The Lieutenant grinned. "I'll teach them all I know," he said; "but I'll bet the best dinner that can be served in Berlin that if this ship returns I'll still be her navigator." "That is a case of heads-I-win, tails-you-lose," said Gridley. "And to return to the subject of preparedness," said Tarzan, "I am going to ask you to let my Waziri help the mechanics and engineers. They are highly intelligent men, quick to learn, and if some calamity should overtake us we cannot have too many men familiar with the engines, and other machinery of the ship." "You are right," said Zuppner, "and I shall see that it is done." The great, shining ship sailed majestically north; Ravensburg fell astern and half an hour later the somber gray ribbon of the Danube lay below them. The longer they were in the air the more enthusiastic Zuppner became. "I had every confidence in the successful outcome of the trial flight," he said; "but I can assure you that I did not look for such perfection as I find in this ship. It marks a new era in aeronautics, and I am convinced that long before we cover the four hundred miles to Hamburg that we shall have established the entire air worthiness of the O-220 to the entire satisfaction of each of us." "To Hamburg and return to Friedrichshafen was to have been the route of the trial trip," said Tarzan, "but why turn back at Hamburg?" The others turned questioning eyes upon him as the purport of his query sank home. "Yes, why?" demanded Gridley. Zuppner shrugged his shoulders. "We are fully equipped and provisioned," he said. "Then why waste eight hundred miles in returning to Friedrichshafen?" demanded Hines. "If you are all agreeable we shall continue toward the north," said Tarzan. And so it was that the trial trip of the O-220 became an actual start upon its long journey toward the interior of the earth, and the secrecy that was desired for the expedition was insured. The plan had been to follow the Tenth Meridian east of Greenwich north to the pole. But to avoid attracting unnecessary notice a slight deviation from this course was found desirable, and the ship passed to the west of Hamburg and out across the waters of the North Sea, and thus due north, passing to the west of Spitzbergen and out across the frozen polar wastes. Maintaining an average cruising speed of about 75 miles per hour, the O-220 reached the vicinity of the north pole about midnight of the second day, and excitement ran high when Hines announced that in accordance with his calculation they should be directly over the pole. At Tarzan's suggestion the ship circled slowly at an altitude of a few hundred feet above the rough, snow-covered ice. "We ought to be able to recognize it by the Italian flags," said Zuppner, with a smile. But if any reminders of the passage of the Norge remained below them, they were effectually hidden by the mantle of many snows.