The Notebooks of Leonardo Da Vinci (10 page)

[Footnote III: This text has already been published with some slight
variations in Dozio's pamphlet
Degli scritti e disegni di Leonardo
da Vinci
, Milan 1871, pp. 30—31. Dozio did not transcribe it from
the original MS. which seems to have remained unknown to him, but
from an old copy (MS. H. 227 in the Ambrosian Library).]

Prolegomena.

110.

You must first explain the theory and then the practice. First you
must describe the shadows and lights on opaque objects, and then on
transparent bodies.

Scheme of the books on Light and shade.

111.

[Having already treated of the nature of shadows and the way in
which they are cast [Footnote 2:
Avendo io tractato.
—We may
suppose that he here refers to some particular MS., possibly Paris
C.], I will now consider the places on which they fall; and their
curvature, obliquity, flatness or, in short, any character I may be
able to detect in them.]

Shadow is the obstruction of light. Shadows appear to me to be of
supreme importance in perspective, because, without them opaque and
solid bodies will be ill defined; that which is contained within
their outlines and their boundaries themselves will be
ill-understood unless they are shown against a background of a
different tone from themselves. And therefore in my first
proposition concerning shadow I state that every opaque body is
surrounded and its whole surface enveloped in shadow and light. And
on this proposition I build up the first Book. Besides this, shadows
have in themselves various degrees of darkness, because they are
caused by the absence of a variable amount of the luminous rays; and
these I call Primary shadows because they are the first, and
inseparable from the object to which they belong. And on this I will
found my second Book. From these primary shadows there result
certain shaded rays which are diffused through the atmosphere and
these vary in character according to that of the primary shadows
whence they are derived. I shall therefore call these shadows
Derived shadows because they are produced by other shadows; and the
third Book will treat of these. Again these derived shadows, where
they are intercepted by various objects, produce effects as various
as the places where they are cast and of this I will treat in the
fourth Book. And since all round the derived shadows, where the
derived shadows are intercepted, there is always a space where the
light falls and by reflected dispersion is thrown back towards its
cause, it meets the original shadow and mingles with it and modifies
it somewhat in its nature; and on this I will compose my fifth Book.
Besides this, in the sixth Book I will investigate the many and
various diversities of reflections resulting from these rays which
will modify the original [shadow] by [imparting] some of the various
colours from the different objects whence these reflected rays are
derived. Again, the seventh Book will treat of the various distances
that may exist between the spot where the reflected rays fall and
that where they originate, and the various shades of colour which
they will acquire in falling on opaque bodies.

Different principles and plans of treatment (112—116).

112.

First I will treat of light falling through windows which I will
call Restricted [Light] and then I will treat of light in the open
country, to which I will give the name of diffused Light. Then I
will treat of the light of luminous bodies.

113.

The conditions of shadow and light [as seen] by the eye are 3. Of
these the first is when the eye and the light are on the same side
of the object seen; the 2nd is when the eye is in front of the
object and the light is behind it. The 3rd is when the eye is in
front of the object and the light is on one side, in such a way as
that a line drawn from the object to the eye and one from the object
to the light should form a right angle where they meet.

114.

This is another section: that is, of the nature of a reflection
(from) an object placed between the eye and the light under various
aspects.

115.

As regards all visible objects 3 things must be considered. These
are the position of the eye which sees: that of the object seen
[with regard] to the light, and the position of the light which
illuminates the object,
b
is the eye,
a
the object seen,
c
the
light,
a
is the eye,
b
the illuminating body,
c
is the
illuminated object.

116.

Let
a
be the light,
b
the eye,
c
the object seen by the eye
and in the light. These show, first, the eye between the light and
the body; the 2nd, the light between the eye and the body; the 3rd
the body between the eye and the light,
a
is the eye,
b
the
illuminated object,
c
the light.

117.

The first kind of Light which may illuminate opaque bodies is called
Direct light—as that of the sun or any other light from a window or
flame. The second is Diffused [universal] light, such as we see in
cloudy weather or in mist and the like. The 3rd is Subdued light,
that is when the sun is entirely below the horizon, either in the
evening or morning.

118.

The lights which may illuminate opaque bodies are of 4 kinds. These
are: diffused light as that of the atmosphere, within our horizon.
And Direct, as that of the sun, or of a window or door or other
opening. The third is Reflected light; and there is a 4th which is
that which passes through [semi] transparent bodies, as linen or
paper or the like, but not transparent like glass, or crystal, or
other diaphanous bodies, which produce the same effect as though
nothing intervened between the shaded object and the light that
falls upon it; and this we will discuss fully in our discourse.

Definition of the nature of shadows (119—122).

119.

Shadow is the absence of light, merely the obstruction of the
luminous rays by an opaque body. Shadow is of the nature of
darkness. Light [on an object] is of the nature of a luminous body;
one conceals and the other reveals. They are always associated and
inseparable from all objects. But shadow is a more powerful agent
than light, for it can impede and entirely deprive bodies of their
light, while light can never entirely expel shadow from a body, that
is from an opaque body.

120.

Shadow is the diminution of light by the intervention of an opaque
body. Shadow is the counterpart of the luminous rays which are cut
off by an opaque body.

This is proved because the shadow cast is the same in shape and size
as the luminous rays were which are transformed into a shadow.

121.

Shadow is the diminution alike of light and of darkness, and stands
between darkness and light.

A shadow may be infinitely dark, and also of infinite degrees of
absence of darkness.

The beginnings and ends of shadow lie between the light and darkness
and may be infinitely diminished and infinitely increased. Shadow is
the means by which bodies display their form.

The forms of bodies could not be understood in detail but for
shadow.

122.

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.

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.

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.

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.

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?

Why, when you estimate the direction of an object with two sights
the nearer appears confused. I say that the eye projects an infinite
number of lines which mingle or join those reaching it which come to
it from the object looked at. And it is only the central and
sensible line that can discern and discriminate colours and objects;
all the others are false and illusory. And if you place 2 objects at
half an arm's length apart if the nearer of the two is close to the
eye its form will remain far more confused than that of the second;
the reason is that the first is overcome by a greater number of
false lines than the second and so is rendered vague.

Light acts in the same manner, for in the effects of its lines
(=rays), and particularly in perspective, it much resembles the eye;
and its central rays are what cast the true shadow. When the object
in front of it is too quickly overcome with dim rays it will cast a
broad and disproportionate shadow, ill defined; but when the object
which is to cast the shadow and cuts off the rays near to the place
where the shadow falls, then the shadow is distinct; and the more so
in proportion as the light is far off, because at a long distance
the central ray is less overcome by false rays; because the lines
from the eye and the solar and other luminous rays passing through
the atmosphere are obliged to travel in straight lines. Unless they
are deflected by a denser or rarer air, when they will be bent at
some point, but so long as the air is free from grossness or
moisture they will preserve their direct course, always carrying the
image of the object that intercepts them back to their point of
origin. And if this is the eye, the intercepting object will be seen
by its colour, as well as by form and size. But if the intercepting
plane has in it some small perforation opening into a darker
chamber—not darker in colour, but by absence of light—you will see
the rays enter through this hole and transmitting to the plane
beyond all the details of the object they proceed from both as to
colour and form; only every thing will be upside down. But the size
[of the image] where the lines are reconstructed will be in
proportion to the relative distance of the aperture from the plane
on which the lines fall [on one hand] and from their origin [on the
other]. There they intersect and form 2 pyramids with their point
meeting [a common apex] and their bases opposite. Let
a b
be the
point of origin of the lines,
d e
the first plane, and
c
the
aperture with the intersection of the lines;
f g
is the inner
plane. You will find that
a
falls upon the inner plane below at
g
, and
b
which is below will go up to the spot
f
; it will be
quite evident to experimenters that every luminous body has in
itself a core or centre, from which and to which all the lines
radiate which are sent forth by the surface of the luminous body and
reflected back to it; or which, having been thrown out and not
intercepted, are dispersed in the air.