LECT. XVIII. QUALITIES OF THE VOICE. 343 



3d. Sounds produced when the vocal cords are but 

 slightly stretched, differ in their intensity, but not in their 

 tone, according as the glottis is more or less contracted ; 

 when the vocal cords touch, the sound is as strong and as 

 full as it can possibly be. 



4th. If the force of the current of the air be increased, 

 the tension of the vocal cords remaining equal, the sound 

 rises a fifth, or even more. 



5th. The parts of the larynx, and all the rest of the tube 

 situated above the vocal cords, seem to act in the appa- 

 ratus of the human voice, like tubes adjusted upon the 

 reeds ; and we remark in the whole, that possibility of 

 compensation which is always desired in musical instru- 

 ments, and by means of which the tones remain the same, 

 notwithstanding great differences in the intensity of the 

 cause of sound. 



Compensation. Weber discovered a method of con- 

 structing a compensating reed-tube, in such a way that the 

 sound has always the same purity for the piano as for the 

 forte, notwithstanding the great changes in the force of the 

 blast. The note of a reed-pipe may be raised by increasing 

 the force of the current of air, and may be lowered by 

 means of the tongue. Hence, we may conceive the pos- 

 sibility of compensating these effects by means of a certain 

 length of the column of air. 



Qualities of the Voice. As for the force or strength of the 

 voice, it evidently depends in part on the aptitude of the 

 vocal cords for vibration ; and, in part, on the fitness of 

 the membranes and cartilages of the larynx, as well as 

 of the pectoral, nasal, and buccal cavities, for resonance. 

 The peculiar timbre of voice, which each person possesses, 

 and its imperfections, evidently depend on the differences 

 of these resonances, or on different aptitudes for vibration 

 which the parts of the organ possesses. The intensity of 



