Astounding Stories of Super-Science, August 1930

"Through the centuries, while on the land our races of green men have been struggling upward, the Ralas have oppressed them. Long ago the Ralas left all their other cities to build this one great amphibian city at the sea's center. Entrance to it is only by the water-tunnel from without, and being frog-people entrance thus is easy for them since they can move for many minutes under water, though they drown like any other breathing animal if kept under too long. Humans dare not try to enter it thus by the water-tunnel, since, before they could find it and make their way up through it, they would have drowned. "So the Ralas have ruled from this impregnable amphibian city. Its colossal metal dome is invulnerable to ordinary attack, and though solid and without openings it is always as light beneath the dome here as outside, since the Ralas' scientists contrived light-condensers and conductors that catch light outside and bring it in to release inside. So when it is day outside the sunlight is as bright here, and when night comes the Earth-light shines here the same as without. "From this city their raiding parties have gone out endlessly to swoop down on the cities of us green men. Since we learned to make flying-boats like theirs, with molecular-motors, and to make the guns like theirs that fire shells filled with annihilating force, we have resisted them stoutly but their raids have not ceased. And always they have brought their prisoners back in to this, their city.