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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)
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L. E C Y. XV.
Flas instancias, Facilitatis sraria, ita propoluimus, qua (i punctum
R, una cum duobus oculis O, P in plano existeret ad superticiem in-
Aectentem recto. id quod urrum in experiendo praecise contingat
néene; parum retert; duas urcunque species apparere liquet. quin
Facile concipitur etiam eo polito rem non aliter se habitura.
Elis praelibatis, illud discuriamus, quod innuimus, Lcvsoze aenu
quo nempe P. Eericonins propolicionem hanc luam comprobatum it:
ec Si oculus, e aspectabile sint in diversis mediis se mutuo contingen-
ecribus, imago apparebit in concursu cacheri, ee radii ab oculo per
cpunctum retractionis directe producti.
Sit utique punctum F in medio dentiori HI L M N collocatum, quod
aet oculos A, B radioS F F A, F D B emittat retractos ad B, _D;
E recta A P, BD conveniant in C; sit aurem superticiei retringenti
perpendicularis recta F C; erit (inquir) puncti P imaso in recta
FC5. id quod ita demonstrat: Ouoniam dicta imaso cam in retracto
AF, quam in retracto B D existir, erso in horum intersectione C
exister verum intersectio C in recta FC existet; quoniam haec
communis est sectio planorum AP P, BD F superticiei retringenti
rectorum. ergo liquet propolitum.
Inhanc denionstrationem adverto; T. Supponie ea refractos AF,
B D concurrere; quod tamen Falsum est, praeterquam in uno vel al-
tero calu; quum nempe planum AB P in eodem existit cum ipsa
recta FC plino; vel, cum puncta A, B sunt in superticie coni recti,
cujus axis est recta F C. quod si prior casus ponatur, e supra demon-
Pratis manitectum est retractos AF, BD non in recta FC, sed intra
angulum FC HI convenire; quod e principiis nostris elicitum illum
Taltem constringere deber, qui principia ista admitrit ac amplectitur.
2. Elinc, illa demonstratio iplam se perimit: Nam, quoniam (in po-
Cito casu) puncti Fimaso tam in recta A F, quam in recta B D existie,
adeoque in harum concursu; concursus aurem ilte non est in recta
FC; ergo liquet dictam imaginem extra rectam PC vertari. 3. Sup.
vonit ilte discursus (ut ex suppar ille jamjam prolatus) puncti F uni-
cam oculo unrique imasinem apparere; quod asuror Eus O erat;
anobis paullo supra retutarum. Enimrero diversi oculi lunt reipsa
diversi spectatores. haec, opinor, ratiocinium illud latis enerrant. (
TH Dioper.
F18. 182.