The Notebooks of Leonardo Da Vinci (58 page)

The eyes in the Lion tribe have a large part of the head for their
sockets and the optic nerves communicate at once with the brain; but
the contrary is to be seen in man, for the sockets of the eyes are
but a small part of the head, and the optic nerves are very fine and
long and weak, and by the weakness of their action we see by day but
badly at night, while these animals can see as well at night as by
day. The proof that they can see is that they prowl for prey at
night and sleep by day, as nocturnal birds do also.

Advantages in the structure of the eye in certain animals (828-831).

828.

Every object we see will appear larger at midnight than at midday,
and larger in the morning than at midday.

This happens because the pupil of the eye is much smaller at midday
than at any other time.

In proportion as the eye or the pupil of the owl is larger in
proportion to the animal than that of man, so much the more light
can it see at night than man can; hence at midday it can see nothing
if its pupil does not diminish; and, in the same way, at night
things look larger to it than by day.

829.

The eyes of all animals have their pupils adapted to dilate and
diminish of their own accord in proportion to the greater or less
light of the sun or other luminary. But in birds the variation is
much greater; and particularly in nocturnal birds, such as horned
owls, and in the eyes of one species of owl; in these the pupil
dilates in such away as to occupy nearly the whole eye, or
diminishes to the size of a grain of millet, and always preserves
the circular form. But in the Lion tribe, as panthers, pards,
ounces, tigers, lynxes, Spanish cats and other similar animals the
pupil diminishes from the perfect circle to the figure of a pointed
oval such as is shown in the margin. But man having a weaker sight
than any other animal is less hurt by a very strong light and his
pupil increases but little in dark places; but in the eyes of these
nocturnal animals, the horned owl—a bird which is the largest of
all nocturnal birds—the power of vision increases so much that in
the faintest nocturnal light (which we call darkness) it sees with
much more distinctness than we do in the splendour of noon day, at
which time these birds remain hidden in dark holes; or if indeed
they are compelled to come out into the open air lighted up by the
sun, they contract their pupils so much that their power of sight
diminishes together with the quantity of light admitted.

Study the anatomy of various eyes and see which are the muscles
which open and close the said pupils of the eyes of animals.

[Footnote: Compare No. 24, lines 8 and fol.]

830.

a b n
is the membrane which closes the eye from below, upwards,
with an opaque film,
c n b
encloses the eye in front and behind
with a transparent membrane.

It closes from below, upwards, because it [the eye] comes downwards.

When the eye of a bird closes with its two lids, the first to close
is the nictitating membrane which closes from the lacrymal duct over
to the outer corner of the eye; and the outer lid closes from below
upwards, and these two intersecting motions begin first from the
lacrymatory duct, because we have already seen that in front and
below birds are protected and use only the upper portion of the eye
from fear of birds of prey which come down from above and behind;
and they uncover first the membrane from the outer corner, because
if the enemy comes from behind, they have the power of escaping to
the front; and again the muscle called the nictitating membrane is
transparent, because, if the eye had not such a screen, they could
not keep it open against the wind which strikes against the eye in
the rush of their rapid flight. And the pupil of the eye dilates and
contracts as it sees a less or greater light, that is to say intense
brilliancy.

831.

If at night your eye is placed between the light and the eye of a
cat, it will see the eye look like fire.

Remarks on the organs of speech

(832. 833).

832.

a e i o u
ba be bi bo bu
ca ce ci co cu
da de di do du
fa fe fi fo fu
ga ge gi go gu
la le li lo lu
ma me mi mo mu
na ne ni no nu
pa pe pi po pu
qa qe qi qo qu
ra re ri ro ru
sa se si so su
ta te ti to tu

The tongue is found to have 24 muscles which correspond to the six
muscles which compose the portion of the tongue which moves in the
mouth.

And when
a o u
are spoken with a clear and rapid pronunciation, it
is necessary, in order to pronounce continuously, without any pause
between, that the opening of the lips should close by degrees; that
is, they are wide apart in saying
a
, closer in saying
o
, and
much closer still to pronounce
u
.

It may be shown how all the vowels are pronounced with the farthest
portion of the false palate which is above the epiglottis.

833.

If you draw in breath by the nose and send it out by the mouth you
will hear the sound made by the division that is the membrane in
[Footnote 5: The text here breaks off.]…

On the conditions of sight (834. 835).

834.

I say that sight is exercised by all animals, by the medium of
light; and if any one adduces, as against this, the sight of
nocturnal animals, I must say that this in the same way is subject
to the very same natural laws. For it will easily be understood that
the senses which receive the images of things do not project from
themselves any visual virtue [Footnote 4: Compare No. 68.]. On the
contrary the atmospheric medium which exists between the object and
the sense incorporates in itself the figure of things, and by its
contact with the sense transmits the object to it. If the
object—whether by sound or by odour—presents its spiritual force
to the ear or the nose, then light is not required and does not act.
The forms of objects do not send their images into the air if they
are not illuminated [8]; and the eye being thus constituted cannot
receive that from the air, which the air does not possess, although
it touches its surface. If you choose to say that there are many
animals that prey at night, I answer that when the little light
which suffices the nature of their eyes is wanting, they direct
themselves by their strong sense of hearing and of smell, which are
not impeded by the darkness, and in which they are very far superior
to man. If you make a cat leap, by daylight, among a quantity of
jars and crocks you will see them remain unbroken, but if you do the
same at night, many will be broken. Night birds do not fly about
unless the moon shines full or in part; rather do they feed between
sun-down and the total darkness of the night.

[Footnote 8: See No. 58-67.]

No body can be apprehended without light and shade, and light and
shade are caused by light.

835.

Sight is better from a distance than near in those men who are
advancing in age, because the same object transmits a smaller
impression of itself to the eye when it is distant than when it is
near.

The seat of the common sense.

836.

The Common Sense, is that which judges of things offered to it by
the other senses. The ancient speculators have concluded that that
part of man which constitutes his judgment is caused by a central
organ to which the other five senses refer everything by means of
impressibility; and to this centre they have given the name Common
Sense. And they say that this Sense is situated in the centre of the
head between Sensation and Memory. And this name of Common Sense is
given to it solely because it is the common judge of all the other
five senses
i.e.
Seeing, Hearing, Touch, Taste and Smell. This
Common Sense is acted upon by means of Sensation which is placed as
a medium between it and the senses. Sensation is acted upon by means
of the images of things presented to it by the external instruments,
that is to say the senses which are the medium between external
things and Sensation. In the same way the senses are acted upon by
objects. Surrounding things transmit their images to the senses and
the senses transfer them to the Sensation. Sensation sends them to
the Common Sense, and by it they are stamped upon the memory and are
there more or less retained according to the importance or force of
the impression. That sense is most rapid in its function which is
nearest to the sensitive medium and the eye, being the highest is
the chief of the others. Of this then only we will speak, and the
others we will leave in order not to make our matter too long.
Experience tells us that the eye apprehends ten different natures of
things, that is: Light and Darkness, one being the cause of the
perception of the nine others, and the other its absence:— Colour
and substance, form and place, distance and nearness, motion and
stillness [Footnote 15: Compare No. 23.].

On the origin of the soul.

837.

Though human ingenuity may make various inventions which, by the
help of various machines answering the same end, it will never
devise any inventions more beautiful, nor more simple, nor more to
the purpose than Nature does; because in her inventions nothing is
wanting, and nothing is superfluous, and she needs no counterpoise
when she makes limbs proper for motion in the bodies of animals. But
she puts into them the soul of the body, which forms them that is
the soul of the mother which first constructs in the womb the form
of the man and in due time awakens the soul that is to inhabit it.
And this at first lies dormant and under the tutelage of the soul of
the mother, who nourishes and vivifies it by the umbilical vein,
with all its spiritual parts, and this happens because this
umbilicus is joined to the placenta and the cotyledons, by which the
child is attached to the mother. And these are the reason why a
wish, a strong craving or a fright or any other mental suffering in
the mother, has more influence on the child than on the mother; for
there are many cases when the child loses its life from them, &c.

This discourse is not in its place here, but will be wanted for the
one on the composition of animated bodies—and the rest of the
definition of the soul I leave to the imaginations of friars, those
fathers of the people who know all secrets by inspiration.

[Footnote 57:
lettere incoronate
. By this term Leonardo probably
understands not the Bible only, but the works of the early Fathers,
and all the books recognised as sacred by the Roman Church.] I leave
alone the sacred books; for they are supreme truth.

On the relations of the soul to the organs of sense.

838.

The soul seems to reside in the judgment, and the judgment would
seem to be seated in that part where all the senses meet; and this
is called the Common Sense and is not all-pervading throughout the
body, as many have thought. Rather is it entirely in one part.
Because, if it were all-pervading and the same in every part, there
would have been no need to make the instruments of the senses meet
in one centre and in one single spot; on the contrary it would have
sufficed that the eye should fulfil the function of its sensation on
its surface only, and not transmit the image of the things seen, to
the sense, by means of the optic nerves, so that the soul—for the
reason given above— may perceive it in the surface of the eye. In
the same way as to the sense of hearing, it would have sufficed if
the voice had merely sounded in the porous cavity of the indurated
portion of the temporal bone which lies within the ear, without
making any farther transit from this bone to the common sense, where
the voice confers with and discourses to the common judgment. The
sense of smell, again, is compelled by necessity to refer itself to
that same judgment. Feeling passes through the perforated cords and
is conveyed to this common sense. These cords diverge with infinite
ramifications into the skin which encloses the members of the body
and the viscera. The perforated cords convey volition and sensation
to the subordinate limbs. These cords and the nerves direct the
motions of the muscles and sinews, between which they are placed;
these obey, and this obedience takes effect by reducing their
thickness; for in swelling, their length is reduced, and the nerves
shrink which are interwoven among the particles of the limbs; being
extended to the tips of the fingers, they transmit to the sense the
object which they touch.

The nerves with their muscles obey the tendons as soldiers obey the
officers, and the tendons obey the Common [central] Sense as the
officers obey the general. [27] Thus the joint of the bones obeys
the nerve, and the nerve the muscle, and the muscle the tendon and
the tendon the Common Sense. And the Common Sense is the seat of the
soul [28], and memory is its ammunition, and the impressibility is
its referendary since the sense waits on the soul and not the soul
on the sense. And where the sense that ministers to the soul is not
at the service of the soul, all the functions of that sense are also
wanting in that man's life, as is seen in those born mute and blind.

[Footnote: The peculiar use of the words
nervo
,
muscolo
,
corda
,
senso comune
, which are here literally rendered by nerve,
muscle cord or tendon and Common Sense may be understood from lines
27 and 28.]

On involuntary muscular action.

839.

This is most plainly seen; for you will see palsied and shivering
persons move, and their trembling limbs, as their head and hands,
quake without leave from their soul and their soul with all its
power cannot prevent their members from trembling. The same thing
happens in falling sickness, or in parts that have been cut off, as
in the tails of lizards. The idea or imagination is the helm and
guiding-rein of the senses, because the thing conceived of moves the
sense. Pre-imagining, is imagining the things that are to be.
Post-imagining, is imagining the things that are past.