MOVEMENTS OF ATMOSPHERE GULDBERG AND MOHN 



129 



Altitude. English feet. 



Observed f/f 



Computed f/f 



Computed f/f 



28000 



0.04 

 0.04 



§ 5. Expansion and contraction of the air 



The pressure and temperature of a mass of air that experiences 

 any transformations whatsoever depend on the quantity of heat 

 which it has gained or lost. We will first consider the case in which 

 the air experiences a series of transformations without gaining or 

 losing heat at any moment. The equation between the pressure 

 and the volume represents a line that has been called the adiabatic 

 line. 



In the study of meteorology it is also necessary to find the equa- 

 tion between the pressure and the temperature. It is necessary to 

 distinguish between several cases. The air can be dry or moist, 

 and the aqueous vapor water can remain without condensation or 

 it can pass into the liquid state or into the solid state. 



Representing by U the internal energy of a mixture; by V its 

 volume and by A the mechanical equivalent of heat, we have 



0=d U + A pdV (1) 



(1) Dry air. 



Applying equation (1) to dry air we shall find from the mechan- 

 ical theory of heat 



p /273 + r 

 p = \273 +T 0/ 



eg 



m = 



A a 



(2) 

 (3) 



where c represents the specific heat of dry air at constant pres- 

 sure, whence we have, 



m = 3.441 



(2) Moist air without condensation. 



Supposing Ave have one kilogram of dry air and x kilograms of 

 aqueous vapor we shall find 



1 + 2.023.* N 



m = 3.441 



1 + e x 



(4) 



