Once the adventurers got used to the different motion of the projectile, which was now falling in some unknown direction of its own weight and not forced onward by the power of the motor, they did not notice anything strange. "Let's begin at the pilot house and work back," proposed Andy. "If that crazy machinist did the damage, it would be natural for him to want to get as far away as he could from the engine-room. That place would be the pilot house." So they searched there, but there was no sign of any one. Indeed, it would have been a pretty small person who could have concealed himself in the prow of the projectile, occupied as it was with all sorts of mechanism. "Well, he isn't here, that's certain," declared Andy, who had brought his gun along. "Now for the bunk-room." There they had no better luck. They peered under the berths, above them, and even turned back the sheets and blankets to look for the intruder. He was not to be found. Nor was he in the living-room, which was looked over from top to bottom, and every corner examined. "If he's any place, it must be in the storeroom," declared Jack. "Unless he's outside the projectile," suggested Mark. "He couldn't live for a minute in a place without atmosphere," was Jack's opinion. "No, he's in here somewhere, and we must find him." But it was more easily said than done. The storeroom contained many things, piled together, and it would have been easy for a person to conceal himself among them. The boys and the old hunter looked in every possible place, as they supposed, even taking down many boxes and barrels to peer behind them, but they did not find the man they sought. "I don't believe he's here," said Jack as he paused in the hunt. "Say, do you know, I have an idea," said Mark. "Maybe that motor broke itself." "How could it do that?" "Well, it might have got to going too fast, and the power may have broken the plates. Anyhow, we didn't hear any person in the engine-room, and there doesn't seem to be any one here." "That's so." "I'll make an affidavit that there ain't a person on this airship but ourselves," declared Andy. "Let's ask Mr. Roumann if it's possible that the motor smashed itself," proposed Jack, and, having no further place to search, they went back to where the two scientists and Washington were busily engaged. "Yes," replied Mr. Roumann, after Jack had stated his question. "It's possible for that to have happened, but not very probable. I think some person is hiding on board here, and that he did it." "But we can't find any one." "That may be. He is well concealed. Well you can't do anything more. Suppose you two boys turn in and help us?"