IREGON RULE CO. 1 U.S.A. 2 jiiiiiiiiijliiiljiiiiiiiiiiiiiiiiiiiijuiiiiiiijuiij 1 BF 233 .S8 Copy 1 AN ELEMENTARY TREATISE SENSE-PERCEPTION ■ S \0* ' \ Julian Munson Sturtevant Ex-President of Illinois College *& NEW HAVEN : T U T T L E , MOREHOUSE & TAYLOR, PRO T IS R S , 1863. } NOTE This little treatise is printed for the benefit of the classes under my instruction, not published. I have, however, taken the liberty of sending copies of it to a few teachers and particular friends, whose judgment of it I am very desirous of obtaining-, because I have tbe greatest respect for their opinions of such a matter. An expression .of their judgment addressed to me at Jacksonville. Illinois, will be very gratefully received. J. M. BTUETEVANT. WARREN, Conn.. July 26th, 1883. Copyright, 1883, by J. M. Sturtevani SENSE-PERCEPTION. CHAPTER I. Preliminary. § 1. It is unnecessary at the beginning of this Trea- tise, to say more of the nature of the human soul than that every man consciously. possesses the power to know, to feel and to choose. The human soul is that entity to which these powers belong. The existence of these powers and of this entity admits of no question. If we cannot know this, we cannot know anything. Inquiry is meaningless and science impossible. It is equally unquestionable, that, at the beginning of human life, we are in the profoundest ignorance of everything. It will also appear more and more in the progress of this Treatise, that all knowledge is acquired through the activities of a rational soul, exerting its own powers through the bodily organism with which it is connected. It is the design of the Treatise now under- taken to point out the conditions under which and the processes by which the soul so exerts these activities, as to find its way out of the ignorance in which it begins to be, into a clear knowledge of itself and of the mate- 1 2 SENSE-PERCEPTION. rial universe. Itself it must know, as a condition of knowing anything else ; for the beginning of all knowl- edge is self-knowledge. "Know thyself" is not only a rule of wisdom, but of necessity. § 2. In the construction of a Treatise on any science, the meaning of certain words must be assumed without any definition. The knowledge of their meaning can- not be communicated from one mind to another by a definition, but must spring up in each mind through its own experience independently of the action of any other mind. If there is not in any mind such an independent experience, the meaning of the word which expresses that experience can in no manner be known. Many minds all having the same idea derived from experience, or occasioned by it, can agree together upon a word by which that idea shall be expressed. Such a word is " knowledge." Its meaning can only be understood by an experience of knowing. In the progress of this Treatise, we must often employ words of which the same is true. All men use such words, not only in science, but in all human intercourse. The use of such words always assumes and implies the inde- pendent mental activity both of him who employs them and of those to whom they are addressed. Human inter- course itself thus assumes the individual personality of all human beings, that is, that every individual possesses or rather is a rational soul. We can make no progress in the inquiries upon which we are entering without assuming the fundamental facts of human consciousness. It is therefore necessary to de- fine that word. Definition.— Consciousness is the knowledge or the power of knowing one's own mental states and activi- ties. SENSE-PERCEPTION. 3 In consciousness therefore all knowledge begins. It is in consciousness, the conscious experience of joy or sorrow, of desire, gratification or purpose, that the fact of our own existence is originally revealed to us. It is by the experiences of which we are conscious, that all those activities are excited and stimulated by which knowledge is acquired and a human life rendered possi- ble. It is unnecessary to our present purpose to enter into any of those inquiries respecting the nature of con- sciousness which have attracted the attention of the curious. It is quite enough to recognize the fact that the human soul has the power of knowing its own thoughts, its own experiences of pain or pleasure, its own activities and purposes. This power we call conscious- ness. § 3. It is necessary in this place to say a few words respecting those bodily organs which are the instru- ments employed by the soul in the various processes of sense-perception. Every portion of the bodily organism is, in greater or less degree, subsidiary to these processes. It is, however, important to our purpose, to call special attention to three distinct systems of the bodily organ- ism, — the muscles, the nerves, and the special senses. All these sustain an intimate relation to our subject. The muscles are those parts of the bodily organism by the contraction and relaxation of which all the motions of the body are produced. Without them we shall see as we proceed, the whole arrangement of nerves and special senses would be powerless to convey to the mind any knowledge of the material universe. This fact it is important to our purpose distinctly to recognize. Be- yond this it is unnecessary to go further in the examina- tion of the muscular system. For such an examination the student must be referred to the anatomists. 4 SENSE-PERCEPTION. Important as the nervous system confessedly is to our subject, it is unnecessary for us to enter upon its exami- nation, more than simply to recognize two of its func- tions. Those functions are voluntary motion and sensi- bility. To each of these functions certain nerves are distinctly appropriated. Every muscle of the body is furnished with its own appropriate nerve through which it communicates with the brain, and without the health- ful action of which the power of the muscle cannot be exerted. Some of these nerves are called into action only by the will, and always obey its behests. These are the nerves of voluntary motion. Other nerves act spontaneously, without the action of the will, and main- tain in perpetuity the vital movements of the heart, the lungs and other vital organs. These are nerves of in- voluntary and spontaneous motion. They begin to act with the very beginning of life and cease their activity only at death. § 4. The other function of the nervous system is that of sensibility or feeling. The nerves which are appro- priate to this function originate, like those already de- scribed, in the brain, and are distributed, in greater or less degree, to every portion or tissue of the living organism. On the presence of these nerves, the sensi- bility of the whole body depends. Their function is twofold, general sensibility and special sensation. The former of these functions is present in every portion of the body with the exception of the hair and finger and toe nails. It is found even in the hardest bones. At this point the two functions of general sensibility and motion are very intimately united. To every muscle of the body, a nerve of sensibility and a nerve of motion are conveyed enclosed in the same sheath. Along the one any sensation experienced is reported at the nervous SENSE-PERCEPTION. 5 center, to which the nerve of motion spontaneously re- sponds by exciting such muscular action as the exigency requires. Thus if the light admitted to the eye is pain- ful to the optic nerve, a reflex muscular action takes place, by which the pupil is contracted, so as to admit less light to the eye. A similar relation between nerves of sensibility and nerves of motion pervades the living organism. Motion so produced must however be sharply distinguished from voluntary motion. The latter is very intimately, the former not at all, related to sense- perception. § 5. The nervous system, as the source of the sensi- bility of the living organism, must be viewed in a three- fold aspect. 1. The general sensibility. This, as already stated, pervades the whole living organism. It responds to the slightest touch of the surface of the body by any ma- terial substance, to the change of temperature of any portion of the body whether internal or superficial, and to all irritations or lesions from whatever causes origi- nated. It is connected in greater or less degree with the spontaneous action of all the vital organs. When, however, the vital organs are in normal condition, and their functions are healthfully performed, their action is attended by little or no sensibility. A man in perfect health scarcely knows that he has a bodily organization. But when they are deranged by disease, their action is often attended with most distressing and painful sensi- bility. 2. Another aspect in which the nervous system as related to sensibility must be viewed is, the muscular sensibility. In this aspect of it, we find the first step which the mind takes towards a knowledge of the ex- ternal universe. The action of every voluntary muscle 6 SENSE-PERCEPTION. of the body is attended by its own peculiar sensibility. It is by the experience of that sensibility, that the soul learns what muscle must be brought into action to pro- duce any given motion, and what muscle is in action when a given motion is produced. It is by observing the sensibility of each muscle that the soul acquires the power of voluntary motion. The almost incessant mo- tions of the limbs of a new-born infant are neither guided by the intelligence nor controlled by the will. The first problem which the rational soul has to solve is? to gain the control of the motions of the body and the limbs. It is only by the muscular sensibility that the solution of this problem is rendered possible. We shall learn as we proceed that it is here that the soul acquires its first idea of an extended and external universe. 3. The remaining aspect in which the nervous system is to be viewed, has reference to the action of the special senses. These are commonly said to be five in number, viz : touch, sight, hearing, taste, smell. From this state- ment it seems necessary to dissent. What is called touch cannot with propriety be regarded as one of the special senses. The reasons for this dissent, however, cannot be fully stated in this place, but will be ren- dered apparent as we proceed. One reason however is here apparent. The special senses have each a special organ, by which only the function of the sense can be performed. Touch has no such organ, but is found in greater or less degree in all parts of the surface of the living body. This alone is a full justification for class- ifying it as a part of the general sensibility and not as a special sense. We cannot, however, regard this enumeration of the special senses as exhaustive. Sex appears to be entitled to be ranked with the special senses. It however per- SENSE-PERCEPTION. 7 forms so small a function in the soul's knowledge of the external universe, that a consideration of the indelicacy of the subject seems to justify its omission in a treatise on sense-perception. Its function is very closely analo- gous to that of taste, sustaining the same relation to the perpetuation of the species that taste does to the life and health of the individual. CHAPTER II. Three Fundamental Questions Considered. § 6. Every student of the human mind must neces- sarily meet, almost at the outset of his enquiries, three questions, which underlie the whole subject. I. What is the origin of the idea of duration ? II. How does the mind acquire the idea of an ex- tended surface or body ? III. How does the mind acquire the idea of exter- nality or outness ? I. These questions are to be considered in the order in which they have been propounded. We here encoun- ter one of the words which admit of no definition. He who has not derived from his own mental activities and experiences the idea expressed by the word dura- tion can never get that idea from a definition. Two persons both of whom have it may agree upon the name by which it shall be called ; but we must account for its origin in every mind by its own independent action. 8 SENSE-PERCEPTION. The soul knows itself to exist as a permanent entity by its experiences of pleasure or pain, activity or rest.* From the beginning of our existence these experiences occur in almost unceasing succession. We now expe- rience pleasure, next we suffer pain, next we are active, next we have ceased to act and are at rest. We know these changes as successive one to the other. One goes before, another follows after. This necessarily gives the idea of duration, now and then, longer and shorter. Since one event, many soul experiences have occurred, since another, very few. Thus every being that exists and is capable of knowledge, and is con- scious of existing in a succession of mental states, must know events as involving duration. If a soul could exist having no knowledge of things external, but only of himself, that soul would not lack the idea of dura- tion. He would know himself as existing in a perpet- ual succession of changes. § 1. II. How then originates the idea of extension ?f This word is also incapable of definition. It stands in this respect on precisely the same footing as duration. We all have the idea which the word expresses, and can- not divest ourselves of it. We conceive of all bodies as having length, breadth and thickness. But like dura- tion this idea has come to us not by any definition, but by the activity of our own minds. How then does this idea arise in the mind by occasion of the experiences to which it has been subjected ? It is obvious that this question is far more complicated than the question of the origin of duration. That in- volves nothing but a succession of soul-experiences ; but this involves the soul's use and control of the bodily * "Reid's Collected Writings, pp. 342, 343. fReid's Collected Writings, pp. 123-126. 142-144, 528. SENSE-PERCEPTION. 9 organism. It is only through the organs of the body, that the mind deals with material things. It seems to me that few persons will be disposed to deny the proposition, that if the body and all its organs were incapable of motion, the mind could never so mal^e use of the senses as to acquire the notion of ex- tension. To a soul so limited in its powers, there could be no here and no there, as there could be no now and no then to a soul that experiences no changes. We have yet made but little progress in our task; yet by this assertion we are brought into direct conflict with writers of the highest authority. This assertion however we shall endeavor fully to substantiate as we proceed. It must here be taken, not as a proposition which we claim to have proved, but as one which we expect to establish.* In our judgment, the only answer which can be given to the question, what the origin of the idea of exten- sion is, that it springs up of necessity with the earliest exercise of the soul's power of controlling the motions of the body. How different the development of the human infant, from that of the young of brute animals ! The latter are for the most part able to control their limbs, and to use them for their own help and preserva- tion, from the moment of birth, and must depend upon them or perish, and where this is not true of all their bodily organs, as in the case of the young bird in the nest, it is still true of certain organs. The young bird must stretch up its neck and open wide its mouth, to receive the food which the parent bird drops into it, or it will starve to death. In the case of the human in- fant, the source of its food must be placed within its lips, and the action of obtaining its food is as sponta- * Porter's Elements, Sec. 83. 2 10 SENSE-PERCEPTION. neous and unintelligent as the beating of its heart. At this point, human and brutal life are on the same level. Beyond this the infant's preservation and well-being must depend alone on intelligence. Over the motions of its limbs and head the new-born infant has no control. It is utterly helpless, and must perish very speedily unless its wants are supplied by the intervention of an intelli- gence not its own. From this condition of utter helplessness, the human infant can only escape by learning, in the use of its own rational powers, to control and guide the motions of the limbs and organs of the body. The hands and feet of an infant are often in motion ; but those motions are at first controlled by no intelligence or will power. They are aimless, and useless for the supply of the wants of the child. The first lesson of infancy is to learn to con- trol and guide these motions ; and in the process by which this acquisition is made, the idea of extension begins to manifest itself. The notion of place, here and there, is necessarily suggested by all motion voluntarily and consciously begun, continued and terminated. The child voluntarily moves his own hand. The beginning of that motion is here, the end of it is there, and the continuance of it suggests the extension that separates them. The distinction between the ego and the non-ego may not yet have been thought of; but the position of that something which I voluntarily move must be recog- nized as changed, here and there must be distinguished, and the intervening distance. This is the idea of exten- sion in its most rudimentary form, and it must spring up in the mind with the first exercise of the power of volun- tary motion. The child that has learned intentionally to move his hand, or to open and shut it, or to turn his eyes from side to side, or to turn his head on the joint SENSE-PERCEPTION. 11 of his neck, must have learned the distinction between here and there, and that distance separates them. It is not claimed that this is the fully developed idea of extension in its three dimensions, or even of an ex- tended surface. In order to acquire the full conception of an extended surface, the notion of body must have been gained, and the ego must have been distinguished from the non-ego. § 8. III. Our next inquiry is, how is this acquisition made ? Perhaps the gravest difficulty we must encoun- ter in our enquiries into the genesis of human knowledge is here. How does the soul pass from the knowledge of itself to the knowledge of that outer universe which is not itself ? Before, however, proceeding to answer this question, it seems necessary to define two terms which we can hardly avoid using in the discussion. They are the two cor- relative terms "subjective" and "objective." In using these two terms, we regard them as an exhaustive divis- ion of all the knowable. All the objects in the universe are comprehended either in myself or in the universe outside of myself. All then which I know of myself, my own thoughts, feelings, joys, sorrows, acts, intentions, is subjective knowledge. All which I know of the uni- verse outside of myself is objective knowledge. At the threshold of this inquiry we meet the stubborn, indisputable fact, that at the beginning of the soul's ac- tivity, all its knowledge is purely subjective. It is true from the very first, that most of our experiences are caused by impressions which the universe outside of our- selves makes upon us. But these impressions are purely subjective.* The new-born infant knows nothing of the causes which produce them. For example, a loud noise * Porter's Elements, Sec. 83. 12 SENSE-PERCEPTION. is made near an infant's ear. He experiences the sensa- tion, and is startled and distressed by it ; but he knows nothing of its cause. It is to him only a subjective feel- ing, and suggests no idea of anything external to him- self. The same is true of all the impressions which are made upon him through any of his senses. All the im- pressions which are made upon the inexperienced infant, through the eye, the ear, the taste, the smell, are mere subjective sensations. This statement will be called in question by some and will be more fully discussed fur- ther on. We shall however at this point sufficiently anticipate the subsequent discussion to illustrate it by a single ex- ample. Let us suppose that a man of good natural un- derstanding had been, up to a certain time of his mature life, quite destitute of the sense of smell, and had never been informed that other people had such a sense. At last, while he is quite alone in his room, he is suddenly endowed with that sense in full acuteness. At the same moment his room happens to be filled with some intense and disgusting odor, say of assafcetida ; I affirm that the new sensation would be purely subjective, and he would probably think himself attacked with disease, and per- haps hastily call a physician. Sitting still in his chair, the offending substance probably being in some remote part of the room, he would not even have the power of referring the new sensation to that part of the nostril where the nerve of smell is situated. We do not make such a reference of a sensation of smell to that nerve, even after years of experience. We have learned indeed that the nostril is the place of the sensation, by finding that the odorous object must be applied to the nostril in order that the sensation may be most intense ; but we do not know, till we have studied the matter ana- SENSE-PERCEPTION. 13 tomically, in what particular part of the nostril that nerve is situated, or how extensively the nostril is per- vaded by it. In such a case as we have supposed, the man would have no power of locating the sensation in the nostril even. The same will hereafter be proved to be true of all the special sensations. They are all sub- jective experiences, which the soul has no original power of referring either to their external causes, or to the part of the body where they are produced. § 9. Our question then is narrowed down to a point : how does the soul acquire the power of referring the impressions that are made upon it by the outside uni- verse to the causes by which they are produced ? How does it pass from the knowledge of subjective impres- sion to a knowledge of objective causation ? One thing must here be conceded by all. By the mere experience of subjective sensation, the mind never can acquire a knowledge of an external objective cause. For exam- ple, a hard substance touches the surface of one's body. It is purely a subjective sensation, and no repetition of it can give any more idea of the objective cause than the first experience of it. We shall find no answer to our question till we go back to the same cause which conducted us to the first idea of extension. Here we shall find the solution. Let us suppose that the infant had at last subjected his mus- cles and the limbs which those muscles move, to the con- trol of his intelligence and his will. He is perfectly con- scious of a power to move his hand in any direction at pleasure. But on a certain occasion, he finds a motion of the hand which he is perfectly conscious of being able to make, resisted and effectually stopped. Here then is the ego conscious of power to do a given thing, stand- ing face to face with a resisting non-ego, that is, a power 3 14 SENSE-PERCEPTION. resisting and hindering his own power in action. Nor let us suppose that the infant mind stops here. It is true that it is chiefly employed in the problems of sense- perception ; but all the faculties cooperate from the first. We shall show further on, and in doing so be sustained by the highest authority, that infancy does use induc- tive reasoning* in the solution of some of the simplest problems of sense-perception. It is just as reasonable to believe that it employs in like cases the intuition of cause and effect as -the law of induction. What diffi- culty then in admitting that in resistance experienced it sees a resisting cause? Indeed the whole problem of sense-perception necessarily involves the notion of caus- ation. To perceive is to refer our sensations to their appropriate causes. If the infant has not the power of passing from a known effect to a knowledge of its cause, it has no power of sense-perception, for this is sense-per- ception. He does not infer an objective cause from a subjective sensation, but the existence of a resisting agent from an experience of his own activity resisted. President Porter claims that the non-ego which is known in sense-perception is " the bodily organism itself or that part of the sensorium which is excited to action." To this it may be replied, that in the proper place it has been abundantly shown, that in many cases of sense- perception, if not indeed in most cases, we never do refer the sensation to the part of the organism in which it is produced. We see perfectly without referring the sensation of vision to the retina of the eye, or knowing that we have any retina. The same thing holds in re- spect to all the senses. The non-ego which is discerned is not our own organism but that which resists our will power. It is by such resistance alone that we learn the existence of the non-ego.f * Porter's Elements, Sec. 109. f Porter's Elements, Sec. 86. SENSE-PERCEPTION. 15 It is important to be noticed, that in acquiring such a notion of a resisting non-ego, the mind does not neces- sarily employ the aid of either of the special senses. In the act of voluntary motion and in the cognition of the resistance experienced to it, the mind employs only its muscular power and muscular sensibility. Even in recognizing the existence of a resisting power, the mind does not necessarily call into exercise what is commonly called the sense of touch. The muscular sensibility alone conveys to the mind the consciousness of the act of voluntary motion and the experience of its resistance and arrest. § 10. This notion of externality is only rudimentary, sustaining nearly the same relation to the fully devel- oped idea that the notion of extension which is implied in all voluntary motion, does to the completed concep- tion of an extended surface. Perhaps, however, it will not be found difficult at this point of the discussion, to indicate the manner in which the development of both these ideas is completed. At this stage of the process, the mind will soon perceive that this resistance is expe- rienced only within certain boundaries. Nothing hin- ders but that these boundaries should be definitely ascer- tained, and ascertained on all sides. In this process the mind has become master of all the conditions of the full development of the idea of a straight line and of a resist- ing extended surface. With this latter also the idea of hardness is inseparably linked. Indeed the two ideas are identical. This, however, only accounts for the origin of the idea of extension in the two dimensions of length and breadth. The question still remains, how does the mind pass to the third dimension of space, or to the knowl- edge of solid bodies ? In order to answer this question, 16 SENSE-PERCEPTION. it is not necessary to introduce into the discussion any- other factor than voluntary motion and muscular sensi- bility. The mind is capable of cognizing the fact of a change of direction in that motion, and of continued resistance in that changed direction, when the resistance is interrupted in a straight line. This is sufficient to reveal two resisting surfaces standing at an angle to each other. This process is capable of being extended to all the plane surfaces by which a solid body is bounded. In a similar manner the lines in which the several planes bounding a body meet may be traced, its solid angles may be discovered and a conception of its outline completed. In tracing the bounding lines of the several planes, the general sensibility to contact will render important aid. It is also easy to see, that when the dimensions of the body are not greater than can be grasped by one hand or by the two hands, the muscular power of one hand may be exerted in the direction oppo- site to that of the other, and thus it will become obvious to the mind that the body has two surfaces separated from each other by its third dimension. In no part of the process does the mind require any other aid than voluntary motion and muscular sensibility. In all these processes doubtless the action of what is commonly called the sense of touch and the sense of sight, will be present and consciously active, but their activity will not be necessary to the processes we have been describing. It will, however, be readily admitted that the general sensibility of the surface of the body greatly facilitates the process by which we pass from a knowledge of the extended surface to that of the solid body ; yet it cannot be admitted that it is indispensable. § 11. It does not fall in with the plan of this treatise to enter upon any extended discussion of the intuitive SENSE-PERCEPTION. 17 faculty of the soul ; but it is necessary at this point to assume the existence of such a faculty, and its activity in these earliest processes of the mind. A rational soul cannot act in such a manner as to acquire knowledge, without recognizing the relation of cause and effect. It may be objected to the foregoing argument, that in these earliest processes of the infant mind, it has as yet no notion of this relation. But why not ? It is a con- dition of the very first step toward any knowledge of the external, that the soul should know itself as a cause, that it should be conscious of power in action. It is in this very consciousness, that the notion of cause and effect originates in the soul. He that knows himself as a doer, knows a cause, knows the thing done as an effect, and is fully prepared to know that which resists his causative power as another cause distinguished from and set over against the cause which is resisted. This con- clusion cannot be set aside otherwise than by denying that the infant has a rational soul, and to deny this is to deny that it has any power of acquiring knowledge. CHAPTER III. The Special Senses. § 12. In the incipient processes thus far described, the soul has laid for itself a substantial foundation upon which the whole superstructure of its knowledge of the material world is to be built. It now remains to exam- ine those processes by which the soul in the use of the 1 8 SENSE-PERCEPTION. special senses constructs and rears up that superstruc- ture. As preparatory to this examination, it is neces- sary to call the attention of the student to two words, the use of which we have as far as possible avoided. They are "sensation" and "perception."* These words are used in popular speech in a wide diversity of import, and so must they continue to be used. Sensation is not only used to express all those feelings which we are liable to experience in consequence of change of bodily condition, but even the mental emotions whichare in no way caused by any affection of the body. We call the coldness which we experience on laying the hand on a piece of marble, or a pain in the head or hand, or the excitement which an eloquent orator produces on his audience, a sensation. In like manner we speak of per- ceiving the force of an argument, or the point of a witti- cism, or the truth of a proposition, or the beauty of a landscape. In popular discourse, there is no objection to this ; but in order that these words may do service as the technical terms of a science, they must be limited to a precise and exact meaning. The following definitions are proposed :f Definition. — Sensation is the impression made on the mind by the action of an appropriate external object on the organ of some one of the special senses. Definition. — Perception is the reference of a sensation to the external object by which the sensation was pro- duced, by which reference the mind comes to know that external object as having a causal power to produce that sensation. § 13. It seems necessary to render our conception of the relation of these two factors in sense-perception to * Porter's Elements, Sec. 83, 85-87. f Reid's Collected Writings, p. 182. Porter's Elements, Sec. 81-87 . SENSE-PERCEPTION. 19 each other and to the whole process, as precise and clear as possible. It is asserted by some that though these two stages in the process are distinguishable in thought, neither can ever exist without the other, that there can neither be any perception without sensation, or any sen- sation without perception.* To us it seems obvious that while there certainly can be no perception without sensation, there can and must be, especially in the first experiences of infancy, many sensations without any corresponding perceptions. Does the infant in the first hour after its birth experience no change of sensation, when the gas is extinguished, and total darkness follows bright illumination ? Must there not be a sensation of light, though he has not yet learned to interpret that sensation into a discernment of objects or surfaces, or of his eyes, as the place of his sensation ? Must not an infant of good hearing have the sensation of sound, while he is yet entirely unable to refer it to any external cause, or to distinguish it from a purely subjective feel- ing ? The case is too obvious to require further eluci- dation. The natural order of things is, that the infant first experiences a sensation, and then by the exercise of his active powers and his rationality interprets it, by referring it to its proper external cause. § 14. It is also maintained that the mind always refers the sensation to the organ of sense in which it is pro- duced. This cannot be admitted. There are many sen- sations which even in mature life we do not so refer, till we are instructed to do so by the accurate observations of anatomical science. We do indeed learn by experi- ence while very young, that the ear is the organ of hearing; but we never learn to locate the sensation in * Hamilton's Metaphysics, p. 320, Bowen's edition. Porter's Ele- ments, Sec. 80. 20 SENSE-PERCEPTION. the acoustic nerve, situated in the inner chamber of the ear, where only it originates, till science has taught us to do so by its accurate observations. No one ever does refer the visual sensation to the retina, lining the interior chamber of the eye, till science has taught him that that is the place of its origin, and even then we never acquire the consciousness that such is the fact. It is evident that the soul has no original power of referring visual sensations to the retina as their source. No one knows that sensations of smell originate in the interior of the nostril, or ever learns the situation or extent of that organ in the nostril till science has taught him. No man knows till he learns by experiment or by instruction from others, the limits of the sense of taste in his own mouth. The assertion that the mind at once refers its sensations to their proper place in the organism, and that even in infancy, is destitute of any foundation in truth. It is even contradictory to known fact. § 15. It has been claimed that in intensity, sensation and perception bear to each other an inverse ratio, that is, that the more intense the sensation the less accurate and discriminating is the perception.* The facts ad- duced to substantiate this claim are such as these : that if the light is too intense, for example, if one looks di- rectly at the sun shining in its strength, the eye is daz- zled and no distinct vision takes place, or when the surface of the body is pressed or crushed with a certain degree of violence, or when the touching body is so hot or so cold as to be painful, there is no perception. There is a confusion of thought in the language in which some of these examples are expressed, which will require at- tention in another place. It is enough to say here, that * Hamilton's Metaphysics, page 320, Bowen's edition. Porter's Elements, Sec. 89. SENSE-PERCEPTION. 21 these are all cases in which there is an actual injury- inflicted on the organ. The light may be so intense as to destroy the optic nerve, or at least temporarily to paralyze it. So also the contact may be such and under such conditions as to injure or disorganize the surface to which it is applied. It must also be borne in mind, that the sensibility which is excited by temperature is by no means entitled to be classed with special sensa- tions. Notwithstanding these facts, it is none the less true that, up to the point at which the light begins to be painful and disorganizing, it strictly holds, that the more intense the sensation the clearer and more dis- criminating the perception. If you wish to discern the finest possible black line drawn on white paper, you must place it in the intensest light which the organ can bear without injury. Authors have fallen into this error by failing to notice that, for the most part, the sensations have a double function. One of these functions is to furnish the mind with the necessary data of perception. The other func- tion is to impart to the soul a high and peculiar delight. Both these functions pertain in greater or less degree to the sensations furnished by each of the senses, though in very different degrees. It will be shown, as we pro- ceed, that in addition to the practical uses of the special sensations, they are made to minister in a high degree to the pleasures of life, and even to the most dignified and elegant culture of the intellect. The esthetic nature of man has for the most part its source in the sensations of the eye and the ear. § 16. It has already been incidentally remarked, that each of the senses has its own peculiar organ through which alone the sensation appropriate to the sense can be experienced. If that organ is destroyed or rendered 4 22 SENSE-PERCEPTION. inactive, no other part of the body can yield the sensa- tion. If the organ has been permanently destroyed, the soul must remain destitute of the sensation. From this sensation, in the case of each of the special senses, is furnished to the soul a peculiar and original idea, which can be derived only from that sense, so that if that sense is wanting, the soul remains utterly destitute of the peculiar idea which is appropriate to it. It has already been remarked that what is commonly called the sense of touch has no such special organ. To this it must be added, that neither does it furnish the soul with any peculiar idea for the acquisition of which the soul is entirely dependent on that sense. If it is the source of any such peculiar idea, what is that idea? Temperature is often spoken of as an idea acquired by the sense of touch. But this cannot be so. The feeling of heat or coldness is not confined to the surface of the body, as touch is, if there is any such sense. It is capa- ble of being experienced in any part of the interior of the body as well as on the surface. It clearly belongs, not to the special sensations, but to what has already been defined as general sensibility. None of the pains of the body, whether resulting from disease or lesion, are to be ranked with the special sensations. The idea of outness cannot, as has been already shown, be furnished by contact. That is a mere subjective feeling until it is interpreted to the mind through volun. tary motion and the experience of resistance. It should be mentioned that the mind derives important assistance in distinguishing the parts of its own body from other material bodies touched or handled, from the fact, that when we touch parts of our own bodies, the feeling is experienced both in that which touches and that which is touched ; while on the other hand when we touch some SENSE-PERCEPTION. 23 material thing which is not a part of our bodies, that which is touched does not return the feeling which is experienced in the touching part, say the hand. Neither is the idea of extension furnished by the sense of touch. The contrary has been earnestly maintained by some writers, but cannot be substantiated. It is claimed, indeed, that as every extended body when in contact is felt over a certain surface of the bodily organ- ism, extension must be cognized by touch alone. This contradicts facts which any one may easily establish by experiment. If a person is blindfolded, and the hand laid palm upwards upon the table, the palm may be pressed by substances presenting plain surfaces but a great variety of forms and sizes, and the blindfolded man has no power to discriminate the forms and sizes of the touching bodies. He cannot distinguish a triangle from a circle, a surface of a half square inch from one of an inch square, or an oblique parallelogram from a rec- tangle. In order that any of these discriminations may be made, it is necessary that the hand or finger should be moved over the touching surface and trace its out- lines. This experiment is decisive. Neither is it possible for the mind to discriminate with any degree of accuracy the part of the surface of the body at which the contact takes place. All the power of discriminating the part of the body touched which we ever acquire is evidently gained by experience, and never makes any considerable approach to accuracy. If we have any irritation on some part of our bodies which is inaccessible to our eyes, we can only place our finger upon the irritated point by successive trials. § 17. It is claimed by some that we judge of the ex- tension of the touching surface by the fact that there are two or more nerve-terminations embraced within it. 24 SENSE-PERCEPTION. This can hardly be sustained. It is true that the nervous system is ramified so as to reach every part of the living organism, and that these nerve-termini are more numer- ous in some parts of the body than in others. It is also true that those parts of the surface of the body in which the nerve-termini are most numerous are proportionally more sensitive to contact. But this does not affect th e question we are considering. Those parts of the body in which the nerve-termini are most numerous, as the lips or the ends of the fingers, have no more power, without the aid of motion, of discriminating the form or size of the touching body, or the precise place of con- tact, than those parts of the body which are less sensi- tive to contact, because furnished with fewer nerve- termini. In all cases, whether the sensibility of the parts be great or small, motion is equally a condition of such discrimination. The infant while learning to make these discriminations knows nothing of nerves as a cause of sensibility, and of course knows not whether a given contact embraces one or many nerve-termini. How then can this consideration enable him to appreciate the extension of the touching body ? Even in mature life, we never acquire the power to discern the contact of an external body with the surface of our own by what is called the sense of touch, with any degree of certainty. We are often ourselves at a loss to determine whether an excitement experienced on the surface of our bodies is caused by external contact or an irritation from some unknown cause. Undoubt- edly the quick general sensibility of the surface of our bodies to external contact is of great importance to our welfare. It gives us warning of the presence of ene- mies, yet so gently as to inflict no pain, in the most unobtrusive manner. It excites us to attend to that SENSE-PERCEPTION. 25 which needs attention, and to put forth the activity which the present exigency requires ; but it cannot be claimed that either the idea of contact or the idea of resistance or hardness is exclusively furnished by the sense of touch, as the idea of sound is by the sense of hearing. § 18. It may perhaps be claimed that our notion of the outline and limits of our own bodies is derived from the sense of touch. But we learn the form of our own bodies and distinguish their limits in the same manner, in all respects as we do those of any other solid body. We learn to distinguish the different sides of our own bodies by moving the hands from one side to the other, just as we would learn to distinguish the different sides of a stone or a block of wood. There is indeed a pecu- liarity in our knowledge of the relation of the different parts of our body to each other which does not pertain to our knowledge of any body but our own. But this peculiarity is purely the result of experience in connec- tion with voluntary motion, and muscular and general sensibility. In early childhood we remember to have had great difficulty in distinguishing the right hand from the left or the right side from the left side. But we learned in time so to distinguish both the muscular and the general sensibility of one side from those of the other, as to know the right hand from the left under all circumstances, by an instantaneous judgment. This judgment, however, is not founded in any peculiar manner on that general sensibilty which we call touch, but more especially on the muscular sensibility of the two sides which we have learned by experience to dis- criminate from each other. In early childhood when I wished to distinguish my right hand from my left, I used to look for a scar which I knew was on my right 5 62 SENSE-PERCEPTION. hand. A few years later in life I could distinguish by an instantaneous judgment without looking for the scar. In the same manner we learn to estimate distance without the aid of the feeling produced by contact. We have already seen that the idea of distance is sug- gested by the experience of the motion of our own limbs or bodies, and our consciousness of producing those motions by the action of our own muscles. We estimate distance by the amount and continuance of the muscular effort required. A lady was once reported, on taking her seat for her first journey by rail to the dis- tance of seventy-five miles, to have taken out her knit- ting and commenced work. When the station which was to be the end of her journey was announced, she ex- claimed with surprise, " if I had known it was no further I would have walked." She had judged of the distance by the amount of muscular effort she had made with her fingers upon her knitting needles. So the child always judges of distance. If the distance is not greater than can be compassed by the thumb and fingers of one hand, or by stretching the two hands, the movement of the hands forms the standard. If greater than can be so compassed, the feet and the motion of the whole body must be resorted to as a standard of distance. The child never learns the meaning of the word mile till he has become accustomed to walk a mile. It is thus made apparent that all our ideas of distance origi- nate, not in the action of the senses but in the exercise of our power of voluntary motion. § 19. In view of all these considerations, it seems im- possible to admit the existence of any thing in the hu- man constitution which can be properly called the sense of touch. In taking this position we are not entirely alone. The suggestion is not entirely new. But we SENSE PERCEPTION. 27 are painfully aware that the weight of authority is overwhelmingly against us. Some of the ablest wri- ters have not only felt no hesitation in classifying touch with the special senses, but have given it preeminence among them, and spoken of it as the leading sense. If this be an error, as we suppose, writers have fallen into it by failing to define their language. They have in- cautiously ascribed to the sense of touch ideas, of tem- perature, weight, and distance, and even of pain and lesion, which certainly have a very different origin.* There is also another consideration which strongly tends to the same conclusion. If there is a sense of touch which is to be ranked with the other special senses, it has no emotional function, as it has already been remarked all the other senses have. It does not open to the soul any peculiar source of happiness superadded to its practical uses, as the other senses do. If it could be shown that our ideas of form are derived from the sense of touch as our ideas of color are from the sense of sight, it might perhaps be claimed, that the sense of touch is to a considerable extent the source of our conception and enjoyment of beauty. But it has already been shown, that our idea of form has another origin, that it comes through the action of the muscles and not through the sense of touch. In addition to this, even if it should be admitted that our idea of form is derived from the sense of touch, it would still remain true, that our conception of the beautiful in form comes chiefly through form as presented to the eye, rather than as presented to the touch. How far the man who has always been destitute of eye-sight is capable of appreciating and enjoying the beautiful in form, it is not perhaps easy for seeing men to determine. But surely * Reid's Collected Writings, p. 119 and onwards. 28 SENSE-PERCEPTION. he must have that power in a very limited and low degree, if in any degree at all. What can St. Peter's at Rome or any of the great architectural structures of the world, or even the noble human form be to the blind man, as compared with what it is to one who is fully endowed with the sense of sight ? It seems to us then impossible to classify the feeling produced by external contact «of our bodies, with the special sensations. For convenience we shall hereafter use the feeling of contact instead of the sensation of touch. CHAPTER IV. Examination of the Special Senses. Sight. § 20. In proceeding to the examination of the special senses, there are decisive reasons for first directing our attention to the sense of sight. It is but a very meagre and barren conception of this universal frame of things with which the mind becomes acquainted by those pro- cesses which we have thus far considered, and it is chiefly by the aid of the sense of sight that this outline is filled out, that this dry skeleton is clothed with flesh and sinews and filled with life and beauty. It is this sense more than any other which enlarges our knowl- edge of this material universe, till the definiteness of knowledge is lost in the indefinite wonder which the In- finite inspires. At the point of this discussion at which we have now arrived, the mind is prepared for this en- largement, and will be the better fitted for the interest- SENSE-PERCEPTION. 29 ing details furnished by the other senses, after having taken in the comprehensive sweep of the universe which the noble sense of sight renders possible. The special organ of the sense of sight is the eye. This is an exquisitely constructed optical instrument, and the model after which all the optical instruments having for their object to assist vision are modeled. For a description of its structure, we must refer the student to the treatises on anatomy. It is only neces- sary here to remark, that the one design of the delicate and refined structure of the eye is, to form a clear and exact image of all material objects in the field of vision on the retina, which is a network of nerves situated in the back part of a cavity, in the front part of which the eye is situated. The image is formed by the refraction of light, according to laws which are familiar to every optician, and which therefore we need not here explain. Every material object reflects more or less of the light which falls upon it. A portion of the light so reflected enters the eye through the opening in its front called the pupil, passes through a most delicately constructed system of lenses, where it undergoes a refraction which brings the rays to a focus on the retina, by which means an image of the object from which they are reflected is formed. The retina or screen on which this image is received is a network formed by ramifications of the optic nerve or nerve of vision. § 21. Thus far we are able to trace the process of vision on purely optical principles, precisely as the opti- cian traces the formation of the image on the screen of the camera obscura. Beyond this point the optician can render us no aid toward the solution of the problem of vision. We here meet a fact which we must accept as ultimate, that when such an image is formed on the ret- 30 SENSE-PERCEPTION. ina of the eye, vision follows. On the other hand, no vision can be produced otherwise than by forming such an image on that one pair of nerves, no other nerve in the body will answer the purpose. On this one pair of nerves the image must be formed, or no vision can take place. These facts we say are ultimate, and are deter- mined only by experiment. We have said that when such an image is formed on the optic nerve under nor- mal conditions, vision will take place. Yet if that be the optic nerve of a newly born infant, vision will not take place. No knowledge of the objects in the field of vision, however perfectly represented on the retina, will be conveyed to the mind. A rational soul must first in- tervene, and acquire the power of interpreting the indi- cations of that image, so as from it to take cognizance of the object from which it comes. Till a rational soul has thus interpreted that image, it can convey no intel- ligence to the mind. The question we have to solve, then, is, by what steps and processes the soul acquires the power of interpreting this image, so as to learn from it the qualities and powers of the external universe, which when interpreted it does represent to the rational mind. We must next endeavor to answer this question. § 22. I. The peculiar class of ideas which the mind acquires by this sense is light, in all its modifications of color and shade. But to furnish the mind with this class of ideas in all their delicacy and beauty, by no means exhausts the function of this sense. The eye not only paints with inimitable minuteness and delicacy of detail on the optic nerve a picture of the material universe, but furnishes the mind with a system of arrangement by which, by the study of this picture, the rational soul comes to know that universe. The full function of the sense is to enable the soul to know the external world SENSE-PERCEPTION. 31 by means of a colored picture of it on the optic nerve. The eye is the painter, the photographer, the mind inter- prets the picture by means of the muscular organization with which the eye is furnished. II. Though the eye is certainly capable, by its own voluntary motion, of forming a rudimentary notion of extension and place, in the manner already described, it is not capable of forming the idea of outness. It is not conceivable that this should be furnished otherwise than by the experience of resistance to the soul's conscious power of voluntary motion. It is not easy to conjecture how it is possible for such resistance to be consciously experienced through the motions of the eye. We must go back to the very point from which we commenced our inquiries into the results of the muscular sensibility. We there saw how the mind does, in the motion of the hands or other limbs or parts of the body, experience such resistance, and learn from that experience the pres- ence of a resisting non-ego. We here call attention to the fact that the mind has or is liable to have a triple experience at the same instant. While the attention is fixed on the resisting non-ego, a feeling of contact and a sensation of color are likely to be experienced, and can- not long fail to attract the mind's attention. While voluntary motion resisted gives a non-ego, the cessation of that motion gives place, and to that place the mind refers the feeling of contact and the sensation of color, and comes to regard them as products of the causal power of the non-ego. The action of the mind therefore in referring the sensation of color to an external resist- ing cause is dependent on the action of the muscular sensibility. If the mind had not learned through the muscular sensibility the existence of the resisting non- ego, it never could have acquired the notion of an exter- nal surface or body. 32 SENSE-PERCEPTION. § 23. It has been maintained by some writers that the eye gives the notion of an extended surface directly without any dependence on voluntary motion, and that the sensation of color necessarily implies the existence of the idea of extension.* They suppose that the connec- tion in our minds of color with an extended surface is not formed by experience, but is natural and necessary. To us on the contrary it seems that the idea of extension is necessarily derived from the activity of the soul in voluntary motion. All the varying sensations of color are certainly produced by the impression of variously modified light on the nerve of vision. Each modifica- tion of the light produces by its direct action on that nerve a corresponding variation either of color or shade. If the human body were as motionless as a marble statue, the constitution of the eye remaining in the same relation to the knowing mind, as now, it can hardly be supposed that there would not be changes in the sensa- tions corresponding to every change in the light that fell on the retina of the eye. Doubtless the change from day to night and from night to day, from the green of spring and summer to the white of the snow-clad land- scape of winter would be noticed just as now. Would the landscape also be known as extended ? Would its different colored and shaded localities be distinguished from each other? Would a mind thus limited in its control of the bodily organs distinguish one place from another, and apply the words here and there to the dif- ferent points of the view ? Let the supposition be made that a circular disk were placed before an entirely un- trained eye, painted with parallel bands of strongly con- trasted colors^ would the mind necessarily distinguish the different bands of color from each other and thus recognize the disk as extended ? * Porter's Elements, Sec. 101. SENSE-PERCEPTION. 33 To this it may be replied, that in such a case, neither the disk nor the bands of color painted on it would be distinguished by the untrained mind, from the other objects in the field of vision. In order to make a test case, it would be necessary to suppose, that the un- trained eye is in a dark room, and that the colors were in stained glass filling an opening in the shutter, so that no light could enter the eye except through the stained glass. Would then the eye, however untrained, distin- guish the bands of color and locate them each in its proper place, and thus recognize the extension of the surface of stained glass on which they were painted ? Would a motionless eye ever do it ? § 24. I had not long ago my attention called acci- dentally to a fact which seems to answer the question. In a room in which I pass a good deal of time, a varie- gated flower bloomed. The ground was a very pale pink, while scattered irregularly over the petals were patches of deep red, not shaded into the ground, but abruptly contrasted with it, and separated from it by sharp and definite and in some cases straight lines. To a spectator standing near the flower these definite lines were easily traced with the most perfect distinctness ; but on removing the eye to a considerable distance, not only was it impossible to distinguish the patches of deep red from the pale pink of the ground, but the whole flower appeared of a uniform color, which was neither the pale pink of the ground nor that of the red patches, but a compromise between them, being evidently the color which would result from a combination of all the colors of the flower. So soon as by reason of distance the eye was no longer able, by the motions of its own axis, to trace the lines which separated the red from the pale pink, it lost its power of distinguishing the colors which all ran together into one compromise color. 6 34 SENSE-PERCEPTION. This is exactly what would take place, if the piece of painted glass were placed before an eye incapable of mo- tion in the shutter of such a dark room as supposed. The separate colors could not be distinguished from each other, but all would be blended into a mixture in due proportions of all the colors present. Our assertion is made true, that, to such a motionless eye, a variously colored landscape would appear as colored; but no sharp distinctions of contrasted color would be made. All the colors present to the eye would appear as a con- fused mixture. Would then this confused sensation of color suggest to the mind the idea of an extended sur- face ? There is no apparent reason to think so. Cer- tainly the different patches of color would not be dis- tinguished from each other, and no idea would be formed of their relative situation in the landscape. The idea of externality may not have been yet originated. The sensation of color may have been purely subjective, not suggesting to the mind any notion of external surface or body at all, like a flash of light the origin of which the mind forms no conception of. The sensation may be permanent, but as devoid of any association with an extended surface as the eye is of motion. § 25. III. As it was shown in a former chapter how the continuity of resistance to voluntary motion leads to the notion of the line and the surface, it might be shown that the continuity of the sensation of color in connec- tion with the voluntary motion of the axes of the two eyes over any colored surface, might lead the mind to the same notion, as readily as it was lead to it by the muscular sensibility in connection with the motion of the hand. In the same manner if the surface was vari- ously colored, the motion of the axes of the eyes over all parts of the surface would enable the mind to dis- SENSE-PERCEPTION. 35 tribute the various colors to their own proper points in it. IV. When however the mind is to pass to the con- sideration of the third dimension of extension, so as to form the notion of planes at an angle with each other and of solid bodies, it must again fall back upon the process of voluntary motion cooperating with the mus- cular sensibility. No action of the eye and its muscles can furnish the mind with the notion of two planes at an angle to each other or of a solid angle. At that point the whole mental movement seems to be neces- sarily dependent either on the muscular sensibility or that general sensibility of the surface of the body which is generally called the sense of touch. The same may be said with equal truth of all curved lines and surfaces. The mind seems incapable of form- ing an idea of such surfaces otherwise than through the continuity either of contact or of muscular sensibility, in connection with voluntary motion which is con- stantly changing its direction, which change of direc- tion is discerned only through the muscular sensibility. The muscles which move the eye are not capable of dis- cerning these delicate changes in the direction of the motion without also experiencing at the same time the resistance of the non-ego. That resistance is never en- countered by the muscles which move the eye. It is not true that we ever get the notion of a curved surface through the general sensibility of the surface of the body, but it is true that we cannot get that notion with- out the experience of resistance to the action of the muscles. We may therefore generalize the proposition that we are dependant on the muscular sensibility at last for all our ideas of the form of bodies. 36 SENSE-PERCEPTION. § 26. V. When however the notion of angular and curved surfaces has been formed in the appropriate man- ner, the eye furnishes the mind with the means of dis- criminating the different forms of bodies from each other with great rapidity and facility, without appealing again either to contact or muscular sensibility. It is the province of the eye, out of the light which comes from any object, to construct an image of that object, and an image formed from a plane surface is distin- guished by different modifications of light and shade from one which is formed from a curved or angular sur- face. The mind soon acquires the power of discriminat- ing between the images so formed, by studying the image of any surface in connection with the muscular and general sensibilities experienced in connection with it. Thus the image which the eye forms from a plane surface is recognized as such, as soon as it appears on the retina, and so of the images of curved and angular surfaces. VI. The question has been much discussed, what is the natural place of the visual object with reference to the eye ?* The answer doubtless is, that there is no nat- ural place for it. The mind cannot place it, except by the aid of the muscular sensibility in connection with voluntary motion, especially that of the hands. As already shown, the experienced resistance is first referred to something external, then the color is referred to the same external something, because it is experienced sim- ultaneously with the resistance of the non-ego, and is therefore referred to the same external cause. The sensation of color accompanies and becomes inseparable from the conception of a plane, curved or angular sur- face, and finally the distance of each particular surface * Reid's Collected Writings, pp. 163, 164. Porter's Elements. Sec. 101. SENSE-PERCEPTION. 37 or part of a surface is determined by the muscular effort necessary to move the hand, or the feet when they must be used, so as to bring ourselves in contact with it. These distances the mind soon learns to estimate with tolerable correctness without any appeal to contact or the muscular sensibility. This point and several others which we are here compelled to allude to, will be more fully illustrated under the head of the Cooperation of the Senses. § 27. VII. Two other questions have seemed to many to present no small difficulty. The image on the retina is always inverted and by optical laws must be; why then is the object seen, not like the image, inverted, but erect ? There is always an image formed on the retina of each eye ; why then, as two images are seen, is not the object seen as double ? Nearly the same considera- tions answer both these questions.* It is only through the discoveries of comparatively recent science that any of us know that we do see by the aid of an image on the retina. Men saw just as perfectly before that discovery was made as they do now, and little children that know nothing of the retina and the image on it have just as perfect vision as the philoso- phers who have studied the anatomy of the eye. Of course, as they do not know that there is any image, neither do they know whether that image is erect or inverted, and its position can have no influence on the judgment they form of the position of the object. The judgment of erectness or inversion is formed in quite another manner. When an object is before the eye we learn by experience only that in order to see one part of it we must turn our eyes upward, and in order to see another part of it we must turn them downwards. The * Porter's Elements, Sec. 100, 101. 7 38 SENSE-P RECEPTION. former is regarded as the top and the latter as the bottom of the object. This judgment is confirmed by our expe- rience in the use of our hands or other parts of the body. If the object is so near and of such size that it can be examined by moving the hand over and along it, we must move both our hands and our eyes upwards to reach the top and downwards to reach the bottom. Thus only the question of top and bottom is determined, and in the same manner the question of right and left. In neither case is the erectness or the inversion of the image taken into consideration at all. Motion alone is appealed to. As we do not know that there is any image on the retina, so we do not know that we have an image on the retina of each eye. The fact of a double image can then have nothing to do with our notion of the object as single or double. That too is determined in quite another manner. We measure the situation of an object with both hands, if we are blind, and if each hand finds the object in the same place, and affecting our sensibility in the same manner, allowing for difference of situation in the two hands, then we recognize the object as single, examined by two hands. In precisely the same way, we examine the object in all respects by each eye, allowance of course being made for the different positions of the eyes, and finding both eyes making the same report, we judge that it is one object seen by both eyes. Sometimes a single object seen by the two eyes will appear double. When the axis of each eye is directed toward the same point in space, an object situated at that point will be seen single; but if the axes are not directed toward the same point where the object is situ- ated, but toward some other point, then the object will be seen double. The reason is, that when we are look- ing at a single object with both eyes we invariably turn SENSE-PERCEPTION. 39 the axis of each eye toward the same point in the object we are looking at. If then we see an object with the eyes fixed on some point not in the object, we shall see it double. This takes place in some forms of disease, in which the will loses the control of the muscles of the eye, so that the axes of the two eyes cannot be at will turned toward the same point. A like illusion may also some- times be practiced upon us through contact. If the fore- finger and the second finger of the hand be crossed, and a pea be placed between them, we shall feel two peas where there is but one, because that in our normal expe- rience we cannot feel the same pea on the opposite side of these two fingers. All such judgments are determined by comparing our present experience with that which is usual and normal ; and when the experience is abnormal, an erroneous judgment is apt to be formed. These facts certainly do prove decisively that all our sense-percep- tions are founded on an act of judgment which is subse- quent to the sensation, and depending on experience. The more carefully we examine all the facts of sense- perception, the more will this be confirmed as a truth. § 28. IX. In the first outlook of the infant mind upon the material universe, all the objects which are in the view at any one time are not seen as individual objects, but as one whole, and it is only by experience very gradually acquired that particular objects are separated from that whole and known in their individuality. For example, the chairs, the tables and other articles of fur- niture of an infant's room, are seen as projected upon the same plane, and are only recognized as several patches of color on that plane. They are seen just as the painter must see them, in order to represent them correctly upon his canvas. The objects which are frequently moved are first detached and individualized. The child is also 40 SENSE-PERCEPTION. aided in this process by being himself removed to differ- ent parts of the room, being thus enabled to see the objects from different standpoints and in different rela- tions to each other and to the permanent parts of the room. This process is gradually carried on till all the individual objects are recognized as such. The same process is extended to the whole outer world. Many objects which are really distinct are regarded as one by the inexperi- enced child and the savage. A savage who had never seen a horse, on seeing a man of new and strange features riding on horseback, regards the man and the horse as one animal, and contemplates it with indescribable terror. This separation of the material universe regarded as a whole has to be extended to the distant heavens, and the completion of it is among the last and highest tri- umphs of science. X. Before leaving the subject of vision, it is appro- priate to remark, that the sense of sight not only has this power of vastly extending our knowledge of the material universe beyond all which could have been possible with- out it, but that it also invests us with the power of read- ing at a glance the minds, hearts and characters of our fellow-men. Every change in the feelings, the thoughts and intentions of our associates is almost sure to manifest itself in the eye, the gestures, the features of the face and the attitudes of the body. Many of these we learn by experience to interpret and understand. Many of them are however entirely outside the field of sense- perception, being wholly spontaneous in their manifesta- tion, and dependent, not like the special sensations for their interpretations, on experience and rationality, but on natural and instinctive intuition. All acquisition of knowledge is the result of rationality acting through experience, but feeling is spontaneous in its origin, and SENSE-PERCEPTION. 41 instinctive in its expression and interpretation. A large portion of this spontaneous intercourse of the feelings is carried on through the sense of sight. CHAPTER V. Examination of the Special Senses. Sense of Hearing. § 29. Next in the natural order of the development of our subject is the sense of hearing. As the sense of sight not only furnishes the mind with a new class of ideas not attainable by us through any other source, but greatly enlarges the sphere of our possible knowledge of the external universe, so the sense we are next to exam- ine both furnishes to the mind a peculiar idea, and opens up sources of knowledge which could not have been reached by the eye. By the last-named sense, we can learn nothing of objects in the absence of light, or when an opaque body is between the eye and the object. These are very serious limitations on our power of becoming acquainted with the objects around us. By the ear these limitations are removed. As color and shade comprehend all the ideas which are revealed to the mind through sight, so the word sound embraces all those which come through hearing. In respect to all these ideas, a mind that is deprived of this sense must remain utterly blank. A great number of persons in every generation are either born destitute of this sense, or are deprived of it by the accidents to 42 SENSE-PERCEPTION. which early childhood is exposed, and as all oral lan- guage is addressed to the ear, such persons never acquire the power of speech. They are not only deaf but mute. The results which have been attained in recent times by the education of deaf-mutes demonstrate, that not only might the human race have existed under these condi- tions, but that had all men been from the beginning without this sense, society might have existed and civil- ization to a certain extent attained. Even in such a silent world the rational soul might have devised means of carrying on intercourse by a lauguage addressed to the eye and not to the ear ; but under what limitations of the possibility of human thought and culture ! § 30. The peculiar organ of this sense is the ear. For a scientific description of this organ, we must refer the student to the treatises on anatomy and acoustics. He will there learn that as the design of the optic apparatus of the eye is to form a colored image of the external object upon the optic nerve, to be the soul's instrument of vision, so the design of the exquisite structure of the ear is, to cause the sound to be repeated upon the rami- fications of the acoustic nerve which are situated in the inner chambers of the two ears, which repetition of the sound is the soul's instrument of hearing. In order to render this perfectly intelligible it is necessary to state that all sonorous bodies, that is all bodies capable of causing the sensation of sound, are also capable of being made to vibrate by a blow or concussion. In order that the sensation of sound may be experienced, this vibra- tory motion must in some manner be communicated to the acoustic apparatus of the ear, and by it repeated upon the acoustic nerve. It is important to notice how close is the analogy be- tween the structure of the ear and that of the eye. In SENSE-PERCEPTION. 43 every case of sensation, through any one of the senses, there must be either contact of the external substance with the organ of sense, as in the case of taste, or else some medium of communication between the object and the organ, as in the cases of sight, hearing and smelling. In vision, the medium is light, in hearing it is atmos- pheric air, or some other substance to which the vibra- tory motion of the sounding body is communicated, and by it borne and imparted to the tympanum and through it and the apparatus of the inner ear, to the acoustic nerve. The analogy referred to may then be noticed step by step. The tympanum of the ear corresponds to the pupil of the eye, the interior apparatus of the ear to the lenses of the eye, the acoustic nerve in the inner chamber of the ear to the retina of the eye, and the impressions of the vibrations of the sounding body to the image on the retina. In both cases perception is brought about through an exact miniature representa- tion of the object on the nerve of special sensation, — on that nerve and on no other in the whole body. As in the case of seeing, so in that of hearing, on the fulfill- ment of this condition sensation will take place, and perception, provided that organism is inhabited by a rational soul that is attentive, and has learned by expe- rience and its own activity to interpret its own sensa- tions. It is our next task to trace the steps by which that rational soul, at first utterly unable to gain any information from this sense, any more than from sight, gradually acquires the power of interpreting the sensa- tions of the ear, so as by means of them to enlarge the boundaries of its knowledge of the material world. §31. I. Previous to experience, this sensation is purely subjective. The mind has no power of referring it, either to an external object as its cause, or to the 44 SENSE-PERCEPTION. organ in which it is experienced. Not only does the mind at first fail to refer this sensation to the acoustic nerve situated in the interior chamber of the ear, where only it is experienced, but even in mature life, after science has informed us what the seat of the sensation is, we have still no consciousness of experiencing it at that point. We learn by experience to refer it in general to the ear, because a sounding body must be brought as near as possible to the ear in order to hear it most loudly. Without this experience to guide us, we should not know even in mature life, till informed by science, that the ear has any more connection with it than the rest of the body. Much less have we the power of referring it to any external cause. II. Before it can be referred either to its proper place in the organism, or to an external cause, the ideas of extension, of extended surfaces and of bodies external to ourselves, must have been formed in the manner already described. This sense is conditioned by the previous intelligent use of the muscular sensibility and of volun- tary motion in the same manner as the sense of sight. III. The mind learns to refer sensations of hearing to their proper external causes by a succession of experi- ments. Some external body with which the learner is already acquainted is brought in collision with some other body, and a peculiar sensation is immediately noticed. The same sensation is produced again and again in the same circumstances, till he has learned that that body will on being struck produce that sensation. The same course of experiment is gone through with in respect to other sensations of sound, till he has learned to refer them each to the sonorous body by which it is produced. Thus in each and every case a sensation of sound is converted into the appropriate perception. SENSE-PERCEPTION. 45 The situation of the sounding bodies with respect to the ear is ascertained in all cases by the muscular sensations, aided in seeing persons by sight. § 32. IV. The ear and the eye estimate the direction and distance of objects in almost the same manner. In vision the object is seen in the direction toward which the axes of the eyes must be turned to see it most dis- tinctly. The axes of the eyes are directed toward the object, either by turning the eye in its socket, or by turning the head on the joint of the neck, or by a move- ment of the whole body, or by all these together. In the case of the ear, the movement of the head and of the whole body only are available, the ear having no motion of its own. The sounding body is judged to be in the direction toward which one of the ears must be turned, to hear the sound most loudly and distinctly. Our judg- ments of direction through the ear are much less accu- rate than those formed through the eye. The reason is that the muscular organization for giving direction to the ear is much less delicate and perfect than that by which the eye is directed toward its object. The eye has many modes of estimating distance. Some of these are not available to the ear. When the eye is left to its own resources to judge of distance by the image on the retina, its method is much the same as that which is used by the ear. In such a case the eye judges of the distance by the distinctness or dimness with which the detail of the picture is filled out. In the same manner the ear gives distance, not so much by the loudness as by the distinctness of the sound. In sounds which are near at hand, there are apt to be mi- nute varieties of sensation which would be inaudible at a greater distance ; but at best our judgments of dis- tance by the ear only are very uncertain. 46 SENSE-PERCEPTION. § 33. V. As an instrument to be used in acquiring a knowledge of the material universe, the ear can bear no comparison with the eye. The distance at which any sounds can be heard by the unassisted ear is only a few miles, and even by the aid of recent inventions, it can only be extended over a very small portion of our planet ; yet the unassisted eye discerns the existence of objects in remote portions of the universe, in contem- plating whose distances from us the mind is over- whelmed and confounded. All the information which hearing can give us of the various material substances around us is confined to their power of causing the sen- sation of sound when coming in collision with other bod- ies. Of size and form, it cannot be trained to give us any information, and as we have seen, its indications of direction and distance are very vague and uncertain. On the other hand, however, its power of giving us a knowledge of the feelings, intentions and characters of our fellow-men by direct intimation is not at all inferior to that of the eye. If it is true that every purpose, feeling and passion of the soul is likely to manifest itself in the faces and gestures of men, it is equally true that they are even more sure to express themselves in tones of the voice, which are natural signs of feeling and character, instinctively uttered and instinctively interpreted. Emotion has a natural language both of the eye and of the ear. Perhaps that addressed to the ear is the more expressive and the more easily under- stood. It is also worthy of notice, that to some extent at least, this natural language is common to us with the brute creation. Especially is this true of the expres- sion of emotion by sounds. The semi-tone proceeding from her offspring reaches the heart of the brute as of the human mother. SENSE-PERCEPTION. 47 In this chapter and in the chapter on the sense of sight, it has been our object for the most part to discuss these senses only so far as they are instruments of per- ception, whereby the soul learns to understand the ma- terial universe. There are other functions of these senses to be discussed in future chapters. CHAPTER VI Examination of Special Senses continued. Smell and Taste. § 34. It is by the sense of sight and hearing for the most part, that man acquires a knowledge of the uni- verse in which he lives. By the muscular sensibility, the feeling of contact and the act of voluntary motion, he learns the existence of an extended and external uni- verse, and by the aid of the senses of sight and hearing, he fills in that knowledge with an endless variety of rich and interesting detail, and extends it on all sides far out towards the limits of existing material things. The two senses remaining yet to be considered have for the most part reference only to limited classes of objects, and stand related to the preservation of life, and, if we embrace along with them the sense of sex, to the preservation of the species. It is also to be no- ticed that, in dealing with these senses, we have forced upon our attention another function of sensation, which has nothing to do with sense-perception, and of which we have thus far made only very brief mention. It is 48 SENSE-PERCEPTION. to furnish man with almost boundless sources of delec- tation, and to lay in human nature itself the foundation of esthetics. All the senses are sources of exquisite pleasure, superadded for the most part, it would seem, to what was really necessary for the practical uses to which the senses were to minister. This is now only named, that we may not seem to be neglectful of it. This function is conspicuous in the senses which remain to be examined. § 35. The sense of smell next demands our attention. This sense is more analogous to those of sight and hear- ing than taste, because by it we may be still dealing with objects which are at some distance from the organ through which the sensation is experienced. The odor- ous object is very rarely in actual contact with the organ, and the sense is capable of acting through a con- siderable intervening space. Its organ is situated in the nostrils, and is a ramifica- tion of the nerve of smell spread over a certain portion of those cavities in a manner very analogous to that in which ramifications of the optic and acoustic nerves line the interior of those chambers. The medium through which the olfactory nerve communicates with the odor- ous body consists of certain particles of the substance of that body which escape into the surrounding atmos- phere, and find their way to the organ of smell. If this is a true account of the matter, the substance of all odorous bodies must be more or less volatile, and capa- ble of diffusing itself through the surrounding air in exceedingly minute division. If this is the true origin of odors, as probably it is, there are two reasons why the organ of smell ought to be situated just where it is. As we are continually breathing the air, in which we are at all times immersed, the particles of any odorous body i SENSE-PERCEPTION. 49 which may be diffused in the air around us are sure to be drawn into the nostril, and thus be brought into con- tact with the organ. One of the functions of this sense is to test the quality of the air we are breathing, and to give us warning when it is vitiated by any deleteri- ous influence dangerous to our health and safety. All the air which is introduced into our lungs in breathing should, as far as possible, be introduced through the nostrils, and is thus subjected to the scrutiny of this sense. Another function of this sense is to scrutinize our food, to detect any deleterious quality in it, that it may be rejected before it is received into the mouth. It was therefore necessary that it should be so situated as to act as a sentinel at the opening of the mouth. It is then situated precisely as it should be, in order that it may exercise a watchful scrutiny over all our food, that noth- ing deleterious may find admission to the organs of digestion and assimilation. § 36. As has been already remarked the sensations of smell are, previous to experience, purely subjective, not referred to the part of the organism where they origi- nate, or to any external cause.* In mature life, when experience has done all in the premises which it can do, none of us not instructed in the anatomy of the organ, knows precisely in what part of the nostril the nerve is situated, or how widely it is diffused. We have no consciousness of its situation, neither are we able to determine where or what the object is from which the odor comes without the aid of voluntary motion and the other senses. We are unable to decide by the sense alone, whether it is an odor widely diffused in the air from some unknown cause, or comes from some object *Dr. Thomas Brown, Lecture XX. Sense of Smell, p. 195. 9 50 SENSE-PERCEPTION. near at hand. Nor can we determine in most cases the direction from which it comes, though in some cases we can form an imperfect judgment of the direction, by methods closely analogous to those used in the sense of hearing. All these points we are able to determine by the aid of voluntary motion and the other senses. The relations of the sensations of smell to perception are, therefore, precisely analogous to those of the senses hitherto examined. Perception may follow or may not, according as they are or are not attended by a rational soul interpreting the sensation by our muscular sensibil- ities and our acts of voluntary motion. § 37. The perceptional function of the sense of taste is to apply still another test to whatever is about to be introduced into the stomach, to ascertain its fitness or unfitness for the nutrition of the body. It also has another function, to increase the inducement to take a sufficient supply of wholesome food by the added pleas- ure of the gratification of this sense in eating it. It is with the former of these functions only that we are at present concerned. The organ of taste is situated in the tongue, and some other parts of the mouth, which are furnished with a peculiar coating of nerves, which alone of all the nerves of the body can yield the specific sensation called taste. As the feeling of contact extends to the interior surface of the mouth, and as the sensation of taste can only be experienced by the actual contact of the substance tasted with the organ, the feeling of contact and the sensation of taste are both experienced at the same time.* This is not invariably and necessarily so. It is possible, by closing a person's eyes, to introduce into the mouth a small quantity of a highly sapid liquid, of the *Dr. Thos. Brown, Lecture XX. Taste, pp. 196, 197. SENSE-PERCEPTION. 51 same temperature of the mouth, which will produce a very decided impression on the organ of taste, without exciting the feeling of contact at all. We often retain in the mouth the taste of some substance, after nothing of it remains in the mouth which can excite the feeling of contact. The sensations of taste and the feeling of contact are not therefore necessarily and universally simultaneous. The fact that we do so generally feel a substance in the mouth at the same moment that we taste it, and that all substances must be introduced into the mouth in order to be tasted, naturally lead the mind almost immediately to regard the sense of taste as situated in the mouth, and to refer the sensation to the food taken into the mouth as its cause. But our sensations of taste are not therefore any the less obviously, before experi- ence, purely subjective. Most of us pass through our whole lives without ever learning over what portion of the interior of the mouth the organ of this sense extends, and the experience of the sensation furnishes us no means of knowing what parts of the cavity are, and what parts are not, susceptible of the sensation. We do indeed early learn that the upper surface of the fore part of the tongue is susceptible of it ; but we learn this only by the fact that the tongue has a motion of its own, and can be by voluntary motion separated from the other parts of the mouth, so as to assure us that sapid sub- stances placed upon its surface and confined to its sur- face are instantly tasted. We thus get the same sort of evidence that the organ of taste is upon the fore part of the tongue, as that by which we learn that the organ of sound is in the ear, or the organ of smell in the nostril. The other parts of the mouth are not furnished with an apparatus of motion of their own, and therefore, in the 52 SENSE-PERCEPTION. ordinary experience of the sensations of taste, we never learn whether the organ of the sense does or does not extend to certain other parts of the mouth. . This in- stance, therefore, instead of furnishing any objection to our general argument on this subject, is very strongly confirmatory of it. Like the sense of smell, this sense can render compar- atively little service in acquiring a knowledge of the material universe. It is confined to its own special class of ideas, and cannot be educated into any discernment of size, form, distance or direction. In its own sphere, however, it is almost preeminent among the senses in the variety, accuracy and delicacy of its discriminations. § 38. This examination of the special senses which we have now completed justifies us in enunciating two pro- positions which are of great importance to the right understanding of our subject. I. All sensation is purely subjective, and becomes objective only by the aid of the muscular sensibility, the activity of voluntary motion and the experience of resistance to it from objects external to ourselves. II. There is no direct and immediate sense-perception. It is always indirect and mediate.* § 39. Before closing this chapter it is desirable more fully to illustrate what has already been alluded to, that the special sensations have two functions, which may be distinguished from each other as the critical and emo- tional. The critical function of sensation is that by which it enables the mind to acquire a knowledge of material things around us. It is by this function of sen- sation that it becomes a factor in sense-perception. To this function almost exclusive attention has been given thus far in this Treatise. * Porter's Elements. Sec. 109. SENSE-PERCEPTION. 53 The emotional function of sensation is that by which it furnishes peculiar sources of delectation, enjoyment, happiness, over and above the essential aid which it ren- ders to the mind in acquiring a knowledge of the mate- rial world. This distinction has hardly been as clearly marked by writers on the subject as it deserves to be. It is however obvious that it is real, and deserves to be fully recognized. For example, the sensation of taste has confessedly a very important function in enabling the mind to judge of the quality of the substances in- troduced into the mouth, with reference to their fitness for the nutrition of the body. But that sense has cer- tainly another function which is no less real and import- ant. It is to connect with the taking of food a unique and intense pleasure which can be derived from no other source, and without which it is improbable that men would provide and take a sufficient supply of various and nutritious food, to nourish the body and bring it to its greatest perfection. This pleasure added to the tak- ing of food greatly increases the happiness of life. The emotional function also requires a subdivision into the sensual and the esthetic. Of these the former is common to man and the lower orders of creation. The grazing ox evidently enjoys in a high degree the pleasure of taking and masticating his food. But the ox has no eye for the beauties of form and color, or for the harmony of sweet sounds. As has been already re- marked, the sensual function seems to be lacking in the senses of sight and hearing, while the esthetic seems for the most part to be confined to those senses, though some may be disposed to regard the art of cookery, and of the compounding of odors as being truly esthetic. Whether or not they are entitled to that rank is a ques- tion of small importance ; it is plain that they can bear 54 SENSE-PERCEPTION. no comparison with those arts which are addressed to the eye and ear, as instruments of the culture and eleva- tion of the human soul. The object of those arts which are addressed to the senses of taste and smell is always sensual not intellectual. § 40. Apparently, the sensual function was connected with the senses of smell and taste (and to speak the whole truth sex should be added), to secure the preser- vation and perfection of the animals and species of ani- mals in which it is found. It is however undeniable that it does immensely increase the happiness of all sen- tient beings. In many of the lower animals it appears to be true, that the senses of taste and smell are much more acute than in man, and very much more important to them in guiding their lives. Guided only by these senses, a large portion of the animal kingdom select their food with unerring accuracy, and that from the very moment of birth, without any of that uncertain expe- rience by which man learns to distinguish food from poison. Seemingly by the sense of smell alone, the dog tracks the footsteps of his master among the footsteps of a multitude of other men ; though we have no posi- tive proof that this is accomplished by the sense of smell. The dog may have some other sense of which we have no more knowledge than a race of deaf mutes would have of the sense of hearing. In the lower orders of creation these senses are an almost infallible guide to the attainment of the highest perfection of which the several species are capable. In man however it is far otherwise. He has a rational and moral nature of which all the senses are but servants, and must be in absolute subjection, or the most disas- trous consequences will follow. No greater ruin can come to a human being than that which results from the SENSE-PERCEPTION. 55 indulgence of the lower senses uncontrolled by the intel- lectual and moral nature. § 41. From the point of vision to which we have now attained, it is easy to see, how widely the rational nature of man separates him from all the irrational creatures that surround him, and to which in some respects he seems nearly akin. The brute has apparently the same senses as man, and some of them even in greater per- fection. But the relation of man's life to the senses is removed from that of the brute to the greatest possible distance. The brute has sensations, but no perceptions. In some way of which we have certainly little experi- ence, his sensations guide him directly to his destiny, without any of the slow processes by which man learns to mature sensation into rational perception. As the sensations of taste and smell guide him with unerring accuracy in the choice of his food, so the sensations of sight and hearing guide him with equal accuracy, in all those activities in respect to which it is necessary he should be guided by them. The use which he makes of his senses as the guide of his life is not the result of thought, nor of intelligence instructed by experience. It may be said in reply to this, that the inability of the infant to use his senses and his limbs at birth is the result of the physical weakness in which he was born. We reply that this is obviously not entirely the fact. Many persons have been born blind, and have acquired the power of vision in mature life. These persons do not, the moment the power of vision is acquired, spring at once into the full use of that sense after the manner of brutes, but must acquire the use of it by experience and the exercise of rationality in the very way already described. It is an intellectual process, just as truly and of the same character as the efforts of the philos- 56 SENSE-PERCEPTION. opher to study nature in any department. We call the use which man makes of his senses sense-perception. It is a truly intellectual process from the beginning. We call the use which the brute makes of his senses instinct. We know little of the nature of the thino- we thus name, because we have little experience of that mode of guid- ing life ; yet we are not entirely without experience of it. The moment the hungry infant feels the source from which his nutriment is to be derived, between his lips, all the muscles concerned in the operation of sucking spring at once into cooperative activity, and the little being that otherwise must soon have died of starvation is nourished and reared up to manhood. There is no human intelligence in this, it is necessary activity ex- cited by instinct. So much we know by experience, though by an experience long ago forgotten. When therefore we ascribe brute activity to instinct, we do not use a word without a meaning. It has meaning in the history of our own lives. It is probable that this brute activity is produced by a method nearly analogous to that by which the chest of the new-born infant con- tracts and expands at the touch of air, or the pupil of the eye at the touch of light. The way in which brute life is guided is one and sim- ple. It is not the way of intelligent sense-perception, but the way of unintelligent sensation. His sensations simply stimulate and guide his activity to the attain- ment of his destiny. All the sensations of the brute direct him invariably and inevitably to a sensual life. He can live no other. To man the senses are the instru- ments which stimulate him to so much of sensuality as is needful for him, and guide his rational powers to that knowledge which is essential to a human life and to such culture as rational powers require to their full develop- SENSE-PERCEPTION. 57 ment. Man therefore requires the three functions of sensation — the critical, the sensual and the esthetic — while the brute requires and is capable of the sensual only. Any account of the origin of man which does not recognize this broad distinction between human and brute life cannot be true. § 42. At this point we can hardly forbear remarking that instinct, as thus explained, seems to be the point at which animal and vegetable life touch each other. A plant growing in a dark place to which a scanty supply of light only is admitted at a single opening, not only inclines from its natural perpendicular position towards the source from which the light comes, but greatly stretches itself beyond its normal length, as if in an effort to reach, if possible, a sufficient supply of light. This is very analogous to the manner in which instincts stimulate the activities of the brute. There are other cases in which the analogy is still stronger. The bee builds his cell on strictly geometrical principles, though he knows nothing of geometry and experiences no pleas- ure from an appreciation of the perfection of his work. In the same manner every plant in the garden, every weed by the roadside, every tree of the forest puts forth leaves and flowers, and seed vessels and seeds of the same form and color and texture and structure, with no intelligence and no appreciation of the perfection and beauty of what it produces. Man is guided by intelli- gence, and feeling, controlled by intelligence; the brute by an impulse of feeling without intelligence, and the plant by an impulse without either intelligence or feel- ing. § 43. At the foundation of the esthetic function of sensation, lies the ultimate fact, that there is in the human soul a natural capability of discerning in the uni- 10 58 SENSE-PERCEPTION. verse that mysterious, undefined and undefinable quality which we call beauty. It is undefinable just as color is undefinable. It can be known only by experience. It is present in the innumerable forms and colors, and com- binations of form and color which are addressed to the eye, and in the endless multitude and variety of sound and combinations of sound which are addressed to the ear. To discern this quality and to present it to the mind as one of the most fertile and elevating sources of human happiness is the esthetic function of sensation. This function involves in a high degree the action of the iutellect, and never reaches its maturity except in the most perfect development of which the intellect is capable. In its maturity it preeminently implies the comparison of one thing with another, and a discern- ment of the relations of one thing to another, and of the part to the whole, and of the whole to its parts. And yet its presence is often most decidedly manifested in very early infancy. Au infant not one year old has been known to break out in hearty laughter at the sight of a handsomely turned bed-post, to cease laughing as soon as its eye was turned away from it, and to give the same manifestation of pleasure when agaiu getting sight of it. Admiration of the beautiful is certainly among the earliest manifestations of an intelligent nature which are seen in childhood. This may truly be termed sense-perception. As soon as the infant recognizes the forms and colors and sounds of external nature he also perceives beauty as one of its qualities just as he perceives its color or its form. It is not possible, however, to present the subject entire in this treatise because it implies more than sense-percep- tion — it involves the consideration of the higher thought- powers of the soul. SENSE-PERCEPTION. 59 CHAPTER VIII Cooperation of the Senses. § 44. Many writers have insisted strongly on the dis- tinction of original and acquired perceptions.* It will readily be perceived that, consistently with the views thus far advocated in this treatise, this distinction can- not be admitted as having any foundation in the phe- nomena we are dealing with. In whatever sense any one perception is original all perceptions are original; and in whatever sense any perception is acquired, all are acquired. It may be said that there are perceptions furnished by one sense alone, and others which cannot be acquired without the aid of more than one sense. Even this, however, can hardly be admitted. The eye can be trained to discern extension and judge of dis- tance ; but this is not accomplished by calling in the aid of another sense, but by the help of the muscular sensi- bility, voluntary motion and the experience of resist- ance from without. Even if we admit touch to a place among the special senses, the eye is not dependent upon it for the formation of its judgments of extension and distance. It is not true, as often asserted, that we edu- cate the eye to do the work of the sense of touch, and of touch to do the work of the eye. Both the sense of sight and touch (admitting touch to be a sense), inde- pendently of each other, derive their judgments of exten- sion and distance from the same sources. The real question in hand relates to the propriety of the distinction expressed by the words " original " and * Reid's Collected Writings, p. 184 ; Porter's Elements, Section 103 and onwards. 60 SENSE-PERCEPTION. " acquired." Whether the mind is dependent on a sin- gle sense or more than one is requisite, in either case the perception is not immediate knowledge, following directly on the sensation without any intervening pro- cess ; but mediate knowledge acquired by the interven- tion of a rational soul to interpret the sensation, and in interpreting it, the mind uses assistance derived from other sources than the sensation itself. It employs the aid, not of some other sense, but of the muscular sensi- bility in connection with voluntary motion. It is thus mediate and acquired, and not immediate knowledge. All perception then is acquired, not original. Neither the touch though admitted to a place among the special senses can discern an extended surface, nor the sight, the colored surface, without the aid of muscular sensi- bility. § 45. There is, therefore, much less dependence of the senses on each other than is apt to be supposed. It is rather true that all the senses are dependent on knowl- edge previously acquired from the same sources than that one sense is dependent on another. The power of perception is not confined to one or two senses, as some authors of the highest respectability have maintained,* but is common to all the senses, and all the senses are alike dependent on the muscular sensibility and the act of voluntary motion for translating their sensations into perceptions. There are, however, certain respects in which there is a necessary cooperation of the senses with each other. For example, the soul must learn to identify the object as presented to one sense with that same ob- ject as presented to another. When one blind from birth has acquired sight at maturity, he has a good deal of difficulty in identifying the object which he has before * Porter's Elements, Sec. 88. SENSE-PERCEPTION. 61 known by handling it, with that which he has now learned to cognize by vision. He may, for example, know the cat and dog by handling them, perfectly well, and he may easily distinguish them as visual objects, after he has acquired the power of vision ; but he must also learn to identify each as felt with the same as seen. He must learn to know how an object which affects the hand so and so when handled, will affect the sense of sight. He must become able to feel with his eyes and see with his hands. This is called an acquired percep- tion ; yet it is acquired in no other sense than any other perception. Both are equally the results of an experi- mental process. It is, however, a true cooperation of the senses of sight and touch (if we admit touch to be a sense), if we do not admit it to be a sense, it is coopera- tion of the sight with the feeling of contact. It is pre- cisely like the process by which the mind acquires the power of distinguishing by vision the plane surface from one which is curved or angular. § 46. All the perceptions of sound involve this same cooperation. According to the definition of an original as distinguished from an acquired perception, there are no original perceptions of sound. All are acquired per- ceptions. They require the aid of the muscular sensi- bility in determining the direction from which the sound proceeds, and either of the eye and of the feeling of con- tact or the experience of external resistance in identify- ing the sounding body. The same thing is equally true of the sensations of taste and smell. We are thus brought back again to our position that no one sense is of itself adequate to any perception. Every possible case of sense-perception is a case of cooperation either of one sense with another, or of a sense with some form of muscular sensibility. 11 62 SENSE-PERCEPTION. By the cooperation of the sense of sight and hearing with each other and with the various forms of muscular sensibility, all the beautiful and eminently important results of oral and written language are produced. The organs of the human voice have a capability of all that variety of sounds, simple and combined, which consti- tutes spoken language, and by the aid of the muscular sensibility acquire the power of uttering these sounds at pleasure, under the control of the judgment and the will. Different minds are capable of agreeing to use certain sounds and combinations of sound as expressions of knowledge, thought and feeling. The ear is capable by its delicate organization of repeating those vibrations which originated in the voice, and by their being so repeated upon the acoustic nerve, the mind takes cogniz- ance of them, and thus the meaning of one soul is con- veyed to another with almost the rapidity of thought itself. The mind is also able to devise for each of these vocal expressions of the soul's meaning, signs addressed to the eye, by which they may be recorded to endure for ages, and be transmitted to any distance, and by the inven- tions of this age with the rapidity of lightning. Thus by the cooperation of the eye and the ear the meaning of one mind may be transmitted to any number of other minds, at any desired distance either of time or space. All this the human soul accomplishes by the intelligent and rational use of the senses. § 47. Or, if the sense of hearing is lacking, signs ad- dressed to the eye may be substituted, instead of vocal sounds as representatives of thought. When, however, the effort is made to reduce this language of signs ad- dressed to the eye to a written language, great difficul- ties are encountered. In the case of an oral language SENSE-PERCEPTION. 63 this is accomplished with comparative ease, because the number of elementary sounds necessary to the formation of a spoken language of the greatest copiousness is very small, not much exceeding forty. For each of these a visible representative is very easily invented and agreed on, and all other visible representatives of vocal signs are mere combinations of these few elementary sounds- Thus only twenty-six characters suffice to write all the fifty thousand words of the English language. It is difficult to conceive how a few elementary signs can ever be invented out of which in like manner all the visible signs necessary to the completeness of the sign language could be compounded. The cooperation of the eye and the ear would seem to be a necessary condi- tion of the construction of a written language which should be in the highest degree comprehensive and ex- pressive, and yet easy of acquisition. The difficulties encountered in the acquisition and use of the language of the Chinese well illustrate the principle. If the sign language were reduced to writing, it must be by the use of visible signs for things and not for souuds. The written language w T hich the deaf mute acquires in our present modes of teaching, is not the sign language reduced to writing, but our own written language as it presents itself to the deaf mute's eye, unaided by the sense of hearing from which we obtain it. It is an exceedingly difficult acquisition. If the human race had all been deaf mutes, their written language, if any at all existed, would have been exceedingly limited and inade- quate. It seems hardly probable that a race of deaf mutes could ever have brought the sign language to its present degree of perfection. § 48. It is a conceded law of language that all terms expressive of mental acts and states are derived from 64 SENSE-PERCEPTION. the various processes of sense-perception. It is only an application of the principle that all language is of ma- terial origin. It is a question of some interest from which of these processes such terms are chiefly derived. It is held by some writers* that they are derived chiefly from the sense of touch, or as we have preferred to call it, from a feeling of contact. This opinion can hardly be sustained. Perhaps it would be nearer the truth to say, that none of them can be said with any propriety to come from that source. On the other hand, they are mostly derived from the action of the muscles. We are said to take or apprehend one's meaning, certainly we do not take or apprehend a thing by touching it. We are said to hold an opinion, to comprehend or grasp a train of thought, to accept a proposition or a system. Not one of these forms of expression has any reference to touch, but all are derived purely from muscular ac- tion. Even that word, which by the common consent of all the philosophers of all schools, is used to express the action of the mind in acquiring a knowledge of the material world, perception, is derived from the Latin capio to take, thus suggesting in all its uses that original source of all our knowledge of the material universe, muscular action. Thus the very phrase sense-perception implies and suggests the truth of the doctrine which has been advocated in this treatise. § 49. Music is also dependent on the cooperation of the senses. The existence of music is quite independent of the sense of sight, but it is certainly dependent on the muscular sensibility. All music depends fundamen- tally on the varieties of pitch which the human voice is able to utter, and the human ear to distinguish. But such control of the element of pitch as is necessary to * Porter's Elements, Sec. 99. SENSE-PERCEPTION. G5 the simplest melody is attainable only through the ex- perience of the muscular sensibilities which attend the modulation of the voice, or the movement of the fingers in playing the instrument. Experience of the same muscular sensibility is equally necessary to harmony, and to the rhythm of music. The production of written music is dependent on the cooperation of the eye and the ear in precisely the same way as written language ; since in music the number of elementary sounds is very few, out of which all others are compounded. It is only necessary to express each of these elementary sounds by a sign addressed to the eye and the problem is solved. We have seen that if the sense of hearing were want- ing, language would still be possible through the eye ; but that this could become a written language only to a very limited extent. The same difficulty would not how- ever exist in the -way of written music, if the sense of sight were lacking. The mind could devise expressions for the elementary sounds of all music which should be addressed to the feeling of contact and the muscular sen- sibility, and with these the blind could read music, just as they now read the page which is printed with raised letters. Neither would the blind have any special diffi- culty in reducing a spoken language to writing, if they could devise means of printing in raised letters without eyesight. If all men were blind, the necessity would be imperative of printing all books and all music in raised characters, or at least in some form which could be read by contact and motion. It is not however prob- able, that without the sense of sight the race could ever have attained to sufficient prosperity or civilization, to have used either written language or music. § 50. All the higher forms of beauty require the co- operation of the senses. There is a degree of beauty 66 SENSE-PERCEPTION. in a single bright color, and a higher degree of it in skillful combinations of color ; but a still higher degree of it is always attainable by combinations of beauty of color with beauty of form. These combinations of course can only be produced by the cooperation of all those powers by which we acquire the ideas of color and form. So in music the highest beauty requires the most skillful combination of pleasing sounds and sounds expressive of emotion with pleasing movement. The highest esthetic effects can only be produced, when art successfully imitates nature. This is the great- est triumph of genius. We have seen that the mind is made acquainted with material objects by a picture formed on the retina of the eye. Imitative art employs just such a combination of light and shade painted on a plain surface, as the lenses of the eye paint on the optic nerve, to represent the object to the mind, and to all minds alike. The perfection of the painter's art lies in conceiving by the imagination precisely the combination of light and shade which any object or group of objects placed before the lenses of the eye would paint on the retina, and in the skill perfectly to imitate that combi- nation on the canvas. Each perfect eye will then trans- fer that representation to its retina, and thus each be- holder will see reproduced the object which the painter meant to represent. He not only perceives the colors of the object, but its form and proportions, not only how it would look but how it would feel. The objects so rep- resented may be anything which the eye cau perceive, a tree, a flower, an animal, a landscape, or the human face divine. In this latter case it would represent to the mind a great deal more than form and color, a great deal more than mere physical qualities, it would repre- sent thought, feeling, purpose, character. Thus the SENSE-PERCEPTION. 67 whole power of the most skillful painter lies in correctly conceiving and representing on the canvas, that combi- nation of light and shade which the lenses of the eye would paint on the retina. Of course this implies that power of the imagination which conceives of a subject worthy in the highest degree to be so represented. CHAPTER IX. The Activity of the Soul in Sense-Perception, and the Products which it Evolves. §51. If the views of Sense-Perception insisted on in this treatise are sound, there is no occasion to raise the question whether the soul is active or passive in that experience. We have traced its activity at every step. We have seen that it commences its career of acquisi- tion in utter ignorance of the universe outside of itself, and that it makes its way out of that prison of darkness and confinement by putting forth its own activity, just as truly as the young oviparous animal makes its way out of the darkness and confinement of its shell into the light and freedom of the world without by breaking its own shell. Its first achievement is to acquire the power of motion under the control of the will. Till this is learned nothing of the external world can be known. No sooner, however, has the soul made this acquisition than it finds that power which it consciously exerts hindered from going out into result by some resistance. By an intuition of which we can give no account, other 68 SENSE-PERCEPTION. than that it is of the nature of the human soul, as soon as it becomes conscious of being itself a cause, to look for a cause for whatever happens, the mind sees in this resistance a resisting cause which is not the acting ego. It is known that the resistance is a non-ego, for the cau- sative power which the ego consciously exerts is hind- ered from going into effect. The condition of his experiencing that resistance is the exertion of his own active power. Thus, the first hint a human soul can ever get of the existence of the non-ego is conditioned by its own conscious activity. His second step in the process is in like manner de- pendent on his conscious exertion of the same power of voluntary motion. As soon as he experiences and rec- ognizes resistance, he finds that that resistance hinders voluntary motion only in a certain direction, while in all other directions it is free. He also finds by trial that that resistance only exists within certain limits, and by successive trials he ascertains the limits within which the resistance is experienced. Moving his hand backwards and forwards he finds that within these limits resistance is continuous ; beyond them motion is free. This reveals to him an extended surface or exten- sion in two dimensions. In like manner it has been shown how by the same exertion of his power of volun- tary motion he is conducted to a knowledge of the third dimension of extension, of solidity, of form, and in gen- eral of external bodies. For all these acquisitions he has been dependent on exerting his power of voluntary motion and his experience of resistance to that power when exerted. § 52. This, however, is not the whole truth. This necessity for the activity of the soul not only pertains to the first acquisition of the power so to use the senses SENSE-PERCEPTION. 69 as to acquire the knowledge which they are able to fur- nish, but it pertains to all the experiences of sense-per- ception throughout life. Innumerable cases which occur in the experience of every man prove that it is quite possible that a sensation many be experienced through the proper organ of sense, and yet without an act of attention, there will be no perception. A man can per- ceive nothing with any of the senses when the attention is wholly absorbed in another direction. One's atten- tion may be so entirely fixed on a mathematical problem, that a friend may enter his room, and even speak his name without being perceived either by the eye or by the ear. Two persons may have been born and reared in the same house and amid the same natural surround- ings, and yet one of them will know a multitude of things about the environment of that home of which the other remains entirely ignorant. Their senses may be equally acute and yet one of them fails to know much which the other learns from childhood. The only reason is that the one gives his active attention to the objects around him, while the other fails to do so. All sense- perception is thus seen to depend on the mind's activity. No matter how keen the senses may be, we perceive what we attend to and that which we do not attend to we do not perceive. No sensation can ripen into per- ception without the interpretation of an active ration- ality. It is like the frequent experience of the mind in reading a book. The eye may pass along the page and see every letter, and yet the activity of the mind to invest those letters with their proper meaning is not ex- erted, and therefore the man finds that he knows noth- ing of the subject matter of that which has passed before his eyes. Some men can read in the midst of conversation and understand what they read, because 12 70 SENSE-PERCEPTION. they fix their attention on the book and do not hear the conversation. Another hears the conversation and therefore understands nothing of what he reads. The mind actively chooses to which it will attend. Of two men who take a journey together, one returns with a mind stored with a knowledge of innumerable objects of interest of which the other has learned noth- ing at all. To one mind the universe, nature, society, history — all things are full of lessons of wisdom. To another mind enjoying the same advantages the whole scene around him is a blank, imparting no instruction and no wisdom. One of these minds is active, the other without activity, putting forth no energy beyond what is necessary for the physical uses of each hour as it passes. The mind exercises the power of selection among the objects presented to the senses, giving atten- tion to those things which it regards as important to be known, and drawing attention away from those things which it regards as unimportant. We thus select our own food by our own mental activity, just as the brute selects its physical nutriment by the acuteness of sensa- tion. § 53. If the views maintained in this treatise are true, we must regard the activity of the mind in sense-percep- tion as of a very high order. The problems which the infant mind solves in the first three years of its life may well excite our wonder and admiration. During this period he not only learns to interpret the indications of his senses, in all the multiplied forms in which sensations must be translated into perceptions, but during the same period he learns at least one oral language. All this is accomplished by the spontaneous activity of the mind, without the intervention of any teacher. The results of this spontaneous activity should inspire our reverence SENSE-PERCEPTION. 71 for the human soul even in its early infancy. Are we not often too much in haste to interrupt this process of spontaneous development by what it may be feared is the impertinent intrusion of direct teaching? Do we not undervalue the results which this spontaneous devel- opment ought to produce and would produce, if not interfered with, in years subsequent to the time when we insist that the process of school education must be commenced ? We here touch a topic which is worthy of more thought than has yet been bestowed upon it. § 54. Our admiration of infant activity will be raised to a still higher point, if we bear in mind that in the solution of these problems of sense-perceptions, the infant must in greater or less degree bring into exercise all his higher mental faculties. His memory must be almost constantly active. It is commonly said, and in a certain sense truly, that sense-perception comes before memory; yet the mind can make no progress in sense- perception without the help of memory. It advances step by step by a series of experiments, and in order that it may derive any benefit from these experiments, it must be able to recall them whenever a similar case arises. Even the infant must practice inductive reasoning. When by experiment he has found that in a given case a certain combination of light and shade indicated the presence of a curved surface, he must infer that this combination always indicates the same thing. He must have and rely upon the intuition of the uniformity of the course of nature. As we have already seen, the intuition of cause and of substance as revealed by attri- butes must be always at his command. Not that he formulates these iu tuitions, and expresses them as gen- eral propositions, but he relies upon them, assumes and 72 SENSE-PERCEPTION. applies them. Without them there can be no activity of a rational soul, no progress in knowledge. It is true that the chief activity of childhood is in the sense-perceptions ; but this activity always implies in greater or less degree all the powers of the intellect. Even an infant in its mother's arms is in a greater or less degree an inductive philosopher. There is no foundation whatever for Her- bert Spencer's assertion, that the " primitive man " has no idea of cause and knows nothing of any course of nature. No man, however " primitive," acquires the notion of cause or learns the uniformity of the course of nature by induction ; but must know both by a natural intuition, as a condition of his learning anything else. A wise man will reverence infancy. It finds its way out of ignorance into knowledge, not by receiving knowledge passively, but by acquiring it by personal activity. § 55. The product of this activity of the soul is a con- ception or notion of the object as an individual thing, which can be recalled and used at pleasure. That con- ception is made up of all the qualities or individual per- cepts which have been found to belong to the object. It is an interesting question, by what constructive law this complex product is formed. In order to explain this matter clearly, it is necessary to define a term which we have not hitherto had occasion to use. A percept is the mind's knowledge of a single quality, attribute or causal power of an object. Thus the culor of an object is the percept of it which is gained through the eye. On the other hand, the perception of an object is the notion of it gained by the use of all the powers which the mind uses in the process of sense-perception, united in one complex whole. Some maintain that this completed product is first formed by uniting the several percepts under the rela- SENSE-PERCEPTION. IS tions of time and space ; that in the first experience of infancy they are united by no other bond than the fact of their having been experienced at the same time and in the same place. Consistently with the principles thus far advocated, we cannot accept this view. In every product of sense-perception, the constructive law is that of the intuition of cause, and of the relation of substance and attribute, the concurrence of the two percepts in time and place being only important as suggesting the notions of cause and quality. We have already seen that the first step made by the mind in acquiring a knowledge of any thing external is the recognition of a resisting cause. We have no knowl- edge of any external object except at least by one of its causal relations. We are dependent on the same recog- nition in taking that second step by which we gain a notion of a surface extended in length and breadth. It is accomplished by noticing the continuity of resistance within a given outline. This assumes that the surface has everywhere the causal power of resistance. In the same manner the boundaries of that surface may be traced by noticing its causal power to produce certain sensations of color. So of all the other percepts. By an inevitable necessity, we form the complex notion of the object by recognizing its causal powers. At the same time we recognize the object as a being or substance manifested to us by these causal powers. The intuition of causal power and of the relation of substance and attributes is thus interwoven with every act of sense-perception. We do, however, learn that each particular impression on the sensibilities is the product of the causal power of the resisting non-ego, by the fact that we experience that impression simulta- neously with our experience of the resistance. 13 74 SENSE-PERCEPTION. §56. It is a question of considerable interest, whether in forming such a complex notion of any individual object, the mind embraces at a single view many or all of the percepts which enter into it, or is by its nature confined at each moment of time to a single percept, and unites them into one whole by passing from one to another with so much rapidity as to seem to itself to contemplate them all at the same instant. The latter of these views, which is defended by Dugald Stewart and some other writers,* assumes that the human mind is incapable of attending to more than one object at the same moment, and can therefore join many objects into one whole only by such rapid transition from one thing to another. For example, when we are listening to an orchestra consisting of many instruments, we do not, as we are apt to suppose, attend to the whole performance at once, and thus experience the effect of the whole, but to each instrument in its turn, passing from one to another with such rapidity that the impression of the whole seems to be received at the same instant. From this view of the subject, President Porter dis- sents, as it seems to us with the best of reasons. The assumption that the human mind can attend to but one thing at the same moment, seems to rest on no substan- tial foundation. If that doctrine is true, it is inconceiv- able that the mind should be able to compare one thing with another. The act of comparison necessarily implies that both objects are present to the view at the same time ; if not, how is it possible that any judgment should be formed of the relations of the two to each other? If I pass instantaneously from intense illumination to total darkness, how is it possible that I should feel the con- * Porter's Elements, Sec. 120, referring to Dugald Stewart's Ele- ments, Ch. II. SENSE-PERCEPTION. 15 trast, unless ray mind contemplates both the darkness and the light at the same moment ? If to this it is re- plied that the mind contemplates at the same moment, one of these objects as present and the other as remem- bered, this does not in the least relieve the difficulty. We can as easily admit that the mind attends to two objects at once, as that it attends to one object and the remembrance of another. One or the other of these sup- positions must be admitted to be true, or the comparison of one thing with another must be forever impossible to the mind. The denial that the mind can attend to more than one thing at once is a virtual denial of the power of comparison. It may be and probably is true that when the mind attends to more than one thing at once, it does not attend to all with equal intensity, that it does give chief attention first to one and then to another, and that these transitions are made with very great rapidity ; but it remains none the less true, that when two or more things are compared they must all be present to the mind and receive a greater or less degree of attention at the same moment. In listening to a musical performance, it is doubtless true that many if not most persons can, if they choose, single out some one instrument and follow it with exclusive attention through the whole performance ; but if one does so he will lose entirely the effect of the harmony of the whole. If that is to be appreciated, the mind must attend to all the instruments at once. In like manner all the percepts which make up the complex notion of any individual thing must be jointly contem- plated by the mind at the same moment. § 57. By these activities of the soul in sense-percep- tion, we come at last to a knowledge of all the qualities of known material things. It is not by the senses alone, 76 SENSE-PEECEPTION. nor even by the senses as aided by the muscular sensi- bilities. The memory, the reasoning powers and the in- tuitions must all bear an essential part in these processes. But the soul can come to a knowledge of none of the qualities of matter without applying to them the pro- cesses of sense-perception. Before we dismiss the sub- ject it is desirable to take a more comprehensive view of these qualities, and to form a classification of them ac- cording to their relations to the powers and methods by which a knowledge of them is acquired. It has been usual with writers on Psychology to divide the qualities of material bodies into two classes ; the primary and the secondary.* The former class embraced all those qual- ities which are inseparable from our notion of a material body. They are such as extension, space-filling power or impenetrability. The second comprehended the rela- tions of material bodies to each other and to the senses. Sir William Hamiltonf suggested three classes ; the pri- mary, the secundo-primary and the secondary. In the primary he embraced the space relations of matter ; in the secundo-primary, the relations of resistance, gravity and inertia, or in general the relation of bodies to one an- other ; and in the secondary the causal powers of matter to produce special sensations. At first view the classifi- cation of Sir William Hamilton seems to be accurate and exhaustive. The views however presented in this treatise, if just, enable us to define the three classes more accurately, by referring each of the classes to the powers through which, or more accurately the method by which the qualities embraced in it are cognized by the mind. The definitions would be as follows : * Reid's Collected Writings, pp. 845, 846. f Hamilton's Metaphysics, p. 334, Bowen's Edition. SENSE-PERCEPTION. 11 The primary qualities are those of which we require a knowledge by voluntary motion. They are the space- relations of matter. The secundary-primary are those which we cognize by experienced resistance to voluntary motion. They are outness, gravity, inertia, hardness, roughness, and the like. They become known to us by the resistance which they offer to our voluntary motions. The secondary are those qualities which we cognize by sensations produced in our special senses. They are color, sound, taste and smell. In this definition of the classes externality or outness should be embraced in the secundo-primary as extension is in the primary. This quality is not embraced in either of the classes suggested by Sir William Hamil- ton. With this addition to the secundo-primary, it is believed the classification is strictly exhaustive, and that the definitions proposed above are accurate. Per- haps it may be regarded as no small confirmation of the views of sense-perception advocated in this treatise, that they conduct by a logical necessity to such a classifica- tion of all the qualities of matter, and furnish defini- tions of the classes so simple and comprehensive. Perhaps it would be wise to drop Sir William Hamil- ton's unmeaning and rather clumsy names for the three classes, and substitute in their stead a nomenclature derived directly from the definitions just given and suggestive of them. Let us call them, qualities cogni- zed through voluntary motion, qualities cognized through resistance experienced to voluntary motion, and qualities cognized through the special sensations. Thus the clas- sification of the qualities of matter will be a compend of the whole complex process of sense-perception. LIBRARY OF CONGRESS 021 068 369 iiiifif R0RY 0F C0NGRESS 021 068 369 LIBRARY OF COWrpcc- * l 68 369 •