and a consequent sensation; and he acquires the notion of a certain length, in the remembered succession of the muscular feelings during the contraction :-he bends another finger; it, too, touches a certain part of the surface of the palm, producing a certain feeling of touch, that co-exists and combines, in like manner, with the remembrance of a certain succession of muscular feelings. When both fingers move together, the co-existence of the two series of successive feelings, with each of which the mind is familiar, gives the notion of co-existing lengths, which receive a sort of unity, from the proximity in succession of the tactual feelings in the contiguous parts of the palm which they touch,-feelings, which have before been found to be proximate, when the palm has been repeatedly pressed along a surface, and the tactual feelings of these parts, which the closing fingers touch at the same moment, were always immediately successive,—as immediately successive, as any of the muscular feelings in the series of contraction. When a body is placed in the infant's hand, and its little fingers are bent by it as before, sometimes one finger only is impeded in its progress, sometimes two, sometimes three,— and he thus adds to the notion of mere length, which would have been the same, whatever number of fingers had been impeded, the notion of a certain number of proximate and co-existing lengths, which is the very notion of breadth; and with these, according as the body is larger or smaller, is combined always the tactual affection produced by the pressure of the body, on more, or fewer, of the interior parts of the palm, and fingers, which had before become, of themselves, representative of certain lengths, in the manner described; and the concurrence of these three varieties of length, in the single feeling of resistance, in which they all seem to meet, when an incompressible body is placed within the sphere of the closing fingers, however rude the notions of concurring dimensions may be, or rather must be, as at first formed, seems at least to afford the rude elements, from which, by the frequent repetition of the feeling of resistance, together with the proximate lengths, of which it has become representative, clearer notions of the kind may gradually arise.

The progressive contractions of the various muscles which move the arms, as affording similar successions of feelings, may be considered in precisely the same light, as sources of the knowledge of extension; and, by their motion in various directions, at the same time with the motion of the fingers, they concur powerfully, in modifying, and correcting, the information received from these. The whole hand is brought, by the motion of the arm, to touch one part of the face or body; it is then moved, so as to touch another part, and, with the frequent succession of the simple feelings of touch, in these parts, is associated the feeling of the intervening length, derived from the sensations that accompanied the progressive contraction of the arm. But the motion is not always the same; and, as the same feeling of touch, in one part, is thus followed by various feelings of touch in different parts, with various series of muscular feelings between the notion of length in various directions, that is to say, of length in various series commencing from one point, is obtained in another way. That the knowledge of extension, or in other words, the association of the notion of succession with the simple feelings of touch, will be rude and indistinct at first, I have already admitted; but it will gradually become more and more distinct and precise as we can have no doubt, that the perception of distance by the eye, is, in the first stages of visual association, very indistinct, and becomes clearer after each

repeated trial. For many weeks or months, all is confusion in the visual perceptions, as much as in the tactual and muscular. Indeed, we have abundant evidence of this continued progress of vision, even in mature life, when, in certain professions that require nice perceptions of distance, the power of perception itself, by the gradual acquisitions which it obtains from experience, seems to unfold itself more and more, in proportion to the wants that require it.

The theory of the notion of extension, of which I have now given you but a slight outline, might, if the short space of these Lectures allowed sufficient room, be developed with many illustrations, which it is now impossible to give to it. I must leave you, in some measure, to supply these for yourselves.

It may be thought, indeed, that the notion of time, or, succession, is, in this instance, a superfluous incumbrance of the theory, and that the same advantage might be obtained, by supposing the muscular feelings themselves, independently of the notion of their succession, to be connected with the notion of particular lengths. But this opinion, it must be remarked, would leave the difficulty precisely as before; and sufficient evidence in confutation of it, may be found in a very simple experiment, which it is in the power of any one to make. The experiment, I cannot but consider as of the more value, since it seems to me,-I will not say decisive, for that is too presumptuous a word, but strongly corroborative of the theory, which I have ventured to propose; for it shows, that, even after all the acquisitions, which our sense of touch has made, the notion of extension is still modified, in a manner the most striking and irresistible, by the mere change of accustomed time. Let any one, with his eyes shut, move his hand, with moderate velocity, along a part of a table, or any other hard smooth surface, the portion, over which he presses, will appear of a certain length; let him move his hand more rapidly, the portion of the surface pressed will appear less; let him move his hand very slowly, and the length, according to the degree of the slowness, will appear increased, in a most wonderful proportion. In this case, there is precisely the same quantity of muscular contraction, and the same quantity of the organ of touch compressed, whether the motion be rapid, moderate, or slow. The only circumstance of difference is the time, occupied in the succession of the feelings; and this difference is sufficient to give complete diversity to the notion of length.

If any one, with his eyes shut, suffer his hand to be guided by another, very slowly along any surface unknown to him, he will find it impossible to form any accurate guess as to its length. But it is not necessary, that we should be previously unacquainted with the extent of surface, along which the motion is performed; for the illusion will be nearly the same, and the experiment, of course, be still more striking, when the motion is along a surface with which we are perfectly familiar, as a book which we hold in our hand, or a desk at which we are accustomed to sit.

I must request you, not to take for granted the result which I have now stated, but to repeat for yourselves an experiment, which it is so very easy to make, and which, I cannot but think is so very important, as to the influence of mere difference of time, in our estimation of longitudinal extent. is an experiment, tried, unquestionably, in most unfavourable circumstances, when our tactual feelings, representative of extension, are so strongly fixed, by the long experience of our life; and yet, even now, you will find, on moving your hand, slowly and rapidly, along the same extent of surface,

though with precisely the same degree of pressure in both cases, that it is as difficult to conceive the extent, thus slowly and rapidly traversed, to be the same, as it is difficult to conceive the extent of visual distance to be exactly the same, when you look alternately through the different ends of an inverted telescope. If when all other circumstances are the same, the different visual feelings, arising from difference of the mere direction of light, be representative of length, in the one case,—the longer or shorter succession of time, when all other circumstances are the same, has surely as much reason to be considered as representative of it, in the other case.

Are we, then, to believe, that the feeling of extension, or, in other words, of the definite figure of bodies, is a simple feeling of touch, immediate, original, and independent of time; or is there not rather reason to think, as I have endeavoured to show, that it is a compound feeling, of which time, that is to say, our notion of succession, is an original element?

LECTURE XXV.

ON THE DISTINCTION BETWEEN SENSATION AND PERCEPTION,—AND BETWEEN THE PRIMARY AND SECONDARY QUALITIES OF MATTER.

My last Lecture, gentlemen, was chiefly employed in considering the nature of that complex process which takes place in the mind, when we ascribe the various classes of our sensations to their various external objects,—to the analysis of which process we were led, by the importance which Dr. Reid has attached to the distinction of sensation and perception ;-a sensation, as understood by him, being the simple feeling that immediately follows the action of an external body on any of our organs of sense, considered merely as a feeling of the mind; the corresponding perception being a reference of this feeling to the external body as its cause.

The distinction I allowed to be a convenient one, if the nature of the complex process which it expresses be rightly understood. The only question that seemed, philosophically, of importance, with respect to it, was, whether the perception in this sense, the reference of the sensation to its external corporeal cause,-implies, as Dr. Reid contends, a peculiar mental power, co-extensive with sensation, to be distinguished by a peculiar name in the catalogue of our faculties, or be not merely one of the results of a more general power, which is afterwards to be considered by us,-the power of association, by which one feeling suggests, or induces, other feelings that have formerly coexisted with it.

It would be needless to recapitulate the argument minutely, in its relation to all the senses. That of smell, which Dr. Reid has himself chosen as an example, will be sufficient for our retrospect.

Certain particles of odorous matter act on my nostrils,-a peculiar sensation of fragrance arises, I refer this sensation to a rose. This reference, which is unquestionably something superadded to the original sensation itself, is what Dr. Reid terms the perception of the fragrant body. But what is the reference itself, and to what source is it to be ascribed? That we should

have supposed our sensations to have had a cause of some sort, as we suppose a cause of all our feelings internal as well as external, may indeed be admitted. But if I had no other sense than that of smell,-if I had never seen a rose, or, rather, since the knowledge which vision affords is chiefly of a secondary kind, if I had no mode of becoming acquainted with the compound of extension and resistance, which the mere sensations of smell it is evident, are incapable of affording,-could I have made this reference to my sensation to a quality of a fragrant body? Could I, in short, have had more than the mere sensation itself, with that general belief of a cause of some sort, which is not confined to our sensations, but is common to them with all our other feelings?

I

By mere smell, as it appears to me, I could not have become acquainted with the existence of corporeal substances,-in the sense in which we now understand the term corporeal,-nor, consequently, with the qualities of corporeal substances; and, if so, how could I have had that perception of which Dr. Reid speaks, that reference to a fragrant body, of which, as a body, I was before in absolute ignorance? I should, indeed, have ascribed the sensation to some cause or antecedent, like every other feeling; but I could as little have ascribed it to a bodily cause, as any feeling of joy or sorrow. refer it now to a rose; because, being endowed with other sensitive capacities, I have previously learned, from another source, the existence of causes without, extended and resisting, because I have previously touched or seen a rose, when the sensation of fragrance coexisted with my visual or tactual sensation; and all which distinguishes the perception from the mere sensation, is this suggestion of former experience, which reminds me now of other feelings, with the continuance or cessation of which, in innumerable former instances, the fragrance itself also continued or ceased. The perception in short, in smell, taste, hearing, is a sensation suggesting, by association, the notion of some extended and resisting substance, fragrant, sapid, vibratory,a notion which smell alone, taste alone, hearing alone, never could have afforded; but which, when once received from any other source, may be suggested by these as readily as any other associate feeling that has frequently co-existed with them. To the simple primary sensations of vision the same remark may be applied. A mere sensation of colour could not have made me acquainted with the existence of bodies, that would resist my effort to grasp them. It is only in one sense, therefore, that which affords us the knowledge of resistance, that any thing like original perception can be found; and even in this, the process of perception, as I formerly explained to you, implies no peculiar power, but only common sensations, with associations and inferences of precisely the same kind, as those which are continually taking place in all our reasonings and trains of thought.

Extension and resistance, I need scarcely repeat, are the complex elements of what we term matter; and nothing is matter to our conception, or a body, to use the simpler synonymous term, which does not involve these elements. If we had no other sense than that of smell, and, therefore, could not have referred the sensations to any fragrant body, what, in Dr. Reid's meaning of this term, would the supposed power of perception, in these circumstances, have been? What would it have been, in like manner, if we had only the sense of taste in sweetness and bitterness, or of hearing in melody, or of vision in colour, without the capacity of knowing light as a material substance, or the bodies that vibrated, or the bodies of another kind that were

sweet or bitter? It is only by the sense of touch, or, at least, by that class of perceptions which Dr. Reid ascribes to touch, and which, therefore, though traced by us, in part, to another source, I, for brevity's sake, comprehend under that term in our present discussion,-it is only by touch that we become acquainted with those elements which are essential to our very notion of a body; and to touch, therefore, in his own view of it, we must be indebted, directly or indirectly, as often as we refer the sensations of any other class to a corporeal cause. Even in the supposed perceptions of touch itself, however, as we have seen, the reference of our feelings to an external cause is not demonstrative of any peculiar power of the mind, to be classed separately from its other faculties. But when a body is first grasped, in infancy, by fingers that have been accustomed to contract without being impeded, we learn to consider the sensation as the result of a cause that is different from our own mind, because it breaks an accustomed series of feelings, in which all the antecedents, felt by us at the time, were such as were before uniformly followed by a different consequent, and were expected, therefore, to have again their usual consequent. The cause of the new sensation, which is thus believed to be something different from our sentient self, is regarded by us as something which has parts, and which resists our effort, that is to say, as an external body;-because the muscular feeling, excited by the object grasped, is, in the first place, the very feeling of that which we term resistance; and, secondly, because, by uniformly supplying the place of a definite portion of a progressive series of feelings, it becomes ultimately representative of that particular length of series, or number of parts, of which it thus uniformly supplies the place. Perception, then, even in that class of feelings by which we learn to consider ourselves as surrounded by substances extended and resisting, is only another name, as I have said, for the result of certain associations and inferences that flow from other more general principles of the mind; and with respect to all our other sensations, it is only another name for the suggestion of these very perceptions of touch, or at least of the feelings, tactual and muscular, which are, by Dr. Reid, ascribed to that single sense. If we had been unsusceptible of these tactual and muscular feelings, and, consequently, had never conceived the existence of any thing extended and resisting till the sensation of fragrance, colour, sweetness, or sound had arisen, we should, after any one or all of these sensations, have still known as little of bodies without, as if no sensation whatever had been excited.

The distinction, then, on which Dr. Reid has founded so much, involves, in his view of it, and in the view that is generally taken of it, a false conception of the nature of the process which he describes. The two words sensation and perception, are indeed, as I have already remarked, very convenient for expressing, in one case, the mere existence of an external feeling,-in the other case, the reference which the percipient mind has made of this feeling to an external cause. But this reference is all, which the perception superadds to the sensation;-and the source of the reference itself we are still left to seek, in the other principles of our intellectual nature. We have no need, however, to invent a peculiar power of the mind for producing it; since there are other principles of our nature, from which it may readily be supposed to flow, the principle by which we are led to believe, that every new consequent, in a train of changes, must have had a new antecedent of some sort in the train, and the principle of association, by which feelings, that