The Notebooks of Leonardo Da Vinci — Complete
obliquely placed ones it appears foreshortened; to those in the
middle, the window shows its full size, to the oblique ones it
appears smaller; the one in the middle faces the whole hemisphere
that is _e f_ and those on the side have only a strip; that is _q r_
faces _a b_; and _m n_ faces _c d_; the body in the middle having a
larger quantity of light than those at the sides is lighted from a
point much below its centre, and thus the shadow is shorter. And the
pyramid _g_ 4 goes into _l y_ exactly as often as _a b_ goes into _e
f_. The axis of every derivative shadow passes through 6 1/2
[Footnote 31: _passa per_ 6 1/2 (passes through 6 1/2). The meaning
of these words is probably this: Each of the three axes of the
derived shadow intersects the centre (_mezzo_) of the primary shadow
(_ombra originale_) and, by prolongation upwards crosses six lines.
This is self evident only in the middle diagram; but it is equally
true of the side figures if we conceive of the lines 4 _f_, _x n v
m_, _y l k v_, and 4 _e_, as prolonged beyond the semicircle of the
horizon.] and is in a straight line with the centre of the primary
shadow, with the centre of the body casting it and of the derivative
light and with the centre of the window and, finally, with the
centre of that portion of the source of light which is the celestial
hemisphere, _y h_ is the centre of the derived shade, _l h_ of the
primary shadow, _l_ of the body throwing it, _l k_ of the derived
light, _v_ is the centre of the window, _e_ is the final centre of
the original light afforded by that portion of the hemisphere of the
sky which illuminates the solid body.
[Footnote: Compare the diagram on Pl. IV, No. 3. In the original
this drawing is placed between lines 3 and 22; the rest, from line 4
to line 21, is written on the left hand margin.]
174.
THE FARTHER THE DERIVED SHADOW IS PROLONGED THE LIGHTER IT BECOMES.
You will find that the proportion of the diameter of the derived
shadow to that of the primary shadow will be the same as that
between the darkness of the primary shadow and that of the derived
shadow.
[Footnote 6: Compare No. 177.] Let _a b_ be the diameter of the
primary shadow and _c d_ that of the derived shadow, I say that _a
b_ going, as you see, three times into _d c_, the shadow _d c_ will
be three times as light as the shadow _a b_. [Footnote 8: Compare
No. 177.]
If the size of the illuminating body is larger than that of the
illuminated body an intersection of shadow will occur, beyond which
the shadows will run off in two opposite directions as if they were
caused by two separate lights.
On the relative intensity of derived shadows (175-179).
175.
ON PAINTING.
The derived shadow is stronger in proportion as it is nearer to its
place of origin.
176.
HOW SHADOWS FADE AWAY AT LONG DISTANCES.
Shadows fade and are lost at long distances because the larger
quantity of illuminated air which lies between the eye and the
object seen tints the shadow with its own colour.
177.
_a b_ will be darker than _c d_ in proportion as _c d_ is broader
than _a b_.
[Footnote: In the original MS. the word _lume_ (light) is written at
the apex of the pyramid.]
178.
It can be proved why the shadow _o p c h_ is darker in proportion as
it is nearer to the line _p h_ and is lighter in proportion as it is
nearer to the line _o c_. Let the light _a b_, be a window, and let
the dark wall in which this window is, be _b s_, that is, one of the
sides of the wall.
Then we may say that the line _p h_ is darker than any other part of
the space _o p c h_, because this line faces the whole surface in
shadow of [Footnote: In the original the diagram is placed between
lines 27 and 28.] the wall _b s_. The line _o c_ is lighter than the
other part of this space _o p c h_, because this line faces the
luminous space _a b_.
Where the shadow is larger, or smaller, or equal the body which
casts it.
[First of the character of divided lights. [Footnote 14: _lumi
divisi_. The text here breaks off abruptly.]
OF THE COMPOUND SHADOW _F, R, C, H_ CAUSED BY A SINGLE LIGHT.
The shadow _f r c h_ is under such conditions as that where it is
farthest from its inner side it loses depth in proportion. To prove
this:
Let _d a_, be the light and _f n_ the solid body, and let _a e_ be
one of the side walls of the window that is _d a_. Then I
say--according to the 2nd [proposition]: that the surface of any
body is affected by the tone of the objects surrounding it,--that
the side _r c_, which faces the dark wall _a e_ must participate of
its darkness and, in the same way that the outer surface which faces
the light _d a_ participates of the light; thus we get the outlines
of the extremes on each side of the centre included between them.]
This is divided into four parts. The first the extremes, which
include the compound shadow, secondly the compound shadow between
these extremes.
179.
THE ACTION OF THE LIGHT AS FROM ITS CENTRE.
If it were the whole of the light that caused the shadows beyond the
bodies placed in front of it, it would follow that any body much
smaller than the light would cast a pyramidal shadow; but experience
not showing this, it must be the centre of the light that produces
this effect.
[Footnote: The diagram belonging to this passage is between lines 4
and 5 in the original. Comp. the reproduction Pl. IV, No. 4. The
text and drawing of this chapter have already been published with
tolerable accuracy. See M. JORDAN: "_Das Malerbuch des Leonardo da
Vinci_". Leipzig 1873, P. 90.]
PROOF.
Let _a b_ be the width of the light from a window, which falls on a
stick set up at one foot from _a c_ [Footnote 6: _bastone_ (stick).
The diagram has a sphere in place of a stick.]. And let _a d_ be the
space where all the light from the window is visible. At _c e_ that
part of the window which is between _l b_ cannot be seen. In the
same way _a m_ cannot be seen from _d f_ and therefore in these two
portions the light begins to fail.
Shadow as produced by two lights of different size (180. 181).
180.
A body in light and shade placed between two equal lights side by
side will cast shadows in proportion to the [amount of] light. And
the shadows will be one darker than the other in proportion as one
light is nearer to the said body than the other on the opposite
side.
A body placed at an equal distance between two lights will cast two
shadows, one deeper than the other in proportion, as the light which
causes it is brighter than the other.
[Footnote: In the MS. the larger diagram is placed above the first
line; the smaller one between l. 4 & 5.]
181.
A light which is smaller than the body it illuminates produces
shadows of which the outlines end within [the surface of] the body,
and not much compound shadow; and falls on less than half of it. A
light which is larger than the body it illuminates, falls on more
than half of it, and produces much compound shadow.
The effect of light at different distances.
182.
OF THE SHADOW CAST BY A BODY PLACED BETWEEN 2 EQUAL LIGHTS.
A body placed between 2 equal lights will cast 2 shadows of itself
in the direction of the lines of the 2 lights; and if you move this
body placing it nearer to one of the lights the shadow cast towards
the nearer light will be less deep than that which falls towards the
more distant one.
Further complications in the derived shadows (183-187).
183.
The greatest depth of shadow is in the simple derived shadow because
it is not lighted by either of the two lights _a b, c d_.
The next less deep shadow is the derived shadow _e f n_; and in this
the shadow is less by half, because it is illuminated by a single
light, that is _c d_.
This is uniform in natural tone because it is lighted throughout by
one only of the two luminous bodies [10]. But it varies with the
conditions of shadow, inasmuch as the farther it is away from the
light the less it is illuminated by it [13].
The third degree of depth is the middle shadow [Footnote 15: We
gather from what follows that _q g r_ here means _ombra media_ (the
middle shadow).]. But this is not uniform in natural tone; because
the nearer it gets to the simple derived shadow the deeper it is
[Footnote 18: Compare lines 10-13], and it is the uniformly gradual
diminution by increase of distance which is what modifies it
[Footnote 20: See Footnote 18]: that is to say the depth of a shadow
increases in proportion to the distance from the two lights.
The fourth is the shadow _k r s_ and this is all the darker in
natural tone in proportion as it is nearer to _k s_, because it gets
less of the light _a o_, but by the accident [of distance] it is
rendered less deep, because it is nearer to the light _c d_, and
thus is always exposed to both lights.
The fifth is less deep in shadow than either of the others because
it is always entirely exposed to one of the lights and to the whole
or part of the other; and it is less deep in proportion as it is
nearer to the two lights, and in proportion as it is turned towards
the outer side _x t_; because it is more exposed to the second light
_a b_.
[Footnote: The diagram to this section is given on Pl. V. To the
left is the facsimile of the beginning of the text belonging to it.]
184.
OF SIMPLE SHADOWS.
Why, at the intersections _a_, _b_ of the two compound shadows _e f_
and _m e_, is a simple shadow pfoduced as at _e h_ and _m g_, while
no such simple shadow is produced at the other two intersections _c
d_ made by the very same compound shadows?
ANSWER.
Compound shadow are a mixture of light and shade and simple shadows
are simply darkness. Hence, of the two lights _n_ and _o_, one falls
on the compound shadow from one side, and the other on the compound
shadow from the other side, but where they intersect no light falls,
as at _a b_; therefore it is a simple shadow. Where there is a
compound shadow one light or the other falls; and here a difficulty
arises for my adversary since he says that, where the compound
shadows intersect, both the lights which produce the shadows must of
necessity fall and therefore these shadows ought to be neutralised;
inasmuch as the two lights do not fall there, we say that the shadow
is a simple one and where only one of the two lights falls, we say
the shadow is compound, and where both the lights fall the shadow is
neutralised; for where both lights fall, no shadow of any kind is
produced, but only a light background limiting the shadow. Here I
shall say that what my adversary said was true: but he only mentions
such truths as are in his favour; and if we go on to the rest he
must conclude that my proposition is true. And that is: That if both
lights fell on the point of intersection, the shadows would be
neutralised. This I confess to be true if [neither of] the two
shadows fell in the same spot; because, where a shadow and a light
fall, a compound shadow is produced, and wherever two shadows or two
equal lights fall, the shadow cannot vary in any part of it, the
shadows and the lights both being equal. And this is proved in the
eighth [proposition] on proportion where it is said that if a given
quantity has a single unit of force and resistance, a double
quantity will have double force and double resistance.
DEFINITION.
The intersection _n_ is produced by the shadows caused by the light
_b_, because this light _b_ produces the shadow _x b_, and the
shadow _s b_, but the intersection _m_ is produced by the light _a_
which causes the shadow _s a_, and the shadow _x a_.
But if you uncover both the lights _a b_, then you get the two
shadows _n m_ both at once, and besides these, two other, simple
shadows are produced at _r o_ where neither of the two lights falls