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of a substance to the skin, and is an uneasy feeling, caused in consequence of some interruption of the natural functions of the part.

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 must be 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 year ago, or with a permanent standard impressed upon his finger sensibility.

12. Qualities of Extension, Size, Form, &c.-I have endeavoured to show in the previous chapter that these qualities are impressed upon us by the movement they cause, and that the feelings they produce are feelings of movement or muscularity. As the origin of our permanent notions of these qualities makes one of the contested and doubtful questions of metaphysics, I shall take an opportunity at some later stage of the exposition, of examining the views opposed to those I advocate; and for the present I shall merely present some farther illustrations by way of making these more intelligible. Although I conceive that the movements of the limbs and body, without any contact with external matter, would impress upon the mind the feeling of extension, this being nothing else than a feeling of the sweep of a moving organ, yet in the actual experience there is usually combined some sensation with the muscular impressions; and this additional sensation mixes itself up, but not inseparably, with the feeling proper to extension or movement.

By drawing the hand over a surface, as, for example, six

inches of wire, we have an impression of the quality of the surface, and also of its length. Transferring the hand to another wire twelve inches long, the increased sweep necessary to reach the extremity is the feeling and the measure of the increased extent. By practising the arm upon this last wire, we should at last have a fixed impression of the sweep necessary for a foot of length, so that we could say of any extended thing, whether it was within or beyond this standard. Nay more, whenever anything brought up a foot to our recollection, the material of the recollection would be an arm impression, just as the material of the recollection of greenness is a visual impression.

If we pass from mere length to some area, as, for example, the surface of a pane of glass, we have only a greater complexity of movement and of the corresponding impression. Moving in one direction we get the length, in the cross direction we bring other muscles into play, and get an impression of movement on a different portion of the moving system. In this way we should have the impression of a right angle, or a builder's square. The full impression of the pane of glass would result from a movement from side to side over its whole length, or from a movement round the edge and several times across, so as to leave behind the sense of a possibility of finding surface anywhere within certain limits of length and breadth. In this shape, and in no other that I know of, would an extended surface be conceived by the mind through muscularity and touch. (The action of vision will be afterwards discussed.)

A eubical block, exemplifying all the three dimensions of solidity, presents nothing radically new. A new direction is given to the hand, and a new class of muscles are brought to contribute to the feeling. The movement must now be over the length, over the breadth, and over the thickness, and the resulting impression will be a complication of the three movements. To get a hold of the entire solidity, it is necessary to embrace all the surfaces one after another, which makes the operation longer, and the notion more complex and more difficult to retain. But the resulting impression, fixed by being

repeated, is of the same essential nature as the notion of a line or a superficies; it is the possibility, the potentiality, of finding surface in three different directions within given limits. A cubical block of one foot in the side means that, commencing at an angle, and going along one edge, a foot range may be gone over before the material cease, that the same may then be done across, and also downwards, and that between every two edges there is an extended solid surface.

The multiplication of points of contact, by our having a plurality of fingers, very much shortens the process of acquiring notions of surface and solidity. In fact we can by means of this plurality measure a length without any movement; the degree of separation of the fingers made sensible by the tension of their muscles being enough. Thus I can appreciate a distance of six or eight inches by stretching the thumb away from the fingers, as in the span of the hand. By keeping the fingers expanded in this way so as to embrace the breadth of an object, and then drawing the hand along the length, I can appreciate a surface by a single motion combined with this fixed span of the thumb and fingers. I may go even farther; by bringing the flexibility of the thumb into action, I can keep the fingers on one surface and move the thumb over another side, so as to have a single impression corresponding to solidity, or to three dimensions. We are, therefore, not confined to one form of acquiring the notion, or to one way of embodying it in the recollection; we have many forms, which we come to know are equivalent and convertible, so that where we find one, we can expect another. But the most perfect combination of perceiving organs remains to be mentioned, namely, the embrace of the two hands. The concurrence of the impressions thus flowing from the two sides of the body to the common centre produces a remarkably strong impression of the solidity of a solid object. The two separate and yet coinciding images support one another, and fuse together in such a way as make the most vivid notion of solidity that we are able to acquire by means of touch. The parallel case of the two eyes, to be afterwards explained, will be found still more striking.

The notion of solidity thus acquired is complex, being obtained through a union of touch and muscularity, and combining perception of surface with perception of extended form. By the swing of the arms alone we have a notion of empty space, which means to us nothing more than scope for movement, and consequently for extended matter. Even when vision is superadded, I can find nothing more in our conception of space than this potentiality of movement. We measure space by the extent of movement permitted in it; this movement being, in the last resort, the movement of our own body or limbs; the very material of the conception in its most refined form, can never, so far as I can see, get beyond an impression of movement, engrained by repetition on the muscular frame-work, just as colour becomes a permanent impression on the visual organs, in connexion with the brain.

13. Distance, direction, and situation, when estimated by touch, involve, in the very same manner, the active organs; the tactile sensations merely furnishing marks and startingpoints like the arrows between the chain-lengths in landmeasuring. Distance implies two fixed points, which the touch can ascertain and identify; the actual measurement is by means of the sweep of the hand, arm, or body from the one to the other. Direction implies a standard of reference; some given movement must fix a standard direction, and movement to or from that will ascertain any other. Our own body is the most natural starting point in counting direction; from it we measure right and left, back and fore. For the up and down direction we have a very impressive lead, this being the direction of gravity. When we support a weight we are drawn downward; when not sustaining the arms by voluntary effort, they sink downward; when our support gives way, the whole body moves downward. Hence we soon gain an impression of the downward movement, and learn to recognise and distinguish this from all others. If a blind man is groping at a pillar, he identifies the direction it gives to his hand, as the falling or the rising direction. Circumstances do not, perhaps, so strongly conspire to impress the standard directions of right and left, but there is an abundant facility in acquiring them

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too. The right deltoid muscle is the one chiefly concerned in drawing the right arm away from the body, and without our knowing anything about this muscle, we yet come to associate the feeling of its contraction with a movement away from the body to the right. All directions that call forth the play of the same muscles, are similar directions as respects the body; different muscles mean different directions. The great pectoral bringing the arm forward, the deltoid lifting it away from the side, the trapezius drawing it backward, indicate to our minds. so many different positions of the guiding object; and we do not confound any one with the other. We learn to follow the lead of each one of these indications; to make a forward step succeed the contraction of the pectoral, a step to the right the deltoid, a step backward the trapezius.

If distance and direction be known, we have everything implied in situation which is measured by those two elements. The situation of another person towards me, is either right, left, before, behind, up, or down, or a medium between some of these; and at a given distance of so many inches, feet, or yards.

Form or shape is appreciated as easily as situation. It depends upon the course given to the movements in following the outline of a material body. Thus we acquire a movement corresponding to a straight line, to a ring, an oval, &c. This is purely muscular. The fixed impressions engrained upon the organs in correspondence with these forms have a higher interest than mere discrimination. We are called to reproduce them in many operations-in writing, drawing, modelling, &c. -and the facility of doing so will depend in great part upon the hold that they have taken upon the muscular and nervous mechanism. The susceptibility and retentiveness of impressions necessary to draw or engrave skilfully are almost entirely muscular properties.

14. So much for the qualities revealed to us by touch, either alone or in conjunction with movement. The accompaniment of activity belongs to every one of the senses; it serves to bring about or increase the contact with the objects of the sense. There is in connexion with each of the senses a parti