NO. 10 SOLAR RADIATION AND WEATHER STUDIES ABBOT 21 



It was recognized that this arrangement was very imperfect because 

 of the irregular wide fluctuations of sun-spot numbers. Hence, if, as 

 seemed indicated, the phases of weather periodicities actually alter 

 with sun-spot activity, it could not be hoped that any such arrangement 

 would eliminate altogether these phase changes. Therefore, some 

 dissimilarity between the periodic curves computed for the different 

 intervals of time given above must certainly be expected. All that 

 could be hoped for would be that periodicities in weather of the 

 lengths found in the solar variation would seem to persist without 

 more than a few months of shifting backward or forward, as between 

 the individual intervals stated above, while during the century there 

 would be so persistent and obvious a tendency for maxima and minima 

 to recur in a certain unchanged phase as to justify a belief in the 

 veridical existence of the periodicity in question. 



12. Corrections of Solar Periods 



It was apparent that since the interval during which daily solar- 

 constant work has been carried on continually is only a little over a 

 decade of years, it is unlikely that the supposed solar periods are de- 

 termined in length to within several percent of probable error. It 

 was hoped that if these periodicities were really reflected in the 

 weather, the records of such stations as Berlin, Helsingfors, Copen- 

 hagen, and others which are published for over a century, might enable 

 the lengths of the solar periodicities to be determined to very high 

 percentage accuracy. A change of periodic length shows itself if the 

 successively determined forms of any assumed period, as for example 

 II months, are plotted successively vertically over one another. The 

 maxima and minima will be found to shift steadily to the left or the 

 right according as the true period is less or greater than ii months. 

 The first station records worked upon were those of Berlin. 



13. Full Lines Required in the Statistical Tabulations 



It is well known that the temperatures and precipitations frequently 

 tend to depart from normal values continually in a given sense during 

 considerable intervals of time. This must be so if the assumption 

 of a plurality of regular periodicities in weather is a true one, for 

 the combination of several periodicities must lead to prevailingly high 

 values at some times and prevailingly low values at other times. Hence, 

 if a table for computing a periodicity is arranged as indicated above 

 in caption 4, it is improper and leads to error if the first and last lines 



