XIY. 



A GRAPHIC METHOD OF DET?]RMINING THE ADIABATIC CHANGES IN THE 

 CONDITION OF MOIST AIR.* 



Bv Dr. H. Hkhtz. 



The theoretical meteorolofjist daily has to discuss considerations as 

 to the changes of condition that take phice in moist air that is com- 

 pressed or expanded without the addition of any heat. Hence he 

 desires to attain answers to these questions with the h^ast possible ex- 

 ]»enditnre of time, and he does not care to use any of the complicate*! 

 formulae of thermo-dynamics. Actually he generally uses the small 

 l)ractical table that Professor Hanu communicated in the year 1S74 

 (Zeit. der Oest. Ges.f. Met., 1874, ix, p. 328). Still it appears that with 

 at least an equal convenience one may attain a greater completeness if 

 one makes use of the graphic method, and the table accompanying this 

 paper ])resents an attempt in this direction. This contains notiiing 

 theoretically new except in so far as that it als.i comiiletely cpnsiders 

 the peculiar behavior of moist air at 0° C, which, so far as I know, has 

 hitherto not been treated of.t In the following 1 will now in Section i, 

 collect together the exact formulae of the probletn, since a complete col- 

 lection of such appears to be wanting. Under Section ii, the presenta- 

 tion of the formulas by the graphic table is described. Finally under 

 Section iii, I explain completely, although purely mechanically, the ap- 

 jilication of the latter to a numerical exami)le. If one Ibllows this ex- 

 ample with the diagram in the hand, one attains a judgment as to the 

 use of the table and a knowledge of the method of using it without the 

 necessity of going through the computations of Sections i and ii. 



In a kilogram of a mixture of air and aqueous vapor let A represent 

 the proportional weight of dry air and /< the proi)ortional weight of un- 

 saturated aqueous vajjor contained therein. Let the i)ressure of the 

 mixture be p and its absolute tem])erature be T. Our problem is: 

 What conditions will the mixture pass through when its pressure is di- 



'Trauslated fron the Meleorolof/ische Ztitsclirift, 1884, vol. i, pp. 421-431. 



tSee, however, Guldberg and Mohu, " Studies on the movement of the atmosphere," 

 part 1, pp. 9-16, and, also, by the same authors, Oest. Zcit.f. Meteorologie, 1878, xiii, 

 p. 117. 



198 



