After a moment of thought, Bormon replied, "Cyclotronic action." There was a short silence, then Calbur resumed. "These Marts shoot the ore across space to the south magnetic pole of Mars. A ground crew gathers it up and transports it to their underground laboratories. As a prisoner explained it, it was simple; those old-time cyclotrons used to build up the velocity of particles, ions mostly, by whirling them in spiral orbits in a vacuum-enclosed magnetic field. Well, there's a vacuum all around Echo, and clear to Mars. By giving these lumps of ore a static charge, they act just like ions. When the stream of ore comes out of the machine, it passes through a magnetic lens which focuses it like a beam of light on Mars' south pole. And there you have it. Maybe you saw what looked like a streak of light shooting off through the chasm. That's the ore stream. It comes out on the day side of Echo, and so on to Mars. They aim it by turning the whole planetoid." "Hm-m-m, I understand, now, why it's always dark here--they keep this side of Echo facing away from Mars and the sun." "Right," said Calbur. "Now we'll have to move. These Marts are heartless. They'll let you die for lack of oxygen if you don't turn in baskets of ore regularly. But we'll meet here again." "Just give me time to size things up," Bormon agreed. The effects of the reverie-gas was wearing off and he was beginning to feel thoroughly alive again and aware of the serious situation which confronted them. "Don't let it get you down, Keith," he added. "We'll find a way out." But his words expressed a confidence that the passing of time did not justify. Again and again he filled his ore-basket, dragged it to the hungry mouth of that prodigious mechanism in the abyss, and in return he received the essentials for continued life. During this time he formed a better idea of conditions around him. Once he wandered far from the Martian's headquarters, so far that he nearly blinded himself in the raw sunlight that bombarded the day side of the tiny planetoid. Again, he was strangely comforted with the discovery of a small space ship anchored deep in the abyss although he was not permitted to go near it. * * * * * He soon found that nothing was to be expected of the horde of Earthmen who slaved like automatons over the few miles of Echo immediately adjacent to the chasm's rim. The accumulative effect of the drug seemed to render them almost insensible of existence. But with Calbur, who had served for a shorter time, it was different. "Keith, we've got to tackle one of the Mart guards," Bormon told him, during one of their conferences in the cave. "We'll take its ray-tubes, fight our way to that ship they've cached in the chasm below the cyclotron power plant, and blast away from here." "How?" asked Calbur. "If you make a move toward one, it'll burn you down--I've seen it happen!"