DIFFERENT KINDS OF SOUNDS 



105 





besides the chief or fundamental tone. These weaker 

 ones are called overtones; their effect is not great 

 enough to make the sound unpleasant or to alter its 

 pitch, but still their presence in the sound can be noticed 

 by the ear. It is the effect of these overtones which 

 gives to a sound its quality. And since the overtones 

 may differ in different instruments, it is plain that one 

 tone may be like another in pitch and loudness and still 

 have a different quality. 



122. Musical Sounds. The sounds in music are usu- 

 ally tones that are nearly pure. They are made by dif- 

 ferent bodies in a state of nearly simple vibration; 

 strings, air columns, metal plates and tubes, sheets of 

 wood and skins, wires, and other devices are used. 

 Sometimes the tones are made singly and often in 

 groups, several being sounded at once. In such cases the 

 tones are generally of such pitch that their waves cause 

 a regular movement upon the 



'ear, making a pleasing sound 

 called a chord. A careless ar- 

 rangement of tones may pro- 

 duce a jarring sound called a 

 discord. A succession of chords 

 is called harmony. 



123. The Voice. The voice 

 is caused by the vibration of the 

 vocal cords. These are narrow 

 strips or folds of membrane (aa) 



on either side of an opening, b (Fig. 79), leading to the 

 lungs. Air passing through 6 causes the cords to vibrate. 



FIG. 79 



