Marlin pondered, then nodded. "Hunt's right," he said. "If we explore this deserted compartment-city beneath we may find some suggestion that will lead us to the great ray's source. And we _must_ find out soon, for only eighty-five days are left before the sun divides into a double star and dooms Earth!" "But we shouldn't risk all of us on this venture," I said. "The safest way would be to keep the space-flier, with two of us inside, hovering here above the city while the other two go down to it and explore it in their space-walkers." This we finally agreed to do, and Marlin and I insisted upon being the two to make the venture, Whitely and Randall reluctantly agreeing at last to remain within the space-flier, watching and waiting for us. So, bringing the space-flier down to a height of a thousand feet above the compartmented city, I set the force-ray to hold it motionless there, Randall taking my place at its controls. Then Marlin and I were quickly getting into our two cylindrical space-walkers. Once inside them, we each gripped in a great pincer-hand the pointed bars of steel that we were to take with us, and then unscrewed the inner door and passed into the vestibule-chamber. Another moment and with the inner door closed, the outer one was swinging open, and the denser and colder air from without was rushing into the vestibule-chamber. We did not feel its cold, however, snug in the insulated and heated cylinders of the space-walkers, but drew ourselves to the outer door, turning on the force-rays from the bottoms of our cylinders. Then as we drew ourselves out through the door and into empty air, we were both sinking gently downward, our fall slowed to a mere floating drop by the down-pressing power of our force-rays. * * * * * Down through the dim pale light of Neptune's day we sank, down until just beneath us lay one of the intersecting black walls. As I saw this I shot my supporting force-ray outward at a slant, and as this sent me down obliquely, I floated down past that wall, Marlin doing the same beside me, and in another moment we had come gently to rest just above the black smooth floor of one of the great compartments, the force-rays from the bottoms of our space-walkers holding us a foot or so above the floor. Resting there, Marlin and I looked up first. Beside us towered the black two-hundred foot wall of the compartment, and far above we could make out the hovering space-flier, its great gleaming polyhedron hanging motionless and watchful above. We waved the great metal arms of our space-walkers toward it, toward Whitely and Randall inside it, and then turned to examine the place in which we stood.