MOTION OF AIR IN LONG PIPES. 253 



The height due to the resistance at the orifice 



= ftl 2~i 

 The height due to the velocity 



*" 



= *9' 



Therefore, the total height 



Also, the total height, from (1) and (6) of Art. 129, 



. (2) 



Therefore, equating (1) and (2), and solving for Q, we 

 have 



= * 



which, from (9) of Art. 129, 



(1 + I 



where /3 = , - 1, and 0, = - 1 (Art. 96). 



Sen. In Paris, Berlin, London, and other cities, it has 

 been found cheaper to transmit messages in pneumatic 



