this vowel i begins with ah, and confifts therefore of ah and ee. Whilft the dipthong ou in our language, as in the word how, begins with ah alfo and ends in oo, and the vowel u of our language, as in the word ufe, is likewife a dipthong; which begins with e and ends with oo, as eoo. The French u is also a dipthong compounded of a and oo, as aoo. And many other defects and redundancies in our alphabet will be feen by perufing the subsequent structure of a more perfect one.

11. PRODUCTION OF SOUNDS.

By our organ of hearing we perceive the vibrations of the air; which vibrations are performed in more or in less time, which conftitutes high or low notes in respect to the gammut; but the tone depends on the kind of inftrument which produces them. In fpeaking of articulate founds they may be conveniently divided firft into clear continued founds, expreffed by the letters called vowels; fecondly, Into hiffing founds, expreffed by the letters called fibilants; thirdly, Into femivocal founds, which confift of a mixture of the two former; and, laftly, Into interrupted founds, represented by the letters properly termed confonants.

The clear continued founds are produced by the ftreams of air paffing from the lungs in refpiration through the larynx; which is furnished with many fmall muscles, which by their action give a proper

tenfion to the extremity of this tube; and the sounds, I suppose, are produced by the opening and clofing of its aperture; something like the trumpet stop of an organ, as may be observed by blowing through the wind-pipe of a dead goofe.

These founds would all be nearly fimilar except in their being an octave or two higher or lower; but they are modulated again, or acquire various tones, in their paffage through the mouth; which thus converts them into eight vowels, as will be explained below.

The hiffing founds are produced by air forcibly pushed through certain paffages of the mouth without being previously rendered fonorous by the larynx; and obtain their fibilancy from their flower vibrations, occafioned by the mucous membrane, which lines thofe apertures or paffages, being lefs tense than that of the larynx. I fuppofe the stream of air is in both cafes frequently interrupted by the clofing of the fides or mouth of the paffages or aperture; but that this is performed much flower in the production of fibilant founds, than in the production of clear ones.

The femivocal founds are produced by the ftream of air having received quick vibrations, or clear found, in paffing through the larynx, or in the cavity of the mouth; but a part of it, as the outfides of this fonorous current of air, afterwards receives flower vibrations, or hiffing found, from fome other paffages of the lips or mouth, through

which it then flows. Laftly the stops, or confonants, impede the current of air, whether fonorous or fibilant, for a perceptible time; and probably produce fome change of tone in the act of opening and clofing their apertures.

There are other clear founds befides thofe formed by the larynx; fome of them are formed in the mouth, as may be heard previous to the enunciation of the letters b, and d, and ga; or during the pronunciation of the femivocal letters, v. z. j. and others in founding the liquid letters r and 1; these founds we shall term orifonance. The other clear founds are formed in the noftrils, as in pronouncing the liquid letters m. n. and ng. these we fhall term narifonance.

Thus the clear founds, except thofe above mentioned, are formed in the larynx along with the mufical height or lownefs of note; but receive afterward a variation of tone from the various paffages of the mouth: add to these that as the fibilant founds confift of vibrations flower than those formed by the larynx, fo a whiftling through the lips confifts of vibrations quicker than those formed by the larynx.

As all found confifts in the vibrations of the air, it may not be difagreeable to the reader to attend to the immediate caufes of thofe vibrations. When any fudden impulfe is given to an elaftic fluid like the air, it acquires a progreffive motion of the whole, and a condensation of the conftituent particles, which firft receive the impulfe; 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 ftream is condensed by the projectile force; and the fucceeding part, being confequently rarefied, requires fome time to recover its denfity, and to follow the former part: this elafticity of the air is likewife the cause of innumerable eddies in it; which are much more frequent than in ftreams of water; as when it is impelled against any oblique plane, it refults with its elaftic force added to its progreffive one.

Hence when a vacuum is formed in the atmofphere, the fides of the cavity forcibly rush together both by the general preffure of the fuperincumbent air, and by the expansion of the elaftic particles of it; and thus produce a vibration of the atmofphere to a confiderable diftance: this occurs, whether this vacuity of air be occafioned by the difcharge of canon, in which the air is displaced by the fudden evolution of heat, which as fuddenly vanishes; or whether the vacuity be left by a vibrating ftring, as it returns from each fide of the arc, in which it vibrates; or whether it be left under the lid of the valve in the trumpet-ftop 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 elafticity of the currents, as it occafions the paufing gufts of wind mentioned above.

Hence when a quick current of air is fuddenly VOL. III, A a

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-flop above mentioned; and a vibration is in confequence produced; which with the great facility, which elaftic fluids poffefs of forming eddies, may explain the production of founds by blowing through a fiffure upon a fharp edge in a common organ-pipe or child's whiftle; which has always appeared difficult to refolve; for the lefs vibration an organ-pipe itself poffeffes, 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 fides of it; though the latter, when it exifts, may alter the tone though not the note, like the belly of a harpfichord or violin.

When a ftream of air is blown on the edge of the aperture of an organ-pipe about two thirds of it are believed to pafs on the outfide of this edge, and one third to pass on the infide of it; but this current of air on the infide forms an eddy, whether the bottom of the pipe be clofed or not; which eddy returns upwards, and ftrikes by quick intervals against the original fiream of air, as it falls on the edge of the aperture, and forces outwards this current of air with quick repetitions, fo as to make more than two thirds of it, and less than two thirds alternately pass on the outfide; whence a part of this ftream of air, on each fide of the edge of the