Shadow partakes of the nature of universal matter. All such matters
are more powerful in their beginning and grow weaker towards the
end, I say at the beginning, whatever their form or condition may be
and whether visible or invisible. And it is not from small
beginnings that they grow to a great size in time; as it might be a
great oak which has a feeble beginning from a small acorn. Yet I may
say that the oak is most powerful at its beginning, that is where it
springs from the earth, which is where it is largest (To return:)
Darkness, then, is the strongest degree of shadow and light is its
least. Therefore, O Painter, make your shadow darkest close to the
object that casts it, and make the end of it fading into light,
seeming to have no end.
Of the various kinds of shadows. (123-125).
123.
Darkness is absence of light. Shadow is diminution of light.
Primitive shadow is that which is inseparable from a body not in the
light. Derived shadow is that which is disengaged from a body in
shadow and pervades the air. A cast transparent shadow is that which
is surrounded by an illuminated surface. A simple shadow is one
which receives no light from the luminous body which causes it. A
simple shadow begins within the line which starts from the edge of
the luminous body _a b_.
124.
A simple shadow is one where no light at all interferes with it.
A compound shadow is one which is somewhat illuminated by one or
more lights.
125.
WHAT IS THE DIFFERENCE BETWEEN A SHADOW THAT IS INSEPARABLE FROM A
BODY AND A CAST SHADOW?
An inseparable shadow is that which is never absent from the
illuminated body. As, for instance a ball, which so long as it is in
the light always has one side in shadow which never leaves it for
any movement or change of position in the ball. A separate shadow
may be and may not be produced by the body itself. Suppose the ball
to be one braccia distant from a wall with a light on the opposite
side of it; this light will throw upon the wall exactly as broad a
shadow as is to be seen on the side of the ball that is turned
towards the wall. That portion of the cast shadow will not be
visible when the light is below the ball and the shadow is thrown up
towards the sky and finding no obstruction on its way is lost.
126.
HOW THERE ARE 2 KINDS OF LIGHT, ONE SEPARABLE FROM, AND THE OTHER
INSEPARABLE FROM BODIES.
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.