Distant objects, the blue of far landscapes, and lost detail
Aerial perspective: why remote things blur, turn blue, and lose their smallest parts first
A text page of the Treatise on Painting gathering several short chapters on aerial perspective. It closes a discussion of battlements, whose gaps swallow the merlons at a distance until only a plain wall shows, then states that an object's edges grow less distinct the farther off it is. Two further chapters explain why distant landscapes appear blue (in proportion to their natural or shadow-cast darkness) and why the smallest parts of bodies, subtending the least visual angle, are the first to be lost from view.
On this page
Why distant landscapes show blue
Of things remote from the eye, whatever their true colour, the one that appears more blue is the one of greater darkness. Leonardo distinguishes natural darkness (a thing dark in itself) from accidental darkness (a thing shadowed by other objects).
Small parts vanish first because they subtend a smaller angle
The parts of a body that are of smaller quantity are the first whose recognition is lost over distance. Their images reach the eye at a smaller angle than the larger parts, so that when even the large mass is reduced to a minimal angle and nearly lost, the small parts fail entirely.
Battlements merge into a plain wall with distance
As a fortress recedes, the gaps between the merlons appear ever larger than the merlons themselves, until at a remote distance the gap covers the whole merlon and the wall reads as straight and without battlements. The edges of any object likewise become less distinct the farther it is seen.