8. It would be vain to attempt to fix any dates for events which took place in such remote antiquity, in the absence of any evidence or document that might be grasped. Yet, by close study of facts, by laborious and ingenious comparing of later texts, of every scrap of evidence furnished by monuments, of information contained in the fragments of Berosus and of other writers, mostly Greek, it has been possible, with due caution, to arrive at some approximative dates, which, after all, are all that is needed to classify things in an order intelligible and correct in the main. Even should further discoveries and researches arrive at more exact results, the gain will be comparatively small. At such a distance, differences of a couple of centuries do not matter much. When we look down a long line of houses or trees, the more distant ones appear to run together, and we do not always see where it ends--yet we can perfectly well pursue its direction. The same with the so-called double stars in astronomy: they are stars which, though really separated by thousands of miles, appear as one on account of the immense distance between them and our eye, and only the strongest telescope lenses show them to be separate bodies, though still close together. Yet this is sufficient to assign them their place so correctly on the map of the heavens, that they do not disturb the calculations in which they are included. The same kind of perspective applies to the history of remote antiquity. As the gloom which has covered it so long slowly rolls back before the light of scientific research, we begin to discern outlines and landmarks, at first so dim and wavering as rather to mislead than to instruct; but soon the searcher's eye, sharpened by practice, fixes them sufficiently to bring them into connection with the later and more fully illumined portions of the eternally unrolling picture. Chance, to which all discoverers are so much indebted, frequently supplies such a landmark, and now and then one so firm and distinct as to become a trustworthy centre for a whole group.