felt, the force of that complaint, which he puts into the mouth of Samson,- —a complaint, which may surely be forgiven, or almost forgiven, to the blind: : The immediate object of vision, we have seen, then, is light, which gives rise to all the various sensations of colour; and, since the days of Berkeley, philosophers have, with scarcely any exception, admitted, that the knowledge of the distance, magnitude, and real figure of objects, which seems at present to be immediately received by sight, is the result of knowledge acquired by the other senses-though they have,-I think without sufficient reason,as universally supposed, that the superficial extension, of length and breadth, becomes known to us by sight originally;—that there is, in short, a visible figure of objects, corresponding with the picture which they form on the retina, and changing, therefore, with their change of position relatively to the eye, and a tangible figure of objects, permanent and independent of their change of place; the latter being the real figure suggested by the former, nearly in the same manner as the conception of objects is suggested, by the arbitrary sounds, or written character, which denote them. The inquiry, with respect to the truth of this visible figure, as a sensation, may, however, be omitted, till we have considered the former opinion, which respects the visual perception of distance, and of the figure and magnitude which are termed tangible. If it had been duly considered, that it is light which is the true object of vision, and not the luminous body, the question, as far as it depends on reasoning a priori, exclusively of any instinctive connexions that might be supposed, could not have admitted of very long discussion. From whatever distance light may come, it is but the point of the long line which terminates at the retina, of which we are sensible; and this terminating point must be the same, whether the ray has come from a few feet of distance, or from many miles. The rays, that beam from the adjacent meadow, or the grove, are not nearer to my eye, at the instant of vision, than those which have been reflected from the mountain, on the very verge of the horizon, or from the cloud that hangs at an immeasurable distance above my head. The light, that converges on our eye, from all the stars of heaven, within what we term the field of our vision, is collected, in a space, that cannot be larger than the retina on which it falls. A cube or a sphere is represented to us, by the two dimensions of a coloured plane, variously shaded, as truly, as by the object itself with its triple dimensions; and, in the determination of the exact correspondence of these double and triple dimensions, in all their varieties of relation to the eye, the whole art of perspective consists. A coin of a single inch in diameter, when placed before the eye, and, of course, intercepting only an extent of light equal to the extent of its own surface, is sufficient to hide from us, by actual eclipse, the fields, and villages, and woods, that seemed stretched in almost endless continuity before us. * Samson Agonistes, v. 93-97. Unless, therefore, there be some instinctive and immediate suggestion, of certain distances, magnitudes, and figures, by certain varieties of the sensation of colour, there is nothing in the mere light itself, or in its relation to the eye at the moment of vision, which seems fit to communicate the knowledge of these. Not of distance; for the rays from distant objects, when they produce vision, are as near to the retina, as the rays from objects that are contiguous to the eye. Not of real magnitude; for an object, with which we are familiar, appears to us of the same size, at distances, at which every thing merely visual is so completely changed, that its magnitude, as far as it depends on mere radiation, may be demonstrated, from the laws of optics, to be equal only to a half, or a tenth part of its apparent magnitude, when nearer. Not of figure; for, without the knowledge of longitudinal distance, we could not distinguish a sphere or a cube from a plane surface of two dimensions; and an object, with the shape of which we are familiar, appears to us of the same form, in all directions; though it may be demonstrated optically, that the visual figure, as far as it depends on mere radiation, must vary with every variety of position. I have said, that the knowledge of the real magnitude, figure, and position of bodies, could not be obtained immediately from the diversities of the mere surface of light at the retina; unless it were the suggestion of some instinctive principle, by which the one feeling was, originally and inseparably, connected with the other and I have made this exception, to prevent you from being misled, by the works on this subject, so as to think, that the original perception of distance implies, in the very notion of it, a physical impossibility. Some diversity there evidently must be of the immediate sensation of sight, or of other feelings co-existing with it, when a difference of magnitude or figure is suggested: the visual affection, which is followed by the notion of a mile, cannot be the same as that which is attended with the notion of half a foot; nor that which is attended with the perception of a sphere, be the same as that which suggests a plane circular surface. Whatever the number of the varied suggestions of this kind may be, there must be, at least, an equal variety of the immediate sensations that give rise to them; and these corresponding series of sensations and suggestions, may originally be associated together by an instinctive principle, as much as any other pairs of phenomena, the connexion of which we ascribe to instinct; or, in other words, suppose an adaptation of them to each other, by the gracious provision of the Power which formed us, for a purpose unforeseen by us, and unwilled at the moment. It is not more wonderful, a priori, that a sensation of colour should be immediately followed by the notion of a mile of distance, than that the irritation of the nostril, by any very stimulant odour, should be immediately and involuntarily, followed by the sudden contraction of a distant muscular organ, like the diaphragm, which produces, in sneezing, the violent expiration necessary for expelling the acrid matter;-or that an increase of the quantity of light poured on the eye, should be instantly, and without our consciousness, followed by a contraction of the transparent aperture. I am far from saying, that there truly is such an instinctive association of our original visual feelings, with corresponding notions of distance and magnitude, in the present case; for, at least in man, I believe the contrary. only, that the question has, a priori, only greater probability on one side, not absolute certainty; and that experience is necessary, before we can decide it with perfect confidence. I mean In the case of the other animals, there seems to be little reason to doubt, that the tedious process, by which man may be truly said to learn to see, is not necessary for their visual perceptions. The calf, and the lamb, newly dropped into the world, seem to measure forms and distances with their eyes, as distinctly, or at least almost as distinctly, as the human reasoner measures them, after all the acquisitions of his long and helpless infancy. Of these races of our fellow animals, Nature is at once the Teacher and the great Protectress, supplying to them, immediately, the powers which are necessary for their preservation,-as, in the long continued affection of the human parent, she far more than compensates to man, the early instincts which she has denied to him. If the other animals had to learn to see, in the same manner with ourselves, it would be scarcely possible, that their existence should be preserved to the period at which the acquisitions necessary for accurate perception could be made; even though the hoof had been an instrument of touch and measurement, as convenient as the hand. For this difference in the relative circumstances of their situation, the Almighty Being, -to whose universal benevolence, nothing which he has created is too humble for his care, has made sufficient provision, in giving them that early maturity, which makes them, for many months, the superiors of him, who is afterwards to rule them with a sway, that is scarcely conscious of effort. "Hale are their young, from human frailties freed, This instinctive suggestion, which, however subsequent it may be to the primary visual sensation, seems like immediate perception in the young of other races of animals, is a very strong additional proof, if any such were necessary, that there is no physical impossibility, in the supposition that a similar original suggestion may take place in man. The question, as I before said, becomes truly a question of observation and experiment. But, in man, there is not that necessity for the instinct, which exists in the peculiar situation of the other animals; and we find accordingly, that there is no trace of the instinct in him. It is long before the little nursling shows that his eye has distinguished objects from each other, so as to fix their place. We are able almost to trace in his efforts the progress which he is gradually making;-and, in those striking cases, which are sometimes presented to us, of the acquisition of sight, in mature life, in consequence of a surgical operation,-after vision had been obstructed from infancy,-it has been found, that the actual magnitude and figure, and position, of bodies, were to be learned like a new language, that all objects seemed equally close to the eye-and that a sphere and a cube, of each of which the tangible figure was previously known, were not so distinguishable in the mere sensation of vision, that the one could be said, with certainty, to be the cube, and the other the sphere. In short, what had been supposed, with every appearance of probability, was demonstrated by experiment,-that we learn to see, and that vision is truly, what Swift has paradoxically defined it to be, the art of seeing things that are invisible. LECTURE XXIX. ANALYSIS OF THE FEELINGS ASCRIBED TO VISION, CONTINUED. THE chief part of my last Lecture was employed in considering the Phenomena of Vision, and particularly in proving, that vision,-simple and immediate, as it now seems to us, even in its most magnificent results,—is truly the application of an art, of long and tedious acquirement, of that art with which we learn to measure forms and distances, with a single glance, by availing ourselves of the information, previously received from other sources; the mixed product of innumerable observations, and calculations, and detections of former mistakes-which were the philosophy of our infancy, and each of which, separately, has been long forgotten,-recurring to the mind, in after-life, with the rapidity of an instinct. Of all the arts, which man can acquire, this is, without question, the richest, both in wonder and in value-so rich in value, that if the race of man had been incapable of acquiring it, the very possibility of their continued existence seems scarcely conceivable; and so rich in subjects of wonder, that to be most familiar with these, and to study them with most attention, is to find at every moment new miracles of nature, worthy of still increasing admiration. "Per te quicquid habet mundus, mirabile nobis, Nativa hinc quamvis ferimur gravitate deorsum On this subject the remarks of Dr. Reid, which I am about to quote, are not less just than they are strikingly expressed. "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 * Judicium Paridis, v. 146-158. Ap. Mus. Anglican, vol. II. p. 274. EDIT. 1741. 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 further 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 is taught most artfully to lie and dissemble, 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."* The same observation has been put in a strong light, by the supposition, that it had been as uncommon, to be born with the power of sight, as it is now to be born incapable of it ;-in which case it has been truly said, that "the few who had this rare gift would appear as prophets or inspired teachers to the many."+ The very easy predictions thus made, would be found, constantly, or almost constantly fulfilled, by those who could form no conception of the means by which the effects predicted were foreseen; and wonderful as the dreams and visions of prophetic inspiration may appear, they surely could not seem more wonderful, as a medium of communication, than that by which the very secrets of the mind, and events apparently the most distant, were made known, through the intervention of a small ball like the eye. In showing the manner by which we learn to combine, with our visual sensations, the knowledge obtained by touch; or, as I am rather inclined to think, for reasons formerly stated, the knowledge falsely ascribed to mere touch; it will not be necessary to go over the different varieties of figure, magnitude, distance. The most striking of these is distance,-which, indeed, may be truly said to involve the other two; since the distance of an object is merely the extension of the long line that intervenes between the object and our eye, and the consequent magnitude of the intervening objects, and that which we consider, regarded as one extended whole. Of this one great whole, what we term the distant object, is nothing more than the boundary. The cottage, at the end of a field, is part of that compound magnitude of which the field and the cottage are separately parts, exactly in the same manner as the wing of a house, is a part of the compound magnitude of the whole building. The line of field which connects our eye with the cottage, may, indeed, be a longer line, but it is a line of precisely the same sort as that which connects the wings of the house with our organ of sight, or with each other. It is vain to think of ascribing the perception of distance to the measurement of the different angles subtended by objects, at different distances, or to an equally nice measurement of the different degrees of inclination of the axes of the eyes, necessary for distinct vision, in particular cases, as if all men were instinctively geometers, and the peasant and the very idiot were |