THERMODYNAMICS OF ATMOSPHERE— VON BEZOLD 



261 



evaporation again depresses the temperature t s below the freezing 

 point, since this would demand considerable space out of proportion 

 to its importance. 



In order now, as in the preceding case, to obtain a definite idea 

 as to how large' are the changes of pressure that may be brought 

 about by the disruption of the supersaturation, the above given 

 example is again worked out numerically in the following table, but 

 under the assumption that there is no supersaturation and that only 

 various degrees of subcooling occur. 



Table 2 



This table shows that under the adopted assumptions of an initial 

 temperature of 25 , an initial pressure of 76o mm , a relative hu- 

 midity of 66 per cent and adiabatic expansion, condensation 

 occurs at the altitude of 834 meters and the freezing point is reached 

 at the altitude of 4063 meters. 



If now the water formed by condensation is carried 300 meters 

 further without freezing (being thereby subcooled 1.9 C.) and if 

 freezing then suddenly occurs, then the (local) pressure suddenly 

 increases 3.2 mm . 



If the sudden freezing first occurs at the altitude 4721 meters, or 

 for a subcooling of 4.o°C, then the change in pressure is 5.9 mm ; for 

 still later freezings this change increases but slightly and in fact 

 eventually diminishes. 



The reason for this latter diminution lies in the fact that in the 

 formula 



h - h 

 & ~ A = A 273 + t t 



the diminution of /? x with increasing altitude is at higher altitudes 



