ιβ΄.
Τῶν εἰς τοὔμπροσθεν μῆκος ἐχόντων τὰ μὲν ἐν τοῖς
δεξιοῖς εἰς τὰ ἀριστερὰ δοκεῖ παρῆχθαι, τὰ δὲ ἐν τοῖς ἀριστεροῖς εἰς τὰ δεξιά.
δεξιοῖς εἰς τὰ ἀριστερὰ δοκεῖ παρῆχθαι, τὰ δὲ ἐν τοῖς ἀριστεροῖς εἰς τὰ δεξιά.
ἔστω δύο ὁρώμενα μεγέθη τὰ ΑΒ, Γ∠, ὄμμα δὲ ἔστω τὸ Ε, ἀφʼ οὗ προσπιπτέτωσαν ἀκτῖνες αἱ ΕΘ, ΕΚ, ΕΑ, ΕΖ, ΕΗ, ΕΓ. λέγω,
ὅτι αἱ μὲν ΕΖ, ΕΗ, ΚΓ δοκοῦσιν εἰς τὰ ἀριστερὰ μετῆχθαι, αἱ δὲ ΕΘ, ΕΚ, ΕΑ εἰς τὰ δεξιά. ἐπεὶ γὰρ ἡ ΕΖ τῆς ΕΗ ἐστι δεξιωτέρα, ἡ δὲ ΕΗ τῆς
ΕΓ, ἐντεῦθεν ἄρα ἡ ΕΓ τῆς ΕΗ δοκεῖ εἰς τὰ ἀριστερὰ μετῆχθαι, ἡ δὲ ΗΕ τῆς ΕΖ. ὁμοίως καὶ αἱ ΕΚ, ΚΑ, ΕΘ δοκοῦσιν εἰς τὰ δεξιὰ μετῆχθαι.
ὅτι αἱ μὲν ΕΖ, ΕΗ, ΚΓ δοκοῦσιν εἰς τὰ ἀριστερὰ μετῆχθαι, αἱ δὲ ΕΘ, ΕΚ, ΕΑ εἰς τὰ δεξιά. ἐπεὶ γὰρ ἡ ΕΖ τῆς ΕΗ ἐστι δεξιωτέρα, ἡ δὲ ΕΗ τῆς
ΕΓ, ἐντεῦθεν ἄρα ἡ ΕΓ τῆς ΕΗ δοκεῖ εἰς τὰ ἀριστερὰ μετῆχθαι, ἡ δὲ ΗΕ τῆς ΕΖ. ὁμοίως καὶ αἱ ΕΚ, ΚΑ, ΕΘ δοκοῦσιν εἰς τὰ δεξιὰ μετῆχθαι.
Optica. Euclid. ed. Johan Ludvig Heiberg, ed. Heinrich Menge. United States. 2018.
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