The pure labial sound is produced by contact between the upper and lower lip; the upper lip being the "place," the lower the "instrument."
All consonants, excluding semi-vowels and sibilants or flatus, are formed by a complete contact between the active and passive organ.
Formation of the Tenuis.
If the voice is stopped sharp by the contact of the organs, so as to allow for the moment no breath or sound to escape, the consonant is called tenuis (ψιλόv), hard or surd (k, t, p).
Formation of the Media.
If the voice is stopped less abruptly, so as to allow a kind of breathing to continue after the first contact has taken place, the consonant is called media (μέσον), soft or sonant (g, d, b). The soft consonant does not arrest the sound at once, but allows it to be heard during a moment of resistance.
The difference between a surd and sonant consonant is best illustrated by a speaking-machine. "The sound p," as Professor Wheatstone says, "was produced by suddenly removing the left hand from the front of the mouth, which it had previously completely stopped; the sound b, by the same action; but instead of closing the mouth completely, a very minute aperture was left, so that the sound of the reed might not be entirely stifled." This coincides fully with the description given by Mr. Ellis. "In pronouncing ba," he says, "the vowel is uttered simultaneously with the act of relieving the lips from contact, or rather before they are quite released. If we separate them before the vowel is uttered, allowing the breath to be condensed during a very brief space of time, the sound pa is heard. There is a similar distinction between ab and ap: in the former the effect of the voice remains throughout the consonant, and we may feel a slight tremor of the lips while it is being produced; in the latter the vowel, properly so called, entirely ceases before the contact is completed."
Formation of Semi-vowels.
If there is only an approach or a very slight contact between the
