Quotation from: The Notebooks of Leonardo Da Vinci

Written by: Leonardo da Vinci

250.

Of several bodies of equal size and equally distant from the eye,
those will look the smallest which are against the lightest
background.

Every visible object must be surrounded by light and shade. A
perfectly spherical body surrounded by light and shade will appear
to have one side larger than the other in proportion as one is more
highly lighted than the other.