THERMODYNAMICS OF ATMOSPHERE VON BEZOLD 



255 



In order to obtain an idea of the magnitude of the changes here 

 considered it is advantageous to choose a definite case and deter- 

 mine the magnitude of the sudden rise in pressure when we assume 

 that the dissipation of supersaturation takes place at different 

 stages of progress successively far apart. 



In the computations I assume that air having a temperature of 

 2 5 C. at sea-level contains such a quantity of vapor as would cause 

 it to cool to its dew-point by adiabatic expansion when rising to 

 an elevation of about 8oo meters. I make this specific assumption 

 because in the Alps where the mountains offer excellent level marks, 

 I have often observed thunderstorm clouds whose lower surfaces 

 had about that altitude above the valleys. 



With this assumption we obtain the group of values shown in the 

 accompanying table. 



In this table all quantities having the subscript 1 belong to the 

 condition of supersaturation before its dissipation; those having 

 the subscript 2 belong to the condition immediately after supersatu- 

 ration is broken up. It need hardly be repeated that h is the alti- 

 tude in meters above sea-level, /? the barometric pressure in milli- 

 meters of mercury, t the temperature Centigrade, y l the number 

 of grams of water contained in a kilogram of the mixture, and 

 y 2 the grams of water needed to produce saturation at the tem- 

 peratures t x and t 2 respectively. Finally, R expresses the relative 

 humidity just before the dissipation of the supersaturation and is 

 therefore the measure of the extent of the supersaturation. The 

 corresponding value R 2 after the breaking up is always 100 and is 

 therefore omitted from the table. 



In these computations I have made use of the graphic method 

 given by H. Hertz, 8 which, although it does not allow of anygreat 

 accuracy, yet is so remarkably convenient and gives the result so 



Met. Zeit., 1884, Vol. I, pp. 421-431. See No. XIV of these translations. 



