PROPAGATION OF SOUND. 



a series of condensations and rare- 

 factions follow each other in rapid 

 succession, and are propagated to 

 our ear; the last particle of air 

 close to the ear vibrates to and fro, 

 exactly like the particles close to 

 the prong of the fork, only a little 

 later. 



The motion of the particles of air 

 luring the propagation of sound 

 may be further demonstrated with 

 ,-he help of fig 210. A narrow slit 

 '.? s is cut out of a piece of stiff paper 

 'B iu the figure), which is either 

 )lack, or at any rate of a dark 



331 



FIG. 210. 



