MECHANICAL EQUIVALENT OF PRESSURE MARGULES 



521 



Heat abstracted 



Temperature . . . r« x' 

 Pressure p. 



Pressure . . higher P x 

 Temperature .... 7" 



Heat added 



(i) At the lower level the air flows from the higher pressure P v 

 to the lower P 2 and at the same time receives an increase of heat. 

 For the sake of the analysis we assume that the adiabatic change 

 of condition prevails in the passage from P t to P 2 and that there 

 has therefore been a cooling from T l to T' 2 but that then an 

 addition of heat under the pressure P 2 suddenly takes place, pro- 

 ducing a rise from T 2 to T 2 . 



(2) An adiabatic ascent at the location of lower pressure P 2 and 

 above it a vertical equilibrium prevails or a condition inappreciably 

 different therefrom, so that the pressure falls to p 2 and the tem- 

 perature falls to t 2 . 



(3) A horizontal movement along the upper level from p 2 to p 1 

 together with cooling by radiation or conduction; this process will 

 for convenience in analysis be decomposed into adiabatic change 

 of condition from p 2 z 2 to p l r 2 then abstraction of heat and cooling 

 from z 2 to t x under the pressure p x to such an extent that, 



(4) When the air descends adiabatically it arrives at the original 

 temperature T x and the pressure P v Here also we assume that the 

 equilibrium is maintained between gravity and the vertical diminu- 

 tion of pressure. 



In both the two vertical portions of this path the change of tem- 

 perature with altitude is at the adiabatic rate — g/C p per unit 

 of length (for dry air C p = 987 m 2 sec' 2 Centigrade" 1 . On any given 

 level the difference of temperature between the two vertical columns 

 is constant. The difference of pressure will diminish with the 

 altitude and become zero at a certain altitude and above that it 

 will increase but with the opposite sign. 



