COMPOSITION OF SOUND WAVES. 301 



of the mouth. The puffs are due to the fact that the air 

 current from i strikes upon the bevelled lip a and breaks 

 into a flutter. The puffing sound thus produced consists 

 of a confused mixture of many faint sounds. The air 

 column of the pipe can resound to only one of these tones. 

 The resonance of the air column brought about in this 

 way constitutes the tone of the pipe. 



(a.) We see, from the above, that it makes little difference how 

 the pulses of air are produced. A vibrating tuning-fork held at 

 the mouth of a pipe of the same pitch is enough to make the pipe 

 sound forth its tone. The production of the tone is strictly analo- 

 gous to the phenomena mentioned in 450. 



47O. Reed Pipes. A simple reed pipe may be 

 made by cutting a piece of wheat straw eight inches 

 (20 cm.} long so as to have a knot at one end. At r, 

 about an inch from the knot, cut inward about a quarter of 

 the straw's diameter ; turn the knife-blade flat and draw it 

 toward the knot. The strip rr' thus raised is a reed ; the 

 straw itself is a reed pipe. When the reed is placed in the 

 mouth, the lips firmly closed around the straw between 



FIG. 236. 



r and s and the breath driven through the apparatus, the 

 reed vibrates and thus produces vibrations in the air col- 

 umn of the wheaten pipe. Notice the pitch of the musical 

 sound thus produced. Cut off two inches from the end 

 of the pipe at s. Blow through the pipe as before and 

 notice that the pitch is raised. Cut off, now, two inches 

 more, and upon sounding the pipe the pitch will be found 

 to be still higher. We thus see that the pipe and not the 

 reed determines the pitch. In each of these three cases 



