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

_XVII._ Ad lentem concavo convexam diverg.

Fig. 160,
161, 162.

_XVIII._ Ad lentem convexo-concavam converg.

Si Acadat extra BC, fiat AB - {R/I} AC. AB : : BC. BZ; ſin A
cadat inter B, & C; fiat AB + {R/I} AC. AB : : BC. BZ.

1. Jam cùm Z cadit extra DK, tum primò ſi {I/R} KZ & gt; DZ, fac
{I/R} KZ - DZ. DZ : : DK. DY, & cape DY adverſus A.

2. Secundò, ſi {I/R} KZ = DZ; imagò infinitè elongabitur.

3. Tertiò, ſi {I/R} KZ & lt; DZ, fac DZ - {I/R} KZ. DZ : : DK. DY; & ſume DY verſus A.

4. Sed quando Z inter D, & K cadit, fiat DZ + {I/R} KZ. DZ : :
DK. DY; & accipiatur DY verſus A.

Hiſce ſubnectam ſequentia; non contemnendum in _engyſcopicis_
uſum præ ſe ferentia _Problemata._

I. _Dati puncti propinqui A perfectam imaginem per lentem concavo-_
_convexam in aliud datum punctum Z lenti vicinius projicere._ (per-
fectam imaginem intelligo, quæ reſultat ex omnibus, quos ipſum A

### 20.1.

Fig. 163.

Fiat I - R. R : : AZ. ZB. & dividatur ZB in C, ut ſit CB. CZ : : I. R. tum centro C deſcribatur circulus EBF. item centro Z
intervallo quovis ZD (majoriquam ZB) deſcribatur circulus GDH; factum erit; nempe lens EFGH puncti A perfectam imaginem in
punctum Z projiciet.

Nota, datâ CB puncta A, Z è propoſitis facilè determinari.

In vitro, ſi CB = 15, erit {ZC = 9 \\ ZB = 24} & {AZ = 16. \\ AB = 40. Adnotetur etiam per lentem EGHF ad Z tendentes radios ad A
refringi.

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