F. Waldo — Contributions to Dynamical Meteorology, 291 



acteristic curves are deduced. These arc the isothermie, adia- 



batic, ami curve- of constant amount of saturation. A short 

 application is then made to the u foehn," and the interohas 

 ol air between cyclones and anticyclones in Bammer. 



(There is a considerable literature treating of the matter of 

 connective equilibrium, but I cannot make special mention of it 

 here. I will only mention that in Maxwell's elementary ik The- 

 ory oi Heat" (1880) there is to be found a popular explanation 

 iveral Important points in this connection. — v. w.) 

 . II. — While this paper is in one Bense a continuation of 

 the preceding, vet the introduction of new conceptions, the 

 chief one o( which is what Helmholtz has termed k * YVarmege- 

 halt," but which, after considering the objections made by von 

 Bezold to this nomenclature, he now prefers to call"poten- 

 tielle Temperatnr." - This potential temperature is that abso- 

 lute temperature which a body assumes when it is brought 

 under the normal pressure without gain or loss of heat — 

 adiabatically or pseudoadiabatically. The graphical determina- 

 tion of potential temperature corresponding to any given con- 

 dition is very neatly worked out for the dry stadium. In the 

 case of condensation the potential temperature rises and becomes 

 the greater the larger the amount of water lost out. Also " adia- 

 batic changes of condition in the free atmosphere — excluding, 

 however, evaporation — leave the potential temperature either 

 unchanged or they elevate it." The author calls attention to 

 the similarity between this and the theorem of Clausius con- 

 cerning entropy. 



The next section treats of the vertical temperature gradients, 

 and the author emphasizes the fact that the thermodynamic 

 cooling and heating in consequence of the expansion or com- 

 pression in ascending or descending currents plays a most im- 

 portant part in the vertical motions of the atmosphere. So 

 long as we consider the free atmosphere in which there is little 

 opportunity for the absorption or emission of heat and where 

 only approximate results are expected, we may consider only 

 the adiabatic conditions ; but in the neighborhood of the 

 ground and in the regions of cloud or fog the conditions are 

 such that this method is no longer satisfactory. 



The author illustrates by a diagram what he calls his "nor- 

 mal plan" of ascending and descending currents; and in it he 

 shows the relation of the ascending current in the dry stadium, 

 its continuation in the stadium of condensation, and finally the 

 curve corresponding to the descending current. The applica- 

 tion then shows the practical application to the interchange 

 of air between cyclonic and anti-cyclonic systems, and some 

 more special cases; next follow over half a dozen pages giving 

 the application of the idea of potential temperature to various 



