If the lower levels had been straight twentieth-century tech with their spark plugs and pistons, Minus One was all modern robotics. Slightly below them was a massive construct that could only be the "mouth" of the "bottle"—the upside-down funnel that accepted and channeled the pulse of hydrogen gas being driven upward by the rising piston. A short distance above that were the bottoms of the six barrels, which were simply cut off at their bases, open to the room. In between those obvious and easy-to-understand elements was an elaborate, massive, rotating contraption that, if Saskia was any judge of these things, had consumed the lion’s share of the engineering resources. She couldn’t really puzzle it out until T.R. issued a command that caused a vertical conveyor system to go into motion. This thing—"Shell hoist" on the cross-sectional diagram—had run parallel to the elevator all the way down from ground level. It served a similar purpose to the lift, but it was smaller and it ran much faster. After it had been whirring along for a minute or so, it slowed.