Barrow, Isaac - Lectiones opticae & geometricae : in quibus phaenomenon opticorum genuinae rationes investigantur, ac exponuntur: et generalia curvarum linearum symptomata declarantur

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6850 BVT, patet rectam VT angulum XVC ſecare. item ob angulum
XYV obtuſum, eſt XV & gt; XY = BX. ergo BV & gt; 2 BX; &
VT & gt; 2 XD. Verùm ang. VTC (major ipſo TVB, vel ipſo
DXB) eſt obtuſus; adeóque VC & gt; VT; itàque magìs YC & gt;
2 X D. ergò AB + AY + YC & gt; 2 AX + 2 XD. hoc eſt
AB + AC & gt; 2 AD : Q. E. D.

XV. Quò paralleli radii rectiùs (vel axi propinquiùs) incidunt,
eò reflexorum concurſus ad axem ſibi viciniores ſunt.

Nempe ſumantur utcunque pares arcus NR, RX; & incidentium
11Fig. 67. MN, QR, VX reflexi NK, RL, XM cum axe conveniant punctis
K, L, M, erit ML & gt; LK. Nam connexæ CN, CR, CX rectæ
ZY occurrant punctis v, ρ, ξ. Eſt itaque (juxta _Lemma_ præcedens)
C ξ + Cv & gt; 2C ρ; hoc eſt, CM + CK & gt; 2 CL. quare CM
- CL & gt; CL - CK; hoceſt ML & gt; LK: Q. E. D.

XVI. Exhinc patet axi propinquam lucem ab hujuſmodi reflectione
magìs magíſque conſtipari; maximè circa punctum Z, ubi perpendi-
cularis ipſius quaſi reflexus terminatur. unde potiſſima conſtat ratio,
quare concavis à ſpeculis ad ſolem expoſitis circa punctum Z _Ignis_
accenditur; enimverò condenſatior, ínque ſpacium arctius quaſi com-
preſſa lux validiorem exerit vim, ac efficaciam.

XVII. Quinetiam ex his conſectatur, longinqui puncti imaginem
oculo in axe conſtitnta circa punctum Z conſiſtere. Sit, inquam,
22Fig. 68. BCO axis Opticns; oculíque dìameter D δ (in plana nempe cir-
culi propoſiti ſita) hujus autem extrema permeent reflexi NKD,
VK δ (ad incidentes MN P, μ ν Π pertinentes) . jam abunde mani-
feſtum eſt imaginem conſpicuam intra KZ ſpatium verſari. Nam
alterius cujuſvis hinc, vel indè cadentis reflexus (ſeu ipſius R S, vel
ρ σ) oculum omnino transgredietur, adeóque nihil quicquam ad viſio-
nem ipſam, vel ad ejus quemcunque modum determinandum conferet;
id autem omne meritó tribuetur radiorum intra peripheriam NV in-
cidentium reflexis; qui ſcilicet oculum ingredientes ſuo quiſque modo
viſum aliquatenus afficiant. quoniam tamen ex his, qui propiores
axi rectiùs incidunt oculo, magíſque pollent idcircò; nec non iidem
proptergà faciliùs ad unum in oculo punctum recolliguntur; præ cæte-
ris etiam illi catervatim ingruunt; rationi conſonum eſt iſthic præſer-
tim imaginem conſiſtere; ſiquidem velut ab eo plures, ac efficaciſſimi
radii videbuntur cmanare, Subjicio, propter admodum exiguam

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