of Sense.—Analysis of their Several Functions
Number of the Senses.—The different senses are usually reckoned as five in number. They may all be regarded, however, as modifications of one general sense, that of touch—or, in other words, the susceptibility of the nervous system to be excited by foreign substances brought into contact with it. This is the essential condition of sensation in any case, and the several senses, so called, are but so many variations in the mode of manifesting this excitability. There is a reason, nevertheless, for assigning five of these modifications and no more, and that is, that the anatomical structure indicates either a distinct organ, as the ear, the eye, etc., or at least a distinct branch of the nervous apparatus, as in the case of smell and taste, while the whole nervous expansion as spread out over the surface of the body contributes to the general sense of touch.
The Senses related to each other.—Distinct Office of each.—It is evident enough that these several senses sustain a certain relation to each other. They are so many and no more, not merely by accident; not merely because so many could find room in the bodily organization; not merely because it might be convenient to have so many. Let us look at the office performed by each, and we shall see that while each has its distinct function, not interchangeable with that of any other, it is a function more or less necessary to the animal economy. Remembering that the design and use of the several senses is to put us in possession of data, by means of which, directly or indirectly, we may gain correct knowledge of the external world, let us suppose the inquiry to be raised, What senses ought man to have for this purpose? What does he need, the material universe remaining what it is?
Function of the Sense of Touch.—Things exist about us in space, having certain properties and relations. We need a sense then, first and chiefly, that shall acquaint us with objects thus existing, taking cognizance of what lies immediately about us in space. This we have in the general sense of touch, making us acquainted with certain objective or mechanical qualities of external objects.
This Sense, how limited.—This, however, avails only for objects within a short distance, and capable of being brought into contact. It operates also synthetically and slowly, part after part of the object being given as we are brought into contact with different portions of it successively until the process is so far complete that, from the ensemble of these different parts, our understanding can construct the whole.
Possibility of a Sense that shall meet these Limitations.—We can conceive of a sense that should differ in both these respects—that should take cognizance of distant objects, not capable perhaps of being brought into contact—and that should also operate analytically, or work from a given whole to the parts, and not from the parts to a whole, thus giving us possession at once of a complete object or series of objects. Such a sense, it is easy to see, would possess decided advantages, and in connection with the one already considered, would seem to bring within the sphere of our cognizance almost the complete range of external nature. This we have, and this exactly, in the sense of vision. It takes in objects at a distance, and takes in the whole at a glance.
This new Sense still limited.—This new sense, however convenient and useful as it is, has evidently its limitations. It is available only through a given medium, the light. Strictly speaking, it is the light only that we see, and not the distant object; that is known indirectly by means of the light that variously modified, travels from it to the eye. When this fails, as it does during several hours of the twenty-four, or when it is intercepted by objects coming between and shutting out the forms on which the eye seeks in vain to rest, then our knowledge from this source is cut off.
Still another Sense desirable.—Under these circumstances, might it not be well, were there given an additional sense, of the same general nature and design, but operating through a different medium, sure to be present wherever animal life exists, so that even in the darkness of the night, or the gloom of the dungeon, we might still have means of knowing something of the surrounding objects. And what of this medium, or avenue of sense, were of such a nature as to be capable of modification, and control, to some extent, on our part, and at our pleasure, so as to form a means of voluntary communication with our fellow-beings. Would not such an arrangement be of great service? Exactly these things are wanted; exactly these wants are met, and these objects accomplished, by a new sense answering to these conditions—the sense of hearing—the cognizance of sound. This we produce when we please by the spoken word, the vocal utterance, whether of speech, or musical note, or inarticulate cry, varied as we please, high, low, loud, soft—a complete alphabet of expression, conveying thus by signals, at once rapid and significant, the varying moods and phases of our inner life to other beings that had else been strangers, for the most part, to the thoughts and feelings which agitate our bosoms.
Senses for another Class of Qualities.—The senses, as thus far analyzed, have reference primarily to the number magnitude, and distance of objects as occupying space—to quantities rather than qualities. Were it possible now to add to these a sense, or senses that should take cognizance of quality, as well as existence and quantity—that should detect, to some extent at least, the chemical properties of bodies as connected especially with the functions of respiration and nutrition—the list of senses would seem to be complete. This addition is made, this knowledge given, in the senses of smell and taste.
Possibility of additional Senses.—To those already named, other senses might doubtless have been added by the Creator, which would have revealed, it may be, properties of matter of which we have now no conception. It is not to be supposed that we know every thing respecting the nature and qualities of even the most familiar and common objects. Many things there may be, actual, real, in the world about us, of which we know nothing, because they come not within the range of any of our senses. But all that is essential to life, and happiness, and highest welfare is doubtless imparted by the present arrangement; and when closely studied, no one of these senses will be found superfluous, no one overlapping the province of another, but working each its specific end, and all in harmony.
The proper Office of Psychology in respect to the Senses.—It is the province of the anatomist and the physiologist to explain the mechanical structure of the several organs of sense, and their value as parts of the physical system. The psychologist has to do with them only as instruments of the mind, and it is for him to show their connection and proper office as such. This has been attempted in the preceding analysis.
The kind of Knowledge afforded by the Senses.—It is to be noticed, in addition, that with the exception of the tactual sense, and possibly of sight, these senses give us no direct, immediate knowledge of external things. They simply furnish data, signs, intimations, by the help of which the understanding forms its conclusions of the world with out. They are the receiving agents of the mind. This is, in fact, the chief office of sense, to receive through its various avenues the materials from which the understanding shall frame conceptions of things without; to convey, as it were, a series of telegraphic despatches along those curious and slender filaments that compose the nervous organization, by means of which the soul, keeping her hidden seat and chamber within, may receive communication from the distant provinces of her empire. These signs the understanding interprets; and in so far as this is the true nature of the process, it is not a process of immediate and proper perception. 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 observed, 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
