By the time Kom had disappeared behind us, the fleet was flying almost two miles high, in wedge-shaped formation, with our time-car and the air-boat of Kethra at the wedge's apex. It was late morning when we flashed high over the colossal metal wall that held back the ice-flood. It soon vanished behind us, and we were again flashing north across the ice-fields. The sun's rays slanting down almost vertically on the ice far below set up a dazzling glare that was almost blinding. Looking back, I saw an air-boat behind and below us crash into the one ahead of it, and both plunged down to destruction on the ice. Some half-dozen cars spiraled down toward the wreckage, but the main body of the fleet swept on, unheeding of such accidents. * * * * * All of that day the fleet raced on, while, in the time-car, Lantin slowed our pace to keep beside them. Sunset came, an arctic sunset, with a crimson globe of fire falling down behind the boundless steppes of ice, suffusing the sky with a glare like blood. Abruptly Lantin uttered a low exclamation, seized binoculars and gazed north through the window beside him. I sprang to his side, and when he handed me the glasses I saw, far ahead, a little cluster of black dots that stood out jet-black against the crimson sunset. But already Kethra too had seen them, and a score of cars leaped forward from the main body of the fleet, in pursuit, our own time-car among them. We flashed up toward them, and they grew in size, resolved themselves into air-boats much like those around us. As we neared them, they turned and fled north. Two of them, much swifter than the others, were out of sight almost in a second, safely beyond our pursuit, but the others, seven in number, saw that escape was impossible, so they turned to fight. For a moment, the fight was on their side, for they turned quite unexpectedly and raced straight toward us, in a solid mass. Lantin's hands flashed over the controls and our car slanted up above the onrushing seven with the speed of lightning, but as it did so a blue flash leapt from the foremost of them and barely missed us. The air-boats behind us were not so fortunate, for as the streaks of blue light from the enemy touched them, four plunged down to the ice, in flames. The seven attackers, unscathed thus far, passed under them in a swooping dip, turned, and came racing back for another blow. But now the surprize of our forces was gone, and they struck back. A sudden sound smote our ears, even in the time-car, a low thrumming sound that rose in pitch higher and higher. I could see the men on our air-boats pointing blunt-nosed metal objects toward the oncoming cars of the enemy, and abruptly the significance of it struck me, and I understood that they were using the sound-ray Kethra had mentioned.