( 370 ) 



Tlie records concerning se^'el•e winters naturally are a very rough 

 material, though the remark has already been made that they are 

 far more reliable than p.//. records about hot summers, the excep- 

 tional formation of ice being an unmistakable criterion. The data 

 must however be carefully and critically arranged and compared. 

 This has already been done l»y Prof. W. Koppen in his well known 

 investigations on the periodicity of severe winters. The data as given 

 by Koppen have therefore been used instead of those of Bruckner, 

 which are simply taken from Pilgram. 



On comparing Köppen's list with Brltkner's curve I was struck 

 by an indication of periodicity in very long periods, different however 

 from what Koppen sought {vh. the regular occurrence of severe 

 wintei's in determined, equidistant years), and also nol consisting of 

 regular oscillations like those suspected by Bruckner, but of a recurrence 

 of the (jenemJ character of the ireather in periods of about 180 years. 

 The distrilmtion of the winters within each of these periods is the 

 same, viz: very many severe winters in I lie first 60 or 70 ^ears 

 of the period (e.g. the 60 years following 1220, 1400 or 1580), 

 very few in the next 20 years, many in the following 20, few and 

 irregularly distributed winters in the remaining part of the period. 



In accordance with what was said above this phenomenon, if 

 it is real, must l)e attributed to a secular oscillation in the solar 

 activity, presenting itself to us in the form of systematic variations 

 of the eleven-year period. For this reason I took as the basis of my 

 investigation a period of 16x^1-13^ al)out 178 years, 11.13 years 

 being the normal period according to Xewcomb. The available material 

 covers a period of more than a thousand years, viz. from the middle 

 of the ninth century to our own time, including the additional data 

 procured by Koppen himself. The reality of this periodicity was 

 made very probable by a statistical investigation in which the year 

 848 was taken as the first of a period of 178 years. We denote 

 the influence of a "normally severe" winter on the climate 

 by a "cold-coetïicient" unity. To an exceptionally severe winter 

 ("winter of first class" of Koppen) the coefficient 3 is assigned, and 

 2 to winters of intermediate severity. It then appears — taking all 

 the periods since 848 together — that the four sub-periods of 67, 22, 

 22 and 67 years have total coefficients of 114, 15, 39 and 62 respec- 

 tively, i.e. 1.70, 0.68, 1.77 and 0.93 respectively for one year. These 

 oscillations are of such amplitude that the proportional number of 

 severe winters in these cold periods of 67 years {e.g. from 1561 

 to 1628) is nearly twice that of the succeeding relatively mild periods 

 of 22 years, the ratio in the case of exceptionally severe winters 



