REED-PIPES. 389 



repeated as long as air is forced into the box. If the 

 tongue is simply bent down with the finger and let go, 

 it will vibrate to and fro, but no sound, or only a faint 

 trace of a sound, will be heard; hence the sound is 

 solely due to the regular periodic interruption of the 

 current of air, in the same way as in the siren. But 

 the pitch of the note does not depend, as in the case 

 of more flexible reeds, upon the length of the vibrating 

 column of air in front of the reed; it depends, in the 

 case of metallic reeds, upon their length, thickness, 

 and shape ; for the velocity with which the vibrations 

 take place depends upon these circumstances precisely 

 as in the case of a vibrating rod or a tuning-fork : a 

 tongue of a definite form will perform a definite number 

 of vibrations in a given time. The whole series of 

 harmonic overtones, especially those which are odd 

 numbered, are contained in great strength in the sound 

 produced by such a metallic reed, but it is not possible, 

 as was the case with the various contrivances hitherto 

 described, to produce overtones by means of a metal 

 reed without producing the fundamental note at the 

 same time. Mathematical reasoning alone can show how 

 it is possible that a note which is produced by a series 

 of single impulses may contain overtones besides the 

 fundamental tone. 



Wind instruments with soft vibrating parts are 

 usually called mouth instruments ; such are a common 

 whistle, a flageolet, &c. Instruments with metal 

 tongues, such as those just described, are termed reed 

 instruments. The simplest form of a ' reed/ or metal 

 tongue, is seen in the Jew's harp; it is also applied in 

 the oboe, the bassoon, the children's trumpet, &c. 



