These strange gods which the infidels had brought with them to their desert home were greatly feared even by these brave, proud men, and it was only the largesse and the promise of still better things to come, from the great white chief, which prevented these sons of the desert from leaving this dreaded spot. The scout pilot, having obtained his wish, now returned to the instrument, for his companion was already beckoning to him. Evidently the approach of the airship had been indicated by the sensitive drum, but, ere Carl reached the margin of the pool, he noticed the Rittmeister emerge from the hangar where he had been decoding the message, and wave for him to approach. "What is it, Rittmeister?" he called. "The message. Come here a moment!" Max, who thought that a faint sound he had just heard from the instrument might portend the distant approach of the liner, left the drum, for he knew there would be plenty of time, and joined the other two by the hangar on the other side of the pool, for he also was curious about the cryptic message, which he had taken earlier in the day. "Was it from the professor?" he asked in his first breath. "Yes, he is in for a bad time, I fear," replied the Rittmeister. "He will not be able to communicate again for some time." "What is the matter?" asked the others simultaneously. "Why, Keane and Sharpe are on his track again. You know the rascals; they were secret service pilots and spies during the war, and now they are scout pilots in the British aerial police. They’re the left-hand and the right hand of that confounded Tempest, the little tin god at Scotland Yard, and the brains of the aerial police." "Himmel! I hope he can outwit them," exclaimed Carl. "They’re keen birds, both of them, and they have some exploits to their credit." "If he can’t, then the length of our existence is the capacity of those remaining eight cylinders of uranis," ventured Max. "And the length of the rope round our necks as well," murmured his companion. They all laughed at this, but Spitzer looked keenly for an instant into the eyes of the two pilots, as though he would search their innermost souls, and make sure that they would be game to the end. But they evidently read his thoughts also, for Max announced:-- "It’s all right, Rittmeister; we’re not going back upon our word. The die is cast!" and Carl in a brave attempt at another sally, added:-- "The cast is--die!" at which they all laughed again, as the old sea pirates laughed before they blew up their ship, when they saw that the game was up. The next instant their thoughts were diverted to another subject. It was already mid-day, for the sun by his altitude announced it. As they approached the drum, they could now distinctly hear the hum of mighty engines though still forty miles away, recorded in that delicate instrument, and one thought, uttered or unexpressed, came instinctively to each mind:-- "Aircraft approaching!"