The keenness of vision of the eaglet[77] has been noted in all ages, and its powers sometimes made even more astonishing than facts can justify. It has been asserted that when the eagle has soared into the air to a height that has rendered it perfectly invisible to human eye, it can discern the motions of the smaller animals upon the earth, and swoop down upon them from the sky, and Homer, in the “Iliad,” it will be recalled, describes Menelaus as “The field exploring, with an eye Keen as the eagle’s, keenest eyed of all That wing the air, whom, though he soar aloft, The lev’ret ’scapes not hid in thickest shades. But down he swoops, and at a stroke she dies.” The eastern writers, ever given to hyperbole, have assigned to the eagle powers of vision of a far more astonishing character than this. One of them, Damir, quoted by Burckhardt, declares that the eagle can discern its prey at a distance of four hundred parasangs—more than a thousand miles—and poets of all periods have drawn striking images from the wonderful power of vision of the king of birds. Mediæval naturalists have asserted that this magnificent eyesight was strengthened even beyond its natural powers by a diet on the eagle’s part of wild lettuce, in the same way that the linnet cleared its sight by means of the eyebright, the swallow through use of the celandine, and divers other birds through use of some special herb that they had proved to be of value to them. Our readers will doubtless remember the fine passage in the “Areopagitica” of Milton: “Methinks I see in my mind a noble and puissant nation rousing herself like a strong man after sleep, and shaking her invincible locks: methinks I see her as an eagle renewing her mighty youth, and kindling her undazzled eyes at the full midday beam.” It was one of the beliefs of our forefathers that the eagle had this power of rejuvenescence. The description of the process has a very prosaic sound about it, but the result is highly successful. When the eagle “hathe darknesse and dimnesse in eien and hevinesse in wings against this disadvantage she is taught by kinde to seeke a well of springing water, and then she flyeth up into the aire as farre as she may, till she bee full hot by heat of the aire and by travaile of flight, and so then by heat the pores be opened, and the feathers chafed, and she falleth sideinglye into the well, and there the feathers be chaunged and the dimnesse of her eien is wiped away and purged, and she taketh againe her might and strength.”[78] It was a strange belief of the writers of antiquity on these natural history topics that the feathers of the eagle, when placed amongst those of other birds, in a short space of time entirely consumed them.