A Treatise on Painting, by Leonardo da Vinci
Senex and Taylor, London
That part of an Object which is nearest the Luminous Body, whence it has its Light, will be the most strongly illumined.
The Images of Objects, lose a Degree of force, at every Degree of distance; that is, in proportion as an Object is seen more remote, its Species is more intercepted in its Passage through the Air, and it strikes the Eye with less Vigour.
Observe that the weakening and alteration of the Colours of Objects, be equal to the diminution of their Magnitudes.