without perceptions whilst capable of perceiving, the idea of time must always be present along with those perceptions, that we may distinguish the order in which they occur.

Thus, then, as we must always act as if space were a real independently existing thing, so must we always act as if time were a real separately existing thing, as these two ideas are necessary to our reception of all the rest of our sensations, whether visible or tangible of sight or touch, and must ever be present to our minds. Our idea of time has also another extraordinary peculiarity, which it has in common with space, or with magnitude as measured by space. That peculiarity is that we have no idea at all, nor can have any, of the abstract velocity of time. Its relative velocity we can measure exactly that is to say, we know, exactly, the length of a minute relatively to the length of an hour; or the length of a month as compared with that of a year. But these are relations merely. If we take the minute singly, and the hour singly, we have no certainty that any two persons have the same perception of either. Nor can we be sure that our own perception of the minute or hour, singly, is at all times alike. All we know is that the relation of the minute to the hour, and of the month to the year, is always the same to us, and to others. In point of fact, if we rigidly investigate the matter, and recur back to experience, we shall find that there is a remarkable uncertainty about our ideas of the abstract velocity of time. An hour sometimes passes like a few minutes. A minute sometimes seems an hour.* Who can decide whether this apparent difference be real or

Some curious evidence as to the occasional celerity of thought, and the number of ideas crowded into a few minutes, may be collected. I have seen a statement by a naval officer, who was taken out of the water insensible but restored to animation, to the effect that, during the few minutes that elapsed before recollection ceased, his whole life seemed to pass in review before him, without the omission of any incident of importance. Without taking this account as literally true, or true in the extreme sense, it is certainly a very extraordinary one. Every fact relative to the question goes to show that time exists only in the mind, and is perpetually modified by changes in our mental conditions. It is impossible to conceive time (as we conceive space) to exist out of the mind of some being or beings. It is only a general idea of succession; and, except in idea, cannot be conceived to exist at all. It is, in short, only the general idea of the order of succession in which particular ideas have been mentally perceived.

not? We attempt to decide by mechanical means. We construct a time-piece by means of springs, or pendulums, and wheels, or we construct an hour-glass, and rectify our apparent differences of perception of time by our perceptions of sight, as given by the clock or the hour-glass. A calm reflection will, however, convince us that this supposed rectification is merely an arbitrary and dogmatical assumption. We have not the slightest evidence that the clock or the hour-glass has measured the time correctly when opposed to our own perceptions. We may as justly assume that they ought to have agreed with our perceptions as to the duration of time. In such case all that can be said is that our visible and mental perceptions are at variance. There is no proof that the visible are more correct than the mental sensations.

Thus, upon the entire view of the case, we find ourselves driven to a conclusion as to the nature of time, the same as that which we felt obliged to admit on the subject of abstract space. We cannot form an idea of time in the abstract. All we arrive at, after every attempt, is the idea of a very long time, which may be indefinitely added to at both ends. This, however, like our idea of abstract space, is a merely imperfect idea. By the human mind abstract time, it is clear, cannot be conceived, nor can we comprehend how an infinite series can possibly be conceived, as a whole, by any mind: for although the infinite may comprehend all that is finite, how can the infinite be contained even by an infinite intellect?

The final conclusion then, of necessity, seems to be that our idea of time is merely a mental instrument, given us to enable us to perceive the natural order in which our impressions follow each other. It is attained in infancy, as is the idea of space, which is an instrument of the same description, attained in infancy, to enable us to apprehend visible and tangible impressions; once attained, these ideas cannot possibly be ever shut out of the mind, even for an instant, as they must accompany all our other impressions and ideas of every kind, without exception.

Before concluding this division of the subject one remark remains to be made. If we assume the independent existence of space and of

time, we must further assume the independent existence, out of the mind, of motion. This we cannot possibly avoid. To realize any

idea of time, we must realize some idea of motion. This we must do, because we can only conceive of time as a fluxion, or a line made up of flowing points. But, in order to do that, the idea of space must also be present. It must be so because it is utterly impossible for motion, or velocity, to be present to the mind, or conceived by the mind, unless the idea of space be also present. This truth Dr. Berkeley has, in his Treatise "De Motû," demonstrated as completely as any truth ever was demonstrated: and I have no hesitation in saying that the man who pretends to be able to conceive the existence of motion, or velocity, without space for the thing moved to move in, pretends to conceive that which no human being ever did or ever will conceive.

Thus then it is manifest that the idea of space, time, and motion are all inseparably linked together. If we assume a real and distinct existence for one, we must assume it for all three. When, however, we come to the consideration of motion in the abstract, we shall find it involved in difficulties and contradictions analogous to those which attend the consideration of abstract space and abstract time. Relative motion we shall find it easy to apprehend and deal with. Beyond that, we shall find our path barred by obstacles as insuperable as those that prevented our realizing the ideas of space and time in the abstract. We must remain content with an imperfect idea; or assert that to exist of which we cannot even conceive the existence.

LETTER V.

MOTION.

If we attempt to define motion, we can only do so by defining it to be a change of place by some object, relatively to some other object or place. When we see an object to be nearer to, or farther from some other, we say one, or both, have moved. If we see the change going on, step by step, we say the object is moving. Beyond this we shall find we cannot go; and that all our idea of motion is relative.

That motion, in the abstract, cannot be conceived a little reflection will show. If one sole globe be imagined to exist in boundless space, we cannot imagine it to move, without the aid of something collateral. If, for instance, we mark in some way the place it occupies, we can conceive it to have moved, or to move, to another place; but this is not motion in the abstract. It has only moved relatively to the place we marked; and, without that mark, this conception of motion would have been impossible.

If there be force in reasoning, therefore, we must conclude that motion, abstractedly, is impossible, for on what rational ground can we conclude that to be possible which is totally inconceivable? This is the conclusion at which Bishop Berkeley arrives; and I must confess I cannot see how his logic is to be impugned. This, however, is only a small portion of the difficulty connected with the subject. If we inquire into the cause of motion, we shall find strange obstacles at every step.

If we assume the real existence of matter, or material substance, we must assume it to exist as defined by those who assert the reality of its existence. The qualities attributed to matter are solidity, extension, and figure. Colour as a secondary quality is also attributed to it; and so, likewise, is gravitation, or the capability of being drawn

towards a centre of attraction; and mobility or the capability of being moved. In these attributes, however, there is nothing that, in the least degree, goes to indicate a power of self-motion in matter. That which is called the evidence of our senses proves the direct contrary. It seems to teach us that matter in a state of rest continues in that state, until some impulse from without is applied to it. It then moves in the direction of the impulse given; and, as far as we can judge, would continue so to move, were not some counteracting force to destroy the effect of that impulse. Thus, a cannon-shot, projected in a certain direction, would go on in it for ever, were it not for the combined counteraction of the earth's attraction and the resistance of the atmosphere, which destroys the impulse given by the gunpowder. But in this supposition of impulse from without being necessary to the motion of material bodies, are involved more than one difficulty, which seem to be insurmountable.

If it be admitted, as I think it must be admitted, that, to enable one substance to act upon another, they must have some properties in common, then that which acts upon material substance must have the qualities of extension and solidity. In short it must be material in its nature. We have already seen, however, that all evidence proves that in material substance no self-moving power is inherent: or in other words no power of commencing motion. This being so, we are at once driven upon the question-How, then, did the first motion of a material substance originate? Being the first, it could not originate by being communicated through the action of some other material body. How, then, did it originate?

To this question there is only one answer possible. We are driven to admit that which seems inadmissible, that is to say, that matter must be moveable by mind; or, in other words, by something that has no qualities in common; that has neither extension, solidity, nor shape, nor any relation to space or to place. Thus, take it which way we will, we are met by difficulty apparently insuperable.

Nor is it possible to avoid these contradictions unless we boldly deny, altogether, the existence of material substance, including, of course, our own bodies. This is very evident, because admitting the