NOTES PRODUCED BY TUBES. 387 



and numerous other overtones, all odd numbered, 

 may be obtained by means of a very long but narrow 

 (1 or l cm -5) tube. 



It is thus that notes are produced in all wind instru- 

 ments, except the flute. In brass instruments the lips 

 form the soft vibrating parts; in wood instruments, for 

 example in the clarionet, the air is forced through 'reeds/ 

 formed of two thin elastic plates of wood or cane. The 

 difference in pitch of the various notes produced by 

 such instruments is obtained by various modes. The 

 tube being in most of them, especially in brass instru- 

 ments, very long, it is possible, by altering the position 

 of the lips and the manner of blowing, to produce a whole 

 series of different overtones. The length of the tube may 

 also be varied by different means. Thus in the tromb- 

 one one part of the tube slides within the other ; the 

 performer can thus alter the length of the tube at will, 

 and therefore produce higher or lower sounds. In the 

 cornet- a-piston the tube forms several convolutions, and 

 by means of pistons placed at different distances the 

 communication with other parts of the tube may be 

 cut off, and thus the length of the column of air altered 

 while the instrument is played. In other cases there 

 are holes at different distances in the side of the in- 

 strument, which may be closed or opened. In such an 

 instrument the whole length of the column of air 

 within vibrates only when all lateral holes are closed. 

 When one of the holes is opened, a ventral segment is 

 produced in the corresponding layer of air, which modi- 

 fies the distribution of nodes and ventral segments 

 throughout the interior, and thus alters the note. 



The soft elastic plates of wood or cane, or ' reeds,' 



c c 2 



