In proportion to the number of times that a b goes into c d will it be more luminous than c d.  And similarly, in proportion as the point e goes into c d will it be more luminous than c d; and this light is useful for carvers of delicate work. [Footnote 5:  For the same reason a window thus constructed would be convenient for an illuminator or a miniature painter.]

[Footnote:  M. RAVAISSON in his edition of the Paris MS. A remarks on this passage:  "La figure porte les lettres f et g, auxquelles rien ne renvoie dans l’explication; par consequent, cette explication est incomplete.  La figure semblerait, d’ailleurs, se rapporter a l’effet de la reflexion par un miroir concave." So far as I can see the text is not imperfect, nor is the sense obscure.  It is hardly necessary to observe that c d here indicate the wall of the room opposite to the window e and the semicircle described by f g stands for the arch of the sky; this occurs in various diagrams, for example under 511.  A similar semicircle, Pl III, No. 2 (and compare No. 149) is expressly called ‘orizonte’ in writing.]

519.

That the light should fall upon a picture from one window only.  This may be seen in the case of objects in this form.  If you want to represent a round ball at a certain height you must make it oval in this shape, and stand so far off as that by foreshortening it appears round.

520.

OF SELECTING THE LIGHT WHICH GIVES MOST GRACE TO FACES.

If you should have a court yard that you can at pleasure cover with a linen awning that light will be good.  Or when you want to take a portrait do it in dull weather, or as evening falls, making the sitter stand with his back to one of the walls of the court yard.  Note in the streets, as evening falls, the faces of the men and women, and when the weather is dull, what softness and delicacy you may perceive in them.  Hence, Oh Painter! have a court arranged with the walls tinted black and a narrow roof projecting within the walls.  It should be 10 braccia wide and 20 braccia long and 10 braccia high and covered with a linen awning; or else paint a work towards evening or when it is cloudy or misty, and this is a perfect light.

On various helps in preparing a picture (521-530).

521.

To draw a nude figure from nature, or any thing else, hold in your hand a plumb-line to enable you to judge of the relative position of objects.

522.

OF DRAWING AN OBJECT.

When you draw take care to set up a principal line which you must observe all throughout the object you are drawing; every thing should bear relation to the direction of this principal line.

523.

OF A MODE OF DRAWING A PLACE ACCURATELY.