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[1]; 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.
No two parts of duration can be certainly known to be equal.§ 21. 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 artificial days, the artificial days or νυχθήμερα were guessed to be equal, which was sufficient to make them serve for a measure: though exacter search has since discovered inequality in the diurnal revolutions of the sun, and we know not whether the annual also be not unequal. These yet, by their presumed and apparent equality, serve 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 distinguish betwixt duration itself, and the measures we make use of to judge of its length. Duration in itself is to be considered as going on in one constant, equal, uniform course: but none of the measures of it, which we make use of, can be known to do so;
