Meteorology. — "Periodicity of Winter Temperatures in Westeim 

 Europe, since A.D. 760". By Dr. C. Easton, Amsterdam. 

 (Communicated by Dr. J. P. van dp:r Stok). 



(Communicated in the meeting of February 24, 1917.) 



In two previous communications on fluctuations in the solar 

 activity and in the climate ') Köppen's historical data on hard 

 winters in Western and Western Middle-Europe *) formed the climat- 

 oiogical foundation. For a closer investigation of a possible period- 

 icity in the climate of Western Europe it seemed desirable to 

 collect these historical data afresh and as completely as possible, to 

 submit them to criticism and then to connect them with the later 

 scientific observations of temperature. In this way it might be possible 

 to obtain over some twelve centuries an uninterrupted (albeit 

 incomplete and only approximate) series of such an important 

 climatological element covering a consideiable area Even if the 

 investigation of the periodicity should piove to be unsuccessful, this 

 material would still retain its value. 



Before publishing the full amount of this very extensive 

 material, and before giving the discussion in all its details, — which 

 under the present unfavourable circumstances may require a con- 

 siderable amount of time — it may be useful to publish a summary 

 of the results which it has yielded. 



Historical data. The historical data concerning abnormal 

 winters have been revised from a threefold point of view : 



1. Restriction of the area to the West-Euiopean climatic province 'j, 



') Oscillations of solar activity and the climate. Two communications. Proc. Royal 

 Acad, of Sciences, Amsterdam, 1U04. Nov. 26, 1905 June 24, Vols. Vil, V!ll. 



2) W. Koppen, "Ueber mehrjahrige Perioden der Witterung Die strengen 

 Winter Europas u s.w. Zeitschrift d. Oesterr. Ges. f. ilfe^ A^F/ (1881). (On 

 weather periods extending over many years; the hard winters of Europe, etc.). 



3) The borders of the climatic province proper were drawn over Rouen, Angers, 

 Bordeaux, Toulouse, St- Etienne, Berne, Gonstanz, Stuttgart, Hanover, Hamburg 

 and Helgoland, so that the greater part of France, N. W. Switzerland, Belgium, 

 the Netherlands, and Western Germany are included, in France the borderline of 

 this climatic province approximately follows the' "ampl. 15° de la variation annuelle" 

 then the Cevennes and further the ampl. 19° as far as Geneva. (Angot, "Glimat 

 de la France", T. I. pi. X). 



