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

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7052 diſtinctius exhibet obtuenti. quod erat propoſitum oſtendere. Et
hæc quidem ad locum imaginis determinandum attinentia pleraque
propter oculum in axe ſitum ſuffecerit attigiſſe. Supereſt ut idem
oculi gratiâ ſecùs conſtituti pertentemus. id operis ſequenti depu-
tamus.

Lect. VI I.

I. ID nunc agimus, ut ab infinito quoad ſenſum intervallo radiantis
puncti, è reflectione circularem ad peripheriam peracta oriun-
dæ imaginis, oculi reſpectu præter axem ſiti, locum exquiramus.
quocirca primùm ipſa recta linea determinanda venit, in qua locus
iſte verſatur; tum ipſiſſimum præciſè punctum eſt deſignandum. In
primi verò propoſiti gratiam hoc _Problema_ confici debet.

II. Dato circulo reflectente BNP (cujus centrum C) rectâque
CB poſitione data; deſignandus eſt huic parallelus radius, cujus re-
flexus per datum tranſeat punctum.

III. Si datum punctum ( puta K) in ipſa CB exiſtat, facilimè pe-
11Fig. 70. ragitur negotium. nam ſi centro K, intervallo KC deſcribatur circulus,
ipſi reflectenti occurrens in N; erit KN reſlexus ducti ad CB paralle-
li; prout ex antedictis abunde perſpicuum eſt.

IV. Si datum punctum (puta jam X) in ipſa reflectentis circumfe-
rentia verſetur; arcûs triſectione ſtatim exhauritur _Problema_. Nam
ducatur XH ad BC parallela (quæ quidem ipſa uno modo proble-
mati ſatisfacit) & interceptus arcus XH ſecetur punctis N, P, ut
22Fig. 71. ſint arcus XN, NP, PH æquales inter ſe; connectantúrque rectæ
XN, NP. dico factum. etenim ducantur CN, XP; & patet an-
gulum CN X ipſi CNP æquari; adeóque fore XN reflexum ipſius
PN; quinetiam ang. NP X æquatur angulo HXP; proindéque
NP ipſi XH, hoc eſt ipſi BC, parallela eſt. itaque factum.

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