452 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 51 



The volumes resulting are V = 1.749 cbm. and v = 1.727 cbm. 



The mass of air cooled during expansion to — 20 C. in this 

 example has the same initial value as was used in the example com- 

 puted by Guldberg and Mohn. The final pressure of 292 milli- 

 meters as computed by them in their "Etudes" is incorrect, as 

 indeed Hertz has already shown. 16 17 



§7. THE GENERAL EQUATION FOR THE ADIABATS OF MOIST AIR 



Considering all the preceding results connectedly, we perceive 

 that the law of variability of temperature and pressure in ascend- 

 ing and descending currents of moist air for the whole series of 

 stages can be represented with mathematical exactness by the 

 general adiabatic equation 



log p' — — m log T = constant 



which without further change is to be used in this form for the com- 

 putation. This equation differs from the original Poisson equation 

 only in form by the corrective term — alp' . 



In all previous attempts to make use of Poisson's equation for 

 moist air during the stages of condensation, as for instance by a 

 variation in the factor m and by the introduction of the so-called 

 virtual temperature, T v on the absolute scale 



T 273 + t 



1 - 0.378 - 



we have been led to very complex and obscure formulas. For 

 example, Guldberg and Mohn 18 found for the rain stage the follow- 

 ing formula 



/ dr de 

 c , + x [ c + _ + r — 

 1 P \ dt dt 



m = 



AR 1 1 



AR 273 + / 



16 Hertz: Postscript to his previous article on a graphic method. Met. Zeit., 

 1884, p. 475- 



17 Note. This error does not occur in the text of the translation as given 

 in this present collection which indeed was entirely revised by Guldberg 

 and Mohn in 1885, so as to constitute a new edition. C. A, 



18 Guldberg and Mohn: Ueber die Temperaturanderung in vertikaler Rich- 

 tung in der Atmosphare. Met. Zeit., 1878, S. 113. 



