Koenig’s flame analyser was, next to the sound synthesizer, one of the clearest expressions of Hermann von Helmholtz’s theory that complex sounds were made up of a spectrum of elemental or pure tones. The adjustable resonators covering a range of 65 notes from sol1 to mi5 (96–1,280 Hz), could each be rendered visible with a connection to a manometric flame capsule. The resonators were connected to a gas-filled capsule with a rubber tube. If activated, the distinctive pattern would appear in the rotating mirror.
Barlow, W. H. (1873) 1873. “On The Pneumatic Action Which Accompanies The Articulation Of Sounds By The Human Voice, As Exhibited By A Recording Instrument”. Proceedings Of The Royal Society Of London 22: 277-286.