Directions of Tree Shadows Under the Rising Sun
Air whitens distant trees to blue; how east, south and west trees shade at sunrise
The leaf first explains that the white-hued air between eye and trees whitens them the more it accumulates, turning the dark parts of distant trees bluer than their lit parts. A chapter on the varieties of tree shadows under one light then maps how much of each tree lies in shadow when the sun is in the east: the eastern tree wholly shaded, the south-eastern (scirocco) three-quarters, the southern half, the south-western (libeccio) a quarter, and the western tree not at all. A final chapter observes that a branch's lit leaf-mass reads as nearly one colour at distance, because its small shadowed gaps shrink faster than its lit parts.
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White air turns the dark parts of distant trees blue
The air between the eye and the trees, being of a white quality, cloaks them more in whiteness the more of it is interposed. Because the trees partake of a dark colour, this interposed whiteness renders their shadowed parts bluer than their lit parts.
How far each tree shades when the sun is in the east
With the sun at the east, Leonardo grades the shadow on trees by their orientation: the eastern tree is wholly shadowed, the one toward scirocco (south-east) three-quarters, the southern tree's shadow covers half, the tree toward libeccio (south-west) a quarter, and the western tree shows no shadow at all. He prefers this finer scheme to the rough division into shadowed, half-shadowed and lit.
A lit leaf-mass reads as one colour at distance
Though every leaf on a lit branch is parted from its fellows by a shadowed gap, at distance the small shadowed part is lost, overtaken by the lit part, which diminishes less with distance than the shadow does. Hence the whole leaf-mass of one branch appears at some remove to be almost a single colour.