584 
Proceedings of the Royal Society 
The authors’ experiments do not prove that a given vowel always 
produces a definite wave form. 
2. A given person pronouncing or singing a vowel sound at a 
constant pitch produces a wave form of remarkable constancy. 
This proves that the relative phases of the simple tones, of which 
the compound tone is built up, do not alter, while a single vowel is 
being sung or intoned on one note. The same person or different 
persons pronouncing the same vowel on different occasions, will 
frequently reproduce wave forms closely similar, but the experiments 
are not yet sufficiently extended to determine whether a given voice 
speaking the same vowel at a given pitch will always produce the 
same wave form. 
3. A given person singing the same vowel throughout an octave, 
often produces wave forms of different appearance on different, notes, 
although he may be endeavouring to keep the quality of his vowel 
constant. It must on this be remarked that up to the present time 
there has been no standard or criterion as to constancy of quality at 
different pitches. This has been a mere matter of appreciation by 
different ears. A standard wave might, indeed, be taken and declared 
to be the form which gives a constant quality at all pitches. The 
phonograph is sufficiently distinct in its utterance to allow it to be 
said that such a standard a or o will be accepted within a consider- 
able range as the same vowel, but it cannot be affirmed that all 
hearers would say that the quality of the vowel was constant in 
their judgment at all pitches. It is, however, possible that hence- 
forth constancy of quality may be defined as that given by constancy 
of wave form. 
4. The vowels are heard equally well, or nearly so, whether the 
machine is run backwards or forwards. The authors put in the 
saving clause “nearly” everywhere, because the sounds obtained 
from the phonograph are not sufficiently clear to warrant more 
absolute conclusions. This reversibility is a necessary consequence 
of Helmholtz’s theory that the ear decomposes the compound tones 
into their harmonic constituents, and is indifferent to the phase 
relation of these. 
5. Hot only the vowels but the consonants are substantially the 
same when produced backwards. This result is novel to the authors, 
and is, they believe, quite unforeseen. There is little to wonder at 
