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# Title: [Lectiones XVIII, Cantabrigiae in Scholis publicis habitae] Lectiones XVIII, Cantabrigiæ in Scholis publicis habitæ (shelfmarks Leibn. Marg. 0; ZEN Leibn. Marg. 0)
# Folio 24, page id 797435492:0044
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L. F C F. I
Pro retractione vero: Incidat radius A B medio F. F in B; _ isthie
retringatur in B ai, dico permutatim radium a B. regredientem in B A
retringi. Nam per occurtum B ducatur Q B P. media dirimenri F F
Derpendicularis; ex in hac urcunque sumpro puncto. P ducatur PC
ad AB prorractam perpendicularis, ut e P II. ad B a; e produca-
tur a BS. FH ergO P C linus rectus anguli incidentix ABO ad
radium BP; _C P EI sinus anguli refracti OBS ad eundem radium
BP. Cuum itaque ratio P C ad P HI retractionem metiatur e luperiori
mediotactatri in inferius; etiam vicissII reCtARHI P FI P G PFOPOr-
tio retractionem determinabit ab inferiori medio factam in superius.
Unde Piradius a B jam ponatur incidens; cum line P FI, PC recti A.
nus anguli incidentia PB FI, SE anguli P BC, liquidum est ipsam LI B
in B A retringi.
IV. Angulo incidenrix majori major comperir angulus infexus.
Carigulum inflexum vocito, qui a perpendiculari continetur e in-
Aexo; is proinde respectire dicitur angulus reAerus, vel retractus.
Angulus aurem inflectionis (hoc est reflectionis respectire, vel retracti.
onis) appellaturis, qui comprehenditur ab incidente ec inAexo; inci-
dentix vero, nequis lecus accipiat, apud nos angulus est, quem con-
rinent incidens de perpendicularis.) Quod provolicum spectat ettatum.
id e poliris principiis manifecte consectatur. Frenim in refectione
ipsi anguli reflexi angulis incidentia proportionalessunt; in retracti
one laltem recri sinus angulorum retractorum sinubus angulorum in-
cidencix proportionantur. Unde liquido constat proxolitum: quortum
verba, quorlum Schemata mulciplicem ?
V. Cumincidentes ad superticiem mediam Pese decustant, Iidem
Tese intlectionem palsi decuslabunt, eodem ordine serrato, quem directé
progedientes habuissent (urique sic ut perpendiculari post inflectionem
propior incedat qui proxior anter tuit.)
Hlaec propolitio revera non differe à praecedente; quo demirer
Heris. Diop. 8. eam à non nemine principia nostra ulurxante aliunde compro-
baxI.
VI. Ansulo incidentix majori major convenit ansulus inflectionis.
Ouoad rellectionem, res exrra dubium eridens est; angulus enim refte-
ctionis incidentia majori conreniens eum plane continer, qui minori
incidentix respondet. Pro refractione vero: lIc recta OB P retrin-
genti perpendicularis; incidant autem radii ABC, D B H (Scilicet AB
obliquius
   =