328 



PROPAGATION OF SOUND. 



preceding one has completed the twelfth part of its cir 

 cular motion ; the portion of its path which each particL 

 has already described at the instant to which each figur< 

 corresponds is shown by the dotted curves. A represent; 

 the surface after the particle has moved through one 

 twelfth of a circle ; B represents the surface after ( 

 has moved through two-twelfths and the particle 

 through one-twelfth of a circle. In C the particle 



FIG. 208. 



has passed through three-twelfths or one-fourth of tl 

 circle ; in D it has described a semi-circle, and in 

 it has returned to its original place. If only a sino; 

 wave passes over the surface, each particle comes 

 rest after describing a circle. F represents the surfai 

 at the moment when the wave has moved onwa 

 through half its whole length further than it was in , 

 and if there are successive waves, each particle 

 its motion, as shown in G. 



