462 OF THE VOICE AND SPEECH. 



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of remark that, in all such experiments, it is found that the two membranes 

 may be thrown into vibration, when inclined towards each other in various 

 degrees, or even when they are in the same plane, and their edges only ap- 

 proximate ; but that the least inclination from each other (which is the posi- 

 tion the vocal ligaments have during the ordinary state of the glottis, 605,) 

 completely prevents any sonorous vibrations from being produced. 



608. The pitch of the note produced by membranous tongues, may be 

 affected in several ways. Thus, an increase in the strength of the blast, which 

 has little influence on metallic reeds, raises their pitch very considerably ; 

 and in this manner the note of a membranous reed may be raised by semitones, 

 to as much as a fifth above the fundamental. The addition of a pipe has 

 nearly the same effect on their pitch, as on that of metallic reeds ; but it can- 

 not easily be determined with the same precision. The effect of the junction 

 of a pipe with a double membranous tongue, is well shown in the Trumpet, 

 Horn, and other instruments ; which require the vibration of the lips, as well 

 as a blast of air, for the production of their sound, having no reed of their 

 own. By some, these instruments have been classed with Flute-pipes ; but 

 the conditions of their action are entirely different. The mouth-piece of the 

 horn or trumpet is incapable of yielding any tone, when a current of air is 

 merely blown through it ; and the lips are necessary to convert it into a musi- 

 cal reed, being rendered tense by the contraction of their sphincter, partly 

 antagonized by the slightly-dilating action of other muscles. The variation 

 of the tension of the lips is effected by muscular effort ; and several different 

 notes may be produced with a pipe of the same length ; but there is a certain 

 length of the column of air, which is the one best adapted for each tone ; and 

 different instruments possess various contrivances for changing this. It has 

 been recently ascertained, that the length of the pipe prefixed to the reed, has 

 also a considerable influence on its tone, rendering it deeper in proportion as 

 it is prolonged, down to nearly the octave of the fundamental note ; but the 

 pitch then suddenly rises again, as in the case of the tube placed beyond the 

 reed. The researches of Mliller, however, have not succeeded in establishing 

 any very definite relation between the length of the two tubes, in regard to 

 their influence on the pitch of the reed placed between them. 



609. From the foregoing statements it appears, that the true theory of the 

 Voice may now be considered as well established, in regard to this essential 

 particular, that the sound is the result of the vibrations of the vocal ligaments, 

 which take place according to the same laws with those of metallic or other 

 elastic tongues : and that the pitch of the notes is chiefly governed by the 

 tension of these lamina?. With respect, however, to the modifications of these 

 tones, induced by the shape of the air-passages, both above and below the 

 larynx, by the force of the blast, and by other concurrent circumstances, little 

 is certainly known. Hence it is, that on the theory of the production of what 

 are called falsetto notes, there is much difference of opinion amongst Physi- 

 ologists. Some have contended, that these tones are produced by the vibra- 

 tion of the vocal ligaments along only a part of their length ; but this is cer- 

 tainly untrue. By Miiller it is believed, that in the falsetto notes merely the 

 thin border of the glottis vibrates, so that the fissure remains distinctly visible ; 

 whilst in the production of the ordinary vocal tones, the whole breadth of the 

 vocal ligaments is thrown into strong vibrations, which traverse a wider sphere, 

 so that a confused motion is seen in the lips of the glottis, rendering its fissure 

 obscure. That the tension of the vocal cords is not diminished (as it ought 

 to be if only a part of their length were being used), but is progressively in- 

 creased, as we pass from the ordinary to the falsetto scale, any one may con- 

 vince himself, by placing his finger on the interval between the thyroid and 



