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

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              <s>
                <pb xlink:href="020/01/359.jpg" pagenum="340"/>
              porre un cannello di piccola luce, e con un occhio guardarci dentro e at­
                <lb/>
              traverso un oggetto. </s>
              <s>Non fa perciò maraviglia se, conosciutosi dagli antichi
                <lb/>
              un tal fatto, si servissero o di un cannellino per osservare i piccoli oggetti,
                <lb/>
              come noi ci serviamo del Microscopio, o facessero uso di un tubo più lungo
                <lb/>
              per le osservazioni celesti, come noi ci serviam de'Canocchiali. </s>
              <s>Di questo
                <lb/>
              tubo e de'macchinamenti annessi, per osservare e per misurare esatto il
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              diametro apparente del sole sull'orizzonte, si trova fatta una descrizione mi­
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              nuta da Archimede nell'Arenario (Opera, Parisiis 1615, pag. </s>
              <s>452, 53) e di
                <lb/>
              uno di questi stessi tubi, per le osservazioni celesti, sembra che si servisse,
                <lb/>
              o fu creduto almeno che si scrvisse lo stesso tolomeo, se dee darsi fede al
                <lb/>
              Mabillon, il quale dice di aver veduto nella biblioteca dell'abbadia di Scheir,
                <lb/>
              diocesi di Frisinga, una copia della Storia ecclesiastica di Pietro Comestore,
                <lb/>
              nel frontespizio della quale, essendovisi voluto personificare le arti liberali,
                <lb/>
              vi si vedeva, per l'Astronomia, rappresentato Tolomeo che osservava gli astri
                <lb/>
              coll'occhio appuntato all'estremità di un lungo tubo, presso a poco a quel
                <lb/>
              modo, che si rappresenterebbe Galileo da un pittore moderno, in atto di ri­
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              guardare attraverso all'oculare del suo Telescopio. </s>
            </p>
            <p type="main">
              <s>Di qui ha avuto, senza dubbio, occasione l'errore di alcuni, un po'si­
                <lb/>
              mile a quel del Dottore argutamente deriso dal Salviati, i quali, trattando
                <lb/>
              della storia delle invenzioni hanno creduto, e voluto far credere che questi
                <lb/>
              tubi o quelle
                <emph type="italics"/>
              diottre,
                <emph.end type="italics"/>
              come le chiamavan Plutarco e Strabone, non fossero
                <lb/>
              propriamente altro che Canocchiali, non molto dissimili dai moderni. </s>
              <s>Una
                <lb/>
              tale erronea opinione, è notabile che fosse accolta anche da Francesco Fon­
                <lb/>
              tana, celebre fabbricatore di Canocchiali, il quale scrisse: “ Antiquissimum
                <lb/>
              fuisse tubi optici usum in comperto est ” imperocchè, soggiunge, rimonta
                <lb/>
              infino a'tempi di Tolomeo che visse 130 anni prima di G. Cristo. (Novae
                <lb/>
              Observat. </s>
              <s>Neap. </s>
              <s>1646, pag. </s>
              <s>11). Ma che quelli di Archimede, di Tolomeo o
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              di altri antichi non fossero veramente canocchiali, ossia tubi muniti di lenti
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              cristalline o di specchi metallici, se ne persuaderà facilmente ciascuno che
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              pensi come quegli antichi cannoni aperti non prestavano altro ufficio, a quei
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              primi osservatori del cielo, da quello in fuori di riparar l'occhio dalle ri­
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              flessioni irregolari, e di diriger la linea di mira, come nell'Alidada, che
                <lb/>
              s'incominciò ad usare agli strumenti geodetici, da'Geometri arabi e dagli
                <lb/>
              egiziani. </s>
            </p>
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              <s>Non è in tal proposito da passar sotto silenzio un modo proposto da
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              Leonardo da Vinci, per veder le cose più da lontano; modo che consiste
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              giusto in far uso di uno di que'tubi nudi o di quelle Diottre, di cui si ser­
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              virono gli antichi. </s>
              <s>Il Venturi respigolò l'invenzione da uno de'celebri Ma­
                <lb/>
              noscritti, e fu così la nota vinciana da lui stesso tradotta e pubblicata in
                <lb/>
              francese: “ Il est possible de faire en sorte que l'oeil voie les obiets eloi­
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              gnes sans qu'ls souffrent toute la diminution de grandeur qui leur est cau­
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              sée par les loix de la vision. </s>
              <s>Cette diminution provient des pyramides de
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              l'image des obiets qui sont coupées a angle droit par le sphericité de l'oeil. </s>
              <s>
                <lb/>
              Dans le fig. (25) on voit qui en pout couper ces pyramides d'une autre ma-</s>
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