"I tell you, Sine, this pull is no gravity effect. No body of such mass could be invisible, unless it were composed entirely of protons. And even then it would yank Jupiter out of shape, making it look like a pear, but there--" Jupiter presented its usual appearance. The solar system's largest planet seemed enormous at this distance of only a few million miles. It showed its usual marked depression at the poles, but no distortion such as might be caused by a nearby body of enormous mass. "What do you think, Lents?" Kass turned to the third occupant of the little space ship. Lents raised his broad placid face from the pad upon which he had been figuring a complicated equation. He was a large man, slow-moving, and fat. He was sensitive to that fact, so that, besides the usual trunks, he also wore a toga-like garment. His brown eyes blinked in folds of flesh. "No doubt you're right, Kass," Lents rumbled in a deep voice. "I can't see how such a body could exist without pulling all of Jupiter's moons to itself. No, we seem to be specially honored by its attention." They looked at one another soberly. "The question is, can it out-pull us?" Sine remarked. "You ought to know," Kass said. "You designed and built her." Sine made his way forward. It was no longer necessary to use the handholds, for the pull of the mysterious body was already so powerful that it entirely eliminated the free floating so familiar to space travelers. Sine looked through the grated outlook windows, past the gracefully curved bow of the ship. At the very tip was the ether screw of his invention, resembling the screws used for water propulsion in ancient times, except that the pitch was extremely sharp. The tachometer showed that the screw had slowed down to 50,000 revolutions a minute, although the thermometer indicated that the molecular bearings were still reasonably cool. But how long could she stand the strain? How long, indeed, could the sturdy little atomic motor keep those blades turning? It was designed to pull directly away at a distance of only a million miles from the sun, and yet it was being beaten far out here in space by an object as yet invisible. "What a crash that'll be!" Sine murmured, watching the agony of tortured metal. Amidship, Kass was again studying the eyepiece of the ampliscope. Suddenly he stiffened. "I see it! Why, it can't be over a couple of hundred feet in diameter. Cylindrical, I think. Head on to us now." They crowded around him. Lents, with hasty computations, determined that they were still about three thousand miles from the object. "No chance to pull away from it, if we pull straight," and his heavy voice was full of energy as his sleepiness vanished with the need for action. "Set her over, Sine, about 40 degrees. Try for a circular orbit around it--if we can get up enough speed centrifugal force will save us!"