142 



WAVE IMPACT ON 



presence of air, impinge on the end of the stationary column 

 with velocity v. At the instant of impact let its length be 

 I feet. Impact is followed by a rise in pressure at the junction 

 of the columns, and a wave of compression (24 v Ibs. per 

 square inch above normal) is propagated in opposite directions 

 from this point. The wave traversing the impinging column 

 reaches its free end after a time, I -f V p seconds. At the same 

 time the wave traversing the stationary column has also 

 travelled a distance of I feet, and at this instant, that portion 

 of the joint column nearest the open end of the pipe, and of a 



length 21 is under an identical state of pressure and velocity, 

 this pressure being 24 v Ibs. per square inch above normal 

 and the velocity v -f 2 towards the closed end. At the open 

 end the stressed layers rebound outwards, the pressure falls to 

 that obtaining at this point, i.e. toh-r 62'4 Ibs. per square foot, 

 or to zero if the face pressure has been removed, and a wave 

 of normal statical pressure and of zero velocity is propagated 

 along the pipe in the rear of the pressure wave. The state of 

 affairs after a further short interval of time 8t is then as repre- 

 sented in Fig. 4. 



When the front of the pressure wave reaches the closed 



