102 SOUND 



in every direction will be full of sound waves (see 

 Fig. 71). Others will follow these so long as the body 

 vibrates. 



Now when the vibration of the body is simple, every 

 sound wave will be just like every other in length and 

 form. The effect of these regular waves upon the ear is 

 a pleasing sound called a tone. A tone may then be 

 denned as the effect upon the ear of a regular succession 

 of like waves. 



115. Noises. Almost no body does really vibrate in 

 this regular manner, however. While a mass may move 

 as a whole, many of its parts vibrate at a rate of their 

 own. Thus, though each single part causes vibrations 

 that are regular, many different sorts of sound waves 

 may be caused by the different vibrating parts at the 

 same time some long and some short. The effect 

 of these many different kinds of waves striking the ear 

 together is a sound which we may call a noise. Note 

 that the difference between tones and noises is not 

 great. Almost no tones are strictly pure, but are mixed 

 with a few weak waves that are not great enough to 

 affect the sound seriously. A noise may be considered 

 as simply a mixture of many tones. 



116. Differences in Tones. Tones may differ from 

 each other in three ways in loudness, pitch, and quality. 

 Since noises are merely mixtures of many tones, the same 

 fact is true of all sounds. 



117. Loudness. The loudness of a sound means the 

 greatness of the sensation. This may depend upon sev- 

 eral things. The greatness of the original vibration may 



