252 THE MECHANICS OF THE EARTH'S ATMOSPHERE. 



A direct proof of the inversion of temperature above the lowlands 

 can only be expected from balloon observations. 



To what extent radiation causes the inversion or at least the dimi- 

 nution of the gradient we shall learn from a work now soon to be pub- 

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

 the vertical gradients of temperature between the Eichberg and the 

 Schueekoppe, as well as between Neuenburg and Obaumont, 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 mouths 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 for a short time exceed the value r, 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 

 in whirlwinds or thunderstorms. Therefore, even for the strongest 

 insolation, the considerations above given continue to hold good. 



On 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 upper 

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

 than v. The reason of this is principally to be sought in the fact that 

 the above views as pr< sented by me, as also by other investigators in 

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

 able to a very limited extent. They are based namely upon 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 temperature or other degrees of moisture, as also that 

 every particle of air considered in the interchange between cyclones 

 and anti-cyclones 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 in contact with or even in close 

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



Siilning, Dievertilcah Temperaturabnahme. Inaugural Dissertation d. Universitiit, 

 Berlin, 1890 



