Aristotle · a new plain-English translation from the original language
1| for in the sleep that follows the taking of food, dreams are least likely to be seen; and it is precisely then that the soul happens to be most in motion, on account of the food that has been brought into it. And a dream occurs whenever sleep comes upon people while they are thinking and setting things before their eyes; this is why we see above all the things that we are doing, or are about to do, or wish to do, for it is about these above all that reasonings and images arise most often. And better people for this reason see better dreams, because even while awake they think about better things, whereas those in a worse condition, either in thought or in body, see worse ones. For the body's condition too contributes to the imagery of dreams, since in the sick person the settled dispositions of thought are also poor, and further, because of the disturbance present in the body, the soul is unable to be at rest. Melancholics for this reason start up suddenly in their sleep, because, there being more heat than is fitting, the soul is in motion beyond what is moderate, and since the motion is more violent, they are unable to sleep. Problems Concerning the Eyes Why, when we rub the eye, do we stop sneezing? Is it because a passage for the moisture opens up in this way? For the eye weeps after rubbing, and sneezing occurs on account of an excess of moisture. Or is it because the lesser heat is destroyed by the greater? The eye, when rubbed, takes on more heat than that in the nose. This is why, too, if one rubs the nose itself, the sneezing stops.
2| Why do people see more precisely with one eye than with two? Is it because with two eyes there come to be more motions, as happens with people who squint? So the motion is not one, whereas with a single eye it is simple. That is why they see less precisely with two. Why do people, when angry, most flush at the eyes, but when ashamed, at the ears? Is it because in shame the parts around the face grow cold (for shame lives in the eyes), so that they cannot look one in the face? And fear is a kind of cold in that region too. But the back changes into the opposite state from the front. The ears lie opposite the front; that is why people flush most there when ashamed. And in itching, the help rushes to the part that is more perceptive and more capable of motion, as though it were being wronged; for in frightened people the blood most fails to reach that part. Why, when one eye is covered, does the other stare more fixedly? Is it because the principles of the eyes are suspended from the same source? So when one eye moves, the common principle moves too, and when it moves, the other eye moves as well. So when one eye is taken out of use, the motion set going in the common source moves the other, so that it is able to stare more fixedly.
3| Why are people blind from birth not bald? Is it because it is an excess of moisture in the region around the head that damages the eyes? That is why physicians, in cases of eye-fluxes, cauterize the veins around the temples, thereby thickening the passages of the fluids, and scrape the head, cutting through the skin on it. Since, then, it is the residue forming in the head that damages the eyes, this same residue, were it to accumulate there from birth in greater quantity, would prevent them from occurring at all — but since hair grows out of residues, and this residue is present in great quantity from birth in the heads of the blind, it is reasonable that they are not bald. Why do people with protruding eyes suffer more from smoke? Is it because whatever projects is struck first and fastest?
4| Why can we turn both our eyes together to the right, and to the left, and toward the nose, and turn one eye alone either to the left or to the right, but are unable to turn one to the right and the other to the left at the same time? And likewise for down and up: for we can move them together to the same place, but not separately. Is it because the eyes, though two, are nonetheless bound together from a single source? Now with all such things, when one extremity moves, the other must follow to the same place, since for the one extremity the other extremity is its starting point. If, then, it is impossible for one thing to move in opposite directions at once, it is also impossible for the eyes to do so. For the extremities would be moving in opposite directions if one moved up and the other down, and the shared starting-point would have to follow both, which is impossible. Squinting occurs in the eyes because the eyeballs have a starting-point, and are able to turn as far as up and down and to the side. So whenever the eyes, holding themselves in a like position relative to one another, and taking their direction of sight midway between moving up and down, and to the side, from the same point relative to themselves, they are then free of squint and most fixed in position;
5| but those which take their direction of sight from the same point, though free of squint, differ from one another. Yet in those who cast their gaze upward, part of the black is hidden and the white shows, as with people about to have a fit; others turn to the side, as maniacs do, and others toward the nostrils, as with tragic masks and with sour-tempered people — for such a gaze looks brooding. As for those whose eyeballs, whether positioned unlike one another, take their direction of sight from the same point, or positioned alike, do not take it from the same point — these people are cross-eyed; that is why they peer from under their brows and draw their eyes together. For they are trying to bring the eyeball into the same configuration; so they let one eye be and reshape the other. For if the lines of sight are not set at the very same point, the eyes must be crossed. For just as, for people who press a finger under the eye, [the one thing] appears double (since in their case too the starting-point has been shifted), the same happens for these people as well. So if the eye is moved upward, the boundary of the field of sight comes to lie below, and if downward, the boundary comes to lie above. In a single eye that is being shifted, what is seen appears, for these reasons, to move up or down, because the direction of sight moves too; but it does not appear double unless there are two separate directions of sight, and this is what causes squinting.
6| Such is the squint that occurs in a person with one weak eye, so that two images appear; but the squint that occurs by position happens because the eye is not set along the middle of the socket. Why do the shortsighted write small letters? For it seems strange that people who do not see sharply should perform a task belonging to people who see sharply. Is it that small things appear large if they are close, and shortsighted people write bringing the page close? Or is it because they write while drawing their eyelids together? For owing to the weakness of their sight, if they write with their eyes wide open, the sight is scattered and sees dimly, whereas drawn together in this way it strikes its object as a compact mass; and making the angle of vision small, it of necessity makes them write small. Why do some people, after an attack of ophthalmia, see more sharply? Is it because their eyes have been cleared out? For often the density on the outside blocks the sight, and this is dissolved once tears have flowed. That is why what stings is beneficial, such as onion, while the other kind is harmful, such as marjoram. Why are people less affected when using a single eye? Is it because the soul is affected less, so that the affection is smaller? Why do things appear double to people who cross their fingers? Is it because the motion from each eye does not arrive at the same point? So the soul, just as it thinks seeing twice is seeing two things, thinks the same in the case of the fingers crossed over one another: the one thing seems two, as though a single thing were touched twice.
7| Why do the perceptions on the right not differ from those on the left, though in everything else the right is superior? Is it owing to habit, because we are accustomed from the start to perceive equally with both? And the right seems to differ by habit, since people who are trained become ambidextrous. Or is it because perceiving is a kind of being acted upon, and the right differs by being more capable of acting and less liable to be acted upon than the left? Why is the right superior in everything else, but the senses are alike? Is it because in the senses we are trained equally on both sides by habit? Further, perceiving is a kind of being acted upon, whereas the superiority of the right lies in acting, not in being acted upon. Why is exercise disadvantageous for sharpness of sight? Is it because exercise dries out the eye, just as it does the rest of the body? And dryness hardens all skin, including the skin over the pupil. That is why the elderly do not see sharply: for old people's skin is hard, and wrinkled as well, so that the sight is covered over.
8| Why do shortsighted people, though they do not see sharply, write small letters? And yet to make out something small belongs to a person who sees sharply. Is it because, their sight being weak, they draw their eyelids together into a narrow slit? For sight going out as a compact mass sees better, whereas with the eye wide open it is scattered. So because of their weakness they draw the eyelid together into a narrow slit, but because they see out of a narrow slit they see a small extent; and whatever extent they see, that much they also write. Why do the shortsighted see by drawing their eyelids together? Is it owing to the weakness of their sight — just as people who bring their hand close for things far off, so too they bring their eyelids close for near things, as though using a hand? They do this so that the sight may go out more as a compact mass, going out through a smaller opening, and not be scattered by going out at once from an eye wide open; for the more compact sight sees a greater extent.
9| Why is it that when we move the eye to the side, one thing does not appear as two? Is it because the starting-point remains on the same line? Two appear when the line changes upward or downward, but moving sideways makes no difference unless it moves upward at the same time. Why, then, does it happen with sight that one thing appears as two if the eyes are set in some particular way relative to each other, but with the other senses it does not happen? Or does it in fact happen with touch too, one thing appearing as two through the crossing-over of the fingers? But it does not happen with the other senses, because they do not perceive things extended outward, nor as two. And this happens [because of] this, which is also why it happens with the fingers, for touch here imitates sight. Why is it that the left side of the rest of the body is weaker, but not so with the eyes — rather, they see equally sharply? Is it because the right parts differ in being more capable of acting, while in being acted upon they do not differ? And seeing is a case of being acted upon.
10| Why is it that we are put in a worse condition by staring intently at other things, but in a better condition by staring at green, grass-like things, such as vegetables and things like them? Is it because we are least able to stare at white and black — for both harm the sight — while colors of this kind occupy a mean between the two? Hence, since the sight is only moderately affected, we are not overtaxed by it, and are put in a better condition. Perhaps, too, just as with our bodies we are worse off from exerting ourselves too violently, while the mean disposes us best, the same holds for sight in the same way. For in staring at solid objects we tax the sight, while with fluid ones, since nothing obstructs it, we do not overtax it. But green things are solid in a moderate degree, and there is enough fluidity in them; hence they do no harm, and they compel the sight to remain fixed on them because the blend of the color is well-proportioned relative to the sight. Why is it that we see other things better with both eyes, but see straight lines of writing better by bringing one eye close to the letters? Is it because both lines of sight, when they converge, produce confusion, as those concerned with optics say, but when we look with one eye, the sight is directed toward a straight line, as toward a ruler, and so what is straight appears more clearly?
11| Why does smoke sting the eyes more than other things do? Is it because they alone are weakest? For the internal parts of the body are always weakest. A sign of this is that vinegar and each of the pungent things do not sting the outer flesh, but do sting the inner, because that is the most porous part of the body and has the most passages; for the visual rays issue out through certain passages, so that whatever is most stinging drops away from the flesh onto the inner part. The same is true of onion, and of whatever else stings the eyes. Oil does so most of all the fluids, because it has the finest particles; being such, it penetrates through the passages, whereas vinegar acts as a remedy for the rest of the flesh. Why is it that the eye alone of the body, though it is weakest, does not feel cold? Is it because the eye is fatty, and has no flesh at all? And things of this kind do not feel cold. It is not, at any rate, because sight is fire that it does not feel cold, for the fire it consists of is not of the kind that produces heat.
12| Why are tears warm if we shed them weeping, but cold if we shed them from straining the eyes? Is it because what is unconcocted is cold, and what has been concocted is warm? And softness in general always comes from lack of concoction, and in those who strain their eyes the tear is unconcocted; hence it is cold. This is also why physicians think that cold sweats are a sign of serious illness, while warm ones are, on the contrary, signs of recovery. For when the residue is copious, the internal heat cannot concoct it, so that it must be cold; but when it is scanty, the heat masters it. And illnesses arise out of residues. Why is it that, though the parts on the right are more easily moved, the left eye contracts more than the right? Is it because everything on the left is more fluid than on the right, and the more fluid parts are naturally more prone to contract? And besides, the eye is able to bring more effect to bear on the right, since the left eye can also act by itself.
13| Why is it that both the short-sighted person and the old person, though each is affected by a certain weakness of the eyes, behave oppositely — the one brings the object close if he wants to see it, the other holds it far away? Is it because the weakness that attends them is not alike? For the old person is unable to see the object itself; wherever his sight happens to converge, he draws the thing he is viewing away, precisely because he is thereby going to see it best; and it converges at a distance. The short-sighted person sees the object itself, but can no longer judge which parts of what is seen are concave and which are convex, and is deceived about these. Concavities and convexities are judged chiefly by the play of light. From a distance, then, he cannot make out by the light how it falls upon the visible object; from close up it is more evident to him. Why is it that of animals a human being alone, or most of all, has his eyes turned askew? Is it because a human being alone, or most of all, becomes subject to epileptic seizure in youth, which is also when the eyes come to be turned askew in all who are affected? Why do humans alone of the other animals have their eyes turned askew? Is it because the distance between the eyes is least in humans, and they lie on a straight line, so that any lack of proper alignment becomes very conspicuous? Or is it because in other animals the eyes are more uniformly one color, whereas if the eye were a single color throughout, there would be no distortion visible? Or is it because humans alone in their kind become subject to epileptic seizures, and the seizure, when it occurs, produces a distortion, just as it does in other parts of the body too? But in some the distortion comes on quite late, namely in those whose affliction is late in onset.