Prof. Helmholtz on Vowel Sounds. 87 
higher pitch there were slight deviations. It was found that 
for the incidental notes of several vowels, certain parts of the 
musical scale are peculiarly favourable, so that these notes, fall- 
ing in this part of the scale, become stronger than when they 
fall in other parts. Thus, for O, the upper half of the octave above 
the lines constitutes such a favourable part of the scale. The third 
and fourth higher notes, which are heard distinctly at a low pitch 
of the vowel, lie in this part, and are not so prominent when O 
is sung on a higher key. For A, the upper half of the second 
octave above the lines is favourable. The second, third, and fourth 
notes, which are weak at the low pitch of the vowel, are very pro- 
minent when A is sung between 4 and 4,. Moreover, I found 
by means of the above-described resonant globes that, especially 
for A, there are feeble but audible notes higher than any to 
which my tuning-forks reach. When the vowel A was sung on 
F, another globe, which was tuned to es, corresponding to four- 
teen times as many oscillations as F, resounded considerably. 
With respect to differences of phase, no effect of the kind 
manifested itself in my experiments. I was able to control the 
phases of oscillation according to the optical method of Lissajou. 
In the first place, by reversing the electrical currents in the 
electro-magnet of every single tuning-fork, the oscillation of 
the latter can be changed by half an undulation, so that the 
maximum and minimum deflections change places with each 
other. Further, by fixing a little wax to them, the tuning-forks 
can be slightly untuned ; their oscillations then become weaker, 
and thus, up to a quarter of an undulation, the phases can be the 
more displaced the greater the discordance of the tuning-forks. 
The change of phase in the weaker notes may be still more 
easily effected. To do so, they may either be weakened by 
removing the forks further from the resonant tubes, whereby 
the phases of the oscillations of the air are not changed, or the 
resonant tubes may be only partially opened; in the latter case 
a change of phase takes place, as I have shown in a theoretical 
memoir on Acoustic Oscillations, which is now being printed in 
Crelle’s Journal (vol. lvii.). The changes of phase produced in 
any one of these ways, however, cause no change in the tone, 
provided the intensities of the notes remain the same; so that the 
former question may in general be answered thus: The musical 
tone depends only upon the presence and intensity of the incidental 
notes in the sound, and not upon their differences of phase. 
I must, however, remark that there are apparent exceptions to 
this rule. When the notes are sufficiently strong, resultant 
notes may become intermixed, which, according to the differences 
of phase, may partly weaken and partly strengthen the primary 
notes, so as to give rise to differences of tone. Here, however, 
