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."