"It's hollow," Atel said succinctly. "The metal, of course, is useless, but the vacuum inside is steel-hard to them. Space crushing into space, and gouts of hard radiation bursting like blood from the contact. That's all we have now, that and a feeble energising process which sometimes seals off the foundations of the city. Walls, and clubs! Our last miserable recourses--and then-- "Then the space-beasts will own the Earth again." II By the time John Kimball had finished disconnecting the leads to the multiple screen and rewiring the master converter he was nearly blind with fatigue and his fingertips jerked and danced uncontrollably on the verniers. The sleepless nights of the previous week, and the emotional strain under which he had been working throughout was taking its toll now. After the wave-splitting effect had first suggested it to him, he had spent most of the week erecting the demonstration, and quite probably the triumphant letter he had mailed to Andreson afterwards had been a little crazy. As soon as he had posted the letter he had managed to get in about twenty hours of deathlike slumber. It was hardly enough, but there was no help for that now. Except for the first, sickening shock--for the discarded, empty envelope on the floor, the splintered fountain pen, and the one screen featureless and flickeringly gray, had told him what had happened in instant detail--he had wasted no time cursing himself for his grandiose "gallery" stunt. The Colossus in the cellar would need many hours of weary, desperate work before the cauterized scars of Andreson's cannoning fall through the tissues of Time would open enough to permit Kimball to follow. A tumbler clicked in the pre-dawn silence, and a flood of magnetons sped through the primary coils. The ensuing process was quiet and invisible, but Kimball could feel it--the familiar, nauseating strain which had first led him to the basic principle. It meant that tiny lacunae were being born in the fabric of Time, spreading and merging as the spinning magnetic field tore at them. He slumped on his stool and waited. He was not sure that the last hour's work had been even approximately right, but his gibbering nerves would no longer permit calculation or delicate mechanical correction. The die was cast, and wherever the nascent achronic gateway led, he would have to follow. After a moment he discovered that the climbing dial needles were hypnotizing him. Getting up from the stool, he proceeded to collect his equipment, moving like a zombie. It was futile to wish he had studied the period more closely, but at least it was clear that the age of the winged colonists had been warfare; best to be armed, though there was a good chance that his pistol would be far outclassed. A flashlight clipped to his belt, and an alcohol compass tuned to the machine's field rather than the Earth's, and he was ready.