Making It

Variability of the eye.

1st. The pupil of the eye contracts, in proportion to the increase

of light which is reflected in it. 2nd. The pupil of the 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 them smaller still, because a smaller part of the pupil

would exercise its function.

[Footnote: 9. _buso_ in the Lomb. dialect is the same as _buco_.]

33.

When the eye, coming out of darkness suddenly sees a luminous body,

it will appear much larger at first sight than after long looking at

it. The illuminated object will look larger and more brilliant, when

seen with two eyes than with only one. A luminous object will appear

smaller in size, when the eye sees it through a smaller opening. A

luminous body of an oval form will appear rounder in proportion as

it is farther from the eye.

34.

Why when the eye has just seen the light, does the half light look

dark to it, and in the same way if it turns from the darkness the

half light look very bright?

35.

ON PAINTING.

If the eye, when [out of doors] in the luminous atmosphere, sees a

place in shadow, this will look very much darker than it really is.

This happens only because the eye when out in the air contracts the

pupil in proportion as the atmosphere reflected in it is more

luminous. And the more the pupil contracts, the less luminous do the

objects appear that it sees. But as soon as the eye enters into a

shady place the darkness of the shadow suddenly seems to diminish.

This occurs because the greater the darkness into which the pupil

goes the more its size increases, and this increase makes the

darkness seem less.

[Footnote 14: _La luce entrerà_. _Luce_ occurs here in the sense of

pupil of the eye as in no 51: C. A. 84b; 245a; I--5; and in many

other places.]

36.

ON PERSPECTIVE.

The eye which turns from a white object in the light of the sun and

goes into a less fully lighted place will see everything as dark.

And this happens either because the pupils of the eyes which have

rested on this brilliantly lighted white object have contracted so

much that, given at first a certain extent of surface, they will

have lost more than 3/4 of their size; and, lacking in size, they

are also deficient in [seeing] power. Though you might say to me: A

little bird (then) coming down would see comparatively little, and

from the smallness of his pupils the white might seem black! To this

I should reply that here we must have regard to the proportion of

the mass of that portion of the brain which is given up to the sense

of sight and to nothing else. Or--to return--this pupil in Man

dilates and contracts according to the brightness or darkness of

(surrounding) objects; and since it takes some time to dilate and

contract, it cannot see immediately on going out of the light and

into the shade, nor, in the same way, out of the shade into the

light, and this very thing has already deceived me in painting an

eye, and from that I learnt it.

37.

Experiment [showing] the dilatation and contraction of the pupil,

from the motion of the sun and other luminaries. In proportion as

the sky is darker the stars appear of larger size, and if you were

to light up the medium these stars would look smaller; and this

difference arises solely from the pupil which dilates and contracts

with the amount of light in the medium which is interposed between

the eye and the luminous body. Let the experiment be made, by

placing a candle above your head at the same time that you look at a

star; then gradually lower the candle till it is on a level with the

ray that comes from the star to the eye, and then you will see the

star diminish so much that you will almost lose sight of it.

[Footnote: No reference is made in the text to the letters on the

accompanying diagram.]

38.

The pupil of the eye, in the open air, changes in size with every

degree of motion from the sun; and at every degree of its changes

one and the same object seen by it will appear of a different size;

although most frequently the relative scale of surrounding objects

does not allow us to detect these variations in any single object we

may look at.

39.

The eye--which sees all objects reversed--retains the images for

some time. This conclusion is proved by the results; because, the

eye having gazed at light retains some impression of it. After

looking (at it) there remain in the eye image