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therefore we fhould as well have the idea of duration, were there no fenfe of motion at all.

§17. Time is Duration fet out by Measures. HAVING thus got the idea of duration, the next thing natural for the mind to do, is to get fome measure of this common duration, whereby it might judge of its different lengths, and confider the diftinct order wherein feveral things exift, without which a great part of our knowledge would be confufed, and a great part of history be rendered very ufelefs. This confideration of duration, as fet out by certain periods, and marked by certain measures or epochs, is that, I think, which most properly we call time.

§ 18. A good Meafure of Time muft divide its whole Duration into equal Periods.

In the measuring of extenfion, there is nothing more required but the application of the ftandard or measure we make use of to the thing, of whofe extenfion we would be informed. But in the measuring of duration this cannot be done, because no two different parts of fucceffion can be put together to measure one another; and nothing being a meafure of duration but duration, as nothing is of extenfion but extenfion, we cannot keep by us any standing unvarying measure of duration, which confifts in a conftant fleeting fucceffion, as we can of certain lengths of extenfion, as inches, feet, yards, &c. marked out in permanent parcels of matter. Nothing then could ferve 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 diftinguished, or confidered as diftinguished and measured by fuch periods, come not fo properly under the notion of time, as appears by fuch phrafes as thefe, viz. before all time, and when time fhall be no more.

19. The Revolutions of the Sun and Moon the propereft Measures of Time.

THE diurnal and annual revolutions of the fun, as having been, from the beginning of nature, conftant, regular, and univerfally obfervable by all mankind, and

Book II. fuppofed equal to one another, have been with reason made ufe of for the measure of duration. But the distinction of days and years having depended on the motion of the fun, 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 neceffary connection one with another; whereas any conftant periodical appearance, or alteration of ideas in feemingly equidiftant spaces of duration, if constant and univerfally obférvable, would have as well diftinguished the intervals of time, as thofe that have been made ufe of; for suppofing the fun, which fome have taken to be a fire, had been lighted up at the fame distance of time that it now every day comes about to the fame meridian, and then gone out again about twelve hours after, and that in the space of an annual revolution it had fenfibly increased in brightness and heat, and so decreased again; would not fuch regular appearances ferve to measure out the diftances of duration to all that could obferve it, as well without as with motion? For if the appearances were conftant, univerfally obfervable, and in equidiftant periods, they would serve mankind for meafure of time as well, were the motion away.

$ 20. But not by their Motion, but periodical Appear

ances.

FOR the freezing of water, or the blowing of a plant, returning at equidiftant periods in all parts of the earth, would as well ferve men to reckon their years by as the motions of the fun; and in effect we fee, that fome 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 fenfe of hunger or thirst, a fmell or a tafte, or any

other idea returning conftantly at èquidiftant periods, and making itself universally be taken notice of, would not fail to measure out the course of fucceffion, and diftinguish the diftances of time. Thus we fee that men born blind count time well enough by years, whofe revolutions yet they cannot diftinguish by motions that they perceive not: And I afk, Whether a blind man, who diftinguished his years either by the heat of summer, or cold of winter, by the fmell of any flower of the fpring, or tafte 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 Cæfar, or many other people, whose years, notwithstanding the motion of the fun, 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 fay all of them from the precife motions of the fun. And if the fun moved. from the creation to the flood conftantly in the equator, and fo equally difperfed its light and heat to all the habitable parts of the earth, in days all of the fame length, without its annual variations to the tropics, as a late ingenious author fuppofes; I do not think it very eafy to imagine, that (notwithstanding the motion of the fun) men fhould in the antediluvian world from the beginning count by years, or measure their time by periods, that had no fenfible 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 faid, without a regular motion, fuch as of the fun, or fome other, how could it ever be known that fuch periods were equal? To which I anfwer, The equality of any other returning appearances might be known by the fame way that that of days was known, or prefumed to be fo at firft; which was only by judging of them by the train of ideas which had paffed in mens minds in the intervals; by which

train of ideas discovering inequality in the natural days, but none in the artificial days or Νυχθήμερα, were guefed to be equal, which was fufficient to make them serve for a measure. Though exacter fearch has fince difcovered inequality in the diurnal revolutions of the fun, and we know not whether the annual alfo be not unequal, thefe yet, by their prefumed and apparent equality, ferve as well to reckon time by (though not to measure the parts of duration exactly), as if they could be proved to be exactly equal. We must therefore carefully diftinguish betwixt duration itself, and the measures we make use of to judge of its length. Duration in itself is to be confidered as going on in one conftant, equal, uniform courfe; but none of the meafures of it, which we make use of, can be known to do fo; nor can we be affured, that their affigned parts or periods are equal in duration one to another; for two fucceffive lengths of duration, however measured, can never be demonftrated to be equal. The motion of the fun, which the world used fo long and fo confidently for an exact measure of duration, has, as I faid, been found in its several parts unequal; and though men have of late made ufe of a pendulum, as a more fteady and regular motion than that of the fun, or (to speak more truly) of the earth, yet if any one should be asked how he certainly knows that the two fucceffive fwings of a pendulum are equal, it would be very hard to fatisfy him that they are infallibly fo, fince we cannot be fure, that the cause of that motion, which is unknown to us, thall always operate equally, and we are fure that the medium in which the pendulum moves, is not conftantly the fame; either of which varying, may alter the equality of fuch periods, and thereby destroy the certainty and exactness of the meafure by motion, as well as any other periods of other appearances; the notion of duration still remaining clear, though our measures of it cannot any of them be demonstrated to be exact. Since then no two portions of fucceflion can be brought together, it is impoffible ever certainly to know their equality. All that we

can do for a measure of time, is to take fuch as have continual fucceffive appearances at feemingly equidiftant periods; of which feeming equality we have no other measure, but fuch as the train of our own ideas have lodged in our memories, with the concurrence of other probable reasons, to perfuade us of their equality.

§ 22. Time not the Measure of Motion.

ONE thing seems ftrange to me, that whilft all men manifeftly measured time by the motion of the great and vifible bodies of the world, time yet fhould be defigned to be the measure of motion; whereas it is obvious to every one who reflects ever fo little on it, that to measure motion, fpace is as neceffary to be confidered as time; and those who look a little farther, will find alfo the bulk of the thing moved neceffary to be taken into the computation, by any one who will eftimate or measure motion, fo as to judge right of it. Nor indeed does motion any otherwise conduce to the measuring of duration, than as it conftantly brings about the return of certain fenfible ideas in feeming equidiftant periods: For, if the motion of the fun were as unequal as of a fhip driven by unfteady winds, fometimes very flow, and at others irregularly very swift; or if being conftantly equally swift, it yet was not circular, and produced not the fame appearances, it would not at all help us to measure time, any more than the feeming unequal motion of a comet does.

§ 23. Minutes, Hours and Years, not neceffary Measures of Duration.

MINUTES, hours, days, and years, are then no more neceffary to time or duration, than inches, feet, yards, and miles, marked out in any matter, are to extension; for though we in this part of the universe, by the conftant use of them, as of periods fet out by the revolutions of the fun, or as known parts of fuch periods, have fixed the ideas of fuch lengths of duration in our minds, which we apply to all parts of time, whose lengths we would confider, yet there may be other parts of the univerfe, where they no more ufe these

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