716 
Proceedings of the Royal Society 
the duplex form is reached the cavity must he suddenly changed so 
as to he approximately if not exactly in unison with the second 
partial. A voice singing u up the scale may sometimes carry the 
duplex form as high as feb, hut the vowel quality of an u so spoken 
is apt to approach o . When attempts were made to slur either up 
or down, past the place at which the change occurred, one or other 
of two things took place — either the sound died away almost 
completely while the critical point was being passed, or the vowel 
quality changed form u to o for an instant. This has been observed 
both directly and by examination of the magnified phonographic 
record, in which either an almost blank space or the well known 
wave-form of o might he seen. 
An examination of the sound o through the lower regions of the 
scale, and by the help of several bass voices, did not show any such 
sudden change as took place in u , hut the number of partials con- 
spicuously present became more and more numerous as the pitch fell. 
The third partial began to appear about /, and on d and e the 
prime second and third were all strongly present, the prime being 
the weakest of the three, and the second the strongest. On c the 
fourth partial was moderately strong, the third stronger, the second 
stronger still, and the prime weaker than any. The first four par- 
tials were all conspicuous on B. On Bh the fourth was much 
stronger than any of the others, and the prime was the weakest of 
the lower ones. The same description applies to A. On G the 
fourth was still much the strongest, and the fifth appeared weakly. 
The lower ones were weak. On F the fifth was much the strongest, 
but the prime, second, third, and fourth were all distinctly present. 
We have not got any trace good enough for analysis below F. We 
reserve the numerical result for more detailed publication. 
The hearing of our experiments on the theory of vowel 
sounds is very important. For a considerable range it will he 
seen that the constituents of o and u might he simply described, 
with no reference whatever to absolute pitch — the u always being 
a simple tone, and the o a compound of two simple tones an 
octave apart. 
When, however, certain limits are passed, phenomena appear 
which are evidently connected in some way with an absolute pitch. 
It seems, however, that this connection is rather due to the neces- 
