UNDULATORY FORCES. ACOUSTICS. 



[CAUSE or TH voice. 



the voice u determined by the prawure of the column 

 of air in the windpipe, and the range of movement 

 described by the vibrating edge* of the glottis. The 

 pitch of the voice doe* not depend solely on the tension 

 of the TOO*! ligament*, but jointly on the variations 

 which thev undergo in length and tension. Hagendie 

 observed, in the larynx of a dog, that a longer portion 

 of the Toeal ligament* vibrated while grave tone* were 

 produced, and that a diminution of length accompanied 

 the succession of acute tone*. Mayo has described the 

 movements of the glottis in a man who had attempted 

 to destroy tiimlf by cutting his throat. The larynx in 

 j . 1 1. this case was cut through 



just above the vocal 

 cords; and, owing to 

 the oblique direction 

 of the wound, an in- 

 jury of the arytcnoid 

 cartilage, and of the 

 vocal cord on one side, 

 hod occurred. When 

 respiration was going 

 on, the glottis was seen 

 to be of a triangular 

 t form ; but when the 

 ' voice was exerted, the 

 vocal cords passed into 

 a parallel direction, and 

 the glottis itself had a 

 linear form. The pos- 

 terior part of the aper- 

 ture appeared to re- 

 main unclosed. 



The cut (Fig. 17) re- 

 presents the prepared 

 head of a corpse, after 

 Miiller. A thread e, 

 which passes over a 

 roller to a scale, is so applied to the larynx that the 

 tension of the vocal cords can be increased by placing a 

 greater weight on the scale. The action of the muscles 

 is thereby imitated. The compressing apparatus seen 

 on the wood-cut, brings the vocal cords nearer to each 

 other, and thus produces the requisite diminution in the 

 width of the vocal fissure. The tube / serves to convey 

 the wind, which throws the tongue-apparatus into 

 action. And thus, if we use the human head, or the 

 head of the dog, the pig, or of any other animal, wo 

 can imitate the voice of man, the bark of the dog, the 

 grunt of the pig, <tc. 



Membranous tongues, like those in the larynx, differ 

 widely from a metal tongue, shutting up the aperture, 

 and necessarily opening and closing as the air issues. 



Objections have been taken to the view which repre- 

 sents the voice as the result of sounds produced by mem- 

 branous tongues set in motion by air 1st, that the 

 vibration of tongues consists in the periodical opening 

 and shutting of the orifice through which the stream of 

 air panes this not being the case in the glottis ; and, 

 2nd, that had it the structure of a reed, the edges of 

 the vocal ligaments which open the chink would be alter- 

 nately separated by the column of air in the larynx, and 

 drawn together by their tension; while it has been 

 found by experiment, that air transmitted through the 

 glottis gives rise to sound, notwithstanding that its edges 

 are from one-sixth to one-fourth of an inch asunder. In 

 these objections, however, there is a mistake as to the 

 essential principle of reeds; for those of the clarionet, 

 bassoon, hautboy, d-c., fail to close entirely the passages 

 through which the breath escapes ; and the case is not 

 otherwise with the natural reed, which the lips of 

 players on the flute and horn represent. In short, a 

 sound can be produced by a tongue apart from the sur- 

 rounding framework, indicating, beyond doubt, that so 

 much importance should not be ascribed to the usual 

 mode of forming reeded and tongued instruments, and 

 to the circumstance of the air passing between the 

 tongue and it* frame. It has been shown, that the law 

 by which the variation in the note* yielded by the 



tongue of a mouthpiece or reed is regulated, is the 

 same when the tongue is made to vibrate by a current 

 of air, as when it is thrown into vibrations by being 

 struck or inflected. By the same law are regulated tire 

 vibrations of vibrating rods ; the frequency of thu vibra- 

 tion* of two rods of the same texture and thickness 

 being in the inverse ratio of the squares of their length. 

 The note afforded by a reed without a tube, is of the 

 same pitch, whether it bo the result of a current of air, 

 or if produced by striking the tongue. The strength of 

 the blast does not, for the most part, determine the 

 pitch or sharpness of the note ; but when the force of 

 the blowing is increased, the strength of the tones is 

 augmented. The size of the fissure between the tongue 

 and the frame within which it vibrates, is of little con- 

 sequence ; when the opening is large there is a greater 

 difficulty in obtaining the tone, but its pitch is not 

 attend 



Some slight difficulties may still exist in the explana- 

 tion of the theory of the voice as considered to be chiefly 

 the result of a double vibrating tongue ; but, altogether, 

 as close a resemblance has been proved to exist, between 

 that kind of artificial musical arrangement and the 

 structure of the living larynx, as can reasonably bo 

 expected in such a case. 



It lias been hinted, that the vocal ligaments may 

 possibly act not only as vibrating tongues in the pro- 

 duction of voice, but also on the principle of musical 

 strings. On this point a few words must be added. It 

 may seem, at first sight, that the remark of so distin- 

 guished a philosopher as Biot, when he says, " What is 

 there in the larynx that resembles a vibrating string ? 

 Where is the space for such a string of sufficient length 

 to yield the lower notes of the voice ? How could sounds, 

 of the compass which the human voice represents, be 

 produced by a string which the larynx would contain ?" 

 would suffice altogether to set aside the idea of the vocal 

 cords acting as musical strings. But Biot here seems to 

 have fallen into error. Deep notes are still produced by 

 a string greatly shortened, if it retain, after a sufficient 

 amount of relaxation, the elasticity required for vibra- 

 tion. His attention does not seem to have been drawn 

 sufficiently to the nature of organic membranes ; strips of 

 india-rubber, and elastic animal membranes, still retain- 

 ing enough of elasticity for this purpose, after being 

 much relaxed. There is, therefore, a perfect agreement 

 between the vocal cords and vibrating strings, though 

 their vibrations, whether as strings or as tongues, are 

 produced not by the direct impulse of a solid body, but 

 by the momentum of air. When the ordinary principles 

 to which musical strings are subject are applied to the 

 vocal ligaments, there is found to bo a very close agree- 

 ment, if allowance be made for the peculiarities of animal 

 substances, as respects their elasticity and the like. 



In their ordinary state, the vocal cords must be re- 

 garded as subject to a considerable tension, which, how- 

 ever, admits of being diminished, so as to add to the 

 range of the lower notes. At the ordinary pitch of the 

 voice, the glottis may be regarded as partially closed, 

 and becoming more open as graver tones are produced ; 

 :his opening of the glottis coinciding with the relaxa- 

 tion of the vocal cords, a double cause is afforded of the 

 owering of tone. When higher notes are uttered, the 

 glottis closes, assuming more of a linear form ; while, at 

 .he same time, the vocal ligaments, though clone; 

 are thrown into a much higher state of tension, in the 

 vords. then, of Mr. Bishop, " Since the vocal ligain 

 lave been proved to extend and contract for acute and 

 [rave sounds respectively, and after death vibrate, in a 

 [roat measure, like musical strings, we think it may be 

 airly inferred, that they likewise obey, to a certain 

 txtent, during life, the laws of the vibrations of such 

 strings. * * * * It is, moreover, observable, 

 h.-it the extension and relaxation of the vocal cord, 

 vhicK, as we have seen, are analogous to those of a 

 musical string, produce a corresponding shortening ami 

 ilongation of its axis, if regarded as a tongue ; and, 

 astly, since one tone only is produced at a time, the 

 vibrations resulting from the double action which 



