The Three Kinds of Light and Towers Seen Through Fog
Particular, universal and composite light, and why higher, more distant objects look darker in even fog
The page opens with a note distinguishing three kinds of light that illuminate opaque bodies: particular (sun, window or fire), universal (cloudy or foggy weather) and composite (when the sun lies wholly below the horizon at dawn or dusk). Leonardo then treats cities and buildings seen at long distance through morning or evening fog, and, with a marginal perspective diagram, argues that of objects of equal height the taller stands out against deeper fog and so appears darker. A visual pyramid drawn at the right, with three towers, illustrates how the eye h reads the summits a, b, c through differing depths of haze.
On this page
The three kinds of light on opaque bodies
The first light is called particular: the sun, or a window or fire. The second is universal, as in cloudy or foggy weather. The third is composite, when the sun in evening or morning is entirely below the horizon.
Buildings seen through fog at long distance
Buildings seen at long distance in evening or morning fog show only the brightness of their parts lit by the sun near the horizon, while the remaining parts stay almost the colour of the moderate darkness of the fog.
Visual pyramid over three objects of equal height
A perspective construction places three things of equal height within the visual pyramid, labelled h - d c b a - e - i r f - g - o, to show how the eye judges their apparent size and darkness through the intervening air.
Taller objects darker in deeper fog
Of things of equal height, that one appears darker which stands against deeper fog. The eye h, seeing towers a b c of equal height, sees the summit c at r through two degrees of fog and the summit of the middle tower b through only one degree; therefore c shows itself darker than b.