250 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 51 



precipitates ice of the same peculiar structure as is observed in 

 Glatt eis and which gives rise to the formation of the so-called 

 Anraum or ice storm. 



If now we try to reason out how the sudden cessation of the state 

 of subcooling or the supersaturation ought to become manifest, 

 we find that it must be followed by a phenomenon that has long 

 since been recognized as a regular accompaniment of thunder- 

 storms, namely, a sudden rise in the atmospheric pressure. This 

 rise, with the subsequent less prominent fall, must show exactly the 

 same peculiarities in continuous barograms that are prominent in 

 the so-called "Gewitter nase" or "thunder nose." 



Moreover, by the more accurate prosecution of the study we have 

 arrived at ideas about the constitution of thunder clouds and of the 

 processes going on therein that appear likely to throw new light on 

 the whole theory of the formation of thunderstorms. 



But in order to understand these questions it is first necessary to 

 investigate from a purely theoretical point of view the consequences 

 of a sudden disruption of the condition of supersaturated vapor 

 or subcooled water. 



SUPERSATURATION 



The influence that the dissipation of any existing state of super- 

 saturation must exert on the thermal condition of the atmosphere, 

 under the assumption of constant pressure, is explained in the pre- 

 ceding third memoir,* although only as a pure hypothesis in the 

 course of the investigation of the mixture of masses of air having 

 different temperatures and humidities. 



It was shown that in such a case there occurs a rise of tempera- 

 ture whose extent can be most easily determined by graphic 

 methods. 



If we know the pressure prevailing in the supersaturated air, 

 we then represent the normal quantity of water 

 y' corresponding to saturation or the quantity 

 contained in a kilogram of the mixture by the 

 ordinate of a curve F'F' in a rectangular sys- 

 tem of coordinates whose abscissae represent 

 the temperatures. (See fig. 30.) 



If now, y x = F l T l or the quantity of vapor 

 contained in the mixture of air and vapor, ex- 

 ceeds the normal quantity required for satura- 

 tion by y x — y x ' = F 1 T 1 — F x ' T x then the temperature t 2 that will 



*S?e the preceding collection of translations, p. 272 — C. A. 



