"Observers," said Burke grimly. "That's right. We can't observe anything because the information would come back at the speed of light. But if we lose, the Enemy will arrive before we can know we've lost." Keller shook his head reproachfully. "Oh, no! Oh, no! I just understood. There are transposers of electric energy, too. Very tiny. In the observers." Burke stared. But it was only logical. If matter could be transposed instead of transmitted between distant places, assuredly miniature energy-transposers were not impossible. The energy would no more travel than transposed matter would move. It would be transposed. The fortress would see what the observer-globes saw, at the instant they saw it, no matter what the distance! Keller glanced at the ten-foot disk with its many small lights and the writhing bright-red sparks which were the Enemy gravity-ships. There was something like a scale of distances understood, now. The red sparks had been not far from the disk's edge when the first space call went out to Earth. They were nearer the center when the spaceship arrived here. They were very, very near the center now. "Five days," said Burke in a hard voice. "Where will the globes meet them?" "They're using full acceleration," Keller reminded him gently. "One hundred sixty gravities." "A mile a second acceleration," said Burke. Somehow he was not astonished. "In an hour, thirty-six hundred miles per second. In ten hours, thirty-six thousand miles per second. If they hit at that speed, they'd smash a moon! They'll cover half a billion miles in ten hours--but that's not enough! It's only a fifth of the way to Pluto! They won't be halfway to Uranus!" "They'll have fifty-six hours," said Keller. The need to communicate clearly made him almost articulate. "Not on the plane of the ecliptic. Their course is along the line of the sun's axis. Meeting, seven times Pluto's distance. Twenty billion miles. Two days and a half. If they miss we'll know." Holmes growled, "If they miss, what then?" "I stay here," said Keller, mildly. "I won't outlive everybody. I'd be lonely." Then he gave a quick, embarrassed smile. "Breakfast must be ready. We can do nothing but wait." But waiting was not easy. On the first day there came a flood of messages from Earth. Why had they cut off communication? Answer! Answer! Answer! What could be done about the Enemy ships? What could be done to save lives? If a few spaceships could be completed and take off before the solar system shattered, would the asteroid be shattered too? Could a few dozen survivors of Earth hope to make their way to the asteroid and survive there? Should the coming doom be revealed to the world?