"I can," spoke the professor quickly. "The Martians are a very learned people. That's why their heads are so large and their bodies so small. They make a special study of the sciences, and geometry and mathematics probably are their favorites. That is why they understand Jack's problem. Science is the same throughout the universe, though conditions may differ on different planets. I think we have arrived at a means of communicating with the Martians, at least until we have learned their language." The Martian with the triangle and squares on his circlet of gold appeared to be a grade higher in authority than the one with the simple triangle. He now addressed the travelers, but they could not understand him. Seeing this, he stooped and drew in the sand another geometrical problem, leaving it half completed. "You finish it, Mark," said Jack, and the boy did so, much to the delight of the crowd. "They all are well up in geometry," declared Mr. Roumann. "But I'd like to understand what force it was that made us move?" spoke Jack. "I'll see if I can find out," said Mr. Henderson, and he made motions to indicate that they would like to know what power it was that moved them away from the projectile. A smile came to the face of the leading Martian. He pointed to his big head, and then to the travelers. Then he fixed his great eyes on them. Instantly they felt themselves being moved backward to the projectile. They went a few feet, then were moved forward toward the crowd again. Then they found themselves stationary. "It's thought force!" cried Jack. "That's what it is. They simply will for a thing to be done, and it is done--at least with persons from another planet. They have the power to make us move by merely wishing it." "Then they ought to be able to read our thoughts," spoke Mark. "Maybe their power extends only to motion," suggested Mr. Henderson. The chief leader spoke again, and it was evident that he was asking if the explanation and demonstration he had given was satisfactory. The professor nodded his head to indicate that it was. The leader addressed the throng of people, and they turned and started away. The leader remained, and turning to the adventurers he pointed off toward a distant city, and indicated that they were to go there. "And leave our projectile behind!" exclaimed Jack. "We don't want to do that." This did not meet with the approval of the others. They were in a strange land, and the Annihilator might be the means of saving their lives. If they left it there was no telling whether or not they would ever see it again. As well as he could Mr. Henderson made motions that they did not like to leave their craft behind. But the Martian, with a frank smile, seemed to say that it would be safe. "Guess we can't help ourselves," remarked Mr. Roumann. "If we don't go they'll make us. Better go willingly. Besides, I want to see their city."