OF THE LARYNX, AND ITS ACTIONS. 929 



degree of elevation ; so that the inner faces of the vocal ligaments are brought 

 into parallelism with each other a condition which may be experimentally 

 shown to be necessary for their being thrown into sonorous vibration. The 

 muscular movements concerned in the act of vocalization appear to be called 

 forth by the instrumentality of the fibres of the Spinal Accessory nerve which 

 are contained in the Pneumogastric ( 719). 



931. We have now to inquire what is the operation of the Vocal Ligaments 

 in the production of sounds ; and in order to comprehend this, it is necessary to 

 advert to the conditions under which tones are produced by instruments of 

 various descriptions having some analogy with the Larynx. These are chiefly 

 of three kinds; strings, flute-pipes, and reeds or tongues. The Vocal Ligaments 

 were long ago compared by Ferrein to vibrating strings ; and at first sight there 

 might seem a considerable analogy, the sounds produced by both being elevated 

 by increased tension. This resemblance disappears, however, on more accurate 

 comparison ; for it may be easily ascertained by experiment, that no string so 

 short as the vocal ligaments could give a clear tone, at all to be compared in 

 depth with that of the lowest notes of the human voice ; and also, that the scale 

 of changes produced by increased tension is fundamentally different. When the 

 strings of the same length, but of different tensions, are made the subject of 

 comparison, it is found that the number of vibrations is in proportion to the 

 square-roots of the extending forces. Thus, if a string extended by a given 

 weight produce a certain note, a string extended by four times that weight will 

 give a note in which the vibrations are twice as rapid; and this will be the 

 octave of the other. If nine times the original weight be employed, the vibra- 

 tions will be three times as rapid as those of the fundamental note, producing 

 the twelfth above it. Now by fixing the larynx in such a manner that the vocal 

 ligaments can be extended by a known weight, Mu'ller has ascertained that the 

 sounds produced by a variation of the extending force do not follow the same 

 ratio ; and therefore the condition of these ligaments cannot be simply that of 

 vibrating cords. Further, a cord of a certain length, which is adapted to give 

 out a clear and distinct note, equal in depth to the lowest of the human voice, 

 may be made by increased tension to produce all the superior notes, which, in 

 stringed instruments, are ordinarily obtained by shortening the strings. 1 But 

 it does not follow that a short string, which, with moderate tension, naturally 

 produces a high note, should be able, by a diminution of the tension, to give 

 out a deep one ; for, although this might be theoretically possible, yet it cannot 

 be accomplished in practice ; since the vibrations became irregular on account 

 of the diminished elasticity. 3 These considerations are in themselves sufficient 

 to destroy the supposed analogy; and to prove that the Chordse Vocales cannot 

 be reduced to the same category with vibrating strings. The next kind of 

 instrument with which some analogy might be suspected is the flute-pipe, in 

 which the sound is produced by the vibration of an elastic column of air contained 

 in the tube ; and the pitch of the note is determined almost entirely by the 

 length of the column, although slightly modified by its diameter, and by the 

 nature of the embouchure or mouth from which it issues. This is exemplified 

 in the German Flute, and in the English Flute or Flageolet ; in both of which 



1 Thus in the Piano-forte, where there are strings for each note, a gradual shortening 

 is seen from the lowest to the highest ; and in the Violin the change of tone is produced 

 by stopping the strings with the finger, so as to diminish their acting length. 



2 Thus it would be impossible to produce good Bass notes on the strings of a Violin, by 

 diminishing their tension; the length aiforded by the Violoncello or Double Bass is requisite. 

 The striking difference between the tone of the Bass strings in the Grand Piano-forte 'and 

 the small upright Piccolo is another exemplification of the same principle ; being chiefly 

 due to the length and tension of the former, as contrasted with the shortness and slackness 

 of the latter. 



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