Majestically the Miran swung along beside the dead ship, a great magnetic tow-cable shot out toward it, to shy off at first, then slowly to be adjusted, and take hold in the magnetic shield of the T-208. The pilots of the watching scout-ships turned away. They knew what would happen. It did. Five--ten--twenty seconds passed. Then the "dead-man" took over the ship--and the stored power in the atostor tanks blasted in a terrible flame that shattered the metal hull to molecular fragments. The interstellar cruiser shuddered, and rolled half over at the blasting pressure. Leaking seams appeared in her plates. The scouts raced back to Luna as the Miran settled heavily, and a trifle clumsily to Phobos. Miran radio-beams were forcing their way out toward the Miran station on Europa, to be relayed to the headquarters on Jupiter, just as Solarian radio beams were thrusting through space toward Luna. Said the Miran messages: "Their ships no longer crumble." Said the Solarian messages: "The ships no longer crumble--but the men die." * * * * * His deep eyes burning tensely, Buck Kendall heard the messages coming in, and rose slowly from his seat to pace the floor. "I think I know why," he said at last. "I should have thought. For that too can be prevented." "Why--what in the name of the Planets?" asked McLaurin. "It didn't kill the men in the forts--why does it kill the men in the ships, when the ships are protected?" "The protection kills them." "But--but they had the protective oscillations on all the way out!" protested the Commander. "Think how it works though. Think, man. The enemy's field is an electric-field oscillation. We combat it by setting up a similar oscillating field in the metal of the hull ourselves. Because the metal conducts the strains, they meet, and oppose. It is not a shield--a shield is impossible, as I have said, because of energy concentration factors. If their beam carried a hundred thousand horsepower in a ten-foot square beam, in every ten square feet of our shield, we'd have to have one hundred thousand horsepower. In other words, hundreds of times as much energy would be needed in the shield, as they used in their beam. We can't afford that. We had to let the beams oppose our oscillations in the metal, where, because the metal conducts, they meet on an equal basis. But--when two oscillations of slightly different frequency meet, what is the result?" "In this case, a heterodyne frequency of a lower, and harmless frequency." "So I thought. I was partly right. It does _not_ harm the metal. But it kills the men. It is super-sonic. The terrible, shrill sounds destroy the cells of the men's bodies. Then, when their dead hands release the controls, the automatic switches blow up the ship." "God! We stop one menace--and it is like the Hydra. For every head we lop off, two spring up." "Ah--but they are lesser heads. Look, what is the fundamental difference between sound and light?"