"You are welcome, children of the Fatherland," he said, extending his hand, and fixing the two strangers with his piercing eyes, after this brief salutation. "I hope we are not late," began von Spitzer, when the first salutation was over and he had introduced his companions. "The sun is amongst the pines and the shadows of the Schwarzwald deepen," replied the professor, speaking in the language of the forest. "It was the time arranged, but"--and here he paused for a second--"there is no time for delay," and an uneasy look spread over his face. "You don’t mean that----" began the chief, but the genius forestalled him by adding:-- "Yes, strangers have crossed the clearing to-day. For the first time since I came here, I heard strange voices amongst the trees." "But they found nothing?" "Nothing!" ejaculated the professor. "Good! Then my friends may view the aeroplane," said Spitzer. "Certainly; let them follow me," and through an opening barely fifteen feet wide, the professor led the way to a combined hangar and workshop, carefully camouflaged and hidden away amongst the trees. The next instant the two young airmen received the greatest surprise of their lives. "Der _Skorpion_!" announced the professor. "Donnerwetter!" came the involuntary cry from both the strangers as their eyes fell upon a new type of aeroplane, with an angry, waspish look about it, that the Bristol Fighter used to wear during the later days of the Great War. Yet it was not a Bristol Fighter by any means, for it was twin-engined, and steel-built throughout, with a central conning-tower, tapering off to a sharp point to improve the stream-line, and a closed-in be-cabined fuselage into which four or six persons might with ease be stowed away. "But her engines!" exclaimed Max. "How small they are." "But how powerful!" replied Spitzer. "Each one develops anything up to 400 horsepower." "Is it possible?" asked Carl, who was already carefully examining the starboard engine, in its covered in and stream-lined casement. "The propellers are different, too; they’re something like the Fokker’s, but shorter, and they have a peculiar twist, which I have never seen before. What is that for, Rittmeister?" asked the Gotha pilot. "For vertical climbs, Max," replied the chief, for while the professor stood by, and looked on, interested and amused at the growing enthusiasm for his idol, the Rittmeister, who had been secretly schooled in the hidden mysteries, explained them point by point, for he was a great mechanic and mathematician was this ex-flight-commander. "Vertical climbs?" echoed the other. "I thought it was impossible." "Impossible? Rubbish! Nothing is impossible to the man of science. Have you never heard of the Helicopter?" "You mean that hybrid mongrel the verdammt Yanks and the Britishers have been experimenting with of late, and which has caused so many accidents?"