110 Additional Notes. 



The hissing sounds are produced by air forcibly pushed through 

 certain passages of the mouth without being previously rendered sono- 

 rous by the larynx; and obtain their sibilancy from their slower vibra- 

 tions, occasioned by the mucous membrane, which lines those aper- 

 tures or passages, being less tense than that of the larynx. I suppose 

 the stream of air is in both cases frequently interrupted by the closing 

 of the sides or mouth of the passages or aperture; but that this is 

 performed much slower in the production of sibilant sounds, than in 

 the production of clear ones. 



The semivocal sounds are produced by the stream of air having re- 

 ceived quick vibrations, or clear sound, in passing through the larynx, 

 or in the cavity of the mouth; but apart of it, as the outsides of this 

 sonorous current of air, afterwards receives slower vibrations, or 

 hissing sound, from some other passages of the lips or mouth, through 

 which it then flows. Lastly the stops, or consonants, impede the 

 current of air, whether sonorous or sibilant, for a perceptible time; 

 and probably produce some change of tone in the act of opening and 

 closing their apertures. 



There are other clear sounds besides those formed by the larynx; 

 some 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 pronun- 

 ciation of the semivocal letters, v. z. j. and others in sounding the 

 liquid letters r and 1 ; these sounds we shall term orisonance. The 

 other clear sounds are formed in the nostrils, as in pronouncing the 

 liquid letters m. n. and ng. these we shall term narisonance. 



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 wbistling 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 conden- 

 sation of the constituent particles, which first receive the impulse; on 



