VELOCITY OF EFFLUX OF AIR. 245 



If the pressure differs from the mean pressure, or if the 

 height of the barometer is not 29.92 inches, but b, (2) be- 

 comes 



0.08076 b 



w = 



1 + at 29.92 



0.002699 b 

 1 + at ' 



(3) 



If we express the elastic force or pressure of the air by the 

 pressure p upon each square inch, then we have 



29^92 = 147' 

 which in (3) gives 



0. 005494 p ,.. 



w = - j^y (4) 



1 + at 



p _ (1 + Q 144 

 w ~ 0.005494 



where p is the pressure on each square foot. 

 Substituting this value in (1), we have 



v = 161.9 \ / 2g (1 + /) log^- (6) 



V Pz 



If 5 is the height of the barometer and h that of the 

 manometer (Art. 46), we have 



which in (6) gives 



v = 1299 \fil + at) log (^-p), (7) 



where v is the velocity in feet, b the height of the barometer 

 in the exterior air, h the height of the manometer for the 

 air inside the vessel, t the temperature of the latter in 

 degrees centigrade, and = 0.003665, the coefficient of 

 expansion of air (Art. 53). 



