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natural endowment in the case, which varieties must have their seat principally in the muscular tissue, and only secondarily in the skin and nerves of the hand.

The feeling of elasticity is only a case of simple resistance to force, exerted in the particular circumstance of a rebound or increasing reaction from pressure. The elasticity implies a perfect return to the original position; air is elastic, and so is steel and ivory, meaning that when in any way compressed or distorted, they recover themselves.

We may next consider the sensations rising out of the qualities of roughness and smoothness. Simple contact, we have seen, gives the sense of a multiplicity of points. The finger resting on the end of a brush would make us aware of its character; that is, we should have the feeling of a plurality of pricks. In this way, we are sensitive to rough and pointed surfaces. We can distinguish between bluntlypointed asperities, like a file, and sharp points, like a horsecomb the sensibility of a blunt point being distinct from a needle-prick. We can also distinguish between thick-set points and such as are more scattered, provided they are not too close for the limits of sensibility of the part, that is to say, one-twelfth of an inch for the finger, and one twentyfourth to one-thirtieth for the tip of the tongue. On the back, the calf of the leg, and the middle of the fore-arm, where points are confounded up to the distance of two and a half to three inches, roughness would be altogether imperceptible.

In these instances, the thing touched is supposed to lie at rest on the finger, or on the part touched. But this does not do full justice to the tactile sensibility; we should move the finger to and fro over the surface, in order to try to the utmost the power of discrimination. We may thus discriminate far nicer shades of roughness; we may appreciate minuter intervals than in the resting position. Supposing the sensibility of the tip of the finger at rest to be one line, by motion we can extend this sensibility to an unknown limit. The case may be illustrated by the micrometer screw on an astronomical instrument. The divisions on the limb of the instrument

extend, we may suppose, to one minute of a degree, and if the index lie between two divisions, its place can be measured by the number of turns of the screw required to bring it up to one of the divisions. So, if a point is undistinguished on the finger, in consequence of not being a line removed from the neighbouring point, we may estimate its distance, nevertheless, by the amount of motion of the finger needed to bring it into the limit of sensibility. I will take as an example a row of five points, one-fortieth of an inch apart, the extremes being one-tenth, which is the sensibility of the tip of the finger. This row would be felt as two points if the finger were stationary. But by the motion of the finger one point would pass away and another would come up, and there would be a feeling of the interval moved over between the perception of the successive points, which would be a measure of the intervals. The sense of movement would thus be brought in to aid the tactile feeling, and to reveal a degree of closeness in asperities beyond the reach of touch unassisted by motion. It is consistent with all experience, that the roughness of a surface becomes far more apparent by drawing the hand over it. We must, however, farther consider that friction creates a new variety of pressure on the skin and nerves; and the kind of friction is so different for a smooth and for a rough body, that by it alone we might learn to distinguish between the rough and the smooth contact.

If any one will make the experiment of drawing over the finger two points, so close that to the touch they seem one when at rest, it will be found that the motion gives the feeling of doubleness. What is the limit of this (for a limit there is) it would take a considerable amount of observation to decide. I venture to affirm that at least half the interval will become sensible by the motion of the points, the motion being by bringing them in train, and not abreast of one another.

A

Whatever may be the explanation of the increase of sensibility due to movement, the fact is an important one. large amount of discrimination turns upon it. From the variety of trace made by different kinds of surface, we can

distinguish them or identify them at pleasure, up to a considerable limit of delicacy. Hence the power of telling substances by the touch, and of deciding on the qualities and merits of texture and of workmanship. Degrees of polish in stone, metal, or wood, the fineness of cloths, wool, &c., the beat of a pulse, the quality of powdered substances, and many things besides, are matters of judgment and comparison to the touch, and put to the proof its natural or acquired delicacy.

These tactile sensations whereby surfaces are discriminated, have a great degree of persistence in the recollection; something intermediate between tastes or smells, and sights. We do not revel in them as imagery, it is true, but this would be accounted for by the superior hold that we have of the very same objects by means of sight. With the blind, the case is different; to them the outer world must be represented as outspread matters of contact; their visions of the surfaces of all things are visions of touch.

Our permanent impressions of touch serve us for comparing present surfaces with remembered ones, and for identifying or distinguishing the successive objects that come before the view. The cloth dealer sees whether a given specimen corresponds with another piece that passed through his hands a week ago, or with a permanent standard impressed upon his finger sensibility.

13. Qualities of Extension, Size, Form, &c.-I have endeavoured to show in the previous chapter, that these qualities are impressed upon us by the movements they cause, and that the feelings they produce are feelings of movement or muscularity. It is now to be seen how far the sense of Touch proper enters into our notions of the fundamental property of the object world, namely EXTENSION, of which Distance, Direction, Position, and Form are only special modes or applications.

When we examine closely the sensibilities obtained by movement alone, as by passing the arm to and fro in empty space, we find that these have various shortcomings as regards the idea of extended matter, or extended space.

In the first place, the absence of some definite marks, to indicate the commencement and the termination of a muscular sweep, leaves a certain vagueness in our feeling of mere movement. The feelings of putting forth power, and of this power taking the form of movement as distinct from dead strain, are present in all cases; but the mind is more alive to them when some definite impression marks where we begin and where we cease. Now, the sense of touch supplies this impression, and furnishes, as it were, a call to attention. Let us suppose the hand moving between two fixed obstacles, for example, from one side of a box to another. There is, to commence with, the contact with one side of the box felt more or less as a sense of touch, pressure, and resistance (a feeling partly muscular, but this need not be considered); the abrupt departure from this state is a mark in consciousness, a call to attention; and the mind is awakened to the feeling of movement that follows. After a time, the other side is struck, and the mind is again roused, and takes note of the cessation of the movement. The antithesis of resisting matter and unresisted movement is well brought out by such an experience; there is in it something more than the contrast of the swing of a limb with its undisturbed quiescence, which is all that movement in vacuo can give us.

In the next place, when the hand is moved over a surface, touching it the while, the feeling of continuance of movement is accompanied by a feeling of continuance of tactile sensation, making the consciousness more marked and acute, and so enabling us to estimate the degree of continuance more nicely. A feeling of the subject (touch proper) is superadded to the great object sensibility (expended energy as movement), and deepens the impress of that sensibility, without being able to take its place, or to constitute the feeling of objectivity. The peculiar tactile sensation that friction causes, is thus a means of suggesting extension and of estimating it, although incompetent to supply the notion itself.

In the third place, movement in vacuo seems unable to

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indicate that distinction between Succession and Co-existence -Time and Space-which must be arrived at before we can say that we recognize Extension. The continuance of movement is a fact that we are conscious of; in other words, we are conscious of a peculiar mode of the putting forth of energy which varies in degree, and we remark one movement as different from another on this point. But if any property of things is indicated by this, it would seem to be not space, but time. In truth, neither is known, for they are a correlative couple, not known at all till they are known together.

Now, we are able to show, how the embodying of our movements in sensation enables us to distinguish between the two facts or properties, called the Co-existing and the Successive.

When, with the hand, we grasp something moving, and move with it, we have a sensation of one unchanged contact and pressure, and the sensation is imbedded in a movement. This is one experience. When we move the hand over a fixed surface, we have, with the feelings of movement, a succession of feelings of touch; if the surface is a variable one, the sensations are constantly changing, so that we can be under no mistake as to our passing through a series of tactile impressions. This is another experience, and differs from the first, not in the sense of power, but in the tactile accompaniment. The difference, however, is of vital importance. In the one case, we have an object moving, and measuring time or continuance; in the other case, we have co-existence in space. The co-existence is still farther made. apparent by our reversing the movement, and thereby encountering the tactile series in the inverse order. Moreover, the serial order is unchanged by the rapidity of our own movements. A more rapid pass of the hand makes the series come up quicker; a less rapid, brings the same series in more slowly. By these experiences, we gradually become aware of a wide distinction between identical movements conducted under such different circumstances; and the distinction is expressed in language, as succession and co