa a fanciulleggiare così tra i fiori della
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              poesia insorse con gran severità il Keplero “ quasi lucis species mente prae­
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              dita esset, qua et densitatem medii et suum damnum aextimaret et proprio
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              arbitratu non extranea vi agendo, non patiendo sese ipsam infringeret ”
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              (Paralip. </s>
              <s>cit., pag. </s>
              <s>84). Ma egli aveva notato però fra le leggerezze di Vi­
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              tellione
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              nescio quid subtile,
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              una sottigliezza di grande importanza ai pro­
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              gressi dell'Ottica, la quale consiste nell'applicare al moto della luce il prin­
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              cipio meccanico della composizione delle forze. </s>
            </p>
            <p type="main">
              <s>Sia AC (fig. </s>
              <s>17) un raggio, che obliquamente discende, e nel punto C
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                <figure id="id.020.01.612.1.jpg" xlink:href="020/01/612/1.jpg" number="82"/>
              </s>
            </p>
            <p type="caption">
              <s>Figura 17.
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              incontra la superfice BE di un dia­
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              fano di varia densità da quello per
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              cui egli è venuto, fuori del qual caso
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              procederebbe per la linea CQ a di­
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              ritto. </s>
              <s>Conducasi nel punto C la GH
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              perpendicolare a BE. “ Motus radii
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              incidentis oblique secundum lineam
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              AC, dice Vitellione, componitur ex
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              motu in partem perpendicularis CG
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              et ex motu facto super lineam quae
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              est perpendicularis super lineam CG ”
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              (Perspectiva cit., pag. </s>
              <s>52). O altri­
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              menti essendo l'atomo lucido C spinto
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              per la direzione CE e per la direzione
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              CG, nè potendo ubbidire nello stesso
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              tempo all'uno impulso e all'altro, prenderà una via di mezzo, e secondo il
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              bisogno o si accosterà di più a CG o si accosterà di più a CE. </s>
              <s>Il bisogno poi
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              sarà dichiarato dalla natura del diafano, il quale se è più denso di quello da
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              cui il raggio è venuto, e allora avendo bisogno di maggior fortezza, per su­
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              perare l'impedimento, il raggio stesso si accosterà alla linea CG perpendi­
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              colare: cessando poi questo bisogno, per essere il diafano più raro, si farà
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              invece l'accostamento alla linea CE, e insomma il raggio rifratto ne'due casi
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              diversi o sarà CI, o sarà CK. </s>
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            <p type="main">
              <s>Ma pur nemmeno procedendo per questa via non s'evitava quel fan­
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              tastico supposto che attribuiva alla luce un senso d'andare a cercar presso
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              alla perpendicolare il rifugio e il conforto alla sua debolezza. </s>
              <s>Perciò il Ke­
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              plero si studiava, così ragionando altrimenti, di giungere alla medesima con-</s>
            </p>
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