We had been puzzled, indeed, that they were able thus to move about unheedingly without protection of any sort in the zero-cold that reigned about us. But now as one or two of them passed close to the door by which we crouched, I gazed closely at the glowing little ball that each had attached to his metal armor, and guessed then what I was later to learn was the truth, that that ball was glowing with radiant heat and had the power of heating to comfortable temperature the atmosphere for a few feet directly around its wearer. Thus the wearer of it moved always in a little volume of warm air, though the air outside that area might be at zero temperature. And thus it was that the Neptunians were able to withstand the bitter cold about us, from which we were protected by our space-walkers. As we gazed toward the Neptunians, they were completing the process of dissembling and stowing away the great mechanisms, and now I moved closer to Marlin, my thoughts being on retreat from the dangerous position in which we were. Not only might we be discovered at any moment by the Neptunians before us, but somewhere in the compartment-city behind us were others, we knew, who had landed in their four cylinders at another point. Whatever had happened to Whitely and Randall in the space-flier, Marlin and myself were in the most perilous of positions. Even were we to escape the Neptunians we could not exist for long in our space-walkers in this dead and deserted city, in the cold of this strange and terrible world of death. Yet to escape from them was our first consideration, and I whispered as much to Marlin through our touching space-walkers. "We've got to get clear of these Neptunians," I whispered to him. "Back farther in the city we can hide until they go." He was gazing toward the strange creatures and their tools and mechanisms with intense scientific interest, but turned toward me at my whisper. "We'll get back, then," he whispered. "It may be that Whitely and Randall----" It was a sentence that he never finished. For we had hardly turned to cross the compartment in which we crouched than we had to stop short in our space-walkers. There behind us a dozen or more great disk-creatures had been standing--a dozen or more great Neptunians! Even as we faced them there in that stunned moment, their bulging glassy eyes upon us, I saw the tracks in the thick dust at our feet, realized that these creatures were of the others who had landed in the compartment-city, and that finding our space-walkers' tracks here and there in the thick dust, they had followed them, had trailed us and stolen behind us while we watched their fellows! Then in the next moment had come a staccato cry from the foremost of the Neptunians, and in the instant following they had flung themselves straight forward upon us! For in this atmosphere sound penetrated our cylinders. CHAPTER VII The Giant Ray