VOICE. 



1481 





the living vocal organs, but in a state of dis- 

 ease, the other on the organs after death. 



Variations in the hygrometric and thermo- 

 metric states of the air exert very powerful 

 influence on the pitch of the voice ; during 

 the prevalence of a cold moist state of the 

 atmosphere, especially in England, the voices 

 of singers become lower by two or three notes, 

 and regain their usual pitch when the air be- 

 comes dry.* In thus tracing out the analogy be- 

 tween the laws of stretched cords and those of 

 the vocal ligaments, it is not intended that those 

 ligaments should be considered as stringed 

 instruments, but only that this analogy is 

 accurate as far as relates to the velocity with 

 which an impulse is propagated along them. 

 Dodart f supposed the tension of the vocal 

 cords to be merely subservient to an altera- 

 tion in the size of the aperture of the glottis, 

 and that the difference of T 1 T of a fibre of silk, 

 or g-i;,: of a hair in the dimensions of that 

 aperture, was sufficient to alter the pitch of 

 the voice ; but this has been so completely 

 refuted by more recent physiologists, and is 

 so directly at variance with acoustic prin- 

 ciples, that we need not give illustrations of 

 its fallacy. M. Savart considered that the 

 action of the air in its passage through 

 the ventricles of the larynx, between the su- 

 perior and inferior ligaments, is really the 

 source of sound, and analogous to the me- 

 chanism of the bird-call or dog-whistle. 

 There is certainly a great resemblance in the 

 structure of that instrument to the space 

 above mentioned in many of the higher ani- 

 mals, which might easily have led to this in- 

 genious hypothesis ; but, as we find neither 

 superior ligaments nor ventricles of Morgagni 

 in many of the order Ruminantia, in which 

 the voice is very sonorous, this theory (as 

 Miiller remarks) is untenable. 



We next come to the consideration of the 

 alleged analogy between the action of the 

 vocal ligaments and that of the reeds of mu- 

 sical instruments. This opinion is maintained 

 by MM. Biot, Cagniard De la Tour, Majendie, 

 Malgaiune, Miiller, and several other distin- 

 guished scientific men. It is opposed prin- 

 cipally by M. Savart, who observes that the 

 essential principle of the action of reeds con- 

 sists in the periodical opening and shutting of 

 the orifice through which the stream of air 

 passes, but that this is wanting in the glottis ; 

 and that were the latter a reed, the edges of 

 the thyro-arytenoid ligaments which form the 

 sides of the chink would be alternately forced 

 asunder by the column of air in the larynx, and 

 brought together by their tension ; whereas 

 he found by experiment that air blown through 



* When Grassini came to this country, owing to 

 the change from the air of Italy to that of England, 

 her voice became one octave lower: after singing 

 for two or three seasons, her natural voice returned, 

 but it had lost its attractions with the low tones 

 which had obtained her the greatest applause. 

 Transactions London Medical Society, New Series, 

 vol. i. 18-lti ; art. Aphonia, p. 36. 



t Mem. de 1'Acad. des Sciences, 1700. 1701. 



j See fig. 81)0. 



the glottis produced sound although its edges 

 were from one-sixth to one-fourth of an inch 

 asunder. M. Savart has however clearly mis- 

 taken the circumstance wherein the essential 

 principle of reeds consists, since those of the 

 clarionet, bassoon, hautboy, &c. do not en- 

 tirely close the apertures through which the 

 breath passes ; and this is likewise the case 

 with the natural reed formed by the lips of 

 players on the flute and horn. There is in 

 all probability a double action of the vocal 

 cords in the production of sound ; the one 

 being a vibratory motion throughout their 

 length similar to that of a musical string, and 

 the other an oscillation like that of a reed, 

 forming a partial opening and closing of the 

 glottis. The author is led to adopt this view 

 of the functions of the vocal orgavis from 

 considering that every circumstance which 

 he has established in his previous investiga- 

 tion of their action when treated as cords, is 

 perfectly consistent with the hypothesis of 

 their vibrating like the tongues of reeds ; for 

 let us now suppose them to be simply mem- 

 branous tongues. In this case the axis of 

 motion is the edge of the ligament attached 

 to the thyro-arytunoid muscle ; the vibrations 

 take place in a plane perpendicular to the 

 axis of that muscle, and the length of the 

 tongue is the breadth of the ligament. The 

 author has observed in repeated experiments 

 on the larynx after death, that the chink of 

 the glottis was partially opened and closed in 

 the production of sound, and Miiller found 

 that by decreasing the breadth of the liga- 

 ment he rendered the note more acute ; but 

 as this breadth is so small, being in its ordi- 

 narv state in an adult generally less than one- 

 tenth of an inch, it is extremely difficult to 

 measure the variations corresponding with 

 different notes ; and the author cannot learn 

 that any one has yet succeeded in determin- 

 ing these van ing lengths with sufficient ac- 

 curacy to form data for the application of the 

 mathematical formulae of elastic vibrating 

 tongues.* We know that the number of vi- 

 brations made by the same tongue in a given 

 time varies inversely as the square of its 

 length. If, therefore, a tongue whose length 

 is only '1 inch give any note, the length ne- 

 cessary to produce the octave will be '07 

 inch, that is, the variation will be only "03 

 inch ; we see then how minute must be the 

 changes answering to the intermediate notes, 

 and consequently how much more difficult it 

 is to determine them in the vocal ligament 

 when considered as a tongue than as a 

 stretched membrane or cord. It is moreover 

 observable that the extension and relaxation 



* The formula of Giordano lliccati is 



= L* V G 



where X is the number of vibrations, D the thickness, 

 and L the length of the tongue or rod, K its rigidity, 

 G its specific gravity, g the space through which a 

 body falls by gravity ill 1", and n a number 'constant 

 for each mode of vibration, depending on the num- 

 ber of nodes. 



