Fourier Analysis
   In March 1984 we paid a visit to the physics department of the University of Toronto to photograph the collection of Koenig apparatus. Prof. Malcolm Graham, our host, told me that this "Manometric Flame Analyser for the timbre of sounds, with 14 universal resonators ... 650 francs" ($130) had recently been put into operation and worked properly. 

   Today we would call this a Fourier analyzer. The adjustable Helmholtz resonators (see the detail at the right, below) are tuned to the fundamental frequency of the sound to be analyzed, plus its harmonics. The holes on the other side of the resonators are connected by the rubber tubes to manometric flame capsules, and the variation in the height of the flames observed in the rotating mirror. The variation is proportional to the strength of the Fourier component of the sound. 

   The picture at the left, below, shows the manometric capsules and the jets where the flames are produced. Note the black background to made the flames more visible.
   The Fourier analyzer at the right in the Garland Collection of Classic Physics Apparatus at Vanderbilt University in Nashville, Tennessee. It arrived from France in time for the opening of Vanderbilt in the fall of 1875.

   This is item number 242 in the 1889 Koenig catalogue.
 

   Koenig also made a smaller version with eight resonators that was fixed to a fundamental of 128 Hz. This was catalogue number 242a and sold for 325 francs. The example at the left, below, is in the lecture demonstration room at Duke University.

   Max Kohl of Chemnitz in Germany made a similar piece of apparatus, which is listed in the ca. 1900 catalogue as "Manometric flame analyzer for the timbre of sounds, with eight spherical resonators .. 285 Marks" (about $65). This apparatus, at the right below, is at the College of Wooster in Ohio, and was bought ca. 1900 to replace apparatus lost in a fire.
 

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