The Physiological Scale of Vowels.
If we recall the process by which the semi-vowels were formed in the three principal classes, and if, instead of stopping the vocal sound by means of that slight remnant of consonantal contact which was characteristic in the formation of the semi-vowels, we allow the full volume of breath to pass over the point of contact and there to vibrate and sound, we get three pure vowel sounds, guttural, palatal, and dental, which can best be expressed by the Italian A, I, U, as heard in bath, ravine, put.
Formation of the Labial Vowel.
Let us pronounce the labial semi-vowel (f. 5.), the English w in woe, and, instead of stopping the vocal sound as it approaches the labial point of contact, let us emit it freely through the rounded aperture of the lips, and we have the vowel u. Here also the experiment of the candle will elucidate the process that takes place, but of which we are hardly conscious. The mere semivowel w, not followed by any vowel, should not produce any disturbance in the flame; at least not more than might be occasioned by the motion of the lips, which would be the same for all consonants. The labial flatus, f, on the contrary, will disturb the flame considerably, and the vowel u may extinguish it.
Formation of the Palatal Vowel.
The same process which changes w into u, changes the guttural semi-vowel h into a, and the palatal semi-vowel y into i. Let us pronounce the y in yea without any vowel after it, and it only requires the removal of that stoppage of sound which takes place between tongue and palate, in order to allow the vowel i, as in pin or ravine, to be heard distinctly.
Formation of the Guttural Vowel.
Let us pronounce the guttural semi-vowel as heard in loch or the Hebrew hain, and, if we try to change this semi-vowel gradually into the vowel a, we feel that what we do is merely to remove that stoppage which in the formation of the semi-vowel takes place at the very point of guttural contact.
