At the back of the room was a bar, which appeared to be floating in the air, for serving ether. Small steel balls covering the floor prevented people for getting close to the bar. The balls circulated around magnetic devices mounted in the openings of the electricity ducts under the floor. The sound of the moving balls clicking against each other was recorded and played back in real time through a concealed sound system. This mingled with the 50-herz hum coming from the electric cables under the floor, which was recorded with a contact microphone and played back in real time through a concealed sound-reproduction system, and also displayed on the screen of an oscilloscope in the corner of the exhibition space.