300 



COMPOSITION OF SOUND WAVES. 



Sonorous tubes are called mouth pipes or reed pipes, 

 according to the way in which the column of air is made 

 to vibrate. 



467. Stopped Pipes. A sonorous tube may have 

 one end stopped or both ends open. In either case, the 

 tones are due to waves of condensation and rarefaction 

 transmitted through the length of the tube. In a stopped 

 pipe, the air particles at the closed end have no oppor- 

 tunity for vibration ; this end of the tube is, therefore, a 

 node. The mouth of the tube affords opportunity for the 

 greatest amplitude. The length of such a pipe is one- 

 fourth the wave length of its fundamental tone. 



468. Open Pipes. In an open 

 pipe, the ends afford opportunity for 

 the greatest amplitude; the node 

 will fall at the middle. The air col- 

 umn will now equal one-half the wave 

 length; the tone will be an octave 

 higher than that produced by a 

 stopped pipe of the same length. 



469. Organ Pipes. The organ 

 pipe affords the best illustration of 

 mouth pipes. Fig. 235 represents the 

 most common kind of organ pipe, 

 which may be of wood or metal, rect- 

 angular or cylindrical. The air cur- 

 rent from the bellows enters through P, 

 passes into a small chamber, emerges 

 through the narrow slit i, and escapes 

 in puffs between a and #, the two lips 



