1105 



On account of the necessarily automatic classification, the contrast 

 between the relatively cold and the relatively warm intervals in 

 this table certainly is not exaggerated; this is also shown by a 

 comparison with table IV. So, for example, the cold winter 1871 

 as well as the severe winter 1895 undoubtedly belong to the 

 third (cold) sub-period, although they lie just outside the auto- 

 matically limited 22-year interval. 



Though the true cause of the periodicity lies for the present in 

 the dark, such a table would seem to offer some base fora weather 

 prognosis a long time in advance, at any rate a limited one, some- 

 what complementary to the weather prognosis from year to year, 

 the prospect of which has been opened by the investigation of 

 Mr. P. H. Ga]>lé, recently published in these Proceedings. Perhaps 

 I may on this point quote Prof. J. C. Kapteyn, who on page 7 of 

 his "Tree-growth and meteorological factors" writes: "What I heard 

 and what 1 read has long brought me to think that in the present 

 state of science any investigation on long period regularity in the 

 weather must be a purely empirical one. Though the empirical 

 finding out of a regularity may hardly be claimed as a scientific 

 achievement, if may nevertheless become in future of the greatest 

 utility in weather forecast a long time in advance". It may still He 

 noticed that although the nature of the relation between the 

 climatological curve and the activity of the sun cannot yet be ex- 

 plained, such a relation undoubtedly exists, so that the foundation 

 for a prognosis is in our case more solid than it would be for a 

 regularity, discovered by purely empirical methods. 



In 1905 I wrote in Peterimann's Milteilungen (Vol. 51, Number 

 VIII, p. 176): "7Aim Beispiel scheint der Schluss auf einen Teilab- 

 schnitt mit aussergewöhnlich wenig kalten Wintern, an deren Beginn 

 wir uns jetzt befanden, gewiss gerechifertigt". (The conclusion seems 

 justified that we are at present at the beginning of a period with 

 an extraordinarily small number of cold winters). Also 

 the diagram in the "Proceedings" of that year shows between ±: 

 1900 and 1913, that an almost total absence of se\ ere winters might 

 be expected (Proc. Acad. Amst. 1904, curves I, C and II«). Now a 

 great positive temperature surplus has indeed occurred during the 

 last series of winters (see our Diagram). 



In the sanie way, the prognosis for the next 22-year interval 

 (1917 to 1938) would point to a considerable fall of the average 

 winter temperature, with at least two very cold winters, of which 

 one severe. 



In what follows the conclusions of our investigation are summa- 



