THE DISCOURSE ON PAINTING.

Perspective, as bearing on drawing, is divided into three principal
sections; of which the first treats of the diminution in the size of
bodies at different distances. The second part is that which treats
of the diminution in colour in these objects. The third [deals with]
the diminished distinctness of the forms and outlines displayed by
the objects at various distances.

17.

ON THE SECTIONS OF [THE BOOK ON] PAINTING.

The first thing in painting is that the objects it represents should
appear in relief, and that the grounds surrounding them at different
distances shall appear within the vertical plane of the foreground
of the picture by means of the 3 branches of Perspective, which are:
the diminution in the distinctness of the forms of the objects, the
diminution in their magnitude; and the diminution in their colour.
And of these 3 classes of Perspective the first results from [the
structure of] the eye, while the other two are caused by the
atmosphere which intervenes between the eye and the objects seen by
it. The second essential in painting is appropriate action and a due
variety in the figures, so that the men may not all look like
brothers, &c.

[Footnote: This and the two foregoing chapters must have been
written in 1513 to 1516. They undoubtedly indicate the scheme which
Leonardo wished to carry out in arranging his researches on