§ 9. The train of ideas has a certain degree of quickness. HENCE I leave it to others to judge, whether it be not probable that our ideas do, whilst we are awake, succeed one another in our minds at certain distances, not much unlike the images in the inside of a lanthorn, turned round by the heat of a candle. This appearance of theirs in train, though perhaps it may be sometimes faster and sometimes slower, yet, I guess, varies not very much in a waking man. There seem to be certain bounds to the quickness and slowness of the succession of those ideas one to another in our minds, beyond which they can neither delay nor hasten.

§ 10.

THE reason I have for this odd conjecture, is from observing, that in the impressions made upon any of our senses, we can but to a certain degree perceive any succession; which, if exceeding quick, the sense of succession is lost, even in cases where it is evident that there is a real succession. Let a cannon-bullet pass through a room, and in its way take with it any limb, or fleshy parts of a man; it is as clear as any demonstration can be, that it must strike successively the two sides of the room: it is also evident, that it must touch one part of the flesh first; and another after, and so in succession; and yet I believe nobody, who ever felt the pain of such a shot, or heard the blow against the two distant walls, could perceive any succession, either in the pain or sound of so swift a stroke. Such a part of duration as this, wherein we perceive no succession, is that which we may call an instant, and is that which takes up the time of only one idea in our minds, without the suc cession of another, wherein therefore we perceive no succession at all.

S 11.

THIS also happens, where the motion is so slow as not to supply a constant train of fresh ideas to the senses, as fast as the mind is capable of receiving new ones into it; and so other ideas of our own thoughts, having room to come into our minds, between those offered to our senses by the moving body, there the sense of motion is lost; and the body, though it really moves, yet not changing perceivable distance with some other bodies, as fast as the ideas of our own minds do naturally follow one another in train, the thing seems to stand still, as is evident in the hands of clocks and shadows of sundials, and other constant but slow motions; where, though, after certain intervals, we perceive by the change of distance that it hath moved, yet the motion itself we perceive not.

§ 12. This train the measure of other successions.

So that to me it seems, that the constant and regular succession of ideas in a waking man, is, as it were, the measure and standard of all other successions: whereof if any one either exceeds the pace of our ideas, as where two sounds or pains, &c. take up in their succession the duration of but one idea, or else where any motion or succession is so slow as that it keeps not-pace with the ideas in our minds, or the quickness in which they take their turns; as when any one or more ideas, in their ordinary course, come into our mind, between those which are offered to the sight by the different perceptible distances of a body in motion, or between sounds or smells following one another, there also the sense of a constant continued succession is lost, and we perceive it not but with certain gaps of rest between.

§ 13. The mind cannot fix long on one invariable idea. Ir it be so that the ideas of our minds, whilst we have any there, do constantly change and shift in a continual succession, it would be impossible, may any one say, for a man to think long of any one thing. By which, if it be meant that a man may have one self same single idea a long time alone in his mind, without any variation at all, I think, in matter of fact, it is not possible; for which (not knowing how the ideas of our minds are framed, of what materials they are made, whence they have their light, and how they come to make their appearance) I can give no other · reason but experience: and I would have any one try whether he can keep one unvaried single idea in his mind, without any other, for any considerable time together.

$ 14.

FOR trial, let him take any figure, any degree of light or whiteness, or what other he pleases; and he will, I suppose, find it difficult to keep all other ideas out of his mind: but that some, either of another kind, or various considerations of that idea (each of which considerations is a new idea) will constantly succeed one another in his thoughts, let him be as wary as he can.

§ 15.

ALL that is in a man's power in this case, I think, is only to mind and observe what the ideas are, that take their turns in his understanding; or else to direct the sort, and call in such as he hath a desire or use of; but hinder the constant succession of fresh ones, I think he cannot, though he may commonly choose whether he will heedfully observe and consider them.

§ 16. Ideas however made, include no sense of motion. WHETHER these several ideas in a man's mind be made by certain motions, I will not here dispute; but this I am sure, that they include no idea of motion in their appearance; and if a man had not the idea of motion otherwise, I think he would have none at all: which is enough to my present purpose, and sufficiently shows, that the notice we take of the ideas of our own minds, appearing there one after another, is that which gives us the idea of succession and duration, without which we should have no such ideas at all. It is not then motion, but the constant train of ideas in our minds, whilst we are waking, that furnishes us with the idea of duration, whereof motion no otherwise gives us any perception, than as it causes in our minds a constant succession of ideas, as I have before showed: and we have as clear an idea of succession and duration, by the train of other ideas succeeding one another in our minds, without the idea of any motion, as by the train of ideas caused by the uninterrupted sensible change of distance between two bodies, which we have from motion; and therefore we should as well have the idea of duration, were there no sense of motion at all.

S 17.

Time is duration set out by measures. HAVING thus got the idea of duration, the next thing natural for the mind to do, is to get some measure of this common duration, whereby it might judge of its different lengths, and consider the distinct order wherein several things exist, without which a great part of our knowledge would be confused, and a great part of history be rendered very useless. This consideration of duration, as set out by certain periods, and marked by certain measures or epochs, is that, I think, which most properly we call time.

§ 18. A good measure of time must divide its whole duration into equal periods.

In the measuring of extension, there is nothing more required but the application of the standard or measure we make use of to the thing, of whose extension we would be informed. But in the measuring of duration this cannot be done, because no two different parts of succession can be put together to measure one another and nothing being a measure of duration but duration, as nothing is of extension but extension, we cannot keep by us any standing unvarying measure of duration, which consists in a constant fleeting succession, as we can of certain lengths of extension, as inches, feet, yards, &c. marked out in permanent parcels

of matter. Nothing then could serve well for a convenient measure of time, but what has divided the whole length of its duration into apparently equal portions, by constantly repeated periods. What portions of duration are not distinguished, or considered as distinguished and measured by such periods, come not so properly under the notion of time, as appears by such phrases as these, viz. before all time, and when time shall be no more.

§ 19. The revolutions of the sun and moon the properest measures of time.

THE diurnal and annual revolutions of the sun, as having been, from the beginning of nature, constant, regular, and universally observable by all mankind, and supposed equal to one another, have been with reason made use of for the measure of duration. But the distinction of days and years having depended on the mution of the sun, it has brought this mistake with it, that it has been thought that motion and duration were the measure one of another: for men in the measuring of the length of time, having been accustomed to the ideas of minutes, hours, days, months, years, &c. which they found themselves upon any mention of time or duration presently to think on, all which portions of time were measured out by the motion of those heavenly bodies; they were apt to confound time and motion, or, at least, to think that they had a necessary connection one with another: whereas any constant periodical appearance or alteration of ideas in seemingly equidistant spaces of duration, if constant and universally observable, would have as well distinguished the intervals of time, as those that have been made use of. For supposing the sun, which some have taken to be a fire, had been lighted up at the same distance of time that it now every day comes about to the same meridian, and then gone out again about twelve hours after, and that in the space of an annual revolution, it had sensibly increased in brightness and heat, and so decreased again; would not such regular appearances serve to measure out the distances of duration to all that could observe it, as well without as with motion? For if the appearances were constant, universally observable, and in equidistant periods, they would serve mankind for measure of time as well, were the motion away.

§ 20. But not by their motion, but periodical appearances. For the freezing of water, or the blowing of a plant, returning at equidistant periods in all parts of the earth, would as well serve mẹn to reckon their years by as the motions of the sun and in

effect we see, that some people in America counted their years by the coming of certain birds amongst them at their certain seasons, and leaving them at others. For a fit of an ague, the sense of hunger or thirst, a smell or a taste, or any other idea returning constantly at equidistant periods, and making itself universally be taken notice of, would not fail to measure out the course of succession, and distinguish the distances of time. Thus we see that men born blind count time well enough by years, whose revolutions yet they cannot distinguish by motions, that they perceive not: and I ask, Whether a blind, man who distinguished his years either by the heat of summer, or cold of winter; by the smell of any flower of the spring, or taste of any fruit of the autumn; would not have a better measure of time than the Romans had before the reformation of their calendar by Julius Cæsar, or many other people, whose years, notwithstanding the motion of the sun, which they pretend to make use of, are very irregular? And it adds no small difficulty to chronology, that the exact lengths of the years that several nations counted by, are hard to be known, they differing very much one from another, and I think I may say all of them from the precise motion of the sun. And if the sun moved from the creation to the flood constantly in the equator, and so equally dispersed its light and heat to all the habitable parts of the earth, in days all of the same length, without its annual variations to the tropics, as a late ingenious author supposes*; I do not think it very easy to imagine, that (notwithstanding the motion of the sun) men should in the antediluvian world from the beginning count by years, or measure their time by periods, that had no sensible marks very obvious to distinguish them by.

§ 21. No two parts of duration can be certainly known to be equal.

BUT perhaps it will be said, without a regular motion, such as of the sun, or some other, how could it ever be known that such periods were equal? To which I answer, the equality of any other returning appearances might be known by the same way that that of days was known, or presumed to be so at first, which was only by judging of them by the train of ideas which had passed in men's minds in the intervals: by which train of ideas discovering inequality in the natural days, but none in the artifical days or Nuxμg were guessed to be equal, which was sufficient to make them serve for a measure. Though exacter search has since discover

* Dr. Burnet's Theory of the earth.

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