The Da Vinci Notebooks at sacred-texts.com
How figures dressed in a cloak should not show the shape so much as that the cloak looks as if it were next the flesh; since you surely cannot wish the cloak to be next the flesh, for you must suppose that between the flesh and the cloak there are other garments which prevent the forms of the limbs appearing distinctly through the cloak. And those limbs which you allow to be seen you must make thicker so that the other garments may appear to be under the cloak. But only give something of the true thickness of the limbs to a nymph 198 or an angel, which are represented in thin draperies, pressed and clinging to the limbs of the figures by the action of the wind.
201:198 9: Una nifa. Compare the beautiful drawing of a Nymph, in black chalk from the Windsor collection, Pl. XXVI.