John Gray McKendrick,
1911 Encyclopædia Britannica, Volume 28…
(1911)
“ This analysis shows: (1) that the man’s resonance rises slightly (half semitone) in ascending seven semitones in the middle of his register, (2) that the boy’s resonance rises three semitones in ascending nine semitones in the upper half of his register; and (3) in the mid register the boy’s resonance is to the man’s as 5:4. Thus, as we sing a vowel in an ascending scale the pitch of the oral cavity slightly changes, or, in other words, the pitch of the resonating cavity for a given vowel may be slightly altered. ”
