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PROF. OSBORNE REYNOLDS ON 



6. There is another way of looking at the problem, 

 which is the first that presented itself to the author. 



Suppose a parallel stream flowing along a straight tube 

 with a velocity u, and take a for the velocity with which 

 sound would travel in the same gas at rest, the velocity 

 with which a wave of sound or any disturbance would 



move along the tube in an opposite direction to the gas 

 would be a — u. If then a = u, no disturbance could flow 

 back along the tube against the motion of the gas ; so 



