Calbur had switched off his light, as a matter of precaution, and his voice came to Bormon from a seemingly far distant point—a voice from out of the darkness, fraught with fantastic suggestion.
"Ships? You say they're building ships? Where?" Bormon asked, his own voice reverberating harshly within the confines of his helmet.
"In a cavern they've blasted out near the south magnetic pole of Mars. You know that's an immense, barren region—lifeless, cold—bordered on the north by impenetrable reed thickets. They need rhodium in large quantities for hull alloys and firing chambers. That's why they're mining it, here on Echo."
"They'll never get it to Mars," Bormon declared quickly. "Every freighter is checked and licensed by the joint governments of Earth and Mars."
"They won't?" Calbur laughed, distantly. "Listen, Neal—every crateful of ore that's dumped into their machine, here on Echo, gets to Mars within a few hours. And it isn't carried by ships, either!"
"You mean—?"
"I didn't get the answer, myself, until I'd been here for some time. You see, Echo is just a gob of metal—mostly magnetite, except for these granules of rhodium—forty miles in diameter, but far from round. Then there's that chasm, a mammoth crack that's gaped open, cutting the planetoid almost in half. The whole thing is magnetic—like a terrestrial lodestone—and there's a mighty potent field of force across that gap in the chasm. The walls are really poles of a bigger magnet than was ever built by Martians or human being. And of what does a big magnet remind you?"
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."