HOW THE VARIOUS PITCHES ARE PRODUCED 297 



fall in pitch. In the oboe (Fig. 189, 2), the air column is set 



into motion by means of two reeds placed in the mouthpiece 



of the tube. The flute (Fig. 189, 3) is the only one of all the 



instruments in which 



the air is set into mo- ^SSS^^ma^^S^gmi^ 



tion by direct blowing 



from the mouth, as 



is done, for instance, 



when we blow into a 



bottle or tube. 



In organ pipes air 



FlG. 189. i, clarinet; 2, oboe; 3, flute. 



is blown across the 



sharp edge at the opening of a narrow tube ; the thin, sharp 

 edge is thrown into vibration, and these vibrations communi- 

 cate themselves to the column of air within the organ pipe. 



For different 

 pitches, pipes of 

 different lengths 

 are used : for very 

 low pitches long, 

 closed pipes are 

 used; for very 

 high pitches 

 short, open pipes 

 are used. The 

 mechanism of the 

 organ is such that 

 pressing a key 

 allows the air to 



FlG. 190. I, horn ; 2, trumpet ; 3, trombone. 



rush into the communicating pipe and a sound is produced 

 characteristic of the length of the pipe. 



In the brass wind instruments such as horn, trombone, and 

 trumpet, the lips of the player vibrate and excite the air 



