Barrow, Isaac
,
Lectiones opticae & geometricae : in quibus phaenomenon opticorum genuinae rationes investigantur, ac exponuntur: et generalia curvarum linearum symptomata declarantur
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DEF concurrentes punctis S, T; </
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ſi DE ſunt ut cubi ipſarum DF, erit ſemper DT = 3 DS; </
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<
s
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mili deinceps modo.</
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<
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<
s
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xml:space
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ne data recta DB; </
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<
s
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xml:space
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">tranſeant etiam per B lineæ EBE, FBF tales,
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ut ductâ quâcunque PG ad DB parallelâ, ſit perpetuò PF eodem or-
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dine media Arithmeticè inter PG, PE; </
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<
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EBE, opertet lineæ FBF tangentem ad B determinare.</
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<
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xml:space
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">Sumptis NM (ordinum in quibus ſunt PF, PE exponentibus)
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fiat N x TD + M \\ - N} x RD. </
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<
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xml:space
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<
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<
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">& </
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<
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tur BS; </
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<
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<
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xml:space
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">Nam utcunque ducta ſit PG, dictas lineas ſecans ut vides. </
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EG. </
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<
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VII.</
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TD. </
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EF x RD. </
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<
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</
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<
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<
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VII.</
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KG x TD:</
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<
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<
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TD:</
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<
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&</
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<
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<
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<
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</
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<
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<
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<
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ptâ communi ratione) FG. </
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<
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<
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EG. </
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<
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<
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<
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VII.</
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itaque punctum L extra curvam FBF ſitum eſt; </
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Propoſitum.</
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<
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dem ordinis Geometricè media liquet (planè ſicut in modò præceden-
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tibus) eandem BS curvam FBF contingere.</
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<
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<
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</
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<
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<
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<
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<
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rectam ad hoc tangentem conſimili pacto deſignari. </
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ducatur recta PG ad DB parallela, ſecans curvam EBE ad E; </
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per E ducatur ER curvam EBE tangens; </
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<
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