"But at last, after further ages of such existence, the tentacle-races saw that again they were menaced with extinction, since in obedience to the inexorable laws of nature their dark star was cooling still further, the molten fires at its center which warmed its surface gradually dying down, while that surface became colder and colder. In a little while, they knew, the fires at its center would be completely dead, and their great world would be a bitter, frozen waste, unless they devised some plan by which to keep warm its surface. "At this moment their astronomers came forward with the announcement that their dark-star world, plunging on through empty space, would soon pass a great star-cluster or Galaxy of suns at a distance of some fifteen billion miles. They could not invade the worlds of this Galaxy, they knew, for they had discovered that upon those worlds lived countless trillions of intelligent inhabitants who would be able to repel their own invasion, if they attempted it. There was but one expedient left, therefore, and that was to attempt to jerk a sun out of this Galaxy as they passed by it, to steal a star from it to take out with them into space, which would revolve around their own mighty dark world and supply it with the heat they needed. "The sun which they fixed on to steal was one at the Galaxy's very edge, our own sun. If they passed this at fifteen billion miles, as their course then would cause them to do, they could do nothing. But if they could change their dark star's course, could curve inward to pass this sun at some three billion miles instead of fifteen, then the powerful gravitational grip of their own gigantic world would grasp this sun and carry it out with it into space. The sun's planets, too, would be carried out, but these they planned to crash into the fires of the sun itself, to increase its size and splendor. All that was needed, therefore, was some method of curving their world's course inward, and for this they had recourse to the great gravity-condensers which they had already used to shift their own planets. "You know that it is gravitational force alone which keeps the suns and planets to their courses, and you know that the gravitational force of any body, sun or planet, is radiated out from it in all directions, tending to pull all things toward that body. In the same way there is radiated outward perpetually from the Galaxy the combined attractive gravitational force of all its swarming suns, and a tiny fraction of this outward-radiating force, of course, struck the dark star, pulling it weakly toward the Galaxy. If more of that outward-radiating force could strike the dark star, it would be pulled toward the Galaxy with more power, would be pulled nearer toward the Galaxy's edge, as it passed.