Quotation from: The Notebooks of Leonardo Da Vinci

Written by: Leonardo da Vinci

459.

When the sun is covered by clouds, objects are less conspicuous,
because there is little difference between the light and shade of
the trees and of the buildings being illuminated by the brightness
of the atmosphere which surrounds the objects in such a way that the
shadows are few, and these few fade away so that their outline is
lost in haze.