the regular variety of colours which they | is taught most artfully to lie and dissemble, exhibit; the invariable laws according to which they are acted upon by other bodies, in their reflections, inflections, and refractions, without the least change of their original properties; and the facility with which they pervade bodies of great density and of the closest texture, without resistance, without crowding or disturbing one another, without giving the least sensible impulse to the lightest bodies. The structure of the eye, and of all its appurtenances, the admirable contrivances of nature for performing all its various external and internal motions, and the variety in the eyes of different animals, suited to their several natures and ways of life, clearly demonstrate this organ to be a masterpiece of Nature's work. And he must be very ignorant of what hath been discovered about it, or have a very strange cast of understanding, who can seriously doubt whether or not the rays of light and the eye were made for one another, with consummate wisdom, and perfect skill in optics If we shall suppose an order of beings, endued with every human faculty but that of sight, how incredible would it appear to such beings, accustomed only to the slow informations of touch, that, by the addition of an organ, consisting of a ball and socket of an inch diameter, they might be enabled, in an instant of time, without changing their place, to perceive the disposition of a whole army or the order of a battle, the figure of a magnificent palace or all the variety of a landscape! If a man were by feeling to find out the figure of the peak of Teneriffe, or even of St Peter's Church at Rome, it would be the work of a lifetime. It would appear still more incredible to such beings as we have supposed, if they were informed of the discoveries which may be made by this little organ in things far beyond the reach of any other sense: that by means of it we can find our way in the pathless ocean; that we can traverse the globe of the earth, determine its figure and dimensions, and delineate every region of it;-yea, that we can measure the planetary orbs, and make discoveries in the sphere of the fixed stars. Would it not appear still more astonishing to such beings, if they should be farther informed, that, by means of this same organ, we can perceive the tempers and dispositions, the passions and affections, of our fellow-creatures, even when they want most to conceal them?-that, when the tongue The thing would be impossible. Let any one try by touch to ascertain the figure of a room, with which he is previously unacquainted, and not alto. gether of the usual shape, and he will find that touch will afford him but slender aid -H. the hypocrisy should appear in the countenance to a discerning eye ?-and that, by this organ, we can often perceive what is straight and what is crooked in the mind as well as in the body? How many mysterious things must a blind man believe, if he will give credit to the relations of those that see? Surely he needs as strong a faith as is required of a good Christian. It is not therefore without reason that the faculty of seeing is looked upon, not only as more noble than the other senses, but as having something in it of a nature superior to sensation. The evidence of reason is called seeing, not feeling, smelling, or tasting. Yea, we are wont to express the manner of the Divine knowledge by seeing, as that kind of knowledge which is most perfect in us. Section II. SIGHT DISCOVERS ALMOST NOTHING WHICH THE BLIND MAY NOT COMPREHEND-THB REASON OF THIS. Notwithstanding what hath been said of the dignity and superior nature of this faculty, it is worthy of our observation, that there is very little of the knowledge acquired by sight, that may not be communicated to a man born blind. One who never saw the light, may be learned and knowing in every science, even in optics; and may make discoveries in every branch of philosophy. He may understand as much as another man, not only of the order, distances, and motions of the heavenly bodies; but of the nature of light, and of the laws of the reflection and refraction of its rays. He may understand distinctly how those laws produce the phænomena of the rainbow, the prism, the camera obscura, and the magic lanthorn, and all the powers of the microscope and telescope. This is a fact sufficiently attested by experience. In order to perceive the reason of it, we must distinguish the appearance that objects make to the eye, from the things suggested by that appearance: and again, in the visible appearance of objects, we must distinguish the appearance of colour from the appearance of extension, figure, and motion. First, then, as to the visible appearance of the figure, and motion, and extension of bodies, I conceive that a man born blind may have a distinct notion, if not of the very things, at least of something extremely like to them. May not a blind man be made to conceive that a body moving directly from the eye, or directly towards it, may appear to be at rest? and that the same motion may appear quicker or slower, according as it is nearer to the eye or farther off, more direct or more oblique? May he not be made to conceive, that a plain surface, in a certain position, may appear as a straight line, and vary its visible figure, as its position, or the position of the eye, is varied?-that a circle seen obliquely will appear an ellipse; and a square, a rhombus, or an oblong rectangle? Dr Saunderson understood the projection of the sphere, and the common rules of perspective; and if he did, he must have understood all that I have mentioned. If there were any doubt of Dr Saunderson's understanding these things, I could mention my having heard him say in conversation, that he found great difficulty in understanding Dr Halley's demonstration of that proposition, that the angles made by the circles of the sphere, are equal to the angles made by their representatives in the stereographic projection; but, said he, when I laid aside that demonstration, and considered the proposition in my own way, I saw clearly that it must be true. Another gentleman, of undoubted credit and judgment in these matters, who had part in this conversation, remembers it distinctly. As to the appearance of colour, a blind man must be more at a loss; because he hath no perception that resembles it. Yet he may, by a kind of analogy, in part supply this defect. To those who see, a scarlet colour signifies an unknown quality in bodies, that makes to the eye an appearance which they are well acquainted with and have often observed-to a blind man, it signifies an unknown quality, that makes to the eye an appearance which he is unacquainted with. But he can conceive the eye to be variously affected by different colours, as the nose is by different smells, or the ear by different sounds. Thus he can conceive scarlet to differ from blue, as the sound of a trumpet does from that of a drum; or as the smell of an orange differs from that of an apple. It is impossible to know whether a scarlet colour has the same appearance to me which it hath to another man; and, if the appearances of it to different persons differed as much as colour does from sound, they might never be able to discover this difference. Hence, it appears obvious, that a blind man might talk long about colours distinctly and pertinently; and, if you were to examine him in the dark about the nature, composition, and beauty of them, he might be able to answer, so as not to betray his defect. We have seen how far a blind man may go in the knowledge of the appearances which things make to the eye. As to the things which are suggested by them or inferred from them, although he could never discover them of himself, yet he may understand them perfectly by the information of others. And everything of this kind that enters into our minds by the eye, may enter into his by the ear. Thus, for instance, he could never, if left to the direction of his own faculties, have dreamed of any such thing as light; but he can be informed of everything we know about it. He can conceive, as distinctly as we, the minuteness and velocity of its rays, their various degrees of refrangibility and reflexibility, and all the magical powers and virtues of that wonderful element. He could never of himself have found out, that there are such bodies as the sun, moon, and stars; but he may be informed of all the noble discoveries of astronomers about their motions, and the laws of nature by which they are regulated. Thus, it appears, that there is very little knowledge got by the eye, which may not be communicated by language to those who have no eyes. If we should suppose that it were as uncommon for men to see as it is to be born blind, would not the few who had this rare gift appear as prophets and inspired teachers to the many? We conceive inspiration to give a man no new faculty, but to communicate to him, in a new way, and by extraordinary means, what the faculties common to mankind can apprehend, and what he can communicate to others by ordinary means. On the supposition we have made, sight would appear to the blind very similar to this; for the few who had this gift, could communicate the knowledge acquired by it to those who had it not. They could not, indeed, convey to the blind any distinct notion of the manner in which they acquired this knowledge. ball and socket would seem, to a blind man, in this case, as improper an instrument for acquiring such a variety and extent of knowledge, as a dream or a vision. The manner in which a man who sees, discerns so many things by means of the eye, is as unintelligible to the blind, as the manner in which a man may be inspired with knowledge by the Almighty, is to us. Ought the blind man, therefore, without examination, to treat all pretences to the gift of seeing as imposture? Might he not, if he were candid and tractable, find reasonable evidence of the reality of this gift in others, and draw great advantages from it to himself? A The distinction we have made between the visible appearances of the objects of sight, and things suggested by them, is necessary to give us a just notion of the intention of nature in giving us eyes. If we attend duly to the operation of our mind cellent writers, we shall avail ourselves of the distinction between the signs that nature useth in this visual language, and the things signified by them; and in what remains to be said of sight, shall first make some observations upon the signs. Section III. in the use of this faculty, we shall perceive | tition of what hath been said by these exthat the visible appearance of objects is hardly ever regarded by us. It is not at all made an object of thought or reflection, but serves only as a sign to introduce to the mind something else, which may be distinctly conceived by those who never saw. Thus, the visible appearance of things in my room varies almost every hour, according as the day is clear or cloudy, as the sun is in the east, or south, or west, and as my eye is in one part of the room or in another; but I never think of these variations, otherwise than as signs of morning, noon, or night, of a clear or cloudy sky. A book or a chair has a different appearance to the eye, in every different distance and position; yet we conceive it to be still the same; and, overlooking the appearance, we immediately conceive the real figure, distance, and position of the body, of which its visible or perspective appearance is a sign and indication. When I see a man at the distance of ten yards, and afterwards see him at the distance of a hundred yards, his visible appearance, in its length, breadth, and all its linear proportions, is ten times less in the last case than it is in the first; yet I do not conceive him one inch diminished by this diminution of his visible figure. Nay, I do not in the least attend to this diminution, even when I draw from it the conclusion of his being at a greater distance. For such is the subtilty of the mind's operation in this case, that we draw the conclusion, without perceiving that ever the premises entered into the mind. A thousand such instances might be produced, in order to shew that the visible appearances of objects are intended by nature only as signs or indications; and that the mind passes instantly to the things signified, without making the least reflection upon the sign, or even perceiving that there is any such thing. It is in a way somewhat similar, that the sounds of a language, after it is become familiar, are overlooked, and we attend only to the things signified by them. It is therefore a just and important observation of the Bishop of Cloyne, That the visible appearance of objects is a kind of language used by nature, to inform us of their distance, magnitude, and figure. And this observation hath been very happily applied by that ingenious writer, to the solution of some phænomena in optics, which had before perplexed the greatest masters in that science. The same observation is further improved by the judicious Dr Smith, in his Optics, for explaining the apparent figure of the heavens, and the apparent distances and magnitudes of objects seen with glasses, or by the naked eye. Avoiding as much as possible the repe OF THE VISIBLE APPEARANCES OF OBJECTS. The In this section we must speak of things which are never made the object of reflection, though almost every moment presented to the mind. Nature intended them only for signs; and in the whole course of life they are put to no other use. mind has acquired a confirmed and inveterate habit of inattention to them; for they no sooner appear, than quick as lightning the thing signified succeeds, and engrosses all our regard. They have no name in language; and, although we are conscious of them when they pass through the mind, yet their passage is so quick and so familiar, that it is absolutely unheeded; nor do they leave any footsteps of themselves, either in the memory or imagination. That this is the case with regard to the sensations of touch, hath been shewn in the last chapter; and it holds no less with regard to the visible appearances of objects. I cannot therefore entertain the hope of being intelligible to those readers who have not, by pains and practice, acquired the habit of distinguishing the appearance of objects to the eye, from the judgment which we form by sight of their colour, distance, magnitude, and figure. The only profession in life wherein it is necessary to make this distinction, is that of painting. The painter hath occasion for an abstraction, with regard to visible objects, somewhat similar to that which we here require: and this indeed is the most difficult part of his art. For it is evident, that, if he could fix in his imagination the visible appearance of objects, without confounding it with the things signified by that appearance, it would be as easy for him to paint from the life, and to give every figure its proper shading and relief, and its perspective proportions, as it is to paint from a copy. Perspective, shading, giving relief, and colouring, are nothing else but copying the appearance which things make to the eye. We may therefore borrow some light on the subject of visible appearance from this art. Let one look upon any familiar object, such as a book, at different distances and in different positions: is he not able to affirm, upon the testimony of his sight, that it is the same book, the same object, whether seen at the distance of one foot or of ten, whether in one position or another; that the colour is the same, the dimensions the same, and the figure the same, as far as the eye can judge? This surely must be acknowledged. The same individual object is presented to the mind, only placed at different distances and in different positions. Let me ask, in the next place, Whether this object has the same appear ance to the eye in these different distances? Infallibly it hath not. For, First, However certain our judgment may be that the colour is the same, it is as certain that it hath not the same appearance at different distances. There is a certain degradation of the colour, and a certain confusion and indistinctness of the minute parts, which is the natural consequence of the removal of the object to a greater distance. Those that are not painters, or critics in painting, overlook this; and cannot easily be persuaded, that the colour of the same object hath a different appearance at the distance of one foot and of ten, in the shade and in the light. But the masters in painting know how, by the degradation of the colour and the confusion of the minute parts, figures which are upon the same canvass, and at the same distance from the eye, may be made to represent objects which are at the most unequal distances. They know how to make the objects appear to be of the same colour, by making their pictures really of different colours, according to their distances or shades. Secondly, Every one who is acquainted with the rules of perspective, knows that the appearance of the figure of the book must vary in every different position: yet if you ask a man that has no notion of perspective, whether the figure of it does not appear to his eye to be the same in all its different positions? he can with a good conscience affirm that it does. He hath learned to make allowance for the variety of visible figure arising from the difference of position, and to draw the proper conclusions from it. But he draws these conclusions so readily and habitually, as to lose sight of the premises: and therefore where he hath made the same conclusion, he conceives the visible appearance must have been the same. Thirdly, Let us consider the apparent magnitude or dimensions of the book. Whether I view it at the distance of one foot or of ten feet, it seems to be about seven inches long, five broad, and one thick. I can judge of these dimensions very nearly by the eye, and I judge them But to be the same at both distances. yet it is certain, that, at the distance of | one foot, its visible length and breadth is about ten times as great as at the distance of ten feet; and consequently its surface is about a hundred times as great. This great change of apparent magnitude is altogether overlooked, and every man is apt to imagine, that it appears to the eye of the same size at both distances. Further, when I look at the book, it seems plainly to have three dimensions, of length, breadth, and thickness: but it is certain that the visible appearance hath no more than two, and can be exactly represented upon a canvass which hath only length and breadth. In the last place, does not every man, by sight, perceive the distance of the book from his eye? Can he not affirm with certainty, that in one case it is not above one foot distant, that in another it is ten ? Nevertheless, it appears certain, that distance from the eye is no immediate object of sight. There are certain things in the visible appearance, which are signs of distance from the eye, and from which, as we shall afterwards shew, we learn by experience to judge of that distance within certain limits; but it seems beyond doubt, that a man born blind, and suddenly made to see, could form no judgment at first of the distance of the objects which he saw. The young man couched by Cheselden thought, at first, that everything he saw touched his eye, and learned only by experience to judge of the distance of visible objects. I have entered into this long detail, in order to shew that the visible appearance of an object is extremely different from the notion of it which experience teaches us to form by sight; and to enable the reader to attend to the visible appearance of colour, figure, and extension, in visible things, which is no common object of thought, but must be carefully attended to by those who would enter into the philosophy of this sense, or would comprehend what shall be To a man newly made to said upon it. see, the visible appearance of objects would be the same as to us; but he would see nothing at all of their real dimensions, as we do. He could form no conjecture, by means of his sight only, how many inches ar feet they were in length, breadth, or thickness. He could perceive little or nothing of their real figure; nor could he discern that this was a cube, that a sphere; that this was a cone, and that a cylinder.† Still they appeared external to the eye.-H. This is a misinterpretation of Cheselden, on whose authority this statement is made; though it must be confessed that the mode in which the case of the young man, couched by that distinguished surgeon, is reported, does not merit all the eulogia that have been lavished on it. It is at once imper. fect and indistinct. Thus, on the point in questions Cheselden says:-"He (the patient) knew not the shape of anything, nor any one thing from another, His eye could not inform him that this object was near, and that more remote. The habit of a man or of a woman, which appeared to us of one uniform colour, variously folded and shaded, would present to his eye neither fold or shade, but variety of colour. In a word, his eyes, though ever so perfect, would at first give him almost no information of things without him. They would indeed present the same appearances to him as they do to us, and speak the same language; but to him it is an unknown language; and, therefore, he would attend only to the signs, without knowing the signification of them, whereas to us it is a language perfectly familiar; and, therefore, we take no notice of the signs, but attend only to the thing signified by them. Section IV. THAT COLOUR IS A QUALITY OF BODIES, NOT A SENSATION OF THE MIND. By colour, all men, who have not been tutored by modern philosophy, understand, not a sensation of the mind, which can have no existence when it is not perceived, but a quality or modification of bodies, which continues to be the same whether it is seen or not. The scarlet-rose which is before me, is still a scarlet-rose when I shut my however different in shape or magnitude; but, upon being told what things were, whose form he before knew from feeling, he would carefully observe, that he might know them again; but, having too many objects to learn at once, he forgot many of them, and (as he said) at first he learned to know, and again forgot a thousand things in a day. One particular only, though it may appear trifling, I will relate: Having often forgot which was the cat and which the dog, he was ashamed to ask; but, catching the cat, which he knew by feeling, he was observed to look at her steadfastly, and then, setting her down, said, 'So, puss! I shall know you another time."" Here, when Cheselden says, "that his patient, when recently couched, knew not the shape of any thing, nor any one thing from another," &c., this objects of different shapes and sizes; for, if this inter. pretation were adopted, the rest of the statement becomes nonsense. If he had been altogether inca. bable of apprehending differences, it could not be said that, being told what things were whose form be before knew from feeling, he would carefully observe, that he might know them again;" for observation supposes the power of discrimination, and, in particular, the anecdote of the dog and cat would be inconceivable on that hypothesis. It is plain that Cheseiden only meant to say, that the things which the patient could previously distinguish and deno. minare by touch, he could not now identify and refer to their appellations by sight. And this is what we might, a priori, be assured of, A sphere and a cube would certainly make different impressions on him; but it is probable that he could not assign to each its name, though, in this particular case, there is good ground for holding that the slightest consideration would enable a person, previously acquainted with these figures, and aware that the one was a cube and the other a sphere, to connect them with his anterior experience, and to discriminate them by Dame-See Philos. Trans., 1728, nu. 402.—H. cannot mean that he saw no difference between eyes, and was so at midnight when no eye saw it. The colour remains when the appearance ceases; it remains the same when the appearance changes. For when I view this scarlet-rose through a pair of green spectacles, the appearance is changed; but I do not conceive the colour of the rose changed. To a person in the jaundice, it has still another appearance; but he is easily convinced that the change is in his eye, and not in the colour of the object. Every different degree of light makes it have a different appearance, and total darkness takes away all appearance, but makes not the least change in the colour of the body. We may, by a variety of optical experiments, change the appearance of figure and magnitude in a body, as well as that of colour; we may make one body appear to be ten. But all men believe, that, as a multiplying glass does not really produce ten guineas out of one, nor a microscope turn a guinea into a ten-pound piece, so neither does a coloured glass change the real colour of the object seen through it, when it changes the appearance of that colour. The common language of mankind shews evidently, that we ought to distinguish between the colour of a body, which is conceived to be a fixed and permanent quality in the body, and the appearance of that colour to the eye, which may be varied a thousand ways, by a variation of the light, of the medium, or of the eye itself. The permanent colour of the body is the cause which, by the mediation of various kinds or degrees of light, and of various transparent bodies interposed, produces all this variety of appearances. When a coloured body is presented, there is a certain apparition to called the appearance of colour. Mr Locke the eye, or to the mind, which we have calls it an idea; and, indeed, it may be idea can have no existence but when it is called so with the greatest propriety. This perceived. It is a kind of thought, and can only be the act of a percipient or thinking being. By the constitution of our nature, we are led to conceive this idea as a sign of something external, and are impatient till we learn its meaning. A thousand experiments for this purpose are made every day by children, even before they come to the use of reason. They look at things, they handle them, they put them in various positions, at different distances, and in different lights. The ideas of sight, by these means, come to be associated with, and readily to suggest, things external, and altogether unlike them. In particular, that idea which we have called the appearance of colour, suggests the conception and belief of some unknown quality in the body which occasions the idea; and it is to this quality, |