THERMODYNAMICS OF ATMOSPHERE VON BEZOLD 231 



The climatological aspect of that second memoir which is now to 

 be considered seems to have remained quite unnoticed and equally 

 so the various conclusions as to the "exchange of heat," 3 which I 

 would also consider of fundamental importance for Climatology. 



I will therefore here develop more fully the results of a climatologi- 

 cal character that were only indicated in the first mentioned memoir 

 and as preliminary will more clearly illustrate the point of departure. 



We must recall the fact that the expansion of saturated moist 

 air without adding or abstracting heat should only be called adia- 

 batic when the precipitated water remains floating in the air. As 

 soon as it wholly or partly falls away as precipitation then this term 

 is no longer strictly applicable since the whole expenditure of the 

 internal energy is not converted into external work. 



In this case the falling particles of water or ice, since they still 

 have the temperature of the mixture and not of absolute zero, 

 withdraw from the mixture energy that has not yet been expended 

 in the work of expansion. 



Therefore I have called such processes "pseudo-adiabatic." 



Since the quantities of energy that are lost by the falling away of 

 the condensation are very small, therefore the formulae for the adia- 

 bats and the pseudo-adiabats differ from each other only very slightly. 

 Therefore in the computations and m the graphic presentations we 

 may consider them as identical, that is to say, we may use the for- 

 mulas and curves for the adiabats instead of those for the pseudo- 

 adiabats. 



On the other hand, an incisive difference is manifest as soon as 

 the expansion changes to compression or when the ascending current 

 becomes a descending one. 



In this case it makes a very great difference whether the water con- 

 densed during the ascent is carried along with the air or falls away 

 from it. If it is carried along, that is, if the expansion truly follows 

 the adiabat, then the compression follows exactly the same law, so 

 that the change of condition is truly reversible ; but if the expansion 

 is ''pseudo-adiabatic" it follows a law entirely different from that 

 which obtained during the expansion. 



Since the water or ice which is formed scarcely ever falls away 

 completely immediately after its formation, for in that case precipita- 

 tion would fall from a clear sky, therefore this departure from the 

 adiabatic law does not immediately follow the passage from expan- 



3 See my memoir of 1892, Sitzb. Berlin Acad., pp. 1139-1178. or No. 

 XV, pp. 316-356 of the Gesammelte Abhandlungen (or No. XIX of this 

 collection of translations). 



