ADIABATIC CHANGES OF MOIST AIR NEUHOFF 



quantity of moisture needed for saturation are introduced for the 

 corresponding values of pressure and temperature. The slight 

 difference between the pressure lines in the two stages does not 

 come into consideration. 



The gram-lines are represented by dashes for each 5 grams. 

 The use of the diagram is now intelligible after the explanations of 

 the preceding section. 



This diagram of adiabats possesses not only the advantage of 

 being easily reproduceable but also the advantage that adiabatic 

 changes of condition can be graphically compared directly with those 

 that are produced by change of either temperature or altitude alone. 



A special diagram for the hail stage which was given by Hertz 

 can be omitted entirely by introducing the altitudes in place of 

 the pressures. In the equation for the isotherm of o° C. of the hail 

 stage, the final pressure varies with the total quantity of moisture 

 £. If now we choose as coordinate log p' and £ then the adiabats 

 for different values of £ can be drawn as 

 straight lines because of their short length, 

 and of the relatively small quantity of water 

 coming into consideration and can all be con- 

 sidered as running parallel to each other. 

 These lines all begin together at the saturation 

 curve of o° C. or the dotted line in fig. 9 

 which indicates that the quantity of moisture 

 needed for saturation at o° C. must be sub- 

 tracted from the total quantity of moisture 

 £ that is present ; the remainder is the quan- 

 tity of water present. 



If now we introduce the altitudes in place of the pressures cor- 

 responding to the formula 



7000m ™°">°& 

 6000 



5000 — 



IOOO 

 O 



700 

 760 



FIG. 9. HAIL STAGE 



h = 18432 log- 



for the constant temperature o° C. then the altitude lines will run 

 parallel to the pressure lines and at equal distances from each other 

 for equal intervals of pressure, and we obtain the following simple 

 result : 



The isothermal change of altitude at o° C. is proportional to the 

 quantity of water present, 

 and we find empirically the formula 



h = 27 y, 



