"No, we can dispense with their services," agreed Mr. Roumann; and, accordingly, Ned and Sam were paid off, and left, promising to say nothing of the wonderful apparatus on which they had been working. The next week was a busy one. Mr. Roumann spent most of his time in the engine-room, assembling the machinery of the two motors, and arranging the connections between them and the pilot house in the "nose" of the projectile. The strange gas had been forced in between the two shells of the projectile, to absorb the heat that would be generated by friction, and nearly all the stores had been put aboard. The electric guns were installed, ready to be run out of the openings of the living-room to repel any attack of the Martians, and then the ports were closed tightly. Finishing touches were being put on the Annihilator, and Mr. Henderson and his German friend were kept very busy. As for the boys, they helped wherever they could, and did considerable work, for they had been well trained by their guardian. Andy remained on guard at the door with his gun. He said he was going to take no more chances with the crazy machinist. Nothing further had been seen or heard of the mysterious thief who had stolen the plates, and it was supposed that he was unable to make any use of them. One afternoon, about three days before the time set to start for Mars, Mr. Roumann was working alone in the machine shop. The boys and Professor Henderson had done all there was for them to do, and the Annihilator was practically finished. "Are you going to take along any extra-sized bullets, Andy?" asked Jack of the old hunter, who was on guard, as usual, at the door. "I don't see why I should. I guess the regular ones will do when I get to Mars." "I don't know about that," went on Jack. "We may find bigger game than elephants or sea lions there." "If we do, I'll use a new kind of explosive electric bullet Mr. Roumann told me about," declared Andy. "It has a charge of electricity in it, and he says it will kill the biggest animal that ever lived, with one shot." "Then you're all right," said Mark. "Well we'll soon be on our way now." "I suppose Washington will want to take some of his chickens along?" ventured Jack. "Well, I don't see why he can't," said Andy. "They take pigeons up in balloons, and I guess chickens would live in the Annihilator--at least, until we ate them." They stood about the entrance to the machine shop, talking of various topics, but they always came back to the subject of the wonderful journey before them. Suddenly Jack, who had strolled a little away from the door, looked toward the rear of the big shed that housed the projectile, and uttered a cry. Mark heard him, and ran to his chum's side. "Look!" exclaimed Jack, pointing to two men who were running away from the shop. "Who are those men?" "One is that crazy machinist!" cried Mark.