MOVEMENTS OF ATMOSPHERE — -GULDBERG AND MOHN I 3 7 



(4) The air is saturated below 0°. • 



By substituting in formula (10) 



To = o, t - - 20°, /„ = 4.6 mm , / = 0.93 mm , p - 476.5 r 

 f = 0.0125, < = 0.00607 



we shall find 



and 



10.08 

 log (/>-/) =2.4613+ ^ 



/> = 312.5 mm , x = 0.00186 



Formula (14) gives h — 3239 meters. 



If we had used formula (17) we should have given to m the value 



5-36- 



Resulting Values 



§6. Causes of the movement of the air 



When the air is in equilibrium, the active forces are the attraction 

 of the earth and the centrifugal force produced by the rotation of 

 the earth. These two forces have a resultant which we call the 

 weight, which varies with the latitude and the altitude. In meteor- 

 ology we consider only the strata of air at a slight elevation and we 

 generally consider the weight constant and express its value for 

 the unit of mass by g. 



In an atmosphere in equilibrium the weight is normal to the level 

 surfaces, and the surface of the earth is itself a level surface. At 

 the same time the density of the air and consequently its tempera- 

 ture vary only from one level surface to the other; we see then that 

 in the state of equilibrium the level surfaces are surfaces of equal 

 pressure and isothermal surfaces. We can consider the earth as ap- 

 proximately spherical, and the level surfaces as spheres concentric 

 with the earth. Then the temperature can vary only with the 



