264 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 5 1 



On the other hand, in the interior of Germany the cyclonic 

 thunderstorms are among the greatest rarities, but the heat thunder- 

 storms are so typically developed that one often recognizes their 

 characteristic peculiarities reproduced in special Scandinavian 

 storms that Mohn and Hildebrandsson have considered as cyclonic 

 thunderstorms. 



For instance, I should consider the thunderstorm of August 6, 

 1 88 1, at least after its penetration into the interior of Scandinavia, 

 as undoubtedly a heat thunderstorm. 



It is precisely the possibility of such fundamental differences in 

 our views that appears to demand that the path to a better under- 

 standing be indicated and the definitions be made more exact than 

 has hitherto been the case. 



As to this matter the most important indications are given us 

 by the great differences in the diurnal and annual periods of the 

 thunderstorms on the coasts and in the interior of continents, as 

 shown in the above-mentioned observations in Scandinavia, as well 

 as in material gathered elsewhere. 



Whereas in the continental interior the maximum frequency of 

 thunderstorms occurs in the afternoon hours and in fact only a little 

 later than the maximum of temperature, while a very feebly indi- 

 cated secondary maximum in the early morning hours can only be 

 demonstrated with much labor; on the other hand, in the neighbor- 

 hood of the oceans the nocturnal thunderstorms are much more 

 frequent. Thus, for instance, in the coast region of Schleswig- 

 Holstein the absolute maximum of destructive lightning occurs 

 between midnight and 3 a.m. 12 Similarly in the maritime regions 

 the winter thunderstorms are much more frequent than in the 

 interior, and it is the winter storms that happen so frequently in the 

 night time, so that in fact these determine the peculiarities of the 

 diurnal period in that region. 



In this respect the oceanic exposure of Norway as compared with 

 Sweden makes itself felt to a most remarkable extent ; whereas in 

 Norway in the ten years 187 1 to 1880 there were 235 January 

 thunderstorms as contrasted with 181 1 July storms, on the other 

 hand, during these same years there were in Sweden 14 January and 

 4419 July thunderstorms. 13 But in the true coast region of Norway 

 the numbers for January and July were in fact 198 and 646, respec- 



12 G. Hellmann, Zeitschrift des Preuss. Statistischen Bureaus, Vol. 26, 

 1886, p. 179. 



13 H. Mohn and H. H. Hildebrandsson. Les Orages dans la P^ninsule 

 Scandinave. Upsala, 1888, p. 39. 



