Quotation from: The Notebooks of Leonardo Da Vinci
Written by: Leonardo da Vinci
The proportions of light and shade in a leaf (423-426).
423.
OF THE SHADOWS OF A LEAF.
Sometimes a leaf has three accidents [of light] that is: shade,
lustre [reflected light] and transparency [transmitted light]. Thus,
if the light were at _n_ as regards the leaf _s_, and the eye at
_m_, it would see _a_ in full light, _b_ in shadow and _c_
transparent.