We turned away into the night that had fallen on the red jungle while we watched. I was sick with horror. Austen's face was white and his hands were trembling. There was a stern, fierce light in his eye. Now I knew, in spite of what he had said, that were the opportunity given him, he would not hesitate to wipe out the masters of the purple slaves. He said nothing, but his hands worked spasmodically, he muttered under his breath, and his dark eyes snapped with angry determination. In a few minutes we set about preparing the apparatus for the work of the night. The spectroscope was set up, with telescopic condensers, to collect and analyze the radiation of the arch of crackling milky flame. We took care to screen ourselves in the jungle fringe, and to expose no more of the equipment to the sight of the beings below than was necessary. Austen had his drawing board set up in a convenient place behind our shelter, and he alternately peered through the telescope at the spectrum, and turned to make intricate calculation in the light of a shaded flashlight. We sat up all night at the work. All night long the white flame played between the spinning blue crystal spheres above the vast green cylinder, filling the air with its ghostly crackle and whisper. All night long the tireless purple human machines toiled in the pit, carrying the great green blocks, and evidently stacking them in the vast cannon-like tube at the side. Whenever Austen did not need me with the analysis, I spent the time searching that amazing scene, but not once did I catch a glimpse of anything that might have been the directing intelligence of all that marvelous activity. Melvar had been very tired, and I had contrived a hammock for her from a great sheet of fibrous bark torn from the trunk of one of the red trees. She spent the night asleep in that, while Austen and I carried on the work, and Naro, not having scientific inclinations, contented himself with a couch composed of a few feathery branches torn from the undergrowth. CHAPTER XI What the Analysis Showed Just before daylight Austen completed his calculations, and stated the result. He was very tired, and his eyes were red. He had worked for a day and two nights since we had found him. He gave his conclusion in a colorless monotone. "You know," he said, "that there are several rare gases in the air, in addition to oxygen and nitrogen. The inert gas argon comprises nearly one per cent of the atmosphere, and there are, in addition, smaller quantities of helium, neon, xenon, and krypton, not to mention the carbon dioxide and water vapor. Those gases are monatomic and do not ordinarily enter into any compounds at all.