the Flow of Ganes. 195 



It thus appears that as long as p falls, the section conti- 

 nuously diminishes to a minimum value when p=f527p lt and 

 then increases again . Substituting this value of p in equa- 

 tion (3), 



u=x / ^m^T m 



V (y+l) p0 T > W 



. / 2 Wo /M^ ..... (10) 



(y+i)fW Vp/ u } 



Hence by equation (6), 



"=V : 



(12) 



7£Pqt 



fyoTo ' 



which is the velocity of sound in the gas at the absolute 

 temperature r. 



It thus appears that the velocity of gas at the point of 

 minimum area of a stream along which the pressure falls con- 

 tinuously is equal to the velocity of sound in the gas at that 

 point. 



8. From the equation of flow (5) it appears that for every 

 value of A other than its minimum value, there are two pos- 

 sible values of the pressure which satisfy the equation, one 

 being greater and the other less than 



It therefore appears that in a channel having two equal 

 minima values of section A and C ; as in fig, 6, the flow from 



A to B may take place in either of two ways when the velo- 

 city is such that the pressure at A and B is *527p l9 i. e. the 

 pressure may either be a maximum or a minimum at C. In 

 this respect gas differs entirely from a liquid, with which the 

 pressure can only be a maximum at C. 



