eyes, it has one magnitude. I remove it ten feet off, and its apparent magnitude is ten times less. Its color is less vivid, and its outline less distinct. I remove it to the distance of an hundred feet, and it is diminished to an indistinct speck. If I would represent it to another person, 1 must represent it thus indistinctly. Hence the distinction made between tactual and visual form and magnitude.

We have the means of associating these two ideas together in a manner hereafter to be considered. We are able to translate the language of sight into the language of touch. This, however, would be unnecessary, were there not this difference in the two perceptions to which I have here referred.

If we observe the relation in which the senses stand to each other, we shall at once perceive the importance of sight. Smell and taste give us simple knowledges, without any cognition of the not me, and, also, I think, without the power of forming conceptions. Hearing suggests the not me, and gives us the power of forming conceptions; but it gives us no knowledge of any of the attributes of the sonorous body, save its power of awakening this sensation. Touch gives us an immediate and positive knowledge of the not me, and of all its primary attributes, and leaves upon the mind a most definite conception. Sight enables us to determine most of the qualities revealed to us by touch, not only near at hand, but at great distances; by the delicacy of its language, it enables us to discover many of the qualities revealed by the other senses; and, while performing all these functions, it is a source of most exquisite pleasure.

That the conceptions of sight are more definite than those received by our sense of touch, I will not affirm. It is, however, certain that they are much more easily retained in the memory. When we recollect an external object, I think we much more readily recall the visual conception

than any other. I I may feel of a sphere, and obtain a knowledge of its form and magnitude; but when I think of it, the visual appearance presents itself most readily to my mind. Almost all the conceptions of figurative language are derived from sight. The power of originating such conceptions is called imagination, or the power of forming images. The fine arts, with the exception of music, address themselves wholly to this mode of perception. Almost all the other senses are, in some manner, tributary to it, and thus enable us to employ it in order to arrive at the most varied and distant forms of knowledge.

Let us now proceed to inquire, what are the qualities of the external world which are cognized by means of this sense?

1. If the above remark be true, that we are so made as to refer our visual conception to the external object, it will follow that we derive our cognition of externality as truly from this sense as from touch. Touch gives us a distinct and immediate notion of the existence and qualities of an external object. Sight gives us a conception of an unknown cause of a known effect; it also teaches us that this cause is numerically distinct from ourselves, and assigns to it its position in space.

The existence of this function of vision has frequently been denied, and it has been affirmed that, until aided by touch, sight gives us no idea of externality, any more than smell or hearing. The principal ground for this opinion is the authority of Cheselden,* who, long since, published an account of a young man whom he couched for cataract, and who, on restoration to sight, thought, at first, that every object touched his eyes. On this statement I would observe, that, on the first admission of light to the unnaturally sensi

Philosophical Transactions, 1778, No. 402.

tive retina, a sensation unlike to sight would be likely to arise, which the patient might very probably designate by saying that the object touched his eyes. Every one, in passing from darkness into a strong light, has felt a sensation of this kind, and he may remember that it is more nearly akin to touch than to sight. If we had before known everything by touch, we should naturally use this language in describing it. On this account, I think the case does not warrant the stress that has been laid upon it. But, secondly, if it were so, if he thought that the objects touched his eye, then, as Sir W. Hamilton has happily remarked, "still they appeared external to the eye," for it is evident that two things cannot seem to touch each other, unless, at the same time, also, they appear numerically distinct. That which is numerically distinct from the eye must be the non ego. Besides, the young of all animals, as soon as they open their eyes, recognize external objects as external, and, with evident design, move either towards or away from them. In fact, they use their eyes at first just as they use them afterwards. A new-born infant teaches us the same truth. Who ever saw a young child place its hand on its eyes when an object was placed before it? It reaches out its hand towards the object, without, it is true, any correct idea of distance, but with a correct conception of externality and direction. I think that all our observation upon cur own use of this faculty must lead us to the same conclusion.

2. From this sense, exclusively, we obtain our knowledge of color. Of the nature of this cognition I have already had occasion to express my opinion. It is a simple knowledge in itself, an affection of the sentient being, which, however, we naturally and immediately refer to the external object. Of this quality, thus recognized, the varieties are numerous, and they are indefinitely multiplied by the cir

cumstances of light and shade, distance and proximity, degree of illumination, and many others. Hence it is that external nature presents to us an exhaustless and ever-varied scene of beauty and sublimity. Every object in the world around us, which the hand of God has formed, is made to minister to our happiness. But this is only a small part of the benefit which we derive from this function of sight. Every change of color, and every variation in the degree of color, is indicative of some change which is originally cognized by some other sense. Hence it is that sight, which acts instantaneously, and cognizes its objects at large distances, is enabled, by changes of visual appearance, to detect an immense number of qualities which vision alone could never have discovered. All the senses become tributary to it, and it does the work of all. Of the manner in which this is done, we shall treat more particularly in the following section.

3. To the qualities of external bodies, rendered cognizable by sight, we must undoubtedly add extension. If we refer our notion of color to an external object, I do not see how it is possible to exclude from our minds the knowledge that the colored object is extended. If we look upon anything colored, that color covers a definite portion of space. Let any one look upon a surface marked alternately by different colors, and the limitations of each are distinctly defined. Hence, also, arises the idea of form in one dimension. We can as well cognize a circle or square by sight as we can do it by touch. We read as rapidly by the eye as the blind by their fingers.

4. Lastly, we must now add solidity, or extension in three dimensions, to the perceptions given us by sight. Until quite lately, this power has been denied to the faculty of vision. It has been the generally received opinion that sight gives us nothing but the different shades of color.

represented on a plane surface, as we perceive them in a painting; but that by touch we learn to associate the shading with the form, and thus indirectly learn to cognize solidity by the eye. This view was universally received, until the researches of Professor Wheatstone, of King's College, London, threw new light upon the whole subject. The brilliant discoveries of this philosopher have added a new function to the organ of vision, and demonstrated that, by the eye alone, we are enabled to cognize solidity as well as simple extension. He has shown that, in consequence of binocular vision, we are able to determine the form of bodies within a certain distance. The manner in which this is accomplished is as follows: It must be obvious to every one, that, inasmuch as the right and left eye occupy different positions in space, the images which an external object forms on the two eyes must be slightly dissimilar. I look upon an inkstand on the table before me, closing first my right eye and then the left. I can clearly discover a difference between the right and left image. Now, it is this difference of figure in the two images that gives us the notion of solidity. This is proved by the stereoscope, an invention of Professor Wheatstone. This instrument is so constructed that we can see separately the image of an object formed on the right eye, and then that formed on the left.

When seen in this manner, each figure appears to us as a mere drawing on a plane surface. When now we look at them with both eyes, we do not perceive two plane drawings, but a distinct, and, I had almost said, palpable solid. It is however evident that this effect can be produced only when the body is at so small a distance, and of such a magnitude, that two images can be formed. If it be far off, so that the rays become parallel, and thus form the same image on both eyes, no effect from binocular vision is produced. We