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

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121103

_Hujuſmodi Vitrum Myopes juvat;_ pro quibus ità conſtruatur:
ſit ZD diſtantia, ad quam optimè cernunt; ſumatúrque ZB utcun-
que paullo minor quàm ZD; & fiat CB = {5/8} ZB; tum centro C
per B deſcribatur circulus EBF, & centro Z per D circulus GDH
deſcribatur; ipſi (Superficiei GDH oculum admoventes) punctum
A diſtinctè ſpectabunt, velut ad Z ſitum.

Quod ſi velit _Myops,_ ad diſtantiam itidem ZD diſtinctè cernens,
aſſignatum punctum A contemplari; adſumpto, ut prius, liberè
puncto B, fiat CB = {2 AB x ZB/5 AB - 3 ZB}; & reliqua fiant, ut priùs.

_II._ Dati puncti A perfectam imaginem, etiam ope lentis concave-
11Fig. 164. convexæ, in datum aliud punctum Z lorginquius projicere.

Fiat AZ. AD : : 1 - R. R. item dividatur AD in C, ut ſit CD.
CA : : 1. R; & centro C per D deſcribatur circulus EDF. item
centro A, quopiam intervallo AB (minori quàm AD) deſcribatur
circulus EDF; factum erit; nempe lens EDF puncti A ima-
ginem in punctum Z projiciet.

Datâ CB, puncta A, Z viciſſim è propoſitis innoteſcunt.

In vitro, ſi CB = 15, erit {ZC = 9. \\ ZB = 24. } & {AZ = 16. \\ AB = 40.

Itidem & hîc, perlentem EF verſus Z tendentes radii in A refrin-
guntur.

Hinc _Presbytis_ utile conficiatur _Vitrum,_ hocpacto: Ad interval-
lum ZD hi diſtinctè videant. Secetur ZD in A, ut ſit AD = {3/5} ZD.
item ſit CD = {5/8} AD (vel ſit CD = {3/8} ZD) centróque C per D
deſcribatur circulus EDF. item utcunque ſumpto puncto B (citra
D nempe, verſus A) centro A per B deſcribatur circulus EBF.
lente EF dicti _Presbyta_ punctum A diſtinctiſſimè conſpicient. ‖

Hiſce demum in cumulum adjiciatur ab amico communicatus _Modus_
_elegans ac expeditus cujuſcunque caſûs imaginem Geometricè deſig-_
_nandi; ut & lentem deſcribendi, quæ imaginem in datum punctum_
_projiciet._

1. Imaginem deſignare.

E centris, & verticibus circulorum lentem conſtituentium erigan-
22Fig. 165,
166, 167. tur ad axin perpendiculares Kj, BP, DQ, CI; deinde per punctum
A ducatur quævis recta API ſecans BP, & CIinP, & I. fac CI.
CR : : I. R. agatur recta RP ſecans DQ, & K ρ in Q, & ρ; fac
K ρ. Kj : : R. I, & agatur 1 Q, quæ producta ſecabit axin in Y, loco
imaginis quæſito. ‖

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