XL 



ON THE GULDBERG-MOHN THEORY OF HORIZONTAL ATMOSPHERIC 



CURRENTS.* 



By Prof. Dr. A. Obkrbkck, of the University of Halle. 



Starting from the generally known results of recent meteorological 

 observations in so far as these relate to the distribution of pressure 

 and the direction and force of the wiud, the author states that one of 

 the most important problems of the mathematical theory of the motion 

 of fluids is to explain quantitatively the connection of the above-named 

 phenomena. The recently published investigations of Guldberg aud 

 Mohn (Etudes sur les mouvements de V atmosphere. Christiauia, 1876 

 aud 1880) are to be considered as a specially successful attempt in this 

 direction. It must be of interest also for the larger number of geog- 

 raphers to know the most important results to which the Norwegian 

 scientists have attained. 



In order to understand the horizontal movements of the atmosphere 

 it is important for a moment to consider their causes. As such we con-, 

 sider the differences of pressure at the surface of the earth as observed 

 with the barometer. But whence do these arise f This question has 

 been answered along time since. It is heat which is to be considered 

 as the prime cause of the disturbance of equilibrium in the atmosphere. 

 Because of the slight conductivity of the air the process of warming 

 can progress only slowly from below upwards, so that as is well known 

 the temperature of the air steadily diminishes as we ascend. The 

 heated air expands. The pressure becomes less. If the heating takes 

 place uuiformly over a large area there will be at first no reason for 

 horizontal currents. But vertical currents can certainly be brought 

 about by this means. If we imagine a circumscribed mass of air trans- 

 ported into a higher region without any increase or diminution of its 

 heat its temperature will sink because it has expanded itself propor- 

 tionately to the diminished pressure. If its temperature is then equal 

 to that prevailing in the upper stratum it will remain in equilibrium 

 at this altitude as well as below. The atmosphere iu this case exists 

 in a state of indifferent equilibrium. If its temperature is lower the 



* Translated from the Verhandlungen des Ziveiten Deutschen Geographentages. Halle, 

 April, 1882. 



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