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NATURE 



[August 30, 191 7 



planation. There are sufficient names, but crowd- 

 ing has been avoided. The British front in June is 

 shown by a red line. It is a clearly printed and 

 useful map with a great amount of detail, and 

 allows the progress of operations, both on the 

 Belgian front and along the coast, to be closely 

 followed. 



LETTERS TO TT1E EDITOR. 

 [The Editor does not hold himself responsible for 

 opinions expressed hy his correspondents. Neither 

 can he undertake to return, or to correspond with 

 the writers of, rejected manuscripts intended for 

 this or any other part of Nature. No notice is 

 taken of anonymous communications.] 



A Forecast of Coming Winters. 



A STATISTICAL examination of ancient records of 

 winter temperatures in Western and Western-Middle 

 Europe led me to the conclusion, in 1904 and 1905, 

 that periodicities of 445 and 89 years have the greatest 



mere chance that exactly the winter 19 16- 17 turned out 

 to be the first cold winter after so many mild winters 

 as we experienced since the beginning of this century, 

 the first really cold winter since 1895 in W. Europe; 

 nevertheless, a change in the weather-type about this 

 time is in perfect agreement with the forecast. 



Since the publication of my first paper on this sub- 

 ject I have been collecting and critically examining 

 all materials on winter temperature that are available 

 on the Continent and in England, in order to trace the 

 vera causa that must lie hidden behind such a period 

 or complex of periods. I did not, however, succeed ; 

 even the Fourier analysis, applied to these data with 

 the kind assistance of Dr. Van der Stok at the R. 

 Institution of Meteorology, in De Bilt, failed to give 

 a clue. 



There remained, however, a means of testing the 

 reality of the suspected 45-year or 89-year periodicity. . 

 If this periodicity were real, the curve representing ] 

 the thermometrical observations, made during the • 

 latter half of the nineteenth century, at some repre- 

 sentative stations in W. Europe, e.g. Paris and 

 Utrecht (De Bilt), should fit in with the 89-year curve i 

 derived from the "historical data." The result of! 

 such a comparison can be seen in the diagram, where 



9-year periodicity of winter-temperaiure in W. Europe, "a " and a (full-drawn lines), historical ; " b," "c" /3, instrumental data. 



influence on the occurrence of mild and severe winters 

 in this part of the world. These periodicities, un- 

 doubtedly related to similar fluctuations in the sun's 

 activity, are especially manifest in lower winter tem- 

 peratures at the beginning, and in higher winter tem- 

 peratures in the latter part, of the periods. Thus, in 

 the 89-year period 1828-1916, the winter temperature 

 is generally lower. in the first and third 22-year inter- 

 val, and comparatively high in the second and fourth ; 

 the interval 1.828-49 being the coldest, the interval 

 1895-1916 the warmest part of the whole period. Not 

 only the monthly means, but also the frequency of 

 mild and severe winters, show this periodicity. 



So early as 1905 I pointed out ^ that a series of 

 warm winters might be expected in the following 

 years, according to these statistics, and that the year 

 19 1 7 marked the beginning of a new period of com- 

 paratively cold winters. Though it seems a matter of 



1 " Oscillations of the Solar Activity and the Climate " (Proc. Roy. Acad. 

 Sci., Amsterdam, vols, vii.-viii. , 1904-5). 



the full-drawn line "a" gives the "historical" 89-year 

 curve, "b" (dotted) the "thermometrical" curve since 

 1852, the crosses marked "c" having been added in 

 order to trace back the instrumental records to the year 

 1828, although this part of the curve had to be taken 

 from less trustworthy data. All this applies only to 

 the western part of Europe. The curves o and ^ 

 represent the same data since 1852, simplified and 

 smoothed. Making allowance for a certam shifting 

 of the phase in the latter part of the curve, the dips 

 and crests show, I think, so much analogy as to pre- 

 clude a purely accidental conformity of the two curves, 

 compiled from absolutely different data. 



Want of space compels me to refer the reader to 

 my paper, just issued by the Amsterdam Academy of 

 Sciences.- I must now confine myself to give a table 

 showing the frequency of cold and severe winters in 

 periods of 22 (22I) years since a.d. 760 ; period 



2 " Periodicity of Winter Temperatures in Western Europe since the Year 

 760 "(Proc. Roy. Acad. Sci., Amsterdam, vol. xxv., iqi?^ 



NO. 2496, VOL. 99] 



