The derived shadow will be darker than the primary shadow where it
is contiguous with it.

On the proportion of light and shade (153-157).

153.

That portion of an opaque body will be more in shade or more in
light, which is nearer to the dark body, by which it is shaded, or
to the light that illuminates it.

Objects seen in light and shade show in greater relief than those
which are wholly in light or in shadow.

154.

OF PERSPECTIVE.

The shaded and illuminated sides of opaque objects will display the
same proportion of light and darkness as their objects [Footnote 6:
The meaning of _obbietti_ (objects) is explained in no 153, lines
1-4.--Between the title-line and the next there is, in the
original, a small diagram representing a circle described round a
square.].

155.

OF PAINTING.

The outlines and form of any part of a body in light and shade are
indistinct in the shadows and in the high lights; but in the
portions between the light and the shadows they are highly
conspicuous.

156.

OF PAINTING.

Among objects in various degrees of shade, when the light proceeds
from a single source, there will be the same proportion in their
shadows as in the natural diminution of the light and the same must
be understood of the degrees of light.

157.

A single and distinct luminous body causes stronger relief in the
object than a diffused light; as may be seen by comparing one side
of a landscape illuminated by the sun, and one overshadowed by
clouds, and so illuminated only by the diffused light of the
atmosphere.

THIRD BOOK ON LIGHT AND SHADE.

Definition of derived shadow (158. 159).

158.

Derived shadow cannot exist without primary shadow. This is proved
by the first of this which says: Darkness is the total absence of
light, and shadow is an alleviation of darkness and of light, and it
is more or less dark or light in proportion as the darkness is
modified by the light.

159.

Shadow is diminution of light.

Darkness is absence of light.

Shadow is divided into two kinds, of which the first is called
primary shadow, the second is derived shadow. The primary shadow is
always the basis of the derived shadow.

The edges of the derived shadow are straight lines.

[Footnote: The theory of the _ombra_ dirivativa_--a technical
expression for which there is no precise English equivalent is
elaborately treated by Leonardo. But both text and diagrams (as Pl.
IV, 1-3 and Pl. V) must at once convince the student that the
distinction he makes between _ombra primitiva_ and _ombra
dirivativa_ is not merely justifiable but scientific. _Ombra
dirivativa_ is by no means a mere abstract idea. This is easily
proved by repeating the experiment made by Leonardo, and by filling
with smoke the room in which the existence of the _ombra dirivativa_
is investigated, when the shadow becomes visible. Nor is it
difficult to perceive how much of Leonardo's teaching depended on
this theory. The recognised, but extremely complicated science of
cast shadows--_percussione dell' ombre dirivative_ as Leonardo
calls them--is thus rendered more intelligible if not actually
simpler, and we must assume this theory as our chief guide through
the investigations which follow.]

The darkness of the derived shadow diminishes in proportion as it is
remote from the primary shadow.

Different sorts of derived shadows (160-162).

160.



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