Barrow, Isaac
,
Lectiones opticae & geometricae : in quibus phaenomenon opticorum genuinae rationes investigantur, ac exponuntur: et generalia curvarum linearum symptomata declarantur
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ſuggerens haud aſpernanda. </
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<
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xml:space
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">relinquantur igitur ei cætera, mihi
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ſuffecerit, quòd veriorem _phænomena{εμ}
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_ detegendi declarandíque me-
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thodum adniſus ſim aliquatenus enucleare. </
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<
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">pergamus ad alios caſus,
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haud ità pertractatos.</
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<
s
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xml:space
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">XIX Objiciatur ſpeculo MBND recta FAG, rectæ CA (per
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ſpeculi centrum C tranſeunti) perpendicularis; </
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<
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">adverto, ſi fuerit ipſa
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">Fig. 189.</
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CA major quàm CZ, quadrans diametri BD, quòd rectæ FAG
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ad infinitum utrinque protractæ ad totum circulum (ejus ad partes
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intelligo concavas ſimul acconvexas) imago abſoluta (quinetiam ima-
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go ad oculum in ipſo centro C conſtitutum relata) erit _Ellipſis_. </
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ſi CA minor ſit, quàm CZ, quòd ipſius FA G imago abſoluta
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(vel dicto modo relata) conſtabit ex hyperbolis oppoſitis; </
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<
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CA ipſam CZ adæquet (vel FG per ipſum Z tranſeat) quòd ad
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parabolam ejuſmodi conſiſtet imago. </
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<
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">Sed modum tranſgrederer hæc
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jam aggrediens demonſtrare. </
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<
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<
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XVII.</
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ſtranda _neceſſariam, alioquin notabilem, Conicarum Sectionum_
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_proprietatem_ imprimìs oſtendemus.</
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finitè protractis lateribus AC, AE, in AC ſumatur quod piam pun-
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ctum X, ducatúrque XG ad CE parallela; </
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CXG recta CZ æqualis ipſi XG; </
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<
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">dico punctum indeterminatum Z ad
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ſectionum conicarum aliquam conſiſtere.</
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<
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</
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<
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">CE) erit punctum Z ad ellipſin, quæ determinatur hoc pacto: </
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guli LCP ſemirecti fiant (ad utramque rectæ CE partem) liquet
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igitur rectas CP ipſi AE occurrere, puta ad puncta R, & </
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