As Kalliboas approached, all saluted him with a profound obeisance, which having gravely acknowledged the old man obtained a pair of the great wings and had them held up while he explained the principle of their use. Much that he told us of the origins and development of flying in the valley I omit for brevity's sake. Suffice it to say that the people had, some hundreds of years back, after a long and systematic study of the feathered creation, begun experimenting in wing-building for themselves, designing their implements so as to unite the best points they had observed about the wings of the best-flying birds. They were soon in possession of a wing that would support the flier in the air, but the perfecting of the pattern and the elimination of accidents had been a work of years, and to this day experiments were still made. The wings we saw were of a very thin, very tough skin, ribbed with some rigid horn-like substance which Kalliboas told us was hollow and hermetically sealed full of a light gas. The buoyancy thus derived was merely an adjunct, however, and should one of the ribs become punctured and the gas escape, the flier was in no danger of falling, since he depended for support in the air almost entirely on wing-purchase. When in use the wings were worn on the shoulders, being hinged together by a most ingenious device on the principle of a ball-and-socket joint; there were thong loops on the under side of the main rib, through which the arms of the wearer could be slipped in or out at will, and lower down a light framework serving as a rest for the feet during flight. The distance from tip to tip of the wings Kalliboas showed us was something over twenty feet. When he had explained their construction he bade the tutor select a boy to demonstrate how the wings were used. A youth of about sixteen years was chosen. As he came forward, I noticed a faint trace of a smile on the face of the tutor, and when the demonstrator had donned his wings and stood waiting, the other pupils broke into a downright cry of derision. The tutor quelled this outburst, and turned to us. 'I have chosen this boy, O Kalliboas,' he said, 'that the strangers may see what our least skilful can do. He is my most backward scholar. See, he waits for a favourable wind. No bird does that.'