Full text: Barrow, Isaac: Lectiones Opticæ & Geometricæ

ſimplicibus triplicatas ſubſtituendo rationes, eſt γ Q. QB & gt; YP . PB. & his æquales rationes adjungendo eſt QN. γ Q + γ Q. QB& gt; PN . YP + YP. PB; hoc eſt QN. QB & gt; PN. PB. compo-
nendóque BN. QB & gt; BN. P B. ergo QB & lt; PB. unde rurſus
liquet rectam X Qipſis AB; ZP interjacere: Q. E. D.

XVII. Conſimili prorſus argumentatione conſtabit obliquio-
rum incidentium refractos ultra punctum Z ipſam KN interſe-
care.

XVIII. Quinimò rurſus exertiùs apparet non niſi binos refractos
in eodem puncto convenire.

XI X. Addo cum ipſo KN concurrentes refractos circa punctum
Z conglomerari, præſertim illos, qui ad partes F (obliquius) inci-
dentes pertinent.

Nam accipiantur, exempli causâ, ſibi pares N S, ST ; & ſit BP
quarta proportionalis in ratione YB ad BN; & BQ quarta proportionalis
in ratione YB ad BS; & BR itidem quarta talis in ratione YB ad
BT; & à punctis P, Q, R erectæ perpendiculares ipſam NKZ
ſecent in Z, X, & V. patet (è mox oſtenſis) omnium ſpatio NS
incidentium refractos cum NK concurrere intra ZX; nec non omnes
ipſi ST incidentium refractos intra XV cum eodem convenire. por-
rò rectæ BP , BQ, BR ſe habent invicem ut _Cubi_ rectarum BN,
BS, BT, ( vel ſunt in ipſarum BN, BS, BT _ratione triplicata_ : nam
BP. YB : : BN cub. BY cub. & YB . BQ : : YB cub. BS cub. adeóque ex æquo BP. BQ : : BN cub . BS cub. & conſimili ratione
BP. BR : : BN cub. BT cub.) undè faciiè monſtrabitur eſſe PQ
multo minorem quàm QR; xel ZX quàm XV (verbis parco multis
in re ſatis manifeſta) . quare dicti refracti circa punctum Z ſpiſſiùs
ipſum NK decuſſabunt.

14.1.

Fig. 61.

XX. Ex his demùm conficitur omnibus bene trutinatis, oculo
(O) centrum habenti in refracto NK uſpiam conſtituto, puncti A
imaginem ad ipſum conditione præditum toties inſinuatâ punctum Z
conſiſtere. Sit enim CD pupillæ (in plano ABC jacens) _Diameter;_ _axi Optico_ KN perpendicularis; & per ejus extrema C, D tranſeant
refracti IM LR ipſi KN occurrentes punctis X, V. ex oſtenſis patet
omnium intra ſpatium MN incidentium radiorum refractos intra ten-
minos ZX principalem refractum interſecare; neque non omnes ad

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