derek daventry had passed through several medical examinations since his entry as a cadet of the r.a.f. but this one in particular was a thoroughly strenuous test. having been put through the usual ordeal as regards his keenness of vision and hearing, lung capacity, and heart action only a few weeks previously, it came as a surprise that he should again be "put through the mill". it was but one example of the solicitude of the r.a.f. for its budding airmen, and of the determination to receive the very best material for flying. the authorities realize that it is easy for a reckless youth to ruin his constitution in a very short time, and consequently no steps are spared to keep the quirks in the very pink of condition.

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."

the finding of k5, signifying the fifth hangar in k lines, afforded no difficulty. already the machine was out, four or five mechanics being busily engaged in tuning-up the engine and testing the controls under the observant eye of a young officer, who, apparently bored stiff with the whole performance, was smoking a cigarette and fondling a terrier pup—but one of the small army of mascots maintained by the averleigh t.d.s.

lieutenant rippondene, derek's instructor, was in appearance an overgrown schoolboy. as a matter of fact he was just twenty, and had been flying at the front for more than two years, until a piece of shrapnel had put a temporary stop to his activities in strafing the boche. until he could prevail upon a normally adamant medical board to allow him to cross the channel again, he was being employed as flight-instructor to the quirks of averleigh flying school.

he was full-faced, and showed a decided tendency towards corpulence. in his flying-helmet and leather coat he strongly resembled a jovial friar, and it would have been difficult to realize that those podgy hands were capable of keeping a shrapnel-torn "'bus" under absolute control. on one occasion he had been beset by five huns, yet, according to the testimony of his observer, "the old merchant was grinning from ear to ear during the whole strafe".

"hop in!" was the lieutenant's greeting, much in the manner of a motorist offering a youngster a lift on the road.

derek obeyed, clambering into the fuselage of the double-seater "dromedary" by means of metal-shod niches in the side of the khaki-painted body.

the instructor, throwing aside quite two-thirds of the original length of the cigarette, followed, and, dropping into his seat like a crab retiring to its lair, drew on a pair of gauntlets.

"right-o!" he continued. "tell 'em to swing her."

"contact, sir—contact off," was the continued slogan of the air mechanic, as he strove to swing the large two-bladed propeller, or "prop." as it is invariably termed in the r.a.f.

nothing of the desired nature resulting, derek turned and looked enquiringly at his instructor. rippondene's face was wreathed in smiles, for his pupil had forgotten an elementary task.

"you're doing the job, george—not i," he remarked. "carry on, and make a move."

at the next swing of the propeller the engine fired. only the skids under the landing prevented the dromedary from rolling forward over the ground. now was the time for derek to put weeks of theoretical instruction to the test. a touch of the throttle and the powerful engine roared "all out", the vast and seemingly slender fabric of the 'bus quivering under the strain, while the tyro pilot was almost beaten backwards against the coaming of the seat by the terrific blast from the rapidly-revolving prop.

the cadet waved his hand over the side of the fuselage—the recognized signal for the mechanics to remove the skids. slowly at first, then gradually gaining speed, the dromedary ambled across the ground, the propeller raising enormous clouds of dust, while small spurts of warm castor oil were ejected from the engine and blown back by the wind into the goggled face of the young pilot. unable to gauge the biplane's speed, derek held on until the instructor bellowed plaintively into his ear:

"get a move on, my lad; you're in a 'bus, not trundling a hoop along a road."

thus stimulated daventry actuated the elevating-lever. submissively the huge machine parted company with mother earth, so gently and evenly that it was only the change of vibration that told derek of the fact.

"by jove!" muttered the lad. "i'm up now. wonder how i'll get down again." ahead, owing to the tilt of the blunt nose of the machine, he could see nothing but sky and fleecy clouds. it was only when he glanced over the side that he saw the hangars already dwarfed to the size of dolls' houses.

the ecstacy of it all! to find himself controlling a swift aerial steed, to handle the responsive joystick, and to make the machine turn obediently to a slight pressure on the rudder-bar. anxiety was cast to the winds. the sheer lust of flight in the exhilarating atmosphere gripped the cadet in its entirety.

again derek leant over and surveyed the now distant earth from a height of three thousand feet, as shown by the altimeter. but for the furious rush of wind there was little sensation of speed, nor was he in any degree affected by the height above the ground. without the faintest inconvenience he could watch the vast panorama beneath him, and distinguish white ribands as dusty roads, and the variegated patches of green denoting cultivated fields, meadows, and clumps of trees. although previously warned of the fact, he was nevertheless surprised at the aspect of the ground, which presented the appearance of a flat plain. hills—and there were plenty in the vicinity of averleigh—had visually ceased to exist.

suddenly the pleasing prospect was interrupted by a disconcerting movement of the hitherto docile biplane. akin to the sensation of being in a lift that is unexpectedly put in motion, derek found himself dropping, while at the same time the clinometer, an instrument for indicating the heel of the aerial craft, showed a dip of thirty-five degrees. instinctively derek sought to regain a state of stability, but the joy-stick seemed powerless to essay the task.

for a brief instant daventry wondered what was happening. it seemed to him that, notwithstanding his efforts, the 'bus was dropping earthwards, and that the tractive powers of the prop. were futile. then, with a series of sharp jerks, the 'plane regained its normal state of progression.

"pocket," explained rippondene, speaking into the voice-tube that formed a means of communication between instructor and pupil. "you'll soon get used to them; carry on—up to four thousand."

it was derek's first "bump"—a vertical fall through fifty or a hundred feet, owing to the machine encountering a patch of thin air, or what is known to airmen as a pocket.

"look ahead!" came the warning. "there's another 'bus."

approaching each other at an aggregate speed of a hundred and fifty miles an hour the two biplanes swerved discreetly, for both were steered by quirks who took no risks. there are certain hard-and-fast rules of the air which have to be obeyed with as much precision as the mariner has to conform to the rule of the road at sea.

they passed a good two hundred yards apart, but almost immediately derek's 'bus started rocking and rolling in a disconcerting fashion as it encountered the backwash of air from the now rapidly receding biplane.

revelling in the novel situation, derek held on, occasionally turning his machine in a wide circle and resisting any great inclination to bank. he felt as if he could carry on indefinitely, so exhilarating was the rush through the air, until the voice of his mentor sounded in his ear.

"how about it?" it enquired brusquely. "i want my lunch even if you don't. back you go, my festive."

derek swung the machine round until the needle of the compass showed that the dromedary was flying in the reverse direction, but very soon the disconcerting truth became apparent. in his wild joy-ride he had neglected to take bearings and allow for the side-drift of the wind. he was lost.

"won't do to admit that," he soliloquized. "i'll bluff the old buffer, and trust to luck."

for nearly ten minutes he flew by compass course, the while studying the expanse of ground three thousand feet below. away to the south'ard he could discern the coast-line, quite forty miles distant. evidently under the action of the south-westerly breeze the biplane had side-drifted more than thirty miles.

flecks of whitish vapour glided rapidly beneath the aeroplane. the sky was beginning to become overcast. viewed from the ground those clouds would probably appear dark and semi-opaque. viewed from above, and bathed in the brilliant sunshine, they were white as driven snow.

setting a compass course to counteract the current, daventry flew steadily for twenty minutes. by the end of this time the ground was invisible. reluctantly he resolved to dive through the clouds in order to verify his position. it seemed a thousand pities to plunge out of the sunshine, but his instructor was becoming impatient. the novelty of joy-riding in the air had long since worn off as far as rippondene was concerned, whereas the pangs of hunger are not easily to be denied.

a slight touch of the aileron actuating-gear and the descent began. cutting out the engine, derek let the machine vol-plane. it was a delicious, exciting, nerve-tingling sensation. in silence, save for the rush of the air past the struts and tension-wires, the huge fabric glided with great rapidity, momentarily nearing the extensive bank of snow-white clouds.

instinctively derek shut his eyes as the dazzling mantle of vapour appeared to rise and envelop him. the next moment the biplane was plunging through the mist, in which the light gradually diminished until it was like being in a room in the twilight.

no longer was the needle of the compass visible. even the luminous point failed to show so much as a faint glow. sense of stability, too, was lost. whether the machine was banking steeply or volplaning naturally was a matter for conjecture. all derek knew was that the 'bus was moving rapidly, not under its own volition, but solely under the unseen and unfelt force of gravity. then, like an express train emerging from a tunnel, the old 'bus, rocking and plunging, shot out of the cloud-bank. shaking the moisture from his goggles, derek restarted his engine, and then looked somewhat anxiously over the side. almost the first object that met his gaze was the averleigh aerodrome at a distance of about two miles.

"in sight of home," soliloquized the lad grimly; "but now comes the hardest part—landing. hope i don't pancake or try to land below the ground."

"pancaking", it must be explained, consists in getting as much way off the machine as possible, and dropping practically vertically. unless the correct height and drop be gauged normally about three feet—the machine is almost sure to "crash". pancaking is only deliberately resorted to when one is forced to land in standing corn, stubble, or flooded ground.

"landing below the ground" is a term applied to an underestimation of the vertical distance when pancaking. although of comparatively rare occurrence, its results are even more disastrous than overestimating the fall, and the crash almost invariably wrecks the machine completely and costs the pilot his life.

turning, so as to fly into the wind, daventry made the plunge. intent upon his task, he completely forgot the presence of his mentor, who, ready at an instant's notice to operate the "dual-control" mechanism, was silently yet critically watching his pupil.

the ground appeared to be rising to greet the descending aeroplane—slowly at first, then with disconcerting acceleration. there was no time to stop and think; what had to be done must be done promptly, almost automatically. an error of judgment would certainly result in a crash of more or less seriousness.

"now!" exclaimed derek aloud, although he knew not why. the nose of the machine rose slightly; there was a perceptible jar, another, and then a series of bumps that decreased in force although they increased in duration. mechanically the young pilot cut off his engine, and after travelling a few yards the 'plane came to a standstill.

"by jove! i've landed," he soliloquized. "wonder how i did it?"

rippondene clambered out, sliding to the ground, and began to swing his arms to restore the circulation.

"hurry up, old bird!" he exclaimed pleasantly. "we're the last down, and lunch will be over if we don't look sharp. yes, we'll make a good airman of you yet. you've got it in you. matter of fact i only had to touch the joy-stick once, and that was when you tried to loop the loop in that cloud. didn't know you did, eh? i'm not surprised. we've all been in the same boat."