pleasures on the other hand, are in general, faint and rare, in comparison with others.

The sense of taste, (considered as extending not only over the mouth, but through the whole alimentary duct,) conveys sensations of flavours, and of hunger and thirst. It undergoes remarkable changes in passing from infancy to old age; partly from the universal effect of custom, to diminish the vividness of sensations and feelings, and partly from the influence of associated circumstances. Its pleasures are considerable, especially in the early part of life, and constitute one grand source of our elementary mental pleasures. (See Chap. xi. p. 247.) Its pains are only such as are necessary to prevent excessive abstinence or gratification, and the employment of improper food. The most common are those arising "from excess, and the consequent indigestion. This excites and supports those uneasy states which attend upon melancholy, fear, and sorrow."

The sense of smell is nearly allied to that of taste. Its pains are obviously desigued to assist us in the proper choice of food, and to excite us to avoid such vapours, as may render the air injurious to health. Offensive odours do also, in various circumstances, contribute to produce the feelings of shame, decency, &c. Its pleasures, besides aiding those of taste, contribute to the formation of some of those mental pleasures, derived from the beauties of nature.

The sense of hearing furnishes us with sensations of sound; and many of its simple pleasures aid in the formation and growth of the mental pleasures. By association, sounds become the signs of ideas; and they are of essential service in the formation or reception of our most complex notions. The more refined pleasures of this sense are greatly indebted to association; and in their turn contribute, in an important degree, to exalt and refine the system of feeling. The early loss of sight only impedes the progress of the mind from sensation to intellect and affection: those who have never heard, have much greater disadvantages to undergo. The use of words is neces

sary to the full improvement of intellect, and the enlargement of affection; and therefore, during the early periods of mental progress, the ear is of much more importance to us, as spiritual beings, than the eye. The means of knowledge are, however, it is evident, most abundantly increased by the possession of sight.

Sense of Sight. Rays of light proceeding from every point of the visible object, enter the eye, and form upon the retina an exquisitely beautiful and distinct, though minute picture of the object. The optic nerve is affected by this impression on the retina; and, by some unknown means, communicates to the mind the sensation of sight.

If this sensation be considered unblended with the relics of other sensations, we find that it is merely what can be communicated by the picture on the retina. The sensation of colour can be thus, and thus alone communicated; and this is the only sensation which can be considered as appropriate to the sight. The sensation of figure can be communicated by the sight, but only of figure in two directions, length and breadth; for the picture on the retina can have only those two dimensions.— The sensation of magnitude can also be thus communicated, but not of real magnitude; for a sensation of real magnitude cannot be conveyed by a picture which is almost indefinitely smaller than the real object. To use the illustration of Adam Smith: "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 visible picture, which you thus see, is immensely great and extensive; but it can be no greater than the visible circle through which you see it. If, while you are looking through the circle, you could conceive a fairy hand and a fairy pencil to come between your eye and the glass, that pencil might delineate upon that little glass, the outlines of all those extensive lawns, and woods, and arms of the sea, and distant mountains, in the dimensions

in which they are seen by the eye." Again, it is obvious that however large, or however small the field of view, the picture occupies an equal extent upon the retina.-Similar observations might be made with respect to distance. The organ of sight can convey only that sensation of distance, which may be produced by a minute picture on the retina; that is, nothing but the sensation of the distances of the different parts of the picture, which may bear no proportion to the real distances, and can only be in two directions.-Similar things may be said of motion, that is, change of position. The visual sensation of motion is merely that produced by the motion of different parts of the picture on the retina.

The fact is, that not the object itself, but the picture formed upon the retina, is the immediate object of the sight. Without the sense of touch, it is probable that the picture would never have conveyed ideas of real figure, magnitude, motion, or position; still more, that it would never have conveyed the idea, that external objects produced the picture. Of colour it does convey sensations which do not receive correction from the touch, and which can be acquired by the sight alone. Persons completely blind have been known to distinguish objects of one colour from those of another; but this is by the feel of the surfaces of those objects. If they have never at all possessed sight, though they may speak of colours, and distinguish coloured objects, and even have a remote idea of the causes of our sensations of colours, yet they can have no sensations, nor consequently ideas of colours. Mr. Locke mentions a blind man, who said that he imagined the colour of scarlet resembled the sound of a trumpet.

The limits here stated of the direct power of the sense of sight, may appear strange to those who have not been accus tomed to distinguish between the sensation, and the perception of which the sensation forms a part. There are, however, numerous circumstances which prove the point; the most satisfactory are those attending the obtaining of the sight, at a period when recollection can register the sensations. One such case fell

Mr. Cheselden When he was

under the observation of the able Cheselden, and we shall state some of the principal circumstances of it. couched a youth of thirteen years of age. allowed to use his sight, all objects appeared to him alike to touch his eyes, as the things, which he felt, touched his skin. He considered solid bodies as planes differently coloured; and when he had learned to distinguish solids by their appearances, he was greatly surprised, when examining the pictures of solids, to find all the parts plain and smooth like the rest; he asked which of his senses deceived him, his sight or his feeling? Being shewn a miniature of his father, which was painted on a watch-case, he at once perceived that it was a representation of his father, but expressed great surprise that so large a countenance could be contained in so small a space; it peared to him as impossible, as for a pint to contain a hogshead. Mr. Ware published in the Philosophical Transactions of 1800, a case which seemed to militate greatly against Mr. Cheselden's conclusions: his patient had from the first, ideas of distance and form. But Mr. Ware himself furnishes a solution of this difficulty; for we find from his paper, that his patient had always been able to distinguish light and vivid colours from shade.

Sensations of colours are, in the early parts of life, very vivid, and assist considerably in the formation of our mental pleasures; but the other sensations derived from this sense, are principally important to us, as being by association the signs of the ideas derived from the touch; and, from their distinctness, well calculated to serve as the connecting bond of union, and to bring those ideas again into the view of the mind. The visual sensations, of themselves considered, are rarely the objects of reflection; we seldom even think of them; and while we appear to give to the visible appearances of objects, our minutest attention, we are, in fact, attending only to the tangible qualities, of which the visible appearance is the sign. Were it not therefore for association, the sight would be of little more use to us than a beautiful picture of objects with

But consider its value in con

which we have no concern. nexion with association, and it must be regarded as the most perfect, and the most permanently valuable of all the senses. The information acquired by the touch, is obtained slowly; and the sensations must be continually repeated, in order to acquire information respecting objects: but the sight takes in a vast variety of objects, and, almost at a glance, can distinguish what is necessary to be known respecting them. Its sensations recall the past impressions derived from the touch, and at once suggest the size, the shape, the distance of their various objects. "If a man," says Reid," were by feeling to find the figure of the Peak of Teneriffe, or even of St. Peter's at Rome, it would be the work of a life-time." Besides, its discovery reaches farther than the touch could carry us; enables us to range through the vault of heaven, and determine the motions of the heavenly luminaries. It traces in the countenance the workings of the mind; it displays the passions and affections of the soul. With association it is every thing. Without its aid, it would be useless as the bright fleeting visions of sleep.*

it

The reader who wishes to enter particularly into the phenomena of sensation, may consult Reid's Inquiry into the Human Mind, and Hartley's Observations, Prop. 23-73, omitting such as relate to vibrations. A judicious summary will be found in Belsham's Elements, p. 56-105.-Respecting the curious class of phenomena, termed Ocular Spectra, see the end of the second part of Darwin's Zoonomia.