252 THE MECHANICS OF THE EARTH'S ATMOSPHERE. 



A direct proof of the inversion of teiui)erature above the lowlands 

 can only be expected from balloon observations. 



To wliat extent radiation causes the inversion or at least tbe dimi- 

 nution of tlie oradient we shall learn from a work now soon to be pub- 

 lished, that Siihring* has executed at my recommendation, andin which 

 the vertical gradients of temperature between the Eichberg and the 

 Schneekoppe, as well as between iNTeuenburg and Chaumont, are inves- 

 tigated according to the separate percentages of cloudiness. 



It is not improbable that also above the ocean, and even at the time 

 of the stronger insolation, a diminution of gradient, if not even an in- 

 version of temperature, occurs, since over the sea the rapid evapora- 

 tion in connection with the mobility of the water puts an impassable 

 limit to the rise of temperature. The stability of the Atlantic anti- 

 cyclone during the summer months may be based upon this circum- 

 stance. 



The cases in which an increase of heat occurs at the earth's sur- 

 face need no special consideration in the questions here considered. 

 The gradient can only fcr a short time exceed the value v, as deter- 

 mined for the expansion or compression of dry air. If this case occurs, 

 then, according to the investigations of Keye and others, we have 

 unstable equilibrium or a condition that can only exist temporarily, as 

 iu whirlwinds or thunderstorms. Therefore, even for the strongest 

 insolation, the considerations above given continue to hold good. 



Un the other hand the fact must excite great consideration that, not 

 only on the average of all cases, but also when we investigate only the 

 region of ascending currents (and of these only those that are below 

 the limit of clouds, that is to say, for moderate elevation of the up|)er 

 station) we find tiiat the vertical gradient is always decidedly smaller 

 than V. The reason of this is i)rincipally to be sought in the fact that 

 the above views as \n\ sented by me, as also by other investigators iu 

 this direction, all rest upon an implied assumption that is only allow- 

 able to a very limited extent. They are based namely u^ton the 

 assumption that the air ascending from the earth experiences no change 

 in its constitution, except that due to the loss of water consequent on 

 the adiabatic expansion, i.e., that it experiences no mixture with masses 

 of air of other temjierature or other degrees of moisture, as also that 

 every i)article of air considered iu the interchange between cyclones 

 and anticyclones describes the whole path from the earth's surface to 

 the limit of the temperature and back again. 



But this is by no means the case. Only a small fraction of the air 

 under consideration actually comes iu contact with or even in close 

 proximity to the earth's surface; and similarly with tlie ascent to the 

 limit of the atmosphere or at least to the highest stratum that at any 

 time takes part in the process under consideration. Moreover in the 



* Snhr\nff, Dierertikale Temperaturahnahme. Inaugural Dissertation d. Universitiit, 

 Berlia, l«i)0 



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