The Fourier analyzer, which was called by Rudolph Koenig an “Analyzer of the timbre of sounds”, is a large device (about 36 inches tall) for simultaneously observing several components of a sound. Each of fourteen adjustable Helmholtz resonators of varying sizes can be connected via rubber tubing to one of eight manometric flames, the light from which is viewed through a hand-driven rotating mirror. The resonators can be individually adjusted to select desired frequencies.
The device was used mainly for demonstration purposes. It could be considered a primitive form of a “multi-channel analyzer”.
Here are two video recordings of a manometric flame as seen in the rotating mirror. In the third clip, a tone of a specific syllable and octave is played, and three flames are used to determine the note. The middle flame is connected to a Fa-3 resonator, while the upper and lower flames are connected to higher and lower frequency resonators. The intense modulation of the middle flame, nearly to the point of extinguishment, indicates that the note is Fa in the 3rd octave (Fa-3).