Vitruvius Pollio, I dieci libri dell?architettura, 1567

Table of figures

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              <subchap2>
                <p type="main">
                  <s id="s.007518">
                    <pb pagenum="405" xlink:href="045/01/419.jpg"/>
                    <figure id="id.045.01.419.1.jpg" xlink:href="045/01/419/1.jpg" number="124"/>
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                    <emph type="italics"/>
                  otto parti, o palmi, ſe uuoi che ſiano palmi. </s>
                  <s id="s.007519">Ma in
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                  Athene, perche Athene sta in altra inclinatione, ſe'l
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                  Gnomone ſarà di quattro parti, l'ombra ſarà di tre. </s>
                  <s id="s.007520">con
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                  la iſteſſa ragione in Aleſſandria, & a Rodi, & in al­
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                  tri luoghi uanno uariando le ombre Meridiane al tem­
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                  po de gli equinottij. </s>
                  <s id="s.007521">dal che anche ſi puo ſapere a chi
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                  ſi leua il Sole piu alto ſul mezo dì, perche proportio­
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                  nandoſi le ombre al Gnomone, dalla proportione del­
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                  l'ombra al Gnomone ſi fa l'altezza. </s>
                  <s id="s.007522">Ecco l'ombra del
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                  Gnomoue in Athene è minore un terzo del Gnomone,
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                  & in Roma un'ottauo, & perche quanto il Sole è piu
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                  alto, tanto l'ombra dritta è minore, però ſi conclude,
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                  che il Sole ſia piu alto in Athene ſul mezo dì al tempo
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                  dello eqninottio, che a Roma; & tanto piu alto quan­
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                  to è l'ombra minore d'una ſubſeſquiterza dell'ombra
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                  d'una ſubſbſquiottaua.
                    <emph.end type="italics"/>
                  </s>
                </p>
                <p type="main">
                  <s id="s.007523">Et però in ogni luogo, che noi uorremo fare
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                  gli horologi, douemo pigliare l'ombra equi—
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                  nottiale. </s>
                </p>
                <p type="main">
                  <s id="s.007524">
                    <emph type="italics"/>
                  Comincia Vitr. ad inſegnarci, come ſi habbia a fare lo Analemma; & perche un ſolo Ana­
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                  lemma non ci puo ſeruire per tutto, ſe non quanto apartiene a quelli circoli, che ſono communi a
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                  tutti gli Analemmi (come io ho detto di ſopra) perche ſono differenti le ombre equinottiali; pe­
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                  rò ne piglia uno, che c'inſegna di ſare quello, che ſerue a Roma. </s>
                  <s id="s.007525">dando prima una regola genera
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                  le, che in qualunque luogo uolemo fare gli horologi, biſogna auuertire all'ombra equinottiale,
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                  & intende di quell'ombra, che ſi fa ſul mezo dì dal Gnomone al tempo dell'equinottio, perche
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                  dalla detta ombra ſi piglia anche la ragione dell'ombra Meridiana fatta, quando il Sole entra in al
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                  tri ſegni, come ci ſarà manifeſto qui ſotto.
                    <emph.end type="italics"/>
                  </s>
                </p>
                <p type="main">
                  <s id="s.007526">Et ſe ſaranno, come è a Roma, noue le parti del Gnomone, & otto le parti dell'om­
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                  bra, egli ſi farà nel piano una linea dritta, ſopra la quale ne cadera un'altra a ſquadra, che ſi
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                  chiama Gnomone, & dalla linea del piano da piedi del Gnomone ſi miſurano noue ſpatij
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                  fin alla cima, & doue termina la nona parte in ſu quel punto ſi faccia il centro con la lette­
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                  ra. </s>
                  <s id="s.007527">a. & aperta la ſeſta da quel centro alla linea del piano a piedi del Gnomone doue ſarà
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                  la lettera. </s>
                  <s id="s.007528">b. ſi faccia un circolo, che ſi chiama il Meridiano. </s>
                  <s id="s.007529">Dapoi delle noue parti,
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                  che ſono dal piano alla cima del Gnomone, la doue è il centro ſe ne pigliano otto, le qua
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                  li ſi ſegnano dal piede del Gnomone ſopra la linea del piano, doue è la lettera. </s>
                  <s id="s.007530">o. queſto
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                  termine ſarà dell'ombra Meridiana equinottiale del Gnomone, & da quel ſegno doue
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                  è la lettera. </s>
                  <s id="s.007531">c. per lo centro. </s>
                  <s id="s.007532">a. ſia tirata una linea doue ſerà il raggio equinottia—
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                  le del Sole. </s>
                </p>
                <p type="main">
                  <s id="s.007533">
                    <emph type="italics"/>
                  Lo Analemma per Roma ſi fa in queſto modo. </s>
                  <s id="s.007534">prima egli ſi tira una linea in un piano, la qua­
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                  le non è Orizonte, ma è quel piano ſopra lo quale è drizzato il Gnomone, & è il piano dell'horo­
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                  logio egualmente diſtante all'Orizonte: ſopra quella linea del piano ſi drizza il Gnomone di quel­
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                  la grandezza, che l'huomo uuole, poi ſi fa centro la cima del Gnomone, & allargata la ſeſta
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                  quanto è lungo il Gnomone, ſi fa un circolo, che rappreſenta il Meridiano, ſopra il quale
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                  s'imagina, che ſia il Sole nel mezo dì al tempo dello equinottio. </s>
                  <s id="s.007535">Hauemo dunque fin hora il
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                  piano, doue batte l'ombra, il Gnomone, che fa l'ombra, & il Meridiano, nel quale ſi ha da ritro­
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                  uare il Sole. </s>
                  <s id="s.007536">Biſogna poi pigliare la lunghezza dell'ombra, il che ſi fa in queſto modo (parlando
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                  della inclinatione di Roma) ſapendoſi, che di noue parti, nelle quali è diuiſo il Gnomone, otto ſi
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                  danno all'ombra, ſi partirà il Gnomone in noue parti, & dal piede ſuo lungo la linea del piano
                    <emph.end type="italics"/>
                  </s>
                </p>
              </subchap2>
            </subchap1>
          </chap>
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    </archimedes>
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