It is plain to me that we have as clear an idea of space distinct from solidity as we have of solidity distinct from motion, or motion from space. But to avoid confusion, it were to be wished, that the name 'extension' were applied only to matter, or the distance of the extremities of particular bodies; and the term expansion' to space in general, with or without solid matter possessing it; so as to say, space is expanded, and body extended.

The knowing what our words stand for, would quickly end the dispute: for men who well examine the ideas of their own minds cannot much differ in thinking, however they may perplex themselves with words according to the schools they have been bred up in. Amongst unthinking men who confound ideas with words there must be endless dispute, especially if they be learned bookish men, devoted to some sect, and accustomed to the language of it. But if two thinking men should really have different ideas, I do not see how they could argue one with another. It is not easy for the mind to put off those confused notions it has inadvertently imbibed from custom; it requires assiduity to examine its ideas, till it resolves them into those simple ones out of which they are compounded. Till a man doth this in the primary and original notions of things, he builds on floating and uncertain principles, and will often find himself at a loss.

CHAPTER XIV.

Of Duration, and its simple Modes.

There is another idea of length which we get from the fleeting parts of succession; this we call duration, the simple modes of which are any lengths of it, of which we have distinct ideas, as hours, days, years, &c. time, and eternity.

The answer of a great man to one who asked what time was, si non rogas, intelligo, (which amounts to

this, the more I set myself to think of it the less I understand it) might perhaps persuade one that time, which reveals all other things, is itself not to be discovered. But however remote from our comprehension duration, time, and eternity may seem, yet, if we trace them, we shall find them derived from the same common original with the rest of our ideas.

It is evident that there is a train of ideas which constantly succeed one another in the mind as long as we are awake. The distance between any part of that succession we call duration: for while we receive successively several ideas' in our minds, we know that we exist, and so we call the continuance of our existence commensurate with the succession of any ideas, the duration of ourselves. When that succession of ideas ceases, our perception of duration ceases with it, which every one experiences in himself when he sleeps soundly; while he sleeps he has no perception of duration, and the moment he leaves off thinking till the moment he begins to think again seems to him to have no distance. So would it be with a waking man, if he could keep one idea in his mind without variation; and we see that any one who fixes his thoughts on one object, so as to take little notice of the succession of ideas, thinks the time shorter than it is. If a man dreams during sleep, then he has a sense of duration : by which it appears that men have the idea of duration by reflecting on the succession of ideas.

A man, having from reflecting on his own thoughts got the idea of duration, can apply that notion to things which exist when he does not think; and, therefore, though he has no perception of the length of duration while he sleeps, yet having observed the revolution of days and nights, he can make allowance for the length of duration while he has been sleeping. Motion produces in the mind an idea of succession only as it produces a continued train of distinguishable ideas for a man looking on a body moving perceives

no motion, unless that motion produces a successive train of ideas :-thus in a calm at sea he may look on the sun, the sea, or the ship, and perceive no motion; but when he perceives one of them to have changed distance with some other body, then a new idea is produced, and he perceives that there has been motion. And this is the reason why slow motions are not perceived, because they cause not a constant train of new ideas to follow one another immediately in our minds. On the contrary, things that move so swift as not to affect the senses distinctly with several distinguishable distances, are also not perceived to move. There seem to be certain bounds to the quickness and slowness of the succession of ideas in our minds, beyond which they can neither delay nor hasten. Let a cannon-ball pass through a room, and take with it a limb of a man, it is clear that it strikes the two sides of the room successively, and that it must touch one part of the body first and another after, but no one could perceive succession either in the pain or sound. Such a part of duration we call an instant, as it takes up the time of only one idea in our minds. Where the motion is so slow as not to supply ideas as fast as the mind is capable of receiving them, and so other ideas coming between them, there the sense of motion is lost, as is evident in the hands of clocks and the shadows of sun dials.

It seems to me that the regular succession of ideas in a waking man is the measure of all other successions, whereof if any one exceeds the pace of our ideas, or is so slow as not to keep pace with them, there the idea of succession is lost. If the ideas of our minds do thus constantly change, it may be said that it is impossible for a man to think long of any one thing. From my own experience I think it is not possible to have one self-same single idea a long time alone in the mind without any variation. All that is in a man's power in this case is to observe the ideas that

take their turns in his understanding, or to call in such as he hath a desire or use of; but I think he cannot hinder the succession of fresh ones. It is not then motion, but the constant train of ideas in our minds, that furnishes us with the idea of duration,

Having got the idea of duration, it is natural for the mind to get some measure of it, whereby to judge of its different lengths. This consideration of duration, as marked by certain measures, we call time.

In measuring extension we apply the standard to the thing to be measured; but we cannot keep by us any measure of duration, which consists in fleeting succession, as we can of certain lengths of extension, as inches, feet, &c. marked on permanent parcels of matter. Nothing then could serve for a measure of time, but what has divided the whole length of its duration into apparently equal portions by constantly repeated periods.

The revolutions of the sun, having been universally observable and supposed equal to one another, have been made use of for the measure of duration. But men, measuring the length of time by the motion of the heavenly bodies, were apt to confound time and motion, or to think that they had a necessary connexion with each other: whereas any constant periodical appearance would have as well distinguished the intervals of time. For supposing the sun had been lighted up at the same distance of time that it now every day comes to the same meridian, and then gone out again twelve hours afterward, would not such regular appearance serve to measure the distance of duration as well without as with motion.

sun.

The freezing of water or the blowing of plants would serve to reckon years by, as well as the motion of the Some people in America count their years by the migration of certain birds. Any idea returning constantly at equidistant periods would not fail to measure the distances of time. A blind man, who

been sailing. A ship is also said to be in the same place, if it has kept the same distance with the parts of the neighboring land, though the earth has turned round. Thus they may be said to be in the same place in some respects, though their distance from other things being varied, they have changed place in that respect.

This modification of distance called place, being made to design the particular position of things, men determine this place by reference to those adjacent things which serve their present purpose. Thus in the chess-board the place of each man is determined within that chequered piece of wood; but when the chessmen are put into a bag, their place is determined by the part of the room in which they are. So if any one should ask in what place is the story of Nisus and Euryalus, it would be improper to say they were in such a part of the world or in such a library; but the proper answer would be that they are in the middle of the ninth book of Virgil's neis, where they always have been, though the book has moved a thousand times.

That our idea of place is but a relative position of any thing is plain, when we consider that we can have no idea of the place of the universe, because beyond it we have not the idea of a distinct object to which it can have relation of distance. The idea therefore of place we have, as we have that of space, by our sight and touch, by either of which we receive into our minds the ideas of extension or distance.

Some would persuade us that body and extension are the same. If by body and extension they mean what other people do, viz. by body, something solid and extended, whose parts are separable and moveable; and by extension, the space between the extremities of those solid coherent parts, and which is possessed by them, they confound different ideas one with another. The idea of space is as distinct from