XXII 



THE RELATION BETWEEN "POTENTIAL TEMPERA- 

 TURE" AND "ENTROPY" 1 



BY L. A. BAUER 

 [Reprinted from the Physical Review, Vol. XXVI, A?o. 2, February, igoS] 



111 1888 the late Professor von Helmholtz incidentally introduced 

 the term " waermegehalt " in connection with his investigation, 2 

 w On Atmospheric Motions." According to him the "waermege- 

 halt" or the actual heat contained in a given mass of air is to be 

 measured by the absolute temperature which the mass would 

 assume if it were brought adiabatically to the normal or standard 

 pressure. It remained for the late Professor von Bezold, however, 

 to perceive the full significance of this term and to reveal its impor- 

 tant bearing in the discussion of meteorological phenomena. 



As the quantity really involved in this new term is not a quantity 

 of heat, von Bezold suggested that the term be replaced by the evi- 

 dently more appropriate one of "potential temperature." 3 This 

 met with von Helmholtz's approval. 



With the aid of this happy idea of "potential temperature" von 

 Bezold was enabled to draw in a simple and beautiful manner a 

 number of important conclusions governing thermodynamic phe- 

 nomena taking place in the atmosphere. Thus, for example, he 

 found that: 



"Strict adiabatic changes of state in the atmosphere leave the 

 potential temperature unchanged, whereas pseudo-adiabatic ones 

 invariably increase the same, the increase being in proportion to the 

 amount of aqueous evaporation." 



1 Presented before the Philosophical Society of Washington, March 16, 

 1907. 



2 Sitzungsberichte Berliner Akademie, 1888, Vol. XLVI, p. 652, " Ueber 

 atmosphserische Bewegungen, " see translation in Abbe's Mechanics of the 

 Earth's Atmosphere, Washington, 1891, p. 83. The symbol Q is used to 

 denote the " Waermegehalt. " 



3 Sitzb. Berliner Akad., 1888, Vol. XLVI, p. 1 189, "Zur Thermodynamik der 

 Atmosphsere; " also in von Bezold's "Gesammelte Abhandlungen, " Vieweg 

 und Sohn, Braunschweig, 1906, p. 128. A translation will be found in Abbe's 

 Mechanics, etc., p. 243. 



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