process, it is not a process of immediate and proper per ception. I hear, for example, a noise. All that I really perceive in this case is the sensation of sound. I refer it, however, to an external cause, to a carriage passing in the street. I specify, moreover, the kind of carriage, perhaps a coach, or a wagon with iron axles. I have ob served, have learned by experience, that sounds of this nature are produced in this way, that is, by carriages passing, and by such carriages. Hence I judge that the sound which I now hear is produced in the same way. It is an inference, a conception merely. All that sense does is to receive and transmit the sign, which the understanding interprets by the aid of former experience. And the same is true of the other senses, with the exceptions named.

Not therefore of little Value. We are not to infer, however, that these senses are on this account of no special value or importance to us. (They do precisely what is needed. They put us in possession of just the data wanted in order to the necessary information concerning external things. It is only the theorist who undervalues the senses, and he only in his closet. No man, in the full possession of his reason, and his right mind, can go forth into this fair and goodly world, and not thank God for every one of those senses sight, hearing, taste, touch, and smell. Their true and full value, however, we never learn till we come to be deprived of their use; till with Milton we exclaim,

"Seasons return; but not to me returns

Day, or the sweet approach of even or morn."

§ V.-AMOUNT OF INFORMATION Derived from the Respective SENSES.

A further Question as to one Class of the Senses.-The relations and specific functions of the several senses have been already described. Some further questions arise, however, respecting the precise amount and kind of infor mation afforded by that class of the senses which, as we

have seen, relates to the spatial properties of bodies, in dis tinction from the chemical, viz.: hearing, sight, and touch.

What is given in Hearing. And first, as to the sense of hearing. What is it precisely that we hear? When we isten to a sound, we speak of hearing the object that produces the sound; we say, I hear a bell, a bird, a gun, etc. Strictly speaking, we do not hear the object, but only the sound. It is not the bell or the bird that we hear, but the vibration of the air produced by bell and bird. This has been already illustrated by reference to a carriage passing in the street. It is only by experience, aided by other senses, that we learn to refer the sound to its producing cause.

Hearing not properly Perception.- Is hearing then a sen sation merely, or is it a perception? If by perception we mean a direct knowledge of the external object-which is the proper sense of the word—hearing certainly is not perception. It gives us no such immediate knowledge. (What we perceive in hearing is merely the sensation of sound.) It may be doubted whether by this sense alone we should ever get the idea that what we hear is any thing external to ourselves.

Affords the means of Judging. As it is, however, we judge, not only of the existence and nature, but of the distance and direction of the external object whence the sound proceeds. We learn to do this with great correctness, and with great facility. No sooner do we hear a sound, in most instances, than we form an opinion at once, from what direction it comes, and what produces it; nor are we often mistaken in our judgment. The faculty of judging by the ear as to the direction of the sound, and the nature of the object producing it, may be cultivated by care and practice to a remarkable degree of accuracy. Napoleon was seldom mistaken as to the direction and distance of a cannonade. It is said that the Indian of the north-western prairies by applying his ear to the ground, will detect the approach of a body of cavalry at a distance beyond the

reach of vision, and distinguish their tread from that of a herd of buffaloes.

Number of Sounds.-The number of sounds which the ear can distinguish is almost without limit. There are, it is said, five hundred distinct tones which an ear of usual accuracy can recognize, and each of these tones admits of five hundred variations of loudness, giving, in all, two hundred and fifty thousand different sounds.

Power of Sound over the Mind.-The power of sound to affect the mind, and especially the feelings, is too well known to require specific statement. The note of an instrument, the tone of a human voice, the wild warbling of a bird, the tinkling of a bell, the variations of speech and of song, from the high and shrill to the low and heavy intonation, from the quick and impetuous to the slow and plaintive movement, these simple varieties of tone affect powerfully the heart, and find their way at once and irresistibly to the feelings. Hence the power of music over even the uncultivated mind; hence too in no small degree the power of the skilful orator over the feelings of his audience. It is not merely, nor so much, the thing said, in many cases, as the way of saying it, that touches and sways the assembled multitude. Tones and sounds have a natural meaning. They are the natural language of the heart. They express emo tion, and hence awaken emotions in others. )

The Question as to Sight.-Turning now from the sense of hearing to that of sight, the question arises, What is it precisely that we perceive by the eye? When we fix the eye upon any object, more or less remote, what is it, strictly speaking, that we see, extension and figure, or only color? Is it by vision that we learn primarily the distance of objects and their locality? These are points requiring investigation.

Does Sight give Extension and Figure. As to the first of these questions, whether extension and figure are objects of direct visual perception. No doubt they are associated

m our minds with the act of vision, so that the moment we see an object we obtain an idea of it as extended, and of such and such dimensions and figure. The question is, whether it is really through the sense of sight that we obtain this idea, or in some other way. Had we no other means of information, would sight alone give us this? When we first open our eyes on external objects, do we receive the idea of extension and figure, or only of color? The fact that as matters are, we cannot in our experience separate the notion of some surface extension from the sensation of color, is not decisive of these questions. We cannot, as Dr. Brown observes, separate the color from the convexity and magnitude of an oak before us, but this does not prove that convexity and magnitude are objects of immediate and original perception. If every surface in nature had been convex, suggests the same writer, we should probably have found the same difficulty in attempting to conceive of color as separate from convexity, that we now find in attempting to conceive of it as separate from length and breadth. As it is, however, our sensation of color has not always been associated with convexity, while it has been always associated with surface extension. Hence it is, he maintains, that we seem to perceive, by the eye, the length, and breadth, and objects along with their color.

Argument from the Affection of a Portion of the Retina. -The fact that in vision a certain portion of the retina in length and breadth is actually affected by the light falling on it, has been supposed by some to be conclusive of the fact that we perceive the length and breadth of the external object by the eye. This does not necessarily follow. As Dr. Brown contends, it is equally true that a certain part of the organ of smell is affected by odors, and a certain part of the auditory nerve is affected by sounds, yet we are not conscious of any perception of extension by either of these organs; we neither smell nor hear the length, and breadth, and magnitude of objects; nor is there any reason to suppose

that the particular portion of the retina affected has any thing to do with the original sensation of sight.

Amount of the preceding Arguments. These arguments, however, do not strike me as conclusive. They merely show the possibility that extension and figure may be ac quired rather than original perceptions. They do not amount to positive evidence that they are so.

An Argument to the Contrary. On the other hand, there is one consideration of a positive character, which to most minds will be likely to outweigh the merely negative arguments already adduced. Color is a property of light, and light comes to us reflected from objects occupying space; we perceive it only as we perceive it spread over and reflected from some surface. Extension, then, surface expansion of the reflecting object, is the indispensable condition of the visibility of light itself, and so of color, as reflected from the object. Now it is difficult to persuade ourselves that what we know to be an essential condition of the perception of color, and what we seem to perceive along with the color, and cannot, even in thought, wholly separate from it, is not, after all, really perceived by the eye.

Argument from recent Discoveries. Indeed, recent discoveries in science seem to vindicate that not only surface extension, but trinal extension, or solidity, may be an object of direct perception by the eye. I refer to the researches of Wheatstone, in binocular vision, which go to show, that in consequence of the difference of the images formed upon the right and the left eye, as occupying different positions with reference to the object seen, we are enabled by the eye to cognize the solidity as well as the extension of objects. The difference of figure in the two images gives us this. That such is the case is shown by an instru ment, the stereoscope, so constructed as to present separ ately the image as formed on each eye, which, when separ ately viewed, appear as mere plane surfaces, but when viewed together, the right image with the right eye, and