A Treatise on Painting/Chapter 197
Chap. CXCVII.—Of the Termination of Bodies upon each other.
When a body, of a cylindrical or convex surface, terminates upon another body of the same colour, it will appear darker on the edge, than the body upon which it terminates. And any flat body, adjacent to a white surface, will appear very dark; but upon a dark ground it will appear lighter than any other part, though the lights be equal.