The story was about a robot/android made of brass and powered by air. His entire world, all the people in it, was built the same way.
He was fascinated by their brain analog which, by self-examination and experimentation, he discovers is a complex set of tiny, thin brass wafers with patterns on them that constantly moved and intermeshed due to air pressure.
All of the beings in this world needed to recharge their air pressure or they would die. The space below their world is a large pressurized air bladder that is slowing equalizing with the upper world.