difficulty of intellectual analysis. The two series therefore cannot co-exist and yet remain distinct, and if they form but one complex series-Dr. Brown's hypothesis must fall to the ground.

In an acute and ingenious article on metaphysics in the British Encyclopædia, another account has been offered of the mode in which we acquire our idea of extension. "Let us suppose," says the author, "a man from his birth destitute of the sense of sight, and the power of local motion, but possessed of intellect and every other faculty which we enjoy. -Such a person, it is obvious, would be capable of every sensation and perception which is original to us except the perception of colours: but we doubt whether it would be possible to give him perceptions of extension, figure, and solidity. Let us try: and as he cannot move a single limb or member of himself, let us suppose a solid substance of small dimensions to be gently pressed against any part of his body: what would such pressure communicate to him? We think it could communicate nothing but a new sensation, to which, as it is neither pleasant nor painful, no name has hitherto been given except the general one of feeling. This sensation he would not know whether to refer to an external or internal cause; or rather he could have no notion whatever of an external cause, though he would at the same time be conscious that the new sensation was not excited by any energy of his.

own will. Were the pressure to be gradually increased till it rose to pain, our blind man would still be conscious of nothing but a sensation, which could not lead him to the notion of extension, figure, or solidity, because mere sensations cannot be conceived as either solid or extended. Let us next suppose the pressure to be applied successively to different parts of his body: he would now indeed be conscious of successive sensations, but he could not assign to them either extension or place. Lastly, let us suppose the dimensions of the pressing substance to be greatly enlarged what would then follow? nothing, we apprehend, but an increase of pain: for though his whole body were pressed ab extra, the pressure could affect the individual being which is sentient, not more extensively but only more violently. It appears therefore that a man blind from his birth, and destitute of the power of local motion, could never be made to perceive extension, figure, or solidity.

"Let us now suppose this man to receive by a miracle the use of his limbs, and to be suddenly prompted, by some instinctive impulse, to arise and walk. So long as he met with no obstacle in his way, he would not, we apprehend, acquire by this exercise any correct notion of extension or figure; but were a stone or log of wood of considerable dimensions to be laid across his usual walk, the case would

soon be altered. He would feel himself interrupted in his course, and he would, at the same time, recognise his wonted sensations of touch. After being twice or thrice thus interrupted, he would learn, from experience, that the interruption or resistance proceeded from the same cause which in this instance communicated to him the sensation of feeling; and were he to run his hand along the surface of the log or stone, he would perceive the resistance and the sensation continued. As every effect must have an adequate cause, this continued resistance would compel him to believe the continuity of something external, in every direction in which he felt his hand resisted; but such continuity of being is all that is meant by the word extension. At the very same time, and by the very same means, he would acquire the perception of figure: for by running his hand in every direction over the surface of the obstacle which opposed him, he would soon perceive it on all sides limited: but the limits of extension is a phrase of precisely the same import with figure."

The manner in which the man is here supposed to acquire his knowledge of extension, is certainly not that in which any man ever did actually acquire it. The resolution however,

of our idea of extension into that of continued resistance in every direction, appears at first sight very plausible; and every one must have ex

perienced that when blindfold he has passed his hand along an object of considerable extent, and felt resistance in every direction, the idea of extension was immediately suggested. But I am afraid that the reason of its plausibility is, that it takes for granted the previous existence of the very idea whose origin it is intended to explain. In trying to imagine what would be the perceptions of the man, we naturally place ourselves in his situation: - we suppose ourselves ignorant of extension, destitute of sight and local motion, and constituted of an insensible material body, and a sentient indivisible soul,— we conceive the several experiments to be made on us, and we find that they could not convey to us any adequate notion of extension. We then suppose ourselves to receive the power of local motion and to rise and walk, and still we find no farther reason for any idea of extension. But when we suppose ourselves driving against the log of wood, and passing our hand over it in various directions, we can no longer maintain our supposed ignorance. We have so often received the perception in this very way, that our own previously acquired notions of extension rush irresistibly upon us, and we feel satisfied that he must perceive extension in these circumstances, because in our minds they are so closely associated with it by frequent repetition, as to be almost inseparable from it.

But let us give more minute attention to this analysis of the idea of extension.-It is the idea of continued resistance in every direction. Here then the idea of direction is presupposed; and does not the idea of direction presuppose that of extension? Every one must consult his own consciousness as to this. I am certain that I can form no conception of direction except in relation to something extended. The notion of direction seems to be posterior to the observation of motion, and motion cannot be conceived without matter and extension.* There may be indeed different muscular feelings in the mind arising from the different directions in which we are capable of moving our arms and hands: but successive changes of feeling alone evidently cannot give us any notion of direction. Removing then the idea of direction, all which is here supposed to give us our knowledge of extension is continued resistance, or in other words an uninterrupted series of feelings of resistance. Thus this analysis as well as Dr. Brown's, resolves it ultimately into succession; and succession, as all must allow, can, at most, give only the perception of length.

What has already been said appears to me

* Mathematicians, indeed, speak of the motion of a mathematical point or of a line, abstractedly from matter; but this abstraction they could not form prior to the observation of motion in material bodies.