CHAPTER V.

THE SENSES.

How many External Senses? -- A group of sensations containing a number of features in common are assigned, we have said, to a special sense. The question may now be raised, how many senses have we? There has been a good deal of disagreement on the point among modern writers, but the decision arrived at does not seem to us to be of very much importance, provided that the various forms of sensibility be recognized. The specialization of the organ, the nature of the stimulus, and the quality of the consciousness, have each been advocated as the true principle of classification, and different plans have consequently been drawn up.^{1} In favour of the old-fashioned scheme of the five senses, taste, smell, hearing, sight, and touch, it may be urged that it recognizes the obvious structural differences of organ, to a great extent the most marked differences in the quality of the consciousness, and also generic differences in the phenomena apprehended. The eye reveals to us colours, the ear sound, the nose smell, the tongue taste, and touch pressure. In the language of the schools, the formal objects of the several senses are generically different. However, if this classification be adopted, it must be remembered that under the sense of touch are comprised many groups of mental states importantly different in quality, and frequently attached to parts of the organism of very specialized character.

Method of Exposition. -- The most convenient order of procedure will be to start from the simpler and more easily described faculties, and to go on gradually to those of a higher, more varied and complex nature. In our exposition we will adopt the usual plan of saying a few words on the formal object of each sense, on the physiological machinery employed, and on the character of the consciousness awakened. In dealing with this last phenomenon, which is the proper subject-matter of Psychology, the two chief features to be attended to are what have been styled the emotional and the intellectual aspects of the sense. By the former is meant, the susceptibility of the faculty to pleasure or pain; by the latter, its efficiency as an instrument of knowledge of the external world. The use of the epithet "intellectual," however, is very inaccurate here, and still more so when applied to individual sensations. The Intellect is a faculty essentially distinct from sensuous powers, and its activity, just as that of any of the senses, may possess a pleasurable or painful character. It will accordingly be more appropriate to term this property of a sense or sensation its cognitional aspect.

Taste. -- Physiological conditions. -- The formal object of the sense of taste is that quality in certain soluble substances in virtue of which they are called sapid. The organ of taste is the surface of the tongue and palate. Over these surfaces are distributed the gustative papiliae, from which nerves proceed to the brain. In order to excite the sensation, the body to be tasted must be in a state of solution in the mouth. The precise nature of the action of the sapid substance on the papillae is unknown, but it is probably chemical.

Sensations. -- The sensations of this faculty do not possess such definite qualitative differences as to fall into well-determined groups, and consequently there is no general agreement in the classification of different tastes. The proper pleasure of the sense is sweetness; its proper pain bitterness. Most gustatory sensations involve elements of tactual, nasal, and organic feelings. Thus, acid, alkaline, fiery, and astringent tastes, are in part the effects of tactual stimulation; feelings of relish and disgust are traceable to the sympathy of the alimentary canal; and sensations of smell also influence our estimation of the sapid qualities of many substances. The cognitional value of this sense is very low. Continuous stimulation rapidly deadens its sensibility; its recuperative power is tardy, its sensations are wanting in precision, and they can be but very imperfectly revived in imagination. The main grounds of its cognitive inferiority, however, lie in its essentially subjective character. Abstracting from the information afforded by concomitant tactual sensations, taste originally gives us no knowledge of external reality, and, consequently, with the exception of the vague systemic feelings of the organism, it must be ranked lowest as a medium of communication with the physical world. On the other hand, viewed from the standpoint of feeling, this sense is capable of intense but short-lived pleasure and pain. Though the lowest of our faculties in point of refinement, and the most subject to abuse, its great utility as a guide in the selection of food throughout the animal kingdom is evident.

Smell. -- Physiological conditions. -- Odorous particles emitted from gaseous or volatile substances constitute the appropriate stimulus of this sense. The organ of smell is the cutaneous membrane lining the inner surface of the nose. The action of the odorous substance is probably of a chemical character, and the simultaneous inhaling of the air is requisite for the production of the sensation. In the act of inhalation the stimulating particles are drawn through the nostrils over the sensitive surface. Even the strongest smelling substances are not perceived as long as we hold our breath.

Sensations. -- This sense resembles that of taste in many respects. Vagueness is a marked feature of each; continuous excitation renders both obtuse; their recuperative power on the cessation of the stimulus is weak; and both are originally of a like subjective character. The close affinity of the two faculties is exhibited in the difficulty of determining how far the recognition of a particular substance is due to taste, and how far to smell; and in the readiness with which most of the adjectives, such as sweet, bitter, pungent, primarily qualifying sensations of taste, are transferred to those of smell. The attempt to distinguish port wine from sherry, apart from sight and smell, is a familiar method of illustrating the former. The delicate susceptibility of smell to some kinds of stimulation is, however, very surprising. The merest trace of a drop of oil of roses awakes a pleasurable feeling, and as infinitesimal a particle as the one thirty-millionth part of a grain of musk is perceptible. The delicacy of this faculty in the dog and other brute animals,^{2} as is well known, far exceeds what it attains in man. Just as in the case of taste, the sensations of smell may be of an extremely agreeable or disagreeable character. They stand higher, however, in order of refinement. They are, too, more easily revived in imagination; and, being awakened by objects at a distance, these sensations, like those of sight, assume the character of premonitory signs of other future experiences. In this way the sense of smell comes to surpass both organic and gustatory sensations, as an instrument of external perception.

Touch. -- Under the generic sense of touch are comprised a variety of classes of feelings widely different from each other. Consequently, very early in the history of Psychology, we meet with discussions as to whether this term does not include several specifically distinct senses. Aristotle^{3} called attention both to the close relationship of taste with touch, and to the divergent nature of sensations of temperature, of softness and hardness, and of contact proper. It would certainly seem that sensations of temperature, differing so much in quality from those of touch proper, awakened, moreover, by distant objects, and seated either in different nerves or different properties of nerve, from those of our tactual feelings, have as strong claims to be considered the utterances of a separate sense as our gustatory states. Since, however, every proposed subdivision of touch into separate senses appears open to grave objections, and since the question is really of no very great importance, the most convenient plan will be to distinguish and describe separately the leading modes of sensibility included under touch in its widest sense, without deciding whether they should be assigned to different faculties. These forms of consciousness are: (1) the organic sensations, (2) the sensations of temperature, (3) touch proper, and (4) the muscular sensations.

The Organic Sensations, Common Sensibility, Coenaesthesis, or the Vital Sense. -- Under these various designations are included the numerous modes of sensuous consciousness attached to the organism as a whole, or to particular portions of it. Their essential function is to inform us, not of the properties of the extra-organic world, but of the good or ill condition of our own body. Prominent among them are the systemic sensations, comprising those of the alimentary canal, such as the feelings of hunger, of thirst, and repletion, the sensations of respiration, of circulation, and such other states as are normal to the system. In addition to these, the chief remaining organic sensations are those arising from disease, and from laceration or fracture of any part of the organism. Estimated from a cognitional point of view, the organic sensations are of little importance. With the exception of particular hurts, they are of an indefinite and obscure character. They can be but very feebly reproduced in imagination. Being in great part beyond the range of touch and sight, they are vaguely and imperfectly localized, and they give us practically no information regarding the external world.^{4} On the other hand, as sources of pleasure and pain, they possess immense influence over the tenour of our existence, and they are of the greatest utility as guardians of our physical health.

Sense of Temperature. -- Physiological conditions. Diffused throughout the organism as a whole, yet specially seated in the skin, the sense of temperature has claims to be grouped both with the organic sensations and with the sense of contact proper. Some writers have maintained that our consciousness of temperature is dependent on a set of nerves distinct from those employed in tactual sensation. This is not yet absolutely proved, but that the properties of the nerve-fibres involved are completely different^{5} is shown by the fact that either class of feelings may be almost entirely suspended, whilst the other remains comparatively unaffected.

Sensations. -- As our consciousness of temperature is relative to that of our own person, this sense can afford little assurance about the absolute heat or coldness of an external object. When the environment is of the same temperature with that of the part of our body exposed, we are unconscious of it. If we pass into the chill night air from a hot room, we are keenly aware of the change, but even before the skin of our face and hands is reduced to the same degree of warmth as the surrounding atmosphere, we become habituated to the stimulus, and consciousness of temperature almost disappears. It has been found, however, that within a moderate range, fine variations can be noticed in comparing the temperatures of two bodies; and the hand is able to detect a difference of 1/4 a degree Cent. in two vessels of water. The effect of heat or cold increases with the extent of the surface exposed. Thus, water which feels only comfortably warm to the hand or arm, may cause severe pain if the whole person is immersed. In extreme heat and cold, the sensation of temperature proper disappears, and, instead, in both cases, a like feeling of keen organic pain ensues. In polar voyages, the sailors speak of cold objects burning their hands. Viewed generally, this sense is of little cognitive, but of much emotional significance. Its appropriate pleasure lies in moderate warmth, its specific pain in extreme heat and cold.

Sense of Contact or Passive Touch. -- Physiological conditions. -- The organ of this sense consists of a system of papillae distributed over the surface of the dermis, or under-skin, which covers the surface of the body. Above this dermis lies the cuticle or external skin, which acts as a protection for the papillae, nerves, and veins lying beneath. From the papillae proceed nerve-fibrils to the spinal column and thence to the brain. The proper stimulus of the sense of touch is simple pressure on the external skin. In order that a sensation be awakened, the effect of the physical excitation at the surface must be transmitted along a sensory nerve to the brain. If the nerve is severed above the point of irritation, no mental state is elicited, and if an intersected nerve is irritated above the point of severance, the cause of the sensation aroused is judged to be at the old peripheral extremity. From this it has been inferred that the sensation occurs not at the surface, but in the brain or central sensorium, and that it is by experience we come to learn the seat of the exterior impression.^{6} If this doctrine is to be interpreted as implying that peripheral stimuli were originally localized by us in the brain, or that the soul is confined within the limits of the brain chamber, and that the action of the excitant impinges upon it there, then it must be rejected as warranted neither by physiological nor psychological evidence. The fact, however, may be held to show that our ability to localize impressions is very largely due to experience, and that our original capacity in this respect was very imperfect.

The physiological process which is the proximate cause of sensation contains three stages. The first is the peculiar action set up in the exterior terminals of the nerves of the various senses. The specialization in structure and constitution of these apparatus, which modern Physiology has brought into prominence, demonstrates the significance of this moment in the operation. The second step is the transference of the excitation by means of a molecular change along the nerve to the brain. Here the last item in the physical process takes place, but of its character we know virtually nothing. On its completion, however, the soul which animates equally every part of the nervous system, and, in fact, every part of the organism, reacts in the form of a conscious sensation. The quality of this mental state is affected by the portion of the body in which the physiological process has taken place; the feeling, for instance, of an impression on the leg or the back is different from that of a similar impression on the arm. Nevertheless, the sensation is not definitely localized from the beginning at the precise spot of peripheral stimulation; the exact site of the starting-point of the neural change is learned by experience. This subject will, however, be discussed more fully in a future chapter.

Cognitional Value of Touch. -- The sense of touch stands very high as a medium of external perception, Yet its sensations possess in many respects the vagueness and want of precision which characterize the faculties hitherto dealt with. Thus there is comparatively little variety in kind among our tactual feelings which are mainly discriminated as rough, smooth, gentle, and pungent. They possess, however, a delicate sensibility to differences in the intensity and duration of the stimulus, and still more important in this connexion, they are endowed with fine local characters on account of which they come to be referred with great accuracy to the place of excitation. By means of this property the mind is able simultaneously to apprehend co-existing points, cognizing them as separate; and in this apprehension there is the presentation of extended space. The simplest form of tactual sensation, such as that of the contact of a feather, does not seem to involve the feeling of pressure, and this is sometimes styled the sense of contact proper, but it scarcely passes beyond the range of the organic sensations. The vast majority of our sensations of contact are sensations of pressure, and this element must be included under the sense of touch.

Discriminative Sensibility. -- The sensibility of the skin to purely tactual pressure varies in different parts of the body. If a particular point on the hand is tested, we can, according to some writers, notice the difference between two successive pressures when it equals the 1/30th of the original weight. Pressures on two different hands can only be observed when one exceeds the other by 1/3. The capacity of touch for local discrimination also varies in different parts of the skin. The method of experiment adopted by Weber, was to place the two points of a pair of compasses on the part to be examined, and then to widen or narrow them until the two points could be just felt as separate. It was found that along portions of the back and forearm the points of the compass required to be from two to three inches apart in order to be distinguished, whilst on the tips of the fingers and the tongue an interval of one twelfth and one twenty-fifth of an inch sufficed. The spaces within which the doubleness of the stimulus is not observed are called "sensory circles," though the figure is not generally an exact circle. The smallness of the circle measures the perfection of the sensibility.

The consciousness of mere contact, of tactual pressure, and, with some writers, that of temperature, comprise the feelings which should be grouped under touch proper. There are, also, a few other special modes of tactual sensation, such as tickling, and itch, which have a very well marked character of their own. Sensations of touch cannot be very vividly reproduced in imagination; yet the reality of these representations is shown by our power of comparing a present sensation of touch, such as that of a brush or piece of silk, with a recollected experience, and also by the manner in which ideal sensations of touch are awakened by the visual appearance of objects. We seem to see the roughness, smoothness, or softness of objects, although, of course, these properties can only be apprehended by touch. This fact, too, marks the high degree of associability possessed by these sensations. These various qualities of the sense of touch give it great importance in the department of objective cognition. We have not, however, hitherto laid stress on the fact that pressure, revealed through tactual sensations, is an influential agent in the generation of our conviction of the externality of the material world, just as the apprehension of co-existing points determines our assurance of its extension. In such sensations of pressure muscular feelings are often implied, and though passively received impressions of contact do really involve the apprehension of something other than ourselves, yet it is when combined with the muscular sensations, and as consequent on the effort put forth by our own energy, that their full significance in the apprehension of the reality of the external world is realized. As a source of pleasure the sense of touch, apart from feelings of temperature and other organic states, ranks low. It has, however, been selected from the beginning as the sense most convenient for the infliction of chastisement, and its capacity in this respect is indisputable.

Active Touch. -- The muscular or kinesthetic sensations. -- Sensations of pressure are commonly blended with muscular feelings of resistance on our part, and occasionally with those of movement. These feelings of impeded energy and of movement constitute the manifestations of the so-called active or muscular sense of modern psychologists, and it is in connexion with these that the intellectual or cognitional importance of touch becomes most conspicuous. The difference between the tactual and muscular consciousness of pressure will be realized by holding up a half-pound weight on our hand, and then placing the same weight on our hand whilst the latter is supported by the table. In the former case there is in addition to the tactual impression a feeling described as a sense of effort or strain. Again, if we allow our arm to be unresistingly moved by another person, we shall have the passive consciousness of pressure or contact, with also faint tactual and organic feelings due to the changing position of the skin, joints, and muscles. But if we ourselves move it, instead of the passive feeling of pressure we have the consciousness of muscular energy put forth, accompanied as before by the faint organic and tactual sensations due to the varying position of the limb.

Physiological Conditions. -- The analysis of this state of consciousness and the determination of the physiological conditions of its various elements have given rise to the Muscular Sense Controversy, an unsettled dispute in which psychological, physiological, and pathological evidence is invoked on both sides.

(1) One theory holds that our muscular consciousness Consists merely of a special class of tactual sensations seated In ordinary afferent nerves in the skin and surface teguments, the crumpling, pressure, and strain of which excite these feelings. To this it is objected that in cases where the skin is rendered insensible by disease or anaesthetics like cocain, the power of movement and the feeling of effort often remain.

(2) The second theory includes among the elements of our muscular consciousness besides those of the skin, sensations located in sensory nerves pertaining to the muscles, tendons, ligaments, and cartilage connexions of the joints. All these feelings, it holds, are the concomitants of in-coming nervous processes along afferent nerves. They report and measure movement, strain, or resistance already accomplished, not something to be done. Among the advocates of this view are W. James, Ferrier, Bastian, and Munsterberg.

(3) The third theory maintains that in addition to, and quite distinct from these incoming or peripherally excited feelings, our muscular consciousness includes a feeling of innervation, of effort put forth, the mental correlate of centrally initiated outgoing currents of motor energy which traverse the efferent nerves in the execution of movement or resistance. Its chief supporters are Bain, Wundt, Ladd, Stout, and Baldwin.

In behalf of (3) it is argued: (a) In children and young animals there is exhibited from the very beginning a fund ot activity and spontaneous movements originated by a surplus of energy rather than by external stimulation. The feelings attached to such primitive activity must have for their physical basis efferent or motor discharges. (Bain.) (b) A patient who strives to move a paralyzed limb is conscious of effort without any sensation of movement -- which does not take place. (c) If the muscles which move the eye to right or left are partly paralyzed, the degree of rotation needed to fixate an object is over-estimated and its position misjudged. This illusion proves that our estimate of the movement is measured by the intensity of the effort or innervation which has to be exerted, not by incoming sensations of muscular contraction actually accomplished in the movement. (Wundt.)

In favour of (2) it is urged by W. James (a) The assumption of this unique active sense or feeling of innervation, opposed in nature to all other forms of sensation, -- which are concomitants of afferent nervous processes -- is "unnecessary." This feeling, were it ever present, would have vanished as a useless link. Movements due to emotions and reflex action occur without it. (b) There is really no introspective evidence for its existence. An anticipatory image of the complex feeling of muscular contractions, involved in the movement plus the volition or fiat of the will -- which is not a sensation -- is the total mental state revealed by careful introspection. (c) To the arguments based on the seeming existence and our apparent estimate of the feeling of effort in cases of paralysis of certain muscles where incoming sensations from them would be impossible, it is answered that the feeling is still really of a purely afferent character coming from the strain of other groups of muscles, especially those of the chest and respiratory organs, as will be noticed if we "make believe" of shutting our fist tight, or pulling the trigger of a gun without really moving our fingers.

We confess the question seems to us as yet not definitely decided. The reader will find it fully discussed in W. James's Principles of Psychology, vol. ii. pp. 189 ff. 493 ff.; and Ladd, Psychology Descriptive and Explanatory, pp. 115 ff. 218 ff.

Cognitional value. -- The discriminative sensibility of our muscular consciousness to varying degrees of resisting force is very delicate. The duration of muscular sensations is also finely felt. This latter property, when we have acquired the power of estimating velocity, is the chief instrument in our measurement of space. A sweep of the arm lasting for a longer or shorter time, velocity being equal, passes through a greater or less space. Estimation of velocity is not an original quality of muscular feeling, but is learned by experience. Velocity has no meaning unless in reference to space, and it is determined by the quantity of space traversed in a given time. We observe that, in a given time, a certain amount of energy is required to move the arm over a definite length of space, known by sight or touch. By association the degree of impetus becomes the symbol of the rate of velocity. The calculation of the quantity of movement executed by our limbs through means of the muscular feelings alone, unless in the case of a familiar act, is generally very imperfect. If we attempt to ascertain the size and shape of a strange room the dark, we shall find how vague are our notions of our movement. Similarly, if the eyes are closed and the arm is bared so that the tactual sensations of the sleeve are eliminated, the inadequacy of motor estimation of space will become apparent when the velocity is increased we invariably undervalue the distance moved through.^{8}

The muscular sensations, like the other organic feelings, cannot be vividly revived in imagination, but our power of determining the exact degree of energy to be put forth in the practice of habitual actions, such as standing, walking, writing, speaking, and the like, is very delicate. The sense of sight, just as well as that of contact, is a heavy debtor to these sensations. Not only the movements of the head and the eyes, but the still more minute changes by which the convexity of the crystalline lens is modified to suit the varying distance of the object, are all effected under the guidance and estimation of muscular sensations, and it is only by means of their acute sensibility that many of the nicest discriminations of the visual faculty are possible.

Movement, moreover, enables us to multiply the experiences of each sense, to vary the relations between the object and the faculty, and to bring the most sensitive part of the latter to bear on the former. Consequently, the sensations which measure movement play an important part in perfecting our knowledge of the properties of matter. Still it is the consciousness of foreign resistance revealed in tactual and muscular feelings combined, which forces upon us most irresistibly the reality of the external material world. In this respect the cognitional importance of the united muscular and tactual sense exceeds that of sight and all the other organic faculties together.^{9}

Capacity for pleasure and pain. -- The muscular feelings may give rise to a good deal of pleasure or pain. When the body is in a healthy condition muscular exercise affords keen enjoyment, as is established by the general popularity of field sports. The proper pain of muscular sensations is fatigue, and this can be very severe when forced activity is maintained under exhausting conditions. Besides these mental states which we have described, the muscles, like other parts of the body, can be the subject of the pains of laceration or disease, but such feelings belong rather to the general group of organic sensations.

Hearing. -- Physical and Physiological conditions. -- This sense is aroused by vibratory movements transmitted from the sonorous substance through the air or other medium to the ear. The organ of hearing consists of three chief parts, the external ear including the pinna and external meatus, the tympanic cavity, drum, or middle ear, and the labyrinth or internal ear. The two extremities of the tympanic cavity are connected by a chain of small bones, and the labyrinth consists chiefly of a number of small cavities, and contains a liquid in which the auditory nerve is distributed. The vibrations transmitted from the sounding object are concentrated by the external ear, and passed on through the middle ear by means of the chain of small bones to the liquid contained in the labyrinth. The disturbance of this substance excites the auditory nerve, and this excitation is the immediate antecedent of the sensation of sound.

Musical Sounds. -- Sensations of hearing naturally divide into two great classes, those of musical, and those of non-musical sounds. Another important division is that into articulate sounds, or the words of language, and inarticulate sounds. When these last are non-musical they are called noises. The musical character of the first class of sounds seems to be dependent on the periodical nature of the vibrations which excite these sensations. The chief properties of musical notes besides intensity, are pitch, quality, and timbre or clang. The pitch of a sound means its altitude on the musical scale, and is determined by the rapidity of the vibration. The terms timbre, clang, and sometimes musical quality, designate the peculiar feature by which the sound of a note on one instrument differs from that of the same note on another. Thus the timbre of the violin differs from that of the cornet and of the human voice.^{10} Particular combinations of notes according to certain relations of pitch produce the agreeable effect known as harmony. Notes which sounded together produce instead an unpleasant sensation, are said to be discordant and inharmonious. Under certain circumstances, however, discords may be pleasant. Groupings of musical sound in particular time periods produce the consciousness of melody, and skilful combinations of various instruments so as to secure harmony, melody, and agreeable blending of timbre conspire to awaken the delightful feelings of a rich symphony.

Non-musical Sounds. -- Of the non-musical sounds the number which are classed as mere noises are practically unlimited. The collisions of different bodies, the cries of the various animals, the roaring of the wind and of the ocean, are instances of such. All forms of sound, both musical and non-musical, are susceptible of discrimination in regard to intensity and duration, as well as in regard to quality. It is owing to the very great delicacy of the ear in these several respects that articulate speech is an instrument of such enormous value. More than five successive excitations per second produce a continuous sensation in the eye, while the recuperative power of the auditory nerve is so perfect that we can distinguish sixteen impressions in the same length of time. The rapid succession of sensations, frequently discriminated by but slight differences in character and intensity, which present to us without fatigue the long series of syllables constituting a speech, exhibit the wonderful perfection of this sense under these various aspects.^{11}

Sounds and Signs. -- Sounds of all kinds are highly susceptible of being conserved in the memory and reproduced in imagination, and they are also readily associated with other mental states. To this latter property is due their aptness to constitute a system of symbols. The repeated conjunction of the sound of a name with the perception of its object causes the former to suggest in the mind of the child the idea of the latter. Later on, with the dawn of intellect and reflexion, words come to be used and recognized as signs of things. In acquiring a foreign language, the primary associations are formed, not, as in learning our mother-tongue, between the foreign words and the objects which they signify, but between the former and the corresponding terms in our own language, by the assistance of which we ordinarily think and reason about the objects of experience. In commencing to read the connexion is first formed between the visual sign and the oral syllable or word, though gradually the intermediate representation of the word tends to drop out of existence, and in the end the written symbol immediately suggests to us the object signified.^{12}

Cognitional importance of Hearing. -- Notwithstanding its very delicate sensibility as to differences in quality, intensity, and duration, in addition to the very revivable and associable character of its sensations, which all conspire to give the ear such high intellectual value as a representative faculty, it ranks very low as a direct medium of objective knowledge. Of itself it affords no information of the extension or impenetrability of bodies -- the two fundamental properties of matter. Indeed, the attribute which it immediately reveals is of purely secondary and accidental character. Nevertheless, of such a high order are the intrinsic excellences of its sensations, and so admirably are they adapted to compose a perfect system of signs, that, when once a few elementary experiences have been gathered by the other senses, this faculty is enabled, by appropriating them, to put us into a position to take possession of the rich treasures of knowledge acquired by the whole human race.

Capacity for pleasure and pain. -- The capacity of the ear for pleasure is large, while its potentialities for pain are comparatively limited. The agreeable feelings awakened by the qualities of musical sound are of the noblest and most refined character. They are rich in variety, they do not pall by long continuance, and they may be frequently renewed. In all these respects they differ from the gratifications of the less refined senses. A far greater part, however, of these higher pleasures are traceable to intellectual and emotional enjoyment afforded by the general character of a musical composition than to the mere sensuous satisfaction produced by pleasant sound. Cultivation increases the refinement and extends the range of this capacity for happiness, but at the same time rendering the faculty more keenly alive to defects and blemishes it annihilates many minor pleasures possible to the less delicate taste. Discord is painful to the musical ear, and harsh sounds of any kind, as well as intense noises, have an unpleasant effect on all normally endowed persons.

Sight. -- Physical and Physiological conditions. -- The formal object of the eye is coloured surface. According to the now generally accepted undulatory theory, the physical conditions of sight consist of vibrations transmitted to the eye through the intervening ether from the reflecting or self-luminous body. Difference of colour depends on variation in the rate of rapidity of the vibratory movements. the organ of vision is an optical instrument of a very complicated and ingenious construction. The eye-ball is a nearly spherical body containing within it three masses of transparent liquid or gelatinous substances called humours, and so arranged as to form a compound lens. The shape of the eye-ball is secured by an outer coating called the sclerotic, which embraces the whole eye with the exception of the circular spot in front, where the transparent cornea takes its place. Under the sclerotic is a second covering, the dark choroid coat, and over the interior surface of this towards the back of the eye is distributed the retina. This is a transparent network composed of several layers of fibres and nerve cells, and connected with the choroid by a layer of rods and cones. These latter seem to be the properly sensitive apparatus. In the centre of the retina is the yellow spot, which is the most sensitive part of the organ, and here cones without rods are packed in greatest abundance. From the retina slightly to the side of the yellow spot the optic nerve proceeds to the brain. Rays falling on it are unperceived, whence it is styled the blind spot. Of the humours filling up the main body of the eye, the middle one, called the crystalline lens, which is of double convex form, is the most important. The shape of this lens is capable of alteration, being rendered more or less convex by the automatic contraction or extension of the ciliary muscle to suit the distance of the object viewed. When something is presented to the eye, the rays passing from it enter the pupil of the eye and are concentrated by the lens arrangements so as to form an inverted image on the retina. From the layer of rods and cones forming the inner stratum of the retina, this impression is conveyed as a neural tremor to the brain, whereupon the sensation is awakened.

Sensations of Sight. -- There are attached to the eye both muscular and visual sensations proper. The former, which measure the movement of the eyeball and the convexity of the crystalline lens, contribute very much to the accurate determination of the special relations of visible objects. The visual sensations proper are those of light and of colour. These are susceptible of very delicate shades of difference, and the various hues of colour and degrees in the intensity of light which can be distinnguished in a landscape are virtually innumerable. It has been estimated by means of some ingenious experiments that an increase in the force of a stimulus equivalent to about one in one hundred within certain limits, be just discerned by the eye. The principal species of colour generally recognized are the seven hues of the spectrum, red, orange, yellow, green, blue, indigo, and violet. There are a large number of distinguishable intermediate tints between these leading colours, and the terms have therefore not a very exactly defined meaning. These various hues are found to result from the analysis of white light. The ether vibrations which excite visual sensations are of enormous rapidity, and the rate increases from about 390 billions per second, for red rays, to about 760 billions in the case of violet.

Helmholtz and others have traced analogies between the colour spectrum and the musical scale. In point of agreement we find (a) a series of seven principal colours, in correpondence with the notes of the gamut, (b) both series produced by variations in the rate of the vibratory stimulus, and (c) both capable of certain agreeable and disagreeable combinations described as harmonious and inharmonious. The points of difference are however greater. (a) The character of each of the tones of the musical octave is so distinct and well marked as to have been recognized from the earliest times; the colours of the spectrum on the contrary are vaguely defined and pass gradually into each other, many intermediate hues having equally good claims to a recognition in the scheme; (b) the change in the musical octave advances regularly in one direction, each succeeding note being farther from the first, while in the spectrum the movement is along a curve, and the last colour, violet, returns nearer than either indigo or blue, to the earlier colours red and orange; (c) the auditory sensation rises regularly with equal increments in the rate of vibration, whilst large changes produce no conscious effect in parts of the spectrum; (d) the range of vision is exhausted by a single octave, while the ear can span from six to eight.

Composite Sensations. -- Although the sensation of white is evoked by a combination of physical stimuli separately productive of other feelings, it is inaccurate, as we have before indicated,to speak of the consciousness of white as being a compound or complex mental state. The sensation, in itself unanalyzable, must be accepted as such. The true type of the compound or complex sensation is that aroused by a union of different voices or instruments, where attention enables us to discriminate the separate elements of consciousness. The analysis of white light, the existence of various forms of colour blindness, of colour harmony, and of what are called negative^{13} images, have suggested the hypothesis that the nerves of vision distributed in the retina are of certain different classes adapted to respond to particular elementary forms of colour. The theory has assumed different forms in the hands of different scientists, but as the question is physiological rather than psychological, we need not enter into it here.^{14}

Tone and Depth. -- The term tone is sometimes used to express the position of a colour in the spectrum, while depth is dependent on the quantity of pure white light blended with the colour in question. The word intensity is occasionally employed as synonymous with depth; properly, however, it should signify the stronger or feebler force of the sensation. In addition to the fineness of the discriminative power of sight in these several respects, visual sensations are in a high degree capable of being retained in memory and recalled in imagination. In fact, so superior in vivacity are the representations of this faculty to those of the other senses, that some writers have been found to deny, but without adequate grounds, the existence of any other kind of images. The eye, Lhough surpassing the other senses, is less delicately sensible to the duration of the stimulus than the ear, The persistence of positive after-images exhibited in the continuous impressions produced by the rapid circular movement of a bright object, prevents us from discerning more than five or six successive excitations in the second.

Cognitional importance. -- These numerous capabilities would be sufficient of themselves to secure to sight high cognitional rank, but it is to the fact that the eye affords an immediate presentation of surface extension, that its fundamental importance as a source of objective knowledge is due. The apprehension of colour necessarily involves that of space in two dimensions. It is undoubtedly true that originally the single eye, if it remained in a fixed position, could have apprehended but a very limited quantity of surface, that its preception of shape would have been extremely vague, and that it could have afforded no information at all as regards distance; but nevertheless the sensation of colour necessarily implies some perception of extension. The point will be made clearer when we come to treat of the development of sense-perception; here, however we would note that the means by which our visual perceptions of shape and distance are elaborated, and our apprehension of surface enlarged, are changes in the position and form of the eye made known to us by muscular sensations. The movement of the axis of the eye round the object viewed, the convergence of the two eyes varying with its distance, the self-adjusting process by which the optical lens is flattened or rendered more convex so as to focus the object upon the retina, are accompanjed by faint feelings of tension which play an important part in giving precision to our spatial cognitions. In mature life the "local" sensibility of the retina is very fine. Close to the centre of the yellow spot irritations as near together as 004 mm. are felt as distinct; but the discriminative power diminishes as we pass towards the circumference. The size of the retinal image, of course, decreases with the distance of the object, still this extreme delicacy of the retina to the local character of the irritation enables the eye to become a very perfect instrument for the accurate appreciation of extension.

Capacity for pleasure and pain. -- As a direct source of pleasure or pain visual sensations rank probably lower than those of any other faculty, though indirectly they may contribute much to our happiness. Bright lights and hues are pleasing, and harmonious combinations have an agreeable effect. A strong glare of light is painful, but the feeling is organic rather than visual. Prolonged confinement in the dark produces an intense desire for light and great joy on first restoration to liberty, but the pleasure soon fades. The contemplation of the beauties of nature and art affords rich and refined delight, but here the effect is of an intellectual and emotional character, and not merely an immediate function of the sense.

The Senses compared. -- In our last chapter we remarked on the inverse ratio subsisting between the perceptional and the pleasurable or painful capacity of the senses. Glancing back at them now, when they have been separately passed under review, and their chief features described in detail, the truth of that observation will be realized. If we divide our tactual consciousness into the two great groups, the organic sensations, including the feelings of temperature on the one side, and the muscular feelings and sensations of touch proper on the other, and proceed to arrange them first according to emotional, and then in regard to cognitional rank, we shall find that the two schemes will assume virtually an inverse order. Viewed as direct sources of pleasure and pain, starting from the highest they seem to stand thus: organic sensation, taste, smell, hearing, muscular and tactual states, and sight. But marshalled as instruments of objective knowledge the order is reversed: sight, tactual and muscular sensations, hearing, smell, taste, and lowest, the organic feelings. This classification regards only the immediate or direct emotional and cognitional properties of the consciousness of each sense, and the intrinsic difficulties of all such comparison would probably cause diversity of view about the former scheme; still, estimated from this limited standpoint, it seems to us approximately correct. Indirectly, indeed, sight is a much more important source of pleasure and pain than the sense of smell, and the knowledge of the universe acquired by hearing far exceeds that gathered from the actual experience of all our other senses combined; but in both cases we have merely appropriation of the results attained by the other faculties, and extension of these results by means of association and inference. Viewed purely as a state of feeling, a sensation of colour or sound can afford much less pleasure or pain than an agreeable odour, or a nauseous stench. Similarly, the sensations of hearing are more precise, more finely discriminable, and more vividly revived in imagination, not only than those of taste and smell, but even than our tactual and muscular consciousness. Yet, inasmuch as they give us immediately no assurance of the reality, or of the extension of the material world, they must be ranked cognitionally higher than taste or smell, but lower than the combined muscular and tactual sense. Touch, indeed, since it reveals the mechanical properties of the world, has claims to stand even before sight as an instrument of objective cognition, and it is certainly more necessary; still, the immense range of the latter faculty, its perfect presentation of the geometrical relations of the universe, and the delicacy of its other cognitive capabilities have led us to place it at the head of the list. We need not attempt any further justification of the arrangement adopted, as the reader, by returning on our treatment of the senses separately, may ascertain the various considerations which have led to our conclusion.^{15}

The "Law of Relativity." -- The quality and intensity of a sensation are affected not only by the character of its own stimulus, but also by the quality and intensity of other simultaneous or immediately preceding sensations. Thus the same water is apprehended as hot or cold if the hand has been previously dipped in a liquid of lower or higher temperature. The same article may feel smooth or rough, heavy or light, according to the opposite character of the previous experience. After tasting a bitter substance water appears sweet. The sudden cessation of a prolonged noise has a startling effect, as when the miller is awakened by the stopping of his mill. A black object produces a stronger impression when seen after or in the midst of a white field, and the several colours are felt more deeply "saturated," that is, come out richer and fuller when observed at the same time or immediately subsequent to those of complementary hue. In general contrast, whether simultaneous or successive, intensifies the force of sensation.

On the other hand, the effect of protracted stimulation of a sense diminishes and may finally cease to be noticed. We are ordinarily unconscious of the contact of our clothes, of the pressure of our own weight upon our limbs, of the continuous hum of the city, of the smell of flowers, or of the oppressiveness of the atmosphere in a room where we have been for some time, and, speaking generally, of any constant uniform excitant.

This influence of variation upon consciousness has been called by recent psychologists the "Relativity of Sensation." It is a well-known experience in our mental life, and a considerable factor in our pleasures and pains. It was familiar to Aristotle and the Schoolmen, who, on account of its effects, laid down the rule that to secure correct apprehension the several sensuous faculties must be in a neutral or normal condition.^{16}

But the sweeping generalization erected upon these facts under the title of the Law of Relativity is untenable. According this doctrine, at least as expounded by some of its best-known advocates, all consciousness is merely feeling of difference or change. Thus Hobbes asserted that "to be always sensible of one and the same thing is the same as not to feel at all." Dr. Bain writes: "The Principle of Relativity, or the necessity change in order to our being conscious, is the groundwork of Thought, Intellect, and Knowledge as well as Feeling. . . . We know heat only in the transition from cold and vice versa . . . We do not know any one thing in itself, but only the difference between it and another thing. . . . The present sensation is in fact a difference from the preceding cold."^{17}

Criticism. -- To us it seems clear that whilst change -- motus de potentia ad actum, as the scholastics termed it -- is an essential element in the awakening of sensation, and also an important factor in its vividness, it is, nevertheless, the very reverse of the truth to assert that all consciousness is a "feeling of difference." In sensation we are primarily conscious of a positive quality, for instance, of a sound or of a colour, not merely of the relation between two feelings. All comparison presupposes the perception of the terms to be compared, and the primitive act of the sense is not comparative, but simply apprehensive. What man's consciousness would be like if he always had but one unvarying form of sensation we do not pretend to know; but experience shows that we may continue aware of a uniform stimulus, for example, of a musical note for an indefinite time if it be not submerged or crowded out by other feelings.^{18} The actual facts on which the "Law of Relativity" and "Law of Contrast" are based seem to receive a simple physiological explanation in the enfeebling effect of fatigue upon the sense-organ and nerves engaged. These latter become habituated to the stimulus, and react with less energy if the same excitation be prolonged, whilst contrasted feelings employ fresh neural elements or other cerebral tracts. Moreover, from the mental side uniform sensation diminishes in interest, and attention being drawn away by rival novel stimuli, the monotonous experience attracts less and less notice.

The Relativity of Knowledge. -- There is another form of the doctrine of the relativity of consciousness, which maintains that all our knowledge is relative to us, and that we have accordingly no real knowledge of things outside of the mind. This latter question will be discussed more appropriately after we have dealt with sense-perception, and we shall treat it under the title of the Relativity of Knowledge at the end of chapter vii. Both doctrines are erroneous, but many writers maintain the second without adhering to the first, although those who adopt the first naturally adhere also to the second.

The Scholastic Doctrine of the Internal Senses. -- In addition to those sensuous faculties by which we are enabled to perceive external objects, the mind is endowed with the capability of apprehending in a sensuous manner, facts of a subjective order. This power or group of powers constitutes those modes of mental life styled by the schoolmen the Internal Senses. The Aristotelian doctrine elaborated by the mediaeval thinkers distinguishes four such faculties, the sensus communis, the vis aestimativa or vis cogitativa, the imagination, and the sensuous memory. They were termed senses, or organic powers, because they operate by means of a material organ, and have for their formal objects individual, concrete, sensuous facts. The word internal marks their subjective character, and the internal situation of the physical machinery of their operations.

Sensus Communis. -- The sensus communis, or common sense, has also been styled the internal sense and the central sense. It has been described by St. Thomas, after Aristotle, as at once the source and the terminus of the special senses. By this faculty we are conscious of the operations of the external sensuous faculties, and we are made aware of differences between them, though we cannot by its means cognize them as different. Apart then from intellect, by which we formally compare and discriminate between objects, some central sense or internal form of sensibility is required, both in the case of man and of the lower animals, to account for the complete working of sensuous life. In the growth and development of sense-perception, the action of this internal form of sensuous consciousness is involved. Antecedent to and independent of intellectual activity, the revelations of the several senses must be combined by some central faculty of the sensuous order, and it is this interior aptitude which has been called sensus communis.^{19}

Vis AEstimativa. -- The vis aestimativa, or sensuous judicial faculty, was a name attributed to those complex forms of sensuous activity by which an object is apprehended as fit or unfit to satisfy the needs of animal nature. It thus denotes that capability in the lower animals which is commonly described as Instinct. The term vis cogitativa was sometimes employed to designate the aptitude for analogous operations in man, at other times to signify a certain mode of internal sensibility operating concurrently with the intellect in the perception of individual objects.^{20}

Sentimento Fondamentale. -- The term sentimento fondamentale, or fundamental feeling, was employed by Rosmini to denote an assumed faculty, or form of sensuous consciousness, by which the soul is continually cognizant of the body in which it is present.^{21} The soul, he teaches, and not the living being composed of both soul and body, is the true principle of this feeling. It is by their modification of the sentimento fondamentale that the impressions of the special senses reveal themselves to the soul. The fundamental feeling, unlike the sensus communis of the scholastics, is held to have been ever in a condition of activity, even antecedent to the exercise of the special senses. "It begins with our life, and goes on continuously to the end of it." Nevertheless, it is rarely adverted to, and considerable power of psychological reflection may be required to discover its existence. By this feeling we have a subjective perception of our organism; through sight and touch, on the other hand, we apprehend it in an extra-subjective manner. Finally, the union of soul and body consists in an immanent perception of the activity of this faculty.

Sensus Fundamentalis. -- Tongiorgi uses the term sensus fundamentalis in a kindred meaning to denote an inferior form of the sensus intimus. By the sensus intimus, he understands a perpetual consciousness both of its own substantial existence and of its acts, with which he maintains the soul to be endowed. This actual cognizance of itself is essential to the soul and independent of all special mental modifications. It is, moreover, natura if not tempore antecedent to them; yet, as the soul exists always in some particular state, it can never apprehend itself unless as determined by an individual affection. The sensus intimus exerts itself in a higher and a lower form, as rational, and as sensuous consciousness. By the inferior order of activity the soul continuously feels its presence in the body which it informs, and thus apprehends the various impressions which occur in different parts of the organism. This sensuous cognizance of the body he styles the sensus fundamentalis, inasmuch as it is the common root or principle of the external senses.^{22}

Suarez' doctrine. -- Accepting the doctrine of Suarez, that there is neither a real, nor formal distinction between the internal senses, it does not appear to us to be of any very profound importance what classification of faculties we select, as best fitted to mark off the various phases of mental life which have been allotted to internal sensibility. Moreover, the brain seems to be the common physical basis for all these different modes of consciousness, so that there is no differentiation of organ corresponding to special operations which might tell decisively in favour of any particular scheme of division.

Internal Sense. -- The term internal sense has had a variety of significations in the history of Philosophy. In the Peripatetic system, sensus internus designated generically the four faculties, sensus communis, vis aestimativa vel cogitativa, phantasia, and memoria sensitiva; but also at times it indicated more specifically the sensus communis. In the Cartesian school, the sensus intimus or conscientia, signified all consciousness of our own states, whether sensuous or intellectual; and the latter term has retained the same connotation with modern scholastic writers.^{23} With Locke, internal sense is equivalent to the intellectual faculty of reflection, by which our mental states are observed. With Kant, it comprises the sensuous intuition of our mental states, not, however, as they are in themselves, but as modified by the a priori form of time. The term internal sense, legitimate in its original signification in the Peripatetic system, is very inappropriate in its modern usage as expressing the intellectual activity of self-consciousness. That activity is neither in point of object, of nature, nor of intrinsic dependence on physical organ akin to the senses.

Basis of Division. -- The scholastic classification of four internal senses was grounded on the existence of generic differences in the formal objects of the several faculties. The formal object of the sensus communis consists of the actual operations of the external senses; that of the imagination is the representation of what is absent; the function of the vis aestimativa is the apprehension of an object as remotely suitable or noxious to the well-being of the animal; that of the sensitive memory is the cognition of past sensuous experiences. Some writers reduced these faculties to two, others augmented them to six. The nature of the distinction between these senses was also disputed. Suarez,^{24} after a careful examination of the various opinions on the point, decides against the existence of either a real or a formal distinction, and contends that Aristotle is with him in looking on the internal senses as merely diverse aspects or phases of a single sensuous faculty.^{25}

Common Sense. -- Common sense is also a very ambiguous term. (1) In the Aristotelian Psychology, it meant only the internal sense above described. (2) It has been since used to express certain universal and fundamental convictions of mankind. It is in this signification that it has been appealed to as a philosophical criterion of truth by the Scotch school. (3) In ordinary langtiage it implies good sense, sound practical judgment. (4) Common sensibility, and also common sense, have been sometimes used by psychologists to indicate (a) the faculty of touch, and (b) the coenaesthesis or the vital sense, and the various forms of organic sensibility.

Readings. -- On classification of the senses, cf. St. Thomas, Sum. i. q. 78. a. 3; De Anima, II. ll. 22-24, et III. l. 1; De Sensu et Sensato, l. I. On the various senses, cf. De Anima, II. ll. 13-24, De Sensu et Sensato Lib. I. Pesch gives an exhaustive account of the Scholastic teaching on the external senses (Instit. Psych. §§ 521-561.) Cf. also Salis Sewis' Della Conoscenza Sensitiva. Of modern works on the special senses, cf. Wyld, Physics and Philosophy of the Senses, Pt. III.: Ladd. op. cit. Pt. I. c. v. and Pt. II. cc. iii. iv. The Five Senses of Man, by Bernstein, is a good popular treatise in many respects, but the author frequently confuses in a very crude manner the physical and the psychological processes. On internal senses, cf. St. Thomas, Sum. i. q. 78. a. 4; De Anima, III. ll. 2, 3; Suarez, De Anima, III. cc. II, 30, 31; Lahousse, Psychologia, c. v. art. 1; Sanseverino, Dynamilogia, cc. iii. v.; Pesch, Instit. Psych. §§ 561-623.

{1} Following Kant, Hamilton styles the five special senses the sensus fixus, and adds to them a sixth general sense, the sensus vagus, common feeling, the vital sense, or caenaesthesis, embracing the feelings of temperature, shuddering, health, muscular tension, hunger, and thirst, &c. Dr. Bain's scheme stands thus: A. Muscular sense. B. Six classes of organic sensations: (1) of muscle, (2) of nerve, (3) of circulation and nutrition, (4) of respiration, (5) of temperature, (6) of electricity. C. The five special senses. G. H. Lewes emphasized the importance of the systemic sensations, e.g., feelings of digestion, respiration, temperature, circulation, &c. Mr. Murray, who adheres consistently to distinction of organ as his principle of division, gives classification: I. The Five Special Senses. II General Senses. A. Connected with a single organ: (1) muscular sensations, (2) pulmonary sensations, (3) alimentary sensations. B. General sensations not confined to a single organ: (1) of temperature, (2) of organic injuries, &c., (3) of electricity. The true principle, however, if it could be satisfactorily applied, would be the quality of consciousness. Differentiation of organ is an extrinsic physiological consideration. Still the difficulty of determining how much qualitative difference justifies the assumption of a special sense renders the former principle of little value once we depart from the old scheme of five senses.

{2} Cf. Bernstein, The Five Senses, p. 290. He says that some animals can, when the wind is favourable, scent the huntsman several miles away. The number and the minuteness of the volatile particles which proceed from objects perceivable at such distances pass comprehension.

{3} Aristotle, in the De Anima, II. II. 22-24, holds a plurality of senses to be contained under the generic faculty of touch. Elsewhere, in the De Gen. Animalium, he seems to adopt the monistic view. St. Thomas, however, prefers to look on these sensations as merely different classes of feelings comprised under one tactual sense, the formal object of which has not received a definite name. (Cf. Sum. i. q. 78. a. 3; also Schiffini, Disp. Metaph. Vol. I. p. 322.)

{4} Common sensibility has, however, great importance from an intellectual standpoint in this respect, that it is the source of much error. It may seriously distort men's judgments. Peace and war have at times depended on the Prime Minister's digestion.

{5} Recent ingenious experiments by Goldscheider and other physiologists, seem to show not merely that the nervous end-apparatus of temperature sensations differs from that of pressure and of pain, but even that there are in the skin distinct "heat-spots" and "cold-spots " -- minute localities sensitive to heat but not to cold, and conversely. This appears surprising when we recollect that to the physicist heat and cold are purely relative. (Cf. Ladd, op. cit. pp. 346-350.)

{6} The doctrine that the true seat of sensation is a limited internal centre is as old as Aristotle. (Cf. St. Thomas, Comm. De Anima, II. ll. 22, 23.) He holds there that the heart is the proper locus of tactual sensation, the intervening flesh being only a medium differing from the air or other external media by the fact that it is not an accidental but a connatural instrument. That our apparent consciousness to the contrary does not suffice to decide the question. he shows by pointing to the fact that if a covering or rigid substance is placed between the skin and the excitant, we then localize the sensation at the outer surface of the new tegument, and not in the skin. In the De Gen. Animalium, however, he seems to pass into the other view. (Cf. also P. S. Seewis, Della Conoscenza Sessitiva, pp. 368-372.) Dr. Stöckl is among the most distinguished of modern scholastic writers who support the view that sensation is elicited, not in the external parts of the sense-organ, but in the brain. (Cf. Empirische Psychologie, § 6, n. 12.)

{8} The fact that our muscular appreciation of velocity is not innate but acquired, and is at best vague and indefinite, constitutes a very serious difficulty to writers like Dr. Bain, who resolve our perception of space into the consciousness of unextended muscular sensations varying in duration and velocity. The latter idea involves the notions both of space and time, and should not be assumed as an innate endowment, least of all by the empirical school. (Cf. Mahaffy, The Critical Philosophy, pp. 138-144.)

{9} Amongst the qualities of matter made known by combined muscular and tactual sensations are solidity, shape. size, hardness, softness, elasticity, liquidity, &c. Consciousness of movement and of variation in pressure are the main factors in such perceptions,

{10} Helmholtz explains the different timbre of different instruments as due to variations in the upper tones which accompany the proper fundamental note. However, this theory cannot, as yet, be held to be established.

{11} A good musical ear is one that possesses a fine sensibility to pitch, to melodious groupings of successive tones, and to symphonic combinations of timbre. A good linguistic ear is one finely discriminative of the quality of sounds, and of the varying degrees of intensity which mark intonation or accent. As a consequence the two aptitudes are not always united. The ear well formed to catch the peculiar characteristics of the French, German, or Italian languages may be insensible to considerable differences in pitch, and therefore unconscious of the discord effected by inharmonious combinations. Perfection in either line implies good individual capacity of retention. Keen susceptibility to differences of pitch, and consequently to musical harmony, may be found where the general power of hearing is comparatively feeble, and vice versa. For a good linguistic ear, however, general acuteness of the sense seems requisite.

{12} The muscular sensations excited in uttering words either aloud or in a whisper, make a parallel line of association with the aural and visual signs, and in persons in whom the faculty of articulation is more retentive, or more frequently exercised in acquisitions of this sort, thinking and reading in silence tend to be accompanied by movements of the lips. Energetic effort to realize the full import of the visual sign occasions the same phenomenon.

{13} After-images, incidental images, or spectra, are of two kinds, positive and negative. The former term is used to denote the images of sensuous perceptions of objects, which frequently continue to persist for some brief time after the cessation of the stimulus. If after gazing steadily for a few minutes at a coloured object we direct our eyes to a white surface, instead of the positive after-image we become conscious of an image of the object, but in the complementary hue. This is termed a negative image, and is explained on the above hypothesis as due to the temporary fatigue and consequent obtuseness of the nerves previously excited, which are now unable to absorb their share of the new stimulus.

{14} The survival of these after-images was observed by Aristotle and the Scholastics: "Si aliquis videt aliquid lucidum ut solem, et subito claudat oculos, non advertendo visum, sed observando illud directe, primo apparebit ei color rei splendidae deinde mutabitur in medios colores successive donec veniat ad nigrum, et omnino evanescat et hoc non continget nisi propter simulacra splendidi derelicti in visu." (St. Thomas, Comm. De Somniis, lect. 2.)

{15} Balmez, Fundamental Philosophy, Bk. IT. cc. x. xi. maintains the inferiority of touch to sight and hearing from a cognitional point of view. He does not, however, distinguish sufficiently in this question between the direct or immediate efficacy of a sense and that which is merely mediate. In range and representative power the more refined senses vastly surpass touch, but to a very large extent their wealth is built upon the capital supplied by the more fundamental faculty.

{16} 'Sicut tepidum in comparatione ad calidum est frigidum in comparatione ad frigidum est calidum. . . . Et oportet quod sicut organum quod debut sentire album et nigrum neutrum ipsorum habet actu sed utrumque in potentia; et eodem modo in aliis sensibus. (St. Thomas, De Anima, Lib. ii. lect. 23. Cf. also De Somniis, lect. 2.)

{17} Cf. Senses and Intellect, p. 321; Emotions and Will, p. 550; Body and Mind, p. 51; also Höffding, Outlines, pp. 114-117, and Wundt, op. cit. pp. 111-119.

{18} Mr. J. Ward has forcibly argued against the supposed law: (1) That the axiom, Idem semper sentire et non sentire ad idem recidunt, though a truism in reference to the totality of mental life, or to consciousness as a whole, is false as regards many individual impressions. (2) That the suggested illustrations, e.g., insensibility to continuous motion, temperature, pressure of the air, &c., are cases of physiological, not psychical habituation, and so are not constant mental tmpressions at all. (3) That "constant impressions" in the form of "fixed ideas" are the very reverse of a "blank." (4) That if every feeling were "two-fold" or a "transition," a man surrounded by a blue sky and ocean, or passing from a neutral to a positive state of consciousness, must be unaware of any impression at all, which is not the fact. (5) There is, too, the old difficulty of Buridan's ass. (6) Moreover differences, which are themselves real presentations or objects of apprehension, are cognized, e.g., degrees of variation in shade, pitch, pressure, &c., and therefore presuppose the perception of the absolute terms. Mr. Ward also rightly traces Dr. Bain's confusion on this subject to his ignoring the difference between the mere successive or simultaneous occurrence of two related feelings, and the intellectual perception of their relation. (" Psychology," Encycl. Brit. 9th Edit. See also Mark Baldwin, Senses and Intellect, pp. 58-61; W. James, Vol. II. pp. 6-20; and Farges, L'Objectivité de la Perception, pp. 104-115, 202-208.)

{19} It has been held by St. Augustine, St. Thomas (cf. Sum. i. q. 78, a. 4. ad 2. and 87. 3. 3), and other philosophers, that no sense can know its own states, and that, not merely for the coordination of the different senses, but for the cognition of any single sensation, an internal faculty in addition to the special sense is requisite. Aristotle (De Anima, III. l. 2) decides against this view on the intelligible ground that such a doctrine would involve an infinite series of sensuous faculties. Elsewhere, however (De Somno et Vigilia, I. 5), he appears to adopt the contrary theory. Suarez argues cogently against this multiplication of faculties as unnecessary, and his teaching appears to us sound. No sense can have a reflex knowledge of its own states, but this does not prevent a sense from having concomitantly with the apprehension of something affecting it an implicit consciousness of its own modifications. A being endowed with the sense of touch or hearing ought to be conscious, it would seem, of tactual or auditory sensations without the intrumentality of any additional faculty. (Cf. Suarez, De Anima, Lib. III. c. ii. and Lahousse, op. cit. pp. 160-163.)

{20} It was urged that intellect, the formal object of which is the universal, cannot directly apprehend individual substances as such. Nevertheless, we have intellectual knowledge of them, for we form singular judgments, e.g. "This plant is a rose," "Peter is a negro." Consequently, it was inferred, there is a special form of internal sensibility through which the concrete object is so apprehended that by reflection upon this sensuous presentation the intellect can cognize the singular nature of the object. St. Thomas thus describes the operation: "Anima conjuncta corpori per intellectum cognoscit singulare, non quidem directe, sed per quandam reflexionem, in quantum scil, ex hoc, quod apprehendit soum intelligihile, revertitur ad considerandum suum actum et speciem intelligibilem, quae est principium ejus operationis, et ejus speciei originem, et sic venit in considerationem phantasmatum et singularium quorum sunt phantasmata. Sed haec reflexio compleri non potest, nisi per adjunctionem virtutis cogitativae et imaginativae." (Q. Un. de Anima, a. 20. ad 1.)

{21} By the fundamental feeling of life we feel all the sensitive parts of our body." (The Origin ef Ideas, Eng. Trans. § 705.)

{22} St. Thomas applies the term sensus fundamentalis to the faculty of touch. The senses fundamentalis, as described by Rosmini and Tongiorgi, has been objected to by modern scholastic writers on grounds. (1) Internal sensibility, since it is an organic apprehending concrete sensuous facts, must, like external sense, pertain not to the soul alone, but to the whole being -- the compositum humanum. (2) The primary function of internal sense is the apprehension of the modifications of the external senses, its exercise must thus follow, and not anticipate, that of the latter. (3) There is absolutely no evidence for the existence of a perpetual cognition of our own body independent of all special activities. (4) The constitution of the union of body and soul in the perception of the former by the latter would reduce their connection to that of an accidental alliance. (Cf. Liberatore, On Universals, Trans. by E. Dering, pp. 130, seq., also Psychologia, §§ 27-29; Labousse, Psych. §§ 348-355. Contra: Tongiorgi, Psych. 271, 280; Rosmini, The Origin of Ideas, Vol. II. Pt. V. c. iii., and Psychology, Eng. Trans. Bk. I. c. vii.)

{23} Cf. Tongiorgi, Psychologia, Lib. III. c. ii.

{24} De Anima, III. c. 2.

{25} Cf. also Lahousse, Psychologia, §§ 221-223; and on the other side Sanseverino, Dynamilogia, cc. 3-6.