It was nothing much to boast of in the way of architecture, this nest of the Kings of the Air--a mere cart-load of sticks and bark and coarse grass, apparently tumbled at haphazard upon the narrow ledge. But in fact its foundations were so skilfully wedged into the crevices of the rock, its structure was so cunningly interwoven, that the fiercest winds which scourged that lofty seat were powerless against it. It was a secure throne, no matter what tempests might rage around it. Sitting half erect on the nest were two eaglets, almost full grown, and so nearly full feathered that Horner wondered why they did not take wing at his approach. He did not know that the period of helplessness with these younglings of royal birth lasted even after they looked as big and well able to take care of themselves as their parents. It was a surprise to him, also, to see that they were quite unlike their parents in color, being black all over from head to tail, instead of a rich brown with snow-white head, neck, and tail. As he stared, he slowly realized that the mystery of the rare "black eagle" was explained. He had seen one once, flying heavily just above the tree-tops, and imagined it a discovery of his own. But now he reached the just conclusion that it had been merely a youngster in its first plumage. As he stared, the two young birds returned his gaze with interest, watching him with steady, yellow, undaunted eyes from under their flat, fierce brows; with high-shouldered wings half raised, they appeared quite ready to resent any familiarity which the strange intruder might be contemplating. Horner lay face downward on his ledge, and studied the perpendicular rock below him for a way to reach the next. He had no very definite idea what he wanted to do when he got there; possibly, if the undertaking seemed feasible, he might carry off one of the royal brood and amuse himself with trying to domesticate it. But, at any rate, he hoped to add something, by a closer inspection, to his rather inadequate knowledge of eagles. And this hope, indeed, as he learned the next moment, was not unjustified. Cautiously he was lowering himself over the edge, feeling for the scanty and elusive foothold, when all at once the air was filled with a rush of mighty wings, which seemed about to overwhelm him. A rigid wing-tip buffeted him so sharply that he lost his hold on the ledge. With a yell of consternation, which caused his assailant to veer off, startled, he fell backwards, and plunged down straight upon the nest.