"And that great band of light that traveled around Triton was their signal, then!" I added.
It was plain now that that was the astounding truth. These countless millions of Neptunians, coming here to Triton for some reason, had been accustomed upon their own great turning planet to a day and night of ten hours each, much like those of Earth. Triton, though, as we had already guessed, kept the same face always toward the sun, it was evident, turning at just such a rate of rotation as compensated for its revolutions around Neptune and its slower movements with Neptune around the sun. Thus, with one face always toward the sun and the other always in darkness, the Neptunians had been forced to establish arbitrary day and night periods, dividing their millions into two great bodies, apparently. While half of them worked on the sunlit side for ten hours, in their day, the other half were sleeping upon the dark side. Then, when the ten hours ended, the great band of light went around Triton as a signal, and the two bodies of them changed places, the millions who had worked upon the sunward side taking their places for an equal period of sleep on the dark side, while those who had slept on the dark side streamed to the sunlit side for ten hours!
Even as we watched from our speeding cylinder we saw that great change taking place, millions upon millions of the Neptunians streaming from one side to the other in great throngs through the compartment-city, while, from farther around Triton's two sides, rushed countless cylinders, in which hosts of others were changing sides. Within a few minutes, it seemed, that change had taken place, and beneath us on Triton's sunward side there thronged in the pale light of its day the vast hordes that so lately had been sleeping, while on the dark side the other masses of the Neptunians had disappeared into the countless shelf-like openings of the sleep-compartments, to lie in sleep for another ten hours. In marveling wonder Marlin and I stared, and then woke suddenly to a realization of our own position.
Beneath us there lay the very edge or dividing line between the dark and sunlit sides, a belt of twilight dusk that was very narrow. Squarely across that belt, we saw, there lay beneath us a great compartment that was largest by far of all that we had yet seen, and that was unique among them in that, instead of being rectangular, it was circular in shape. Down, over and past this mighty circular compartment our cylinders were speeding, and we could but vaguely note some circular object inside it, when we were past it, were speeding low over the thronged and busy compartments of the sunward side. Rapidly the speed of the cylinders decreased, and then they had paused in mid-air, were beginning to descend. And in a moment more they had come smoothly to rest in a great rectangular compartment which seemed reserved as a landing-place, since on it there rested scores of other cylinders, others constantly arriving or departing. Later we were to learn that these landing-compartments were scattered in large number over Triton's surface, on the sunlit and dark sides both.
For the present moment, though, Marlin and I were gazing only at our immediate surroundings. As we landed the guards on either side of us gripped us tightly, the others keeping their tubes pointed toward us, and then, as the throbbing of the cylinder's generators ceased, the Neptunian leader of the crimson-circle insignia uttered a staccato order. At once our guards were thrusting us toward the ladder that led downward, and, holding us above and beneath, were descending that ladder with us into the cylinder's lowest compartment. There the Neptunian leader followed us in a moment, and as the cylinder's door was slid open a flood of warm, heavy air and a babel of sound from about us rolled inside. Before emerging, though, the Neptunians performed an action that for the moment puzzled me completely.
This was to take from the cabinets in the cylinder's side a number of small metal objects that seemed to be disks of gray metal a few inches across with flexible metal straps attached to them. These the Neptunians attached to the bottom or ends of their round, short limbs, as though little round sandals of metal. Then at the order of their leader they took other disks and attached them to the feet of Marlin and myself, one to each foot, binding them to our soles by passing the flexible straps up around our ankles. The thing was as puzzling to Marlin as to myself, for the moment, nor could we understand its object until, a moment later, the Neptunians began to pass out of the cylinder to the paving of the compartment outside. For as they did so I had reached toward one of the unused disks to examine it and had uttered an exclamation to find that, though so small in size and thickness, it was of many pounds weight! Yet as Marlin and I, in answer to the leader's order and gesture, passed out of the cylinder to the landing-compartment's floor, we could not feel at all that weight of dozens of pounds which had been fastened to our feet!
Abruptly, though, light came to my perplexed mind. "Triton!" I exclaimed. "It's of about the same size as Earth's moon and hasn't much more gravitational power. And these Neptunians, used to the far greater gravitational power of Neptune, have to use these weights to add to their weight here on Triton to make it possible for them to move as always!"
Marlin's eyes widened, and then he nodded. "It must be so," he said. "I wondered when I saw them from above how these creatures of Neptune could move so freely on its smaller moon."
It was, indeed, a simple, yet ingenious device which the Neptunians had adopted. Accustomed as they had been to the great gravitational power of Neptune, seventeen times that of Earth, their squat, strange bodies owing their form to that great gravitational power, their muscles would have sent them through the air of Triton in immense and uncontrollable leaps at each step, so much smaller was the moon-world's gravitational power. So they had devised these small disks which fitted to the end of their strange limbs, and which, though so small and thin, yet had great weight, no doubt because the atoms of their substance had been compressed closely together for the purpose. The Neptunians had used disks of some thickness for themselves, and had used thinner ones for Marlin and myself, their smaller weight just sufficing to counteract the difference in gravitational power between Earth and Triton. And now, as we stepped out into the landing-compartment with our guards, it seemed as though we were walking with lead-weighted shoes at the ocean's bottom.