From all this we draw the following inference: that memory is, in certain cases, connected with great effort, in others, with no effort at all. Of one class we may say, that the facts absolutely deposit themselves in the memory; they settle in our memories as a sediment or deposition from a liquor settles in a glass; of another we may say that the facts cannot maintain their place in the memory without continued exertion, and with something like violence to natural tendencies. Now, beyond all other facts, the facts of dates are the most severely of this latter class. Oftentimes the very actions or sufferings of a man, empire, army, are hard to be remembered because they are non-significant, non-characteristic: they belong by no more natural or intellectual right to that man, empire, army, than to any other man, empire, army. We remember, for instance, the simple diplomacy of Greece, when she summoned all States to the grand duty of exterminating the barbarian from her limits, and throwing back the tides of barbarism within its natural limits; for this appealed to what was noblest in human nature. We forget the elaborate intrigues which preceded the Peloponnesian war, for these appealed only to vulgar and ordinary motives of self-aggrandisement. We remember the trumpet voice which summoned Christendom to deliver Christ's sepulchre from Pagan insults, for that was the great romance of religious sentiment. But we forget the treaties by which this or that Crusading king delivered his army from Mahometan victors, because these proceeded on the common principles of fear and self-interest; principles having no peculiar relation to those from which the Crusades had arisen. Now, if even actions themselves are easily dropped from the memory, because they stand in no logical relation to the central interest concerned, how much more and how universally must dates be liable to oblivion--dates which really have no more discoverable connection with any name of man or place or event, than the letters or syllables of that name have with the great cause or principles with which it may happen to have been associated. Why should Themistocles or Aristides have flourished 500 B.C., rather than 250, 120, or any other number of years? No conceivable relation--hardly so much as any fanciful relation--can be established between the man and his era. And in this one (to all appearance insuperable) difficulty, in this absolute defect of all connection between the two objects that are to be linked together in the memory, lies the startling task of Chronology. Chronology is required to chain together--and so that one shall inevitably recall the other--a name and an era which with regard to each other are like two clouds, aerial, insulated, mutually repulsive, and throwing out no points for grappling or locking on, neither offering any natural indications of interconnection, nor apparently by art, contrivance,[21] or fiction, susceptible of any.