Why two separate lights appear joined at a distance
Against the perspectivists: the enlargement comes from two images in the eye, not from glowing air
Beside a sketch of two lit candles, Leonardo notes that two lights separated by some distance appear joined and united. Many perspectivists explain this by saying the air around the lights becomes so illuminated that it seems of the same nature as the lights, so that lights and air look like one body. He rejects this: if the surrounding air really glowed uniformly, the effect would be even clearer close up, where the light's true shape is known, yet in fact that shape is lost with distance; so the enlargement must instead be produced by two images forming in the eye. A right-margin note explains that a light's excess brightness near the eye contracts the pupil and weakens vision, while at a distance the pupil widens and the light appears larger.
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Two separate lights appear united at a distance
Two lights some distance apart look joined. Against the perspectivists who blame uniformly glowing air, Leonardo argues that if the air truly shone it would be more evident near than far; since the light's true shape is instead lost with distance, the merging must come from two images formed in the eye.
The pupil contracts under a near bright light
A bright light near the eye offends and contracts the pupil, weakening the visual power and making the light seem smaller; as the light recedes and loses splendour the offence ceases, the pupil widens, and the light appears larger.