The Notebooks of Leonardo Da Vinci Read Online Free PDF Page B

eye expands
in proportion to the diminution in the day light, or any other
light, that is reflected in it. 3rd. [Footnote: 8. The subject of
this third proposition we find fully discussed in MS. G. 44a.]. The
eye perceives and recognises the objects of its vision with greater
intensity in proportion as the pupil is more widely dilated; and
this can be proved by the case of nocturnal animals, such as cats,
and certain birds—as the owl and others—in which the pupil varies
in a high degree from large to small, &c., when in the dark or in
the light. 4th. The eye [out of doors] in an illuminated atmosphere
sees darkness behind the windows of houses which [nevertheless] are
light. 5th. All colours when placed in the shade appear of an equal
degree of darkness, among themselves. 6th. But all colours when
placed in a full light, never vary from their true and essential
hue.
    25.
OF THE EYE.
    Focus of sight.
    If the eye is required to look at an object placed too near to it,
it cannot judge of it well—as happens to a man who tries to see the
tip of his nose. Hence, as a general rule, Nature teaches us that an
object can never be seen perfectly unless the space between it and
the eye is equal, at least, to the length of the face.
    Differences of perception by one eye and by both eyes (26-29).
    26.
OF THE EYE.
    When both eyes direct the pyramid of sight to an object, that object
becomes clearly seen and comprehended by the eyes.
    27.
    Objects seen by one and the same eye appear sometimes large, and
sometimes small.
    28.
    The motion of a spectator who sees an object at rest often makes it
seem as though the object at rest had acquired the motion of the
moving body, while the moving person appears to be at rest.
ON PAINTING.
    Objects in relief, when seen from a short distance with one eye,
look like a perfect picture. If you look with the eye a , b at
the spot c , this point c will appear to be at d , f , and if
you look at it with the eye g , h will appear to be at m . A
picture can never contain in itself both aspects.
    29.
    Let the object in relief t be seen by both eyes; if you will look
at the object with the right eye m , keeping the left eye n shut,
the object will appear, or fill up the space, at a ; and if you
shut the right eye and open the left, the object (will occupy the)
space b ; and if you open both eyes, the object will no longer
appear at a or b , but at e , r , f . Why will not a picture
seen by both eyes produce the effect of relief, as [real] relief
does when seen by both eyes; and why should a picture seen with one
eye give the same effect of relief as real relief would under the
same conditions of light and shade?
    [Footnote: In the sketch, m is the left eye and n the right,
while the text reverses this lettering. We must therefore suppose
that the face in which the eyes m and n are placed is opposite
to the spectator.]
    30.
    The comparative size of the image depends on the amount of light
(30-39).
    The eye will hold and retain in itself the image of a luminous body
better than that of a shaded object. The reason is that the eye is
in itself perfectly dark and since two things that are alike cannot
be distinguished, therefore the night, and other dark objects cannot
be seen or recognised by the eye. Light is totally contrary and
gives more distinctness, and counteracts and differs from the usual
darkness of the eye, hence it leaves the impression of its image.
    31.
    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.
    32.
    The pupil which is largest will see objects the largest. This is
evident when we look at luminous bodies, and particularly at those
in the sky. When the eye comes out of darkness and suddenly looks up
at these bodies, they at first appear larger and then diminish; and
if you were to look at those bodies through a small opening, you
would see