Since it is proved that every definite light is, or seems to be, derived from one single point the side illuminated by it will have its highest light on the portion where the line of radiance falls perpendicularly; as is shown above in the lines _a g_, and also in _a h_ and in _l a_; and that portion of the illuminated side will be least luminous, where the line of incidence strikes it between two more dissimilar angles, as is seen at _b c d_. And by this means you may also know which parts are deprived of light as is seen at _m k_.
Where the angles made by the lines of incidence are most equal there will be the highest light, and where they are most unequal it will be darkest.
I will make further mention of the reason of reflections.
[Footnote: See Pl. XXXII. The text, here given complete, is on the right hand side. The small circles above the beginning of lines 5 and 11 as well as the circle above the text on Pl. XXXI, are in a paler ink and evidently added by a later hand in order to distinguish the text as belonging to the _Libro di Pittura_ (see Prolegomena. No. 12, p. 3). The text on the left hand side of this page is given as Nos. 577 and 137.]
General suggestions for historical pictures (577-581).
When you compose a historical picture take two points, one the point of sight, and the other the source of light; and make this as distant as possible.
Historical pictures ought not to be crowded and confused with too many figures.
Let you sketches of historical pictures be swift and the working out of the limbs not be carried too far, but limited to the position of the limbs, which you can afterwards finish as you please and at your leisure.
[Footnote: See Pl. XXXVIII, No. 2. The pen and ink drawing given there as No. 3 may also be compared with this passage. It is in the Windsor collection where it is numbered 101.]
The sorest misfortune is when your views are in advance of your work.
Of composing historical pictures. Of not considering the limbs in the figures in historical pictures; as many do who, in the wish to represent the whole of a figure, spoil their compositions. And when you place one figure behind another take care to draw the whole of it so that the limbs which come in front of the nearer figures may stand out in their natural size and place.