OF THE HUMAN VOICE. 
565 
vibrations must in this case be the same for the same note as when we suppose the 
ligaments to obey the laws of cords, the axis of vibration or the breadth of the liga- 
ment must be duly diminished, which may be brought about by the rotation of the 
thyro-arytenoid muscle on its axis. 
Having thus considered how the glottis may act in the falsetto range, let us now 
examine in what way the vocal tube contributes to its formation. We have seen that 
this tube gradually shortens during the ascent of the primary register, suddenly falls 
to its original length when the falsetto commences, and again diminishes during the 
secondary register. Nowit appears from Savart’s experiments that, notwithstanding 
the shortness of this tube, the wave length of a column of air vibrating within it is the 
same as that of a rigid pipe of much greater length, and we have therefore strong 
grounds for believing that the notes of the primary register are reinforced in conse- 
quence of the vibrations of the glottis being always in unison with the fundamental 
pitch of the walls of the tube ; hence in the falsetto, when the vocal apparatus has 
resumed its original condition, there will be less reinforcement of the sound, since the 
parietes of the vocal pipe are no longer in unison with the glottis, but give its grave 
octaves. We have found, by numerous experiments, that a flexible disc will vibrate to 
almost any pitch, but will reinforce the sound in a trifling degree only, unless the pitch 
be in unison with its fundamental note ; and on the same principle we may suppose 
the intensity of the notes in the second register to be diminished, and their quality to 
be modified by the forced vibration of the walls of the tube, whilst in the primary, 
all things concur in augmenting the effects produced by the glottis. Muller agrees 
with Lehfeldt in opinion, that the falsetto notes are produced by the vibrations of 
the inner portion of the borders of the vocal ligaments, and the variation of the pitch 
by their tension ; and, although he does not mention by what mechanism this is 
effected, he seems to attribute it chiefly to the agency of the thyro-arytenoid muscles. 
The author’s explanation is in many points coincident with that of Muller, but he 
has taken into account one or two circumstances which appear to have escaped Mul- 
ler’s attention. The natural key or pitch of the vocal organs may be found by sound- 
ing the voice, without either elevating or depressing the larynx. The grave octave of 
that note will be the fundamental sound of the vocal ligaments vibrating in their most 
relaxed state, with the glottis entirely open. Any tones of a graver pitch, produced 
by an unusually relaxed state of the vocal cords, lose both their quality and intensity, 
and cannot be included in the compass natural to the voice. According to the pre- 
ceding principles, the pitch of the voice being usually an octave, or a fifth graver than 
the length of a column of air within the vocal pipe, we see the cause why a falsetto 
quality of sound cannot be obtained except during the production of acute tones. In 
many persons the speaking pitch is an entire octave graver than corresponds to the 
length of a tube, which would enable a column of air to produce the same sound ; and 
in such persons the falsetto can seldom be effected. In consequence of the pitch of the 
vocal organs thus occupying a middle or central position between the acute and grave 
