The work was almost finished, when Larry Dexter, with Mr. Vardon and the latter's helper, Jack, came across to the sheds. They had come to see the army airships. By this time Lieutenant Larson had finished what he considered was his share of the work, and was on his way to get a brief leave of absence from his captain. At the entrance to the shed he came face to face with Mr. Vardon and Jack. "Oh, so you're the professional aviator they spoke of," said Larson, with a sneer in his tone. "Yes, I'm here," replied Mr. Vardon, quietly. "I did not expect to see you here, though." "The surprise is mutual," mocked the other. "I read about your failure. I suppose now, you will quit fooling with that gyroscope of yours, and give my method a trial." "I never will. I am convinced that I am right, and that you are wrong." "You're foolish," was the retort. Jack Butt stepped forward and whispered in the ear of his employer, so that at least Dick heard what he said. "I believe HE did it!" were the tense words of the machinist. CHAPTER VI DICK'S FIRST FLIGHT Mr. Vardon gave his helper a quick and warning glance. "Hush!" he exclaimed, as he looked to see if Lieutenant Larson had heard what Jack had said. But the army man evidently had not. He gave the machinist a glance, however, that was not the most pleasant in the world. It was evident that there was some feeling between the two. Dick wondered what it was, and what Jack's ominous words meant. Having put away the two biplanes, and requested the cadets to look at them as much as they liked, but not to meddle with the apparatus, the two lieutenants left the sheds, to report to their respective captains. Mr. Vardon and his helper remained with Dick and his chums. "Very fine machines," said the aviator. "Compared to my poor pile of junk, very fine machines indeed!" "But part of yours is good; isn't it?" asked Dick. "You can use part of it, I should think." "Very little," was the hopeless reply. "The damage was worse than I thought. My gyroscope attachment is a total wreck, and it will cost money to build a new one." "Yes, and that gyroscope was tampered with before we started on this last flight!" declared Jack, with conviction. "And I'm sure HE did it!" he added, pointing an accusing finger at the retreating form of Lieutenant Larson. "You must not say such things!" cried the aviator. "You have no proof!" "I have all the proof I want as far as he is concerned," declared Jack. "Maybe he didn't intend to kill us, or hurt us, but he sure did want to wreck the machine when he tampered with the gyroscope." "What is the gyroscope?" asked Dick. "It is an invention of mine, and one over which Lieutenant Larson and I had some argument," said Mr. Vardon.