fundamental note c. In order to know if the sound of the voice contains
harmonics and what they are, it is necessary to sing the fundamental note c
on some particular vowel sound; the resonators corresponding to the
particular harmonics of the vowel sound are thus set in action, and a
glance at the revolving mirror shows which particular gas jets vibrate.
Experiments conducted with this instrument show that the vowel _U=oo_ is
composed of the fundamental note very strong and the third harmonic (viz.
g) is fairly pronounced.

_O_ (_on_) contains the fundamental note, the second harmonic (the octave
c') very strong, and the third and fourth harmonics but weak.

The vowel _A_ (_ah_) contains besides the fundamental note, the second
harmonic, weak; the third, strong; and the fourth, weak.

The vowel _E_ (_a_) has relatively a feeble fundamental note, the octave
above, the second harmonic, is weak, and the third weak; whereas the fourth
is very strong, and the fifth weak.

The vowel _I_ (_ee_) has very high harmonics, especially the fifth, which
is strongly marked.

We see from these facts that there is a correspondence between the
existence of the higher harmonics and the diminished length of the
resonator. They are not the same in all individuals; for they depend also
upon the _timbre_ of the voice of the person pronouncing them, or the
special character of the language used, as well as upon the pitch of the
fundamental notes employed.

Helmholtz inferred that if the particular quality of the vowel sounds is