Illustration of apparatus for producing vowel sounds. From:<cite style="font-style:normal">Willis, Robert (1930). "<a rel="nofollow" class="external text" href="https://archive.org/details/willis-1828b-transactionsofca-03camb">On vowel sounds, and on reed organ pipes</a>". <i>Transactions of the Cambridge Philosophical Society</i> <b>3</b>: 261-268.</cite>
Willis, Robert, 1800-1875
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