"I don't know. Something went wrong. Here comes Professor Henderson and Mr. Roumann. We'll ask them." The two scientists were observed approaching from the pilot-house. They walked along what had been the ceiling, and when they came to the engine room they had to climb over the top part of the door frame. "What's wrong?" asked Jack. "Our center of gravity has become displaced," answered Mr. Henderson. "The gravity machine has either broken, or some one has been tampering with it. Did either of you boys touch it?" "No, indeed!" cried Mark, and his chum echoed his words. "I wonder if Washington could have meddled with it?" went on the scientist. At that moment the colored cook came along, making his way cautiously into the engine room. He was an odd sight. Bits of carrots, turnips and potatoes were in his hair, while from one ear dangled a bunch of macaroni, and his clothes were dripping wet. "My kitchen done turned upside down on me!" wailed Washington, "an' a whole kettle ob soup emptied on my head! Oh, golly! What happened?" The aged scientist looked toward the German. The latter was gazing up at the motionless Cardite motor over his head. "There is but one way," he answered. "We must restore our centre of gravity to where it was before. Then the projectile will right herself." "Can it be done?" asked Mark. "It will be quite an undertaking, but we must attempt it. Bring some tables and chairs, so I can stand up and reach the equilibrium machine." From where they had fallen to the ceiling, which was now the floor, Jack and Mark brought tables and chairs, and made a sort of stepladder. On this Professor Roumann mounted, and at once began the readjusting of the centre of gravity. It was hard work, for he had to labor with his arms stretched up in the air, and any one who has even put up pictures knows what that means. The muscles are unaccustomed to the strain. The German scientist, though a strong man, had to rest at frequent intervals. "We're falling rapidly," announced Jack, in a low voice, as he looked at the height gauge. "I am doing all I can," answered Mr. Roumann. "I think I will soon be able to right the craft." He labored desperately, but he was at a disadvantage, for the _Annihilator_ was not now moving smoothly through space. With the stopping of the motor she was falling like some wobbly balloon, swaying hither and thither in the ether currents. But Professor Roumann was not one to give up easily. He kept at his task, aided occasionally by Professor Henderson and by the boys whenever they could do anything. Finally the German cried out: "Ah, I have discovered the trouble. It is that scoundrel Axtell! See!" And reaching into the interior of the machine he pulled out a small magnet. To it was attached a card, on which was written: "I told you I would have my revenge!" It was signed with Axtell's name.