THERMODYNAMICS OF ATMOSPHERE VON BEZOLD 263 



storms are such as would lead us to expect supersaturation or sub- 

 cooling. 



This study leads us unavoidably to the consideration of thunder- 

 storm phenomena in general and makes it necessary here to say 

 something on this subject. I must, however, first of all, remark 

 with reference to the well-known classification into cyclonic thunder- 

 storms and heat thunderstorms, that it seems to me that often this 

 classification is not made in an appropriate manner. 



Frequently all thunderstorms that are in any way connected with 

 the forerunner of a barometric depression, or are located on the 

 edge of the "low" when this is a very flat or feeble depression, are 

 designated as cyclonic thunderstorms when they may be perfectly 

 characteristic heat thunderstorms. On the other hand, the term 

 heat thunderstorms is often applied only to isolated local thunder- 

 storms, whereas, in my opinion, the majority of all thunderstorms 

 observed in interior regions, with very few exceptions, are decidedly 

 heat thunderstorms. 



In fact one might say that the circumstance that the division into 

 these two classes allows of such different points of view, indicates 

 that this classification is not a natural one. But this is by no means 

 the case. On the other hand, I consider this classification as of the 

 highest importance and if the appropriate definitions have not yet 

 been made so clear and sharp as is desirable, then this is, I think, to 

 be ascribed to the circumstance that the first attempts to make this 

 distinction were undertaken in a country where both groups fre- 

 quently occur and where they merge into each other more than is the 

 case elsewhere. 



So far as I know, this classification originated with Mohn and it is 

 precisely in Scandinavia that one has opportunity to observe true 

 cyclonic thunderstorms more frequently than in Germany where 

 they are confined almost entirely to the coasts and, as above stated, 

 only in a few exceptional cases occur in the interior. 



For this reason therefore one is tempted in Scandinavia to con- 

 sider as cyclonic thunderstorms many that I should call heat thunder- 

 storms, but which are not so typically developed as those observed 

 in the interior of the continent. " 



In fact Mohn and Hildebrandsson in their admirable memoir 11 

 on the thunderstorms of the Scandinavian peninsula, expressly say : 

 "However it is in Sweden impossible to find a well-defined boundary 

 between these two classes of thunderstorms." 



Les Orages dans la Peninsule Scandinave. Upsala, 18S8, p. 



