Free Dark Lightning (Thunder and Lightning) by John Varley

very deep. From up here you could see they were almost as flat as scenery scrims on a stage.
    About halfway down, where the curve of the end cap had become less steep—around forty-five degrees—were the first human habitations, in the medium-grav region. It wasn’t a
lot
lower grav than on the flat inner surface, but it was definitely enough that you could feel the difference. A lot of the older residents lived there.
    It was also the location of Hilltown, home of the hated Hillbillies, the nastiest skypool team, boys and girls both, in the ship. Home of the Horrible Cheryl Chang, the girl who never passed up a chance for an illegal hit. I was pretty sure I could pick out the school from here, looking down on Hilltown. Too bad there was no way to open a hatch and drop something nasty on it.
    Finally, the slope of the North End flattened out to the main floor of the ship. I could see the rivers gleaming silver in the light: the Mississippi, the Amazon, and the Congo. None of them were anything like their namesakes, and they would have qualified as nothing more than quiet trout streams on Earth. But from up here they were lovely, the quietly flowing, life-giving arteries of my world. They fed into small ponds like the one at our house, and each one fed into a single larger lake at a different point in its course: Lake Baikal, the deepest and most placid, Lake Michigan, and Lake Titicaca, which had the best fishing.
    Looking south on the plains, you would immediately see the rings. The interior of
Rolling Thunder
is a series of terraces that run right around the circumference of the cylinder. This is necessary because of the spin gravity and the thrust gravity coming from different directions.
    The spin of the ship forces everything away from the center axis at about two-thirds of a gee.
    The thrust runs parallel to the axis and tends to pull everything to the south at one-twentieth of a gee.
    If the interior were perfectly flat, there would be two bad results. For one thing, all the water inside would flow too fast toward the south. The rivers would become more like cascading mountain streams than the placidly wandering great rivers of Earth they are named for.
    Also, we would all have to walk slightly canted toward the north to overcome the effects of the thrust gravity. Houses would have to be built with one end slightly higher than the other, or else anything you dropped on the floor would roll to the south.
    “I thought of just shortening everybody’s left leg a little,” Uncle Travis told us with a perfectly straight face one day when we were seven. “That would work fine as long as we only walked to the east. But if we walked north or south, we’d be lopsided, and if we walked west, we’d fall over.” We believed this fable for a little while, thinking with a certain horror about operations to shorten legs, until Papa told us his cousin loved to “bamboozle” people, as he put it. After that, we always took anything Uncle Travis said under advisement before we believed it.
    “Girls! What the heck are you doing? This isn’t a field trip.”
    That would be Mama. We raised ourselves from the ground and jetted over to them, stopping ourselves with our hands against the wall near a double door. I got a good look at Papa, and it was no surprise that he was looking green. Papa doesn’t like low-gee, no-gee, and especially variable-gee. The trip up here had been an ordeal for him.
    The elevator doors opened, and we moved in, Polly and I holding Papa’s hands so he wouldn’t smash into the opposite wall. We all grabbed a handrail. The doors closed, and we suddenly had about half a gee as the car accelerated upward. That went away quickly as the car reached its top speed. The shaft is about a mile and a half long.
    “The ceiling will become the floor in forty-five seconds.” It was an automated warning. “Please reverse your position, with your feet on the surface that is blinking green. Hold on to the