VIBRATION OF AIR IN TUBES. 385 



columns of air which have been hitherto considered solely 

 as boundaries of the vibrating mass of air ; they do not 

 take any part in the production of the notes, and do 

 not vibrate at all, or are only agitated to a small extent 

 by the violent motion of the air within. If the finger 

 be placed upon a large sounding organ -pipe, its vibration 

 will be felt, but the pipe may be firmly held without 

 producing any modification of the note given out, while, 

 on the other hand, solid bodies which produce sound by 



B 



FIG. 232. 



their own vibrations are immediately silenced when 

 touched. 



An essentially different mode of producing vibrations 

 of columns of air is that by means of solid but flexible 

 bodies which are made to vibrate at the same time as 

 the air. If a current of air is blown between two flexible 

 bodies which are in moderately firm contact with one 

 another, as for instance between the closed lips, or 

 between the fingers of the hand placed flat upon the 



c c 





