Zahm says: "It is manifest that when a tube yields one of its upper partials the air-column within undergoes spontaneous subdivision into [equal] parts, each of which vibrates independently, but in unison with each of the others. Let us, for instance, cause the long open pipe, called the flute of Bernoulli, to emit its fourth partial [i.e., its fourth harmonic]. The air-column within must now ... divide into four columns of equal length, each of which, vibrating separately, would give the fourth partial... The centers of the [antinodes] corresponding to the partials now sounding, are at [the junctions of the four segments of the flute]. If now the first, second and third upper sections of the pipe are detached in succession, you would remark no change in the pitch. The lower section of the pipe alone yields the same note as was emitted by the whole pipe, or by a pipe whose length is twice or thrice that of each section taken separately." From J. A. Zahm, Sound and Music, second edition (McClurg, Chicago, 1900) pp 228-229. Note that a long, thin pipe, blown with a fair amount of pressure, is necessary to cause the fourth harmonic to sound loudly.

  The 1889 Koenig catalogue lists this as catalogue number 108, "Flute in four parts" and prices it at 12 francs. The black pipe is from Yale University, and the tan one from Union College in Schenectady, New York.

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