There is an hour in every rotating habitat at which the nitrogen speaks. Kira had learned to hear it. It was not an audible thing — it was a felt thing, the pressure-weight of the atmosphere settling into its lowest nocturnal configuration just before the emitter-cycle began to lift, and for any person raised on the chemistry of these places, the hour carried a meaning no cityside commuter could ever quite understand: this air was brought here. Every molecule of nitrogen around her had been taken from Earth and lifted to orbit at cost. The mist of the Scimitar was, in the final accounting, Earth’s mist, displaced.

She stood at the west overlook as the first emitter-light came. The falls were beginning to show their arc. Deflected water, she thought — and she thought also of the Pteroclidae coriopolitana, the ring-doves adapted over three decades to the habitat’s Coriolis regime, which even now were lifting off the west ridge in their dawn pattern and riding the deflected updraft in long sweeping traverses, their flight paths curving as predictably as the falls. A bird and a river obeying the same law. A people, she thought, also obey it: one way or another, everyone in the cylinder rode the deflection they had been born into.

The light strengthened. Across the gap-sky, eighty kilometers of engineered atmosphere began to turn blue; and Kira, who had been assigned to the preserve precisely because her superiors considered her politically unreliable, stood very still and let the air into her lungs, and did not decide, not today, what she would do with the information she had been given two nights before.

— from the private observations of K.D., ranger-hydrologist, Scimitar overlook, ca. 0500 local