Thus the clear sounds, except those above mentioned, are formed in the larynx along with the musical height or lowness of note; but receive afterward a variation of tone from the various passages of the mouth: add to these that as the sibilant sounds consist of vibrations slower than those formed by the larynx, so a whistling through the lips consists of vibrations quicker than those formed by the larynx.
As all sound consists in the vibrations of the air, it may not be disagreeable to the reader to attend to the immediate causes of those vibrations. When any sudden impulse is given to an elastic fluid like the air, it acquires a progressive motion of the whole, and a condensation of the constituent particles, which first receive the impulse; on this account the currents of the atmosphere in stormy seasons are never regular, but blow and cease to blow by intervals; as a part of the moving stream is condensed by the projectile force; and the succeeding part, being consequently rarefied, requires some time to recover its density, and to follow the former part: this elasticity of the air is likewise the cause of innumerable eddies in it; which are much more frequent than in streams of water; as when it is impelled against any oblique plane, it results with its elastic force added to its progressive one.
Hence when a vacuum is formed in the atmosphere, the sides of the cavity forcibly rush together both by the general pressure of the superincumbent air, and by the expansion of the elastic particles of it; and thus produce a vibration of the atmosphere to a considerable distance: this occurs, whether this vacuity of air be occasioned by the discharge of cannon, in which the air is displaced by the sudden evolution of heat, which as suddenly vanishes; or whether the vacuity be left by a vibrating string, as it returns from each side of the arc, in which it vibrates; or whether it be left under the lid of the valve in the trumpet stop of an organ, or of a child's play trumpet, which continues perpetually to open and close, when air is blown through it; which is caused by the elasticity of the currents, as it occasions the pausing gusts of wind mentioned above.
Hence when a quick current of air is suddenly broken by any intervening body, a vacuum is produced by the momentum of the proceeding current, between it and the intervening body; as beneath the valve of the trumpet-stop above mentioned; and a vibration is in consequence produced; which with the great facility, which elastic fluids possess of forming eddies, may explain the production of sounds by blowing through a fissure upon a sharp edge in a common organ-pipe or child's whistle; which has always appeared difficult to resolve; for the less vibration an organ-pipe itself possesses, the more agreeable, I am informed, is the tone; as the tone is produced by the vibration of the air in the organ pipe, and not by that of the sides of it; though the latter, when it exists, may alter the tone though, not the note, like the belly of a harpsichord, or violin.
When a stream of air is blown on the edge of the aperture of an organ-pipe about two thirds of it are believed to pass on the outside of this edge, and one third to pass on the inside of it; but this current of air on the inside forms an eddy, whether the bottom of the pipe be closed or not; which eddy returns upwards, and strikes by quick intervals against the original stream of air, as it falls on the edge of the aperture, and forces outwards this current of air with quick repetitions, so as to make more than two thirds of it, and less than two thirds alternately pass on the outside; whence a part of this stream of air, on each side of the edge of the aperture is perpetually stopped by that edge; and thus a vacuum and vibration in consequence, are reciprocally produced on each side of the edge of the aperture.
The quickness or slowness of these vibrations constitute the higher and lower notes of music, but they all of them are propagated to distant places in the same time; as the low notes of a distant ring of bells are heard in equal times with the higher ones: hence in speaking at a distance from the auditors, the clear sounds produced in the larynx by the quick vibrations of its aperture, which form the vowels; the tremulous sounds of the L. R. M. N. NG. which are owing to vibrations of certain apertures of the mouth and nose, and are so slow, that the intervals between them are perceived; the sibilant sounds, which I suppose are occasioned by the air not rushing into a complete vacuum, whence the vibrations produced are defective in velocity; and lastly the very high notes made by the quickest vibrations of the lips in whistling; are all heard in due succession without confusion; as the progressive motions of all sounds I believe travel with equal velocity, notwithstanding the greater or less quickness of their vibrations.
III. Structure of the Alphabet.
Mute and antesonant Consonants, and nasal Liquids.
- P. If the lips be pressed close together and some air be condensed in the mouth behind them, on opening the lips the mute consonant P begins a syllable; if the lips be closed suddenly during the passage of a current of air through them, the air becomes condensed in the mouth behind them, and the mute consonant P terminates a syllable.
- B. If in the above situation of the lips a sound is previously produced in the mouth, which may be termed orisonance, the semisonant consonant B is produced, which like the letter P above described may begin or terminate a syllable.
- M. In the above situation of the lips, if a sound is produced through the nostrils, which sound is termed narisonance, the nasal letter M is formed; the sound of which may be lengthened in pronunciation like those of the vowels.
- T. If the point of the tongue be applied to the forepart of the palate, at the roots of the upper teeth, and some air condensed in the mouth behind, on withdrawing the tongue downwards the mute consonant T is formed; which may begin or terminate a syllable.
- D. If the tongue be placed as above described, and a sound be previously produced in the mouth, the semisonant consonant D is formed, which may begin or terminate a syllable.
- N. If in the above situation of the tongue and palate a sound be produced through the nostrils, the nasal letter N is formed, the sound of which may be elongated like those of the vowels.
- K. If the point of the tongue be retracted, and applied to the middle part of the palate; and some air condensed in the mouth behind; on withdrawing the tongue downwards the mute consonant K is produced, which may begin or terminate a syllable.
- Ga. If in the above situation of the tongue and palate a sound be previously produced in the mouth behind, the semisonant consonant G is formed, as pronounced in the word go, and may begin or terminate a syllable.
- NG. If in the above situation of the tongue and palate a sound be produced through the nostrils; the nasal letter ng is produced, as in king and throng; which is the french n, the sound of which may be elongated like a vowel; and should have an appropriated character, as thus v.
Three of these letters, P, T, K, are stops to the stream of vocal air, and are called mutes by grammarians; three, B, D, Ga, are preceded by a little orisonance; and three, M, N, NG, possess continued narisonance, and have been called liquids by grammarians.