The preliminary examination over, Derek had to undergo special tests through which every cadet must emerge with credit before being allowed to "take the air". Blindfolded, he was handed a small cube of wood on which was a tuning-fork supported by a small disc. The cube he had to lift vertically up and down three times without upsetting the equilibrium of the fork. Then came the "walking the plank" test, which consisted of traversing the length of a narrow plank while in blindfolded condition. Followed, a variety of seemingly simple but really intricate tests to prove the lad's capability of undergoing various experiences that the art of successful flying entails. The final one consisted of handing Daventry a wineglass brimful of water. This he was told to hold, without allowing a drop to escape, while quite unexpectedly a pistol-shot was fired within a few feet of his left ear. "Passed," was the M.O.'s crisp verdict; and Derek was curtly bidden to dress and proceed to the flying instruction-ground. Outside the cubicle he cannoned into Kaye, who had likewise passed the ordeal. "Didn't half give me a twisting, old man," he confided. "How many more of these stunts are there before we get our wings?" Together the chums made their way between the busy "shops" until they reached the flying-ground--a vast expanse of closely-cropped turf, bounded on three sides by shelters for the various types of 'planes. Some of these shelters, hurriedly erected in the breathless days of '14 and '15, were mere canvas "hangars" supported by a maze of rope shrouds like gigantic tents. Others, prophetic of the permanency of the infant science of aviation, were massive structures of ferro-concrete, provided with huge sliding doors, and capable of withstanding the heaviest gale. At various points long cone-shaped bags of silk served to indicate the direction of the wind, the knowledge of which is of paramount importance to the tyro in his attempts to "take off" and "land" correctly. Ungainly 'planes--for, like swans, they waddle awkwardly when out of their natural element--were being hauled out of their hangars. Others, taxi-ing under their own power, were lurching and rolling over the grassy sward, each with a pair of panting, perspiring mechanics hanging on to its long, tapering tail. Others were already up, practising straightforward flying under the guidance of experienced instructors, for fancy stunts, permitted only to the cadets in the advanced courses, were forbidden in the immediate vicinity of the aerodrome. Donning leather coats and flying-helmets, and drawing on enormous sheepskin garments that resembled exaggerated thigh-boots, the two chums presented themselves at the chief instructor's office. That worthy's reception of them was brief and to the point. "Cadet Daventry, you're for K5; Cadet Kaye, G4. Mornin'." "So we separate for the time being, George," remarked Derek, as the twain left the building. "Good luck, old man. See you at lunch, I hope."