NATURE OF SOUND. 



271 



imagines five boys placed in a row as shown in Fig. 213. " I sud- 



denly push A ; A pushes B and regains his upright position ; B 



pushes C ', G pushes 



D; D pushes E ; 



each boy after the 



transmission of the 



push, becoming him- 



self erect. E, hav- 



ing nobody in front, 



is thrown forward. 



Had he been stand- 



ing on the edge of 



a precipice he would 



have fallen over; had 



he stood in contact 



FIG 213. 



with a window, he would have broken the glass ; had he been close 

 to a drum-head, he would have shaken the drum. We could thus 

 transmit a push through a row of a hundred boys, each particular 

 boy, however, only swaying to and fro. Thus also we send sound 

 through the air, and shake the drum of a distant ear, while each 

 particular particle of the air concerned in the transmission of the 

 pulse makes only a small oscillation." 



423. Sound Waves. The layers of air are crowded 

 more closely together by each outward vibration of the 



FIG. 214. 



sounding body; a condensation of the air is thus produced 

 As the sonorous body vibrates in the opposite direction, 



