TUB VOICE OF MAX.] 



UNDULATORY FORCES. ACOUSTICS. 



the vocal cords, which form its immediate boundaries, 

 as the essential source of voice ; while the windpipe 

 simply conveys air ; and the cavities above the glottis, 

 comprehending the upper part of the larynx and the air 

 passages through the mouth and nostrils, correspond to 

 the tube of a musical instrument, by which the sound is 

 modified, but not generated. 



It has been already remarked,* that the vocal liga- 

 ments are composed of elastic tissue ; and it is owing to 

 this elasticity that they are adapted to the office which 

 they perform. While, then, it is quite certain that no 

 proper vocal sounds can be produced, except in the 

 glottis, it seems manifest that the adjacent and some- 

 what abundant tissue of the same kind, is susceptible of 

 a vibration and resonance in unison, so as at least to 

 modify the sounds of the voice. 



In reference to the second question what is the nature 

 of the change produced in the glottis during the forma- 

 tion of voice ? no inconsiderable difficulty is met with. 

 The points of debate which have arisen on this subject 

 are, whether the vocal ligaments be a set of membranous 

 cords obeying the laws of musical strings ; if the aper- 

 ture of the glottis be a reeded instrument, in which the 

 vocal ligaments play the part of vibrating tongues ; or 

 even whether the real source of the sounds of the voice 

 bo not a molecular vibration of the air, produced by its 

 passage through the narrow aperture of the glottis ; and, 

 lastly, whether the organ of the voice does not, in part, 



mbine all these three sources of sound, so as to be at 

 , in some respects, a stringed instrument, a tongued 

 instrument, and a simple wind instrument. 



The ancients regarded the sounds of the voice as 

 analogous to those of a flute. According to this view, 

 the vibrations of the larynx are of little account, the 

 actual sounds Ixsing produced by a molecular undulation 

 of the air. That the organ of voice is, in some degree, 

 analogous to this kind of musical instrument, is not to 

 bo absolutely denied ; but it is certain that this U not 

 the principal mode in which the sounds are produced. 



One of the earliest ideas of modern times on the sub- 

 ject of the voice is, that the larynx is analogous to a 

 horn ; that is to say, to a wind instrument, in which 

 the vocal cords act the same part as the lips of the per- 

 former on a horn. Not much more than a hundred 

 years ago arose the idea that the larynx is a set of 

 musical cords namely, that the vibrations of these 

 cords, on the same principle as a stringed instrument, 

 produce the sound, which was then conveyed outwards 

 by the air. 



The prevailing opinion of the present day is, that the 

 larynx is a wind instrument, but a reeded one. 



This common view may be expressed as follows : The 

 expired air is thrown into the larynx through the wind- 

 rig. !. 



f 



<' 



No. 5. 



, o. . 



pipe, by the muscular action of the chest; and the 

 proper muscles of the larynx being contracted, create a 



Bee ante, p. 280. 



I sufficient tension of the vocal cords to permit them to 

 be thrown into vibration by the impulse of the air. 

 The sound so produced is conveyed through the mouth 

 and nasal passages, undergoing various modifications in 

 its passage outwards. 



Let us consider, then, in the first place, what evidence 

 there is that the organ of the voice is a reeded instru- 

 ment, with a double membranous tongue. 



In short, the action of the organ of voice may be best 

 explained, in general terms, by comparing it with the 

 pipe of an organ. Let us suppose t' (No. J , Fig. 16) to 

 be the wind-tube, into which the air is driven from 

 below ; b, the stopper, in which is placed the tongue ; 

 o and (, the body-tube ; and let there be a pipe, o 

 (No. 2), to the wind-box, c c, and the air be driven from 

 the bellows, / / p, through t. The air throws the 

 tongue, a (No. 1), into a state of vibration, and passes 

 out in undulating movements from the body-tube. 

 Such is a general illustration of the nature of voice. 



An experiment may bo made which illustrates the 

 effect of an elastic organic tissue, like that of the vocal 

 ligaments, in producing sound on the principle of a 

 double tongue. Tho extremity of a tube is closed by 

 two bands of moist elastic tissue for example, arterial 

 tissue so applied as to cover the whole end of the tube, 

 with the exception of a slight fissure between the bands. 

 India-rubber, or leather, may be employed for tliis pur- 

 pose. Both these substances produce a similar eliect ; 

 but it appears that the middle arterial coat, being com- 

 posed of the same tissue as the vocal ligaments, and 

 having the same physical properties, forms the best kind 

 of artificial larynx. When this tube is blown through 

 at the free extremity, the tongues not only' vibrate 

 readily, but produce a range of musical tones. To 

 obtain a pure quality of tone, it is necessary that the 

 two membranous bands should be of equal weight and 

 breadth, and subject to equal tension, otherwise they 

 cannot vibrate equally in equal parts of time. 



If the human larynx be dissected out, and the vocal 

 cords bo stretched, they will vibrate like a piece of arti- 

 ficial tissue, such as india-rubber or leather, in a current 

 of air. In conducting these experiments, the same con- 

 ditions must be secured as are required in the experi- 

 ment with the tube, and the two membranous laminae, 

 before referred to. For example, the inner edges of the 

 glottis that is to say, of the vocal ligaments must be 

 turned outwards towards each other, so that they shall 

 be in the same plane and parallel to each other, other- 

 wise they will not produce any sound. Hence it may be 

 inferred, that when the tension of the vocal ligaments 

 takes place in the living animal, they turn upon their 

 axis, till their planes, which, in the state of relaxtion, 

 are inclined to the axis of the vocal tube, become per- 

 pendicular to it; and as the edges of the glottis ap- 

 proximate, its chink is nearly or entirely closed, and they 

 acquire the true vibrating position. The production of 

 the most simple tones of the voice requires the associated 

 action of a most extensive range of organs ; for it is cal- 

 culated that, in the ordinary modulation of the voice, 

 more than one hundred muscles are brought into action 

 at the same time. 



As the air rushes upwards from the windpipe, a por- 

 tion of each edge of the glottis yields to its pressure, 

 and is curved upwards, so as to form an angle with the 

 axis of the vocal tube, and leave between the two edges 

 a narrow aperture, tlirough which the air escapes. The 

 tension and elasticity of the vocal ligaments tend to 

 restore them to the plane of their former position. The 

 air having been rarefied below the glottis during their 

 elevation, becomes dense from their depression, and the 

 necessary force being again accumulated, they are re- 

 elevated, and thus an oscillating movement, consisting 

 of an opening and closing of the glottis, takes place ; 

 which, being communicated to the contiguous air, the 

 sounds of the voice are produced. 



The vibrating edge of the glottis varies in length, 

 according to the pressure of the column of air in the 

 windpipe, and the resistance of the vocal ligaments. 

 When other circumstances are alike, the intensity of 



