"This is evidently urgent; I must get the cipher-key and decode it at once. Meantime, I want you to rehearse the men in the parts they are to play, and give Carl a hand with the vibration drum. The great liner is almost due. You may tell the sheik that in addition to the large cargo of gold which the airship carries, an Indian Prince with jewels worth a king’s ransom is on board." "Your orders shall be carried out, Rittmeister," replied Max, who was glad to be relieved of his monotonous task of listening hour after hour for coded messages, and looked forward with some pleasure to the coming adventure. Shortly afterwards, Max, having delivered his message to the Arabian chief, was standing beside Carl under the shadow of a cluster of trees on the very margin of the pool. That wonderful instrument, the vibrative drum, which is fashioned somewhat on the principle of the human ear, but with a large horn-shaped receptacle for receiving the very minutest sound waves, and focussing them on to a very sensitive drum, was engaging their attention. Every now and then, when they fancied they heard a sound that broke the stillness of the desert, they would listen acutely, turning the horn this way and that way to discover whence came the sound. "They are due about mid-day, the chief says," remarked Carl, after a brief pause in their conversation. "What time do you make it now?" "A quarter of an hour yet," responded Max, consulting his chronometer, and making a rapid calculation to allow for the difference in longitude, for he still carried Central European time. "And they’re sure to follow the 30th parallel?" "Yes, it’s their shortest route," replied the wireless expert. "Then they should pass within three or four miles from here," observed Carl. "Yes, unless they’ve drifted a little out of their course." "But we should hear them on the vibrator even if they were fifty miles away in a silent land like this." "Undoubtedly." "Listen! Can you hear anything?" exclaimed Max in a slightly nervous tone, after a brief silence. "No, I don’t think so, but those fellows over there must be quiet; they’re getting excited about the promised loot." "Go and tell them, Carl; you speak the best Arabic." The German left the drum for a moment and after expostulating for a while with the sheik, he gained his point and the word was passed along for silence. The Arabs were greatly mystified by this strange instrument, as well as by those aerial wires affixed to the trees, and most of all by that strange, weird machine, hidden away behind the sand-proof curtains of the little camouflaged hangar, like the sacred ark in the holy of holies. With wondering eyes they had on occasion watched the _Scorpion_ mount to the heavens with marvellous ease and descend with like facility--bearing its human burden aloft to the very skies and bringing them safely to earth again.