Hydraulis

The pumpers push air into the bronze bowl (the pnigeus) standing upside down in the water. The air pushes the water down inside and up outside: the difference in height is the wind. When the water inside reaches the rim, air bubbles out under it, so the bowl holds the wind up to that and no more.

The last eight seconds. Each stroke lifts the wind, and the water under the rim bounces on the air after it; a chord draws it down; when the pumpers fall behind it sags until they catch up.

The four ranks, one behind another, longest pipes at the left, drawn to scale. A key pushes its slide in under all four; the ranks whose stopcocks are open sound.

Markers: the resonances of the last key’s pipe, every harmonic for an open pipe, only the odd ones for a stopped pipe.

The jets speak their upper modes first, then settle; the pump strokes swell every line a little, slowly.