lower. But one millennium, the clear unembarrassed cyphers of 1,000, whether in counting guineas or years, is a far simpler and a far more rememberable era than any qualifications of this round number; which qualifications, let it not for a moment be forgotten, are not at all better warranted than the simpler expression. One only amongst all chronologers has anything to stand upon that is not as unsubstantial as a cloud; and this is Sir Isaac Newton. And the way in which he proceeded it may be well to explain, in order that the young pupil may see what sort of evidences we have _prior to the Olympiads_ for any chronological fact. Sir Isaac endeavoured by calculating backwards to ascertain the exact time of some celestial phenomenon--as, suppose, an eclipse of the sun, or such and such positions of the heavenly bodies with regard to each other. This phenomenon, whatever it were, call X. Then if (upon looking into the Argonautic Expedition or any other romance of those elder times) he finds X actually noticed as co-existing with any part of the adventures, in that case he has fixed by absolute observation, as it were, what we may call the latitude and longitude of that one historical event; and then using this, as we use our modern meridian of Greenwich, as a point of starting, he can deduce the distances of all subsequent events by tracing them through the sons, grandsons, and great-grandsons of the several actors concerned. The great question which will then remain to be settled is, how many years to allow for a generation; and, secondly, in monarchies, how much to allow for a reign, since often two successive reigns will not be two successive generations, because whilst the two reigns are distinct quantities, the two lives are coincident through a great part of their duration. Now, of course, Sir Isaac is very often open to serious criticism, or to overpowering doubts. That is inevitable. But on the whole he treads upon something like a firm footing. Others, as regards that era, tread upon mere clouds, and their authority goes for nothing at all.