456 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 51 



Since moreover £ — y = x is the quantity of vapor that is tem- 

 porarily present, therefore for the pseudo-adiabat we have 



c + xc 

 Wj = AR ° r m = ^ ^ 



that is to say, m is now to be considered as a function of the 

 quantity of moisture x that is actually present and that can be 

 assumed as constant for small intervals and is to be taken from 

 table 4, column 5 or column 6. 



Therefore whereas for the adiabat the value m = / (f) = / (x^ was a 

 function of the mixing ratio which remained constant during the 

 whole process, now, in the computation of the pseudo-adiabat, m 

 is to be taken as variable during the process of change of con- 

 dition; but in the computation of every new condition developing 

 from the previous one (m) must be taken as a constant and con- 



T 

 sidered as a factor of log - and in fact equal to that value which 



corresponds to the average quantity of vapor x whose numerical 

 value as a function of the temperature and the approximate pres- 

 sure we take from table 3. Hence we see at once that which the 

 practical use of the adiabatic equation (9) has already demonstrated 

 that by reason of the separation of the precipitation the quantity 

 of moisture (£) originally mixed with the air gives a smaller value 



T 



for m than is shown in table 4. But still m as a factor of log — 



-* 2 



remains constant within the limits of the change of condition to 

 be computed. It would be an error to introduce for 7\ a value 

 m x and for T 2 a value ra 2 since in this case the equation would 

 lose its applicability. 



If the moist air is cooled below o° C. then the precipitation 

 assumes the form of snow. Then, besides the latent heat of 

 evaporation r we have also to consider the latent heat of liquefaction 

 of the water r e which enters into the factor a in table 6, and also in 

 place of the specific heat of water c, there occurs c e the specific- 

 heat of ice which enters into the factor in, table 4, column 6, for 

 the snow stage. 



The hail stage can only occur when liquid water is present in the 

 air; for pseudo-adiabatic changes of condition the hail stage is 

 entirely omitted [since the water drops have fallen down] and the 

 final pressure of the rain stage for o° C. holds good as the initial 

 pressure of the snow stage. 



