It was then that I saw the astounding purpose of those projectors of violet force that were set in the walls around the soil-containers. For it was evident that they shot forth upon the containers a force or vibration which held in it the ultra-violet and other radiations which, in sunlight, stimulate the growth of plant-life. These vibrations were projected artificially through the containers of soil with immeasurably greater intensity than in sunlight, and so stimulated the growth of plant-life in those containers immeasurably more. Also I could see that tubes ran from the framework through the soil of the containers, flooding that soil with moisture, and as that water used thus came through special cubical tanks and mixers, it was apparent that it was impregnated with the chemical elements needed by the plant-life in its swift, astounding growth. Thus, stimulated to an intense degree by those influences, the plant-life in those containers could germinate and shoot up and ripen with unbelievable speed. When it was removed, the containers were ready at once for another crop. The whole operation was swift and almost automatic, and as we saw great masses of the white fruits or vegetables being wheeled away from the plant-compartments, we realized at last how the Neptunians, in their great compartment-cities, obtained a ceaseless and inexhaustible food and water supply. As we passed on, marveling, we saw other great mechanisms at work. Some were huge and cogged, operated by seated Neptunians before them, turning out ceaseless great blocks of smooth, black stone-like material that composed the intersecting compartment-walls, which poured out as a thick liquid and hardened in molds into that diamond-hard substance. Others were strange-appearing machines like none we had seen on Neptune, whose purpose we could not guess. Here and there there glowed in its square compartment one of the great heat-radiating globes, sending currents of intensely warm air rushing out from about it, all the mechanisms of those globes seeming to be cased inside themselves. Yet even these things were no more wonderful to us than the throngs of Neptunians that swirled and pressed in their millions in the great compartment-city about us.