The Essays of Adam Smith

by Adam Smith

Colour, the visible, bears no resemblance to solidity, the tangible object. A man born blind, or who has lost his sight so early as to have no remembrance of visible objects, can form no idea or conception of colour. Touch alone can never help him to it. I have heard, indeed, of some persons who had lost their sight after the age of manhood, and who had learned to distinguish by the touch alone, the different colours of cloths or silks, the goods which it happened to be their business to deal in. The powers by which different bodies excite in the organs of Sight the Sensations of different colours, probably depend upon some difference in the nature, configuration, and arrangement of the parts which compose their respective surfaces. This difference may, to a very nice and delicate touch, make some difference in the feeling, sufficient to enable a person, much interested in the case, to make this distinction in some degree, though probably in a very imperfect and inaccurate one. A man born blind might possibly be taught to make the same distinctions. But though he might thus be able to name the different colours, which those different surfaces reflected, though he might thus have some imperfect notion of the remote causes of the Sensations, he could have no better idea of the Sensations themselves, than that other blind man, mentioned by Mr. Locke, had, who said that he imagined the Colour of Scarlet resembled the Sound of a Trumpet. A man born deaf may, in the same manner, be taught to speak articulately. He is taught how to shape and dispose of his organs, so as to pronounce each letter, syllable, and word. But still, though he may have some imperfect idea of the remote causes of 452 the Sounds which he himself utters, of the remote causes of the Sensations which he himself excites in other people; he can have none of those Sounds or Sensations themselves.

If it were possible, in the same manner, that a man could be born without the Sense of Touching, that of Seeing could never alone suggest to him the idea of Solidity, or enable him to form any notion of the external and resisting substance. It is probable, however, not only that no man, but that no animal was ever born without the Sense of Touching, which seems essential to, and inseparable from, the nature of animal life and existence. It is unnecessary, therefore, to throw away any reasoning, or to hazard any conjectures, about what might be the effects of what I look upon as altogether an impossible supposition. The eye when pressed upon by any external and solid substance, feels, no doubt, that pressure and resistance, and suggests to us (in the same manner as every other feeling part of the body) the external and independent existence of that solid substance. But in this case, the eye acts, not as the organ of Sight, but as an organ of Touch; for the eye possesses the Sense of Touching in common with almost all the other parts of the body.

The extension, figure, divisibility, and mobility of Colour, the sole object of Sight, though, on account of their correspondence and connection with the extension, figure, divisibility, and mobility of Solidity, they are called by the same name, yet seem to bear no sort of resemblance to their namesakes. As Colour and Solidity bear no sort of resemblance to one another, so neither can their respective modifications. Dr. Berkley very justly observes, that though we can conceive either a coloured or a solid line to be prolonged indefinitely, yet we cannot conceive the one to be added to the other. We cannot, even in imagination, conceive an object of Touch to be prolonged into an object of Sight, or an object of Sight into an object of Touch. The objects of Sight and those of Touch constitute two worlds, which, though they have a most important correspondence and connection with one another, bear no sort of resemblance to one another. The tangible world, as well as all the different parts which compose it, has three dimensions, Length, Breadth, and Depth. The visible world, as well as all the different parts which compose it, has only two, Length and Breadth. It presents to us only a plain or surface, which, by certain shades and combinations of Colour, suggests and represents to us (in the same manner as a picture does) certain tangible objects which have no Colour, and which therefore can bear no resemblance to those shades and combinations of Colour. Those shades and combinations suggest those different tangible objects as at different distances, according to certain rules of Perspective, which it is, perhaps, not very easy to say how it is that we learn, whether by some particular instinct, or by some application of either reason or experience, which 453 has become so perfectly habitual to us, that we are scarcely sensible when we make use of it.

The distinctness of this Perspective, the precision and accuracy with which, by means of it, we are capable of judging concerning the distance of different tangible objects, is greater or less, exactly in proportion as this distinctness, as this precision and accuracy, are of more or less importance to us. We can judge of the distance of near objects, of the chairs and tables for example, in the chamber where we are sitting, with the most perfect precision and accuracy; and if in broad daylight we ever stumble over any of them, it must be, not from any error in the Sight, but from some defect in the attention. The precision and accuracy of our judgment concerning such near objects are of the utmost importance to us, and constitute the great advantage which a man who sees has over one who is unfortunately blind. As the distance increases, the distinctness of this Perspective, the precision and accuracy of our judgment gradually diminish. Of the tangible objects which are even at the moderate distance of one, two, or three miles from the eye, we are frequently at a loss to determine which is nearest, and which remotest. It is seldom of much importance to us to judge with precision concerning the situation of the tangible objects which are even at this moderate distance. As the distance increases, our judgments become more and more uncertain; and at a very great distance, such as that of the fixed stars, it becomes altogether uncertain. The most precise knowledge of the relative situation of such objects could be of no other use to the enquirer than to satisfy the most unnecessary curiosity.

The distances at which different men can by Sight distinguish, with some degree of precision, the situation of the tangible objects which the visible ones represent, is very different; and this difference, though it, no doubt, may sometimes depend upon some difference in the original configuration of their eyes, yet seems frequently to arise altogether from the different customs and habits which their respective occupations have led them to contract. Men of letters, who live much in their closets, and have seldom occasion to look at very distant objects, are seldom far-sighted. Mariners, on the contrary, almost always are; those especially who have made many distant voyages, in which they have been the greater part of their time out of sight of land, and have in daylight been constantly looking out towards the horizon for the appearance of some ship, or of some distant shore. It often astonishes a landsman to observe with what precision a sailor can distinguish in the offing, not only the appearance of a ship which is altogether invisible to the landsman, but the number of her masts, the direction of her course, and the rate of her sailing. If she is a ship of his acquaintance, he frequently can tell her name, before the landsman has been able to discover even the appearance of a ship.

454 Visible objects, Colour, and all its different modifications, are in themselves mere shadows or pictures, which seem to float, as it were, before the organ of Sight. In themselves, and independent of their connection with the tangible objects which they represent, they are of no importance to us, and can essentially neither benefit us nor hurt us. Even while we see them we are seldom thinking of them. Even when we appear to be looking at them with the greatest earnestness, our whole attention is frequently employed, not upon them, but upon the tangible objects represented by them.

It is because almost our whole attention is employed, not upon the visible and representing, but upon the tangible and represented objects, that in our imaginations we are apt to ascribe to the former a degree of magnitude which does not belong to them, but which belongs altogether to the latter. If you shut one eye, and hold immediately before the other a small circle of plain glass, of not more than half an inch in diameter, you may see through that circle the most extensive prospects; lawns and woods, and arms of the sea, and distant mountains. You are apt to imagine that the Landscape which is thus presented to you, that the visible Picture which you thus see, is immensely great and extensive. The tangible objects which this visible Picture represents, undoubtedly are so. But the visible Picture which represents them can be no greater than the little visible circle through which you see it. If while you are looking through this circle, you could conceive a fairy hand and a fairy pencil to come between your eye and the glass, that pencil could delineate upon that little glass the outline of all those extensive lawns and woods, and arms of the sea, and distant mountains, in the full and the exact dimensions with which they are really seen by the naked eye.

Every visible object which covers from the eye any other visible object, must appear at least as large as that other visible object. It must occupy at least an equal portion of that visible plain or surface which is at that time presented to the eye. Opticians accordingly tell us, that all the visible objects which are seen under equal angles must to the eye appear equally large. But the visible object, which covers from the eye any other visible object, must necessarily be seen under angles at least equally large as those under which that other object is seen. When I hold up my finger, however, before my eye, it appears to cover the greater part of the visible chamber in which I am sitting. It should therefore appear as large as the greater part of that visible chamber. But because I know that the tangible finger bears but a very small proportion to the greater part of the tangible chamber, I am apt to fancy that the visible finger bears but a like proportion to the greater part of the visible chamber. My judgment corrects my eyesight, and, in my fancy, reduces the visible object, which represents the little tangible one, below its real visible dimensions; and, on the 455 contrary, it augments the visible object which represents the great tangible one a good deal beyond those dimensions. My attention being generally altogether occupied about the tangible and represented, and not at all about the visible and representing objects, my careless fancy bestows upon the latter a proportion which does not in the least belong to them, but which belongs altogether to the former.

It is because the visible object which covers any other visible object must always appear at least as large as that other object, that opticians tell us that the sphere of our vision appears to the eye always equally large; and that when we hold our hand before our eye in such a manner that we see nothing but the inside of the hand, we still see precisely the same number of visible points, the sphere of our vision is still as completely filled, the retina of the eye is as entirely covered with the object which is thus presented to it, as when we survey the most extensive horizon.

A young gentleman who was born with a cataract upon each of his eyes, was, in one thousand seven hundred and twenty-eight, couched by Mr. Cheselden, and by that means for the first time made to see distinctly. ‘At first,’ says the operator, ‘he could bear but very little sight, and the things he saw he thought extremely large; but upon seeing things larger, those first seen he conceived less, never being able to imagine any lines beyond the bounds he saw; the room he was in, he said, he knew to be but part of the house, yet he could not conceive that the whole house would look bigger.’ It was unavoidable that he should at first conceive, that no visible object could be greater, could present to his eye a greater number of visible points, or could more completely fill the comprehension of that organ, than the narrowest sphere of his vision. And when that sphere came to be enlarged, he still could not conceive that the visible objects which it presented could be larger than those which he had first seen. He must probably by this time have been in some degree habituated to the connection between visible and tangible objects, and enabled to conceive that visible object to be small which represented a small tangible object; and that to be great, which represented a great one. The great objects did not appear to his sight greater than the small ones had done before; but the small ones, which, having filled the whole sphere of his vision, had before appeared as large as possible, being now known to represent much smaller tangible objects, seemed in his conception to grow smaller. He had begun now to employ his attention more about the tangible and represented, than about the visible and representing objects; and he was beginning to ascribe to the latter the proportions and dimensions which properly belonged altogether to the former.