Section 56

56. Ἴσὸν δὲ τὸ μὲν πρὸς τῷ Ν κτλ. p. 198, ἐὰν γάρ, καθὼς εἴρηται ἐν τῷ λαʹ θεωρήματι, ἀπὸ τοῦ Ν ὄμματος προσπέσωσιν ἀκτῖνες πρὸς τὴν τοῦ κώνου περιφέρειαν ὡς αἱ ΝΤ, ΝΦ, καὶ ἀπὸ τῶν Τ, Φ ἐπὶ τὴν κορυφὴν τὴν ∠ἐπιζευχθῶσιν εὐθεῖαι ὡς αἱ Τ∠, Φ∠, τὸ διὰ τῶν ΝΤ, Τ∠ ἐπίπεδον καὶ τὸ διὰ τῶν ΝΦ, Φ∠ κοινὴν τομὴν ἕξει τὴν ∠Ν, ἐφʼ ἧς ἐὰν τεθῇ τὸ ὄμμα ὡς κατὰ τὸ Ν καὶ τὸ Θ, ἴσον ἀεὶ τοῦ κώνου τὸ ὁρώμενον ὀφθήσεται διὰ τὸ λαʹ θεώρημα· ὁμοίως καὶ ἐπὶ τῆς ΛΣ. Ad prop. XXXV.