Why distant things and their colour fade; towers thin in fog
Detail dissolves progressively with distance; dark towers look narrower at the base against low white fog
A text page of the Treatise on Painting with two chapters on how distance and fog alter appearances. The first explains that a receding object loses recognition part by part, the most minute first, until the whole and even its colour dissolve into the density of intervening air. The second argues that parallel towers seen through fog look thinner at their base than at their top, because the fog forming their background is denser and whiter near the ground, and a dark object diminishes against a bright background.
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Parts and colour dissolve progressively with distance
A thing is less recognizable the farther it lies from the eye: its most minute parts are lost first, then the less minute at greater range, until at last all parts vanish together with the whole. Its colour is lost too, on account of the density of the air interposed between the eye and the thing seen.
Towers look narrower at the base in fog through figure-ground contrast
Fog is thicker and whiter near the ground than higher up. Since a dark thing diminishes against a white background while a white thing swells against a dark one, the whiter low fog appears to encroach on and shrink the tower's lower edges, an effect it cannot produce higher up where the fog is thinner.