It now became obvious that pistons were concealed within those cylinders, and some of them were being pressed up by air from the wind-chest. As they moved they elevated the ends of the brass levers. Each lever pivoted around an oiled fulcrum that was far from the piston, and close to the central mechanism, giving it a large mechanical advantage at the latter end. The rapid upward thrust of each piston caused the opposite end of its lever to press downward slowly, but with great force; and each of those lever-ends bore down upon a slim vertical rod. The rods were thirty-two in number, arranged in a regular picket-line; each of them resisted movement for a few heart-beats and then gave way, as if some barrier had been breached. This sudden yielding enabled the piston at the opposite end to fly up until it tripped a lever affixed to a vertical pushrod on the outside of its pipe. The pushrod transmitted force down to some air-gate at the base of the pipe, which sprang open, allowing the piston to fall down to its starting-place. It was all over in a few moments. Miss Spates pulled the knob that caused all the keys to pop up to the zero position.