# Full text: Barrow, Isaac: Lectiones Opticæ & Geometricæ

I. _CAtoptricâ circulari defunctus ad Dioptricam promovemur;_ quorſum incidentium quotcunque refractis unâ ſimulo perâ
delineandis, adeóque reſractionum ſymptomatis organicè pertentan-
dis modum imprimìs exponemus, præ cæteris, opinor expeditum. Seorſim ad v γ æqualem diametro (NG) circuli refringentis deſcri-
batur circulus v π γ. item habeat v γ ad S γ rationem illam, quæ re-
fractiones determinat (illam autem deinceps, ut antehac, conſtanter
nuncupabo rationem I ad R) & ſuper diametro S γ deſcribatur quo-
que circulus SH γ. Incidat jam radius quilibet MN P, cui con-
veniens deſignandus eſt refractus. ut hoc aſlequamur, circulo adpoſi-
to à V adaptetur v π = NP; & centro γ per π deſcriptus circulus
ſecet circulum SH γ in H; connexáque γ Hcirculum v π γ interſecet
in ξ. demùm connexâ v ξ, circulo NPGaccommodetur NX =
v ξ; erit NX ipſius NP refractus. Etenim (ductis GP, GX) eſt
γ H. γ ξ : : (γ S γ v : :) I. R. hoc eſt γ π. γ ξ: :I. R. hoc eſt
GP. GX: : I. R. cùm itaque ſint ipſæ GP, GX recti ſinus angulo-
rum GN π, GNX(quorum GNPeſt angulus incidentiæ) liquet
propoſitum.

### 19.1.

Fig. 107.
108.

lum refractis competentia; quorum illa pro more primò pertractabi-
circuli refringentis Centrum C punctúmque de longinquo radians
protendatur recta AC Z; tum fiat BZ. CZ: : I. R; nec non di-
vidatur CZ in F, ut ſit FZ. FC: : I. R; & centro F per Z deſcri-
batur circulus EG Z. his peractis, accipiatur jam quilibet ad AC
parallelus MNP(convexis incidens an concavis partibus perinde
fuerit) dico ſi recta NC (ab incidentiæ nempe puncto per refrin-
gentis centrum ducta) circulo EGZprotracta occurrat in G; &

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