DIFFERENT KINDS OF SOUNDS 103 



affect loudness, and this may depend upon the size of 

 the vibrating body or the energy with which it moves. 

 If the ear is at a greater distance from the source of 

 the waves, the sound is less loud ; the kind of medium 

 through which the waves travel and the direction of the 

 wind both have an effect upon the loudness of sounds. 

 The size of the receiver is also an important factor; 

 speaking tubes and ear trumpets (Fig. 78) serve to make 

 sounds louder by collecting many waves. __ < b 

 On a similar principle is the holding of 

 the hand to the ear, as the aged often do. 



118. Pitch. The pitch of a tone is 

 commonly described by the words high 

 or low, shrill or deep. We say that the 

 pitch of a woman's voice is higher than 

 a man's, or that a certain bell has a 

 lower tone than another ; and we know 

 that whatever the pitch of a tone, it is 

 quite different from loudness. 



We have learned that sound waves 

 vary greatly in length, some being long 

 and others short ; the vibrations of a simple pure tone, 

 however, all have the same wave length. Now since all 

 sound waves travel through the air at the same speed, 

 the shorter the wave length, the more vibrations will pass 

 a given point in a second. The pitch of a tone depends 

 upon how many vibrations reach the ear in a second; 

 the greater the number, the higher the pitch. Of course 

 the length of a wave depends upon the vibrations in the 

 body that caused it ; so we may get some idea of the 



