Vitruvius Pollio, I dieci libri dell?architettura, 1567

Table of figures

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                  che torni in dietro. </s>
                  <s id="s.006894">Ecco lo eſſempio. </s>
                  <s id="s.006895">Imaginiamo, che uno cauallo corra intorno un cerchio. </s>
                  <s id="s.006896">
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                  grandiſſimo, & l'huomo fuori, & lontano dal cerchio ftia a guardare, certo è che quel cauallo
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                  gli parer à hora tardo, hora ueloce, hora fermo, hora andar inanzi, hora tornar a dietro ben­
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                  che egualmente egli ſi muoua. </s>
                  <s id="s.006897">Et queſto adiuiene per la natura del circolo, che è fatto di contra­
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                  rij. </s>
                  <s id="s.006898">Come dice Ariſtotile nelle Mechaniche. </s>
                  <s id="s.006899">Coſi il pianeta nell'arco di ſopra il contatto di que­
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                  ſte linee, parerà fermo a noi, che ſtiamo al baſſo, ma nel reſto della circonferenza nel luogo op­
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                  poſto al giogo ci parerà uelociſſimo, & ſimilmente nel giogo al piu lento. </s>
                  <s id="s.006900">Ma nello arco di ſo­
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                  pra dello epiciclo dapoi il contatto delle linee, i luminari ſono portati da leuante a ponente, ma
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                  nell'arco inferiore ſono portati col deferente: Ma gli altri pianeti ſono portati con mouimento con
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                  trario, dalche adiuiene, che il mouimento del pianeta è composto di due mouimenti, l'uno è del
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                  lo epiciclo, l'altro del diferente, come ſe uno fuſſe da una galera portato inanzi, & egli in quel
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                  mezo andaſſe a torno i fori, la doue ſe l'uno, & l'altro mouimento ſarà uerſo leuante allhora eſ­
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                  ſendo il pianeta da due mouimenti portato, piu uelocemente ſi mouerà, come ſe uno da una gale­
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                  ra portato inanzi, egli ſimilmente andaſſe da poppa a prora. </s>
                  <s id="s.006901">Ma ſe'l pianeta anderà con moui­
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                  menti contrarij, ſe quelli ſaranno eguali, cioè che tanto per uno andaſſe inanzi, quanto per l'al­
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                  tro andaſſe in dietro, parerà, che egli ſtia: come ſe uno caminaſſe tanto uerſo la poppa, quanto
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                  dalla galera fuſſe inanzi portato. </s>
                  <s id="s.006902">Ma ſe ſaranno diſeguali uincerà il piu ueloce: però ſe il moui­
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                  mento del deferente ſarà piu gagliardo, che il mouimento dello epiciclo, il pianeta anderà uerſo
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                  Leuante: ma ſe ſarà il contrario, il pianeta anderà uerſo ponente, & a questo modo ſarà retro­
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                  grado: come ſe uno tornaſſe in dietro meno di quello, che è portato inanzi dalla galera, parerà
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                  pure, che egli uadi inanzi, ma ſe piu ſi contraporrà, parerà, che ritorni, & però lo ſtare, & il
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                  regreſſo, auuiene alli cinque pianetinello arco inferiore dello epiciclo, percioche in que luoghi ſo­
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                  no dallo epiciclo portati contra il mouimento del deferente. </s>
                  <s id="s.006903">Et auuiene, che in alcuni luoghi il
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                  mouimento dello epiciclo ſia pari, & in alcuni piu ueloce del mouimento del deferente. </s>
                  <s id="s.006904">Ma al
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                  Sole, & alla Luna, lo ſtato auuenirebbe nello arco di ſopra dello epiciclo, perche in quel luo­
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                  go lo epiciclo ua contra il deferente, ma perche non lo uince, nè gli è pare, però al Sole, & alla
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                  Luna non ſida ſtato nèregreſſo, come accenna Vitr. </s>
                  <s id="s.006905">Daremo adunque al Sole ouero il deferente
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                  eccentrico ſolamente, ouero lo epiciclo col concentrico: imperoche ſe il Sole nella circonferenza
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                  di ſopra dello epiciclo è portato da leuante a ponente, & che il mouimento dello epiciclo ſia tan­
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                  to ſimile al mouimento dello eccentrico, quanto del concentrico, come è dallo ſpatio de i centri,
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                  al ſemidiametro dello epiciclo, in qual ſi uoglia modi di due, ne ha da ſeguire la iſteſſa apparenza
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                  del mouimento. </s>
                  <s id="s.006906">Ma perche il modo dello eccentrico ſi contenta di un ſolo mouimento, però èsta­
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                  to preferito, & eletto piu presto, che il modo dello epiciclo. </s>
                  <s id="s.006907">Ma come ſia ſtata conoſciuta la di
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                  stanza de i centri, & il luogo del giogo dirò breuemente. </s>
                  <s id="s.006908">Quattro punti principali ſono conſide
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                  rati nel zodiaco, due ſono stati attribuiti a gli equinottij, due a i ſolstitij, che ſono di mezo tra
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                  gli equinottij. </s>
                  <s id="s.006909">dalla conſideratione de gli ſpatij, & de i mouimenti come de i tempi, è stata cono­
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                  ſciuta la distanza de i centri, & il luogo del giogo. </s>
                  <s id="s.006910">Ecco imaginiamoci due linee una, che ſi par
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                  ga dal centro del deferente del Sole, che peruenga al centro del Sole, l'altra egualmente distante,
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                  dal centro del mondo fin al zodiaco, che è la linea del mezano mouimento, certo è che mentre
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                  queste linee ſaranno intorno girate, ſerueranno uno isteſſo tenore, perche la linea del uero moui
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                  mento è quella, che trapaſſa dal centro del mondo, per lo centro del Sole, & peruiene fin al zo­
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                  diaco. </s>
                  <s id="s.006911">& quell'arco, che è tra la linea del uero, & la linea del mezano mouimento, è detto
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                  l'agguaglianza del Sole. </s>
                  <s id="s.006912">& nel giogo, & nello opposto al giogo è nullo perche le due linee concor
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