(lp PROFESSOR FLEEMING JENKIN AND A. J. EWING ON THE 
it is possible that the group, consisting of a prime and its octave, might con- 
tinue to give 6 when sounded below the limits within which the voice when 
singing 6 produces this simple group. Our own impression of the effect pro- 
duced when the second of an 6 sung at a high pitch is made to speak in the 
phonograph at a lower speed, supports this view, but the vowel sound given in 
this way is proved by our curves to be different from the human 6, and we do 
not think that a mere subjective impression counts for much. 
On the other hand, there is a decided resemblance, though scarcely an iden- 
tity between the constituents of 6 at a low pitch and a@° or @ at higher pitches. 
The relative partials of 6 in the neighbourhood of b) resemble pretty closely 
those of d@ in the neighbourhood of f or g. Our experiments on a@° and @ are 
not. sufficiently numerous to enable us to draw any very general conclusion as to 
these vowels, but they are sufficient, when taken in conjunction with the experi- 
ments on 6, to show that between certain vowels the main distinction must lie in 
the absolute pitch of the group of reinforced constituent tones. 
We are thus brought back to our original statement, that in distinguishing 
vowels the ear is guided by two factors, one depending on the harmony or 
group of relative partials, and the other on the absolute pitch of the reinforced 
constituents. 
It seems not a little singular that the ear should attach so distinct a unity to 
sounds made up of such very various groups of constituents, as we have obtained 
from different voices and at different pitches, as to recognise all these sounds as 
some one particular vowel. 
We are forced to the conclusion already adopted by HELMHOLTZ and Don- 
DERS, that the ear recognises the kind of oral cavity by which the reinforcement is 
produced ; that although the sounds which come from the cavity differ so much 
that we are unable, when they are graphically represented and mathematically 
analysed, to detect any very prominent common feature, nevertheless by long 
practice the ear is able to distinguish between the different sorts of cavities 
which are made use of in pronouncing given vowels. Something of the same 
kind may, indeed, be observed in other sources of sound than the human voice. 
The characteristic by which we recognise a musical instrument is In many cases 
the peculiar nature of the resonance chamber which it possesses : and we con- 
tinue without difficulty to recognise a substantial unity in the quality of sounds 
given by the instrument at different parts of the scale, where the action of the 
resonance chamber must be very different. 
The question then remains, is the resonance cavity for a vowel sound constant 
at all pitches, and, if so, what properties does it possess which enable its modifica- 
tion of the sound given by the vocal chords to be recognised on a particular vowel? 
And further, if the cavity is not constant, but variable when the vowel is spoken 
at different pitches, what common feature is possessed by the modified forms of 
the cavity? 
