Of the various kinds of light (126, 127).

Separate light is that which falls upon the body.  Inseparable light is the side of the body that is illuminated by that light.  One is called primary, the other derived.  And, in the same way there are two kinds of shadow:—­One primary and the other derived.  The primary is that which is inseparable from the body, the derived is that which proceeds from the body conveying to the surface of the wall the form of the body causing it.

127.

How there are 2 different kinds of light; one being called diffused, the other restricted.  The diffused is that which freely illuminates objects.  The restricted is that which being admitted through an opening or window illuminates them on that side only.

[Footnote:  At the spot marked A in the first diagram Leonardo wrote lume costretto (restricted light).  At the spot B on the second diagram he wrote lume libero (diffused light).]

General remarks (128. 129).

128.

Light is the chaser away of darkness.  Shade is the obstruction of light.  Primary light is that which falls on objects and causes light and shade.  And derived lights are those portions of a body which are illuminated by the primary light.  A primary shadow is that side of a body on which the light cannot fall.

The general distribution of shadow and light is that sum total of the rays thrown off by a shaded or illuminated body passing through the air without any interference and the spot which intercepts and cuts off the distribution of the dark and light rays.

And the eye can best distinguish the forms of objects when it is placed between the shaded and the illuminated parts.

129.

MEMORANDUM OF THINGS I REQUIRE TO HAVE GRANTED [AS AXIOMS] IN MY
EXPLANATION OF PERSPECTIVE.

I ask to have this much granted me—­to assert that every ray passing through air of equal density throughout, travels in a straight line from its cause to the object or place it falls upon.

FIRST BOOK ON LIGHT AND SHADE.

On the nature of light (130. 131).

130.

The reason by which we know that a light radiates from a single centre is this:  We plainly see that a large light is often much broader than some small object which nevertheless—­and although the rays [of the large light] are much more than twice the extent [of the small body]—­always has its shadow cast on the nearest surface very visibly.  Let c f be a broad light and n be the object in front of it, casting a shadow on the plane, and let a b be the plane.  It is clear that it is not the broad light that will cast the shadow n on the plane, but that the light has within it a centre is shown by this experiment.  The shadow falls on the plane as is shown at m o t r.

[Footnote 13:  In the original MS. no explanatory text is placed after this title-line; but a space is left for it and the text beginning at line 15 comes next.] Why, to two [eyes] or in front of two eyes do 3 objects appear as two?