The Da Vinci Notebooks at sacred-texts.com
Make your work carry out your purpose and meaning. That is when you draw a figure consider well who it is and what you wish it to be doing.
With regard to any action which you give in a picture to an old man or to a young one, you must make it more energetic in the young man in proportion as he is stronger than the old one; and in the same way with a young man and an infant.