426 SHORT MEMOIRS ON METEOROLOGICAL SUBJECTS. 



of atmosphere by the condeusatiou of one millimeter of rain; and, under 

 the further assumption that this excess of air can be immediately 

 removed, and is not replaced at the earth's surface by cooler air flowing 

 in from the side, I arrive at the theoretically not uninteresting result, 

 that a barometer under such a column of air must fall to the extent of 

 three-fifths of the dei^th of rain fall. In all this, however, I was per- 

 fectly aware, and have even so stated, that the assumed conditions do 

 not occur in nature. Therefore have I, also, at no time, neither in the 

 text of my book on " Wirbelstlirme" nor elsewhere, referred to this 

 result of computation, and readily acknowledge with Hann, who assails 

 it, that it has no practical importance. Still I believe as before, " not- 

 withstanding perhaps this computation throws some light upon the low 

 barometer that is so often observed in connection with the revolving 

 storms that are accompanied by heavy rain." 



In fact, the assumptions in question are approximately fulfilled in the 

 case of the precipitations accompanying revolving storms; at least, far 

 more nearly than in local thunderstorms, or in quiet, uniform, general 

 rains. Since the air rises very rapidly in the interior of a whirlwind, 

 therefore it and the aqueous vapors or cloud-fog that are carried up with 

 it cannot lose much heat, either by conduction or by radiation ; at the 

 same time, however, the inflow of the lower mass of air from either side 

 is hindered by the centrifugal force and the outflow of the upper layer 

 is facilitated. But this theoretical result is not applicable without 

 further considerations, even to the revolving storms ; for, even if in these 

 we have accounted for the heat which is consumed in the expansion 

 corresponding to the latent heat liberated by the vapor, still there 

 remains unnoticed that quantity of heat which is equivalent to the 

 living force of the whirling mass of air and to the work of expansion 

 performed in consequence of the ascension. For this reason, in my 

 theory of whirlwinds, besides the very complete collection of observa- 

 tions, I refer only to the law of tension of saturated air and to the com- 

 putations in reference to the unstable equilibrium in the atmosphere. 



G. 



ON THE EELATION BETWEEN THE DIFFERENCE OF PKESS- 

 URE AND THE VELOCITY OF THE WIND ACCORDING TO 

 THE THEORIES OF FERREL AND COLDING. 



By Dr. Julius Hann. 



iTranslateil by Cleveland Abbe from the Zeitschrift of the Austrian Meteorological Association, 1875, 



vol. X, pp. 8l-10f).J 



The historical developments of scientific theories, like those of political 

 questions, have their reactionary periods, which, in both ca.ses, are gen- 

 erally called forth by an excessive one-sided [mrsuit of some principle 



