86 Prof. Helmholtz on Vowel Sounds. 
made as prominent as possible, for by the method here em- 
ployed the intensity of the highest is but small. For Ae, the 
fourth and fifth notes are specially important ; for A, the notes 
from the fifth to the seventh. When the third note is com- 
pletely omitted, A has a nasal sound. 
I must, however, remark that the above-mentioned relations 
between the primary and the higher notes refer only to the pitch 
of my tuning-forks. The primary note B corresponds nearly to the 
pitch of moderately deep male voices when speaking. I have not 
yet had time to conclude my researches on vowels at a higher 
pitch, for I was not able to pursue the investigation much 
further with my incomplete set of tuning-forks. When I made 
the former second note 6 my primary, | had only three appro- 
priate higher notes. With these I was able to imitate U, O, Oe, 
E, Ue, and I according to the given rule; but the absence of the 
higher notes rendered my imitation of A and Ae imperfect; so 
that here, as at a lower pitch, the same relation of upper notes 
to the primary one appeared to be essential in the imitation of 
the vowel. This higher pitch corresponds nearly to that in 
which high voices generally speak. 
On the other hand, I carried the investigation further by 
direct observations on the human voice by means of a special 
contrivance, which renders the most inexperienced capable of 
distinguishing the incidental notes of every musical sound,—a 
problem which formerly could be solved only by long practice 
and great attention. I made use of peculiar resonant vessels, 
which were applied to the ear itself. The best vessels of this 
kind are glass globes with two openings, one of which termi- 
nates in a funnel-shaped neck whose end fits into the ear. If 
one ear is provided with such a resonant globe whilst the other 
is closed, most external notes are very much deadened ; those, 
however, which correspond to the proper note of the glass globe 
(in combination with the hollow of the ear) are heard with ex- 
traordinary distinctness, The upper notes of any external sound 
which correspond to the note of the glass globe, are now also 
increased in intensity. If, for example, a globe is placed to the 
ear whose note is f,, and the vowels are sung on B, whose third 
note is f;, it will be found that with U, I, Ue, A, and Ae, the 
note of the globe is only feebly heard, whilst it becomes very pro- 
minent with O and Oe, and extremely intense with E. By the 
help of such resonant globes a number of acoustical phenomena, 
such as objective resultant notes, the incidental notes and their 
beats, which were formerly difficult to investigate, are rendered 
easily accessible. The investigation of the human voice, so con- 
ducted, confirmed the results which I had obtained with the 
tuning-forks when B was the key-note sung upon; for keys of 
