PIPES AND BESONATOBS 283 



The reed-stops of an organ fall in pitch as the temperature 

 rises, owing to the diminished elasticity of the metal tongues ; 

 this is the opposite of what happens with regard to the flute- 

 pipes ( 62). A reed-pipe is tuned by a contrivance which 

 alters the effective length of the vibrating tongue. 



It should be mentioned that there is another class of 

 instruments in which the " reed " has a much smaller elasticity 

 and is mainly controlled by the reaction of the resonant 

 chamber, its own natural frequency being relatively low. The 

 reed is then of the "out-beating type," the aperture being 

 widest when the reed swings outwards, i.e. with the wind. 

 The human larynx comes essentially under this class. 



