409 



of either the whole or part of the tendons, but by the successive 

 explosions which they allow. 



Pressure of the Air. 



Until now, in our remarks on the manner in which the voice is 

 formed, we have only referred to the rigidity of the glottis, a rigidity 

 necessary to accomplish the 1056 vibrations in one second*, which 

 form the do of the chest-voice, and to accomplish the double number 



4 



which produces the octave above in the head-voice. There is, notwith- 

 standing, another indispensable element for the production of vocal 

 sounds, the pressure of the air. Pressure, as is well known, developes 

 an elastic force in this agent, in a degree inverse to the volume 

 which it occupies. It is by means of this power that the intensity 

 of the sounds is obtained. The intensity of the sound can only de- 

 pend on the quantity of air which goes to each sharp explosion. I 

 say sharp explosion, as an express condition : the glottis should 

 close itself perfectly after every vibration ; for if the air found a con- 

 stant passage, as in the notes of falsetto, then the greatest move- 

 ments of the glottis, and the greatest waste of air, would produce 

 precisely the weakest notes. To reject this theory would be to 

 attribute the intensity of the sound to the extent of the vibrations 

 accomplished by the lips of the glottis, and to suppose that these 

 lips, each taken separately, possess the power of producing sounds, 

 suppositions quite contrary to the facts. 



The elastic force of the air arises not only from the compression 

 of the lungs, but also from the contractions of the trachea, which 

 adjusts its calibre to the different dimensions of the glottis. It is 

 by means of this force that the air conquers the continually-in- 

 creasing obstacle presented by the lips of the glottis when they 

 produce sounds more and more intense. 



Thus the problem of the elevation of the voice, always complicated 

 with that of its intensity, in order to be complete, ought to show 

 the connexion which exists between the tension of the lips of the 

 glottis, the pressure of the air, and the number and intensity of the 

 explosions obtained. As a consequence, we may state that the 

 greater pressure of air necessary to produce the greater intensity, 



* Pouillet, Physique, Sixth Edition, vol. ii. page 77. 



