XII 

 ON THE THERMODYNAMICS OF THE ATMOSPHERE 



BY PROF. DR. WM. VON BEZOLD 



[Fourth Memoir, Sitzungsberichte of the Berlin Academy. i8g2, pp. 27Q-309. 

 Translated from the Gesammelte Abhandlungen von Wm. v. Bezold, Braun- 

 schweig, igo6, pp. 184.-215] 



SUPERSATURATION AND SUBCOOLING. FORMATION OF THUNDER- 

 STORMS 



In the third memoir 1 on the Thermodynamics of the Atmos- 

 phere, which was devoted to the investigation of the mixture of 

 masses of moist air as well as the formation of fog and clouds, I 

 have shown what the consequences must be when condensation 

 suddenly occurs in air supersaturated with vapor. 



On that occasion I remarked that I considered it very probable 

 that such supersaturations, whose possibility is demonstrated by 

 laboratory experiments, occur also in the free atmosphere and that 

 they certainly may be the cause of cloudbursts. 



At that time it appeared to me important to restrict myself 

 to a simple suggestion, as I was not able to adduce any proof of the 

 correctness of this idea. Meanwhile it has become clear to me that 

 there exists still another unstable condition for the water contained 

 in the atmosphere, that is, the "Subcooling," whose sudden dis- 

 sipation must result in phenomena similar to those of "Supersatura- 

 tion." Now the subcooling of fog and cloud has been often 

 observed. In regard to this I recall the investigations that Assmann 

 made on the Brocken, 2 as well as the results of the very interesting 

 balloon voyage made fromBerlin, June 19, 1889, by Moedebeck and 

 Gross, and described in an excellent manner by the latter. 3 



The above mentioned observations give convincing evidence 

 that at temperatures below the freezing point there occur clouds 

 that contain no ice but are true water-clouds, but from which there 



1 See p. 272 of the preceding collection of translations. Smithsonian 

 Miscellaneous Collections, Vol. XXXIV. 



2 Met. Zeit., Vol. II, 1885, pp. 41-47. 



3 Zeit. f. Luft-schiffahrt, 1889, Vol. VIII, pp. 249-262. 



249 



