304 OF THE VOICE AND SPEECH. 



pipe at D with strong thread, as in Fig. 79, it will give us an artificial glottis 

 with its upper edges G H, which may be made to vibrate or not, at pleasure, 

 by inclining the planes of the edges. A couple of pieces of cork may be 

 glued to the corners, to make them more manageable. From this machine, 

 various notes may be obtained by stretching the edges in the direction of their 

 length G H ; the notes rising in pitch with the increased tension, although the 

 length of the vibrating edge is increased. It is true that a scale of notes equal 

 in extent to that of the human voice cannot be obtained from edges of leather ; 

 but this scale is much greater in India Rubber than in leather ; and the elas- 

 ticity of them both is so much inferior to that of the vocal ligaments, that we 

 may readily infer that the great scale of the latter is due to its greater elastic 

 powers." By other experimenters, the tissue forming the middle coat of the 

 arteries has been used for this purpose, in the moist state, with great success ; 

 with this, the tissue of the vocal ligaments is nearly identical. It is worthy 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 approximate ; 

 but that the least inclination from each other (which is the position the vocal 

 ligaments have during the ordinary state of the glottis, 404), completely pre- 

 vents any sonorous vibrations from being produced. 



409. 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 cannot 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 w^ell 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 condi- 

 tions 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 musical 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 in- 

 struments possess various contrivances for changing this. It has been recently 

 ascertained, that the length of the pipe prefixed to the reed has also a consider- 

 able 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 sud- 

 denly rises again, as in the case of the tube placed beyond the reed. The 

 researches of Miiller, 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. 



410. 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 ten- 

 sion of these laminae. 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 



