84 Prof. Helmholtz on Vowel Sounds. 
which does not depend upon the above-named accidental cireum- 
stances, the musical tone or quality of the sound; the question 
then arises, Do musical tones differ only in consequence of the 
different intensities of the incidental notes contained therein? 
But in conceiving the form of a wave composed of several 
simple waves, it is of importance to consider not only the am- 
plitudes of oscillation of the latter, but also the differences of 
phase between them and the primary note. We obtain very 
different wave-forms when we combine the wave of a primary 
note and its first higher octave, according as we allow the maxi- 
mum condensation of the primary to coincide with that of the 
octave, or with the minimum condensation of the octave, or with 
any other intermediate phase. The former question, therefore, 
becomes included in the following more special form: Does the 
distinction of musical tones depend only upon the perception of 
higher notes of different intensities, or does the ear also distinguish 
differences of phase? 
This question would be most directly answered by endeavour- 
ing at once to produce sounds of different qualities by direct 
combinations of simple notes, such as can be obtained with 
tuning-forks. The several vowels of the German language ap- 
peared most appropriate as objects for imitation, for they ma 
be produced as uniformly continuous musical sounds, and at the 
same time be kept nearly, though not quite, free from unmusical 
noises. 
My apparatus consists of a series of eight tuning-forks, which 
correspond to B (in the deepest octave of a bass voice), and to 
its harmonic higher notes as far as b, (in the highest octave of a 
soprano), namely to the notes B, b, f,, 5), da, fo, ao, and by. Each 
tuning-fork is fastened between the ends of a horseshoe electro- 
magnet and joined to a properly tuned resonant tube. The mouths 
of the resonant tubes are provided with moveable covers, which 
may be removed by means of threads whose ends are fastened to 
a set of pianoforte keys. The tuning-forks are set in motion by 
means of intermittent electric currents, which are produced ac- 
cording to the principle of Neef’s hammer, and whose number per 
second is equal to 112, the number of the oscillations per second 
of the deepest-toned fork. After overcoming several difficulties, 
I succeeded in so arranging the apparatus that, when put into 
action, the low humming of the forks could scarcely be heard so 
long as all the resonant tubes remained closed; but as soon as 
one or more of the resonant tubes were opened by means of the 
pianoforte keys, the respective notes became distinctly audible. 
he intensity of any note could be easily regulated by opening 
the corresponding tube more or less completely. 
- I combined in the first place the two deepest notes alone, to 
