.S26 



P.IRKKLAM). IHi: NOKWKC.IAN AURORA POLARIS KXPKI >1TION, 19O2--I9O3- 



ANNUAL VARIATION OF STORMINESS. 



99. Observations have not been made for a .sufficiently long time for an exact determination of 

 the annual inequality. The longest period of observations, that of Axeloen, only covers a time of about 

 nine months. 



The average total stonm'ness at Axeloen for each month during this period is given in the 

 following table. 



TABLK XCII1. 



The numbers indicate two maxima, one in the autumn and one in the spring, or about the same 

 type of variation as found (or the annual variation of aurora borealis. Under the heading L is given 

 the average latitude of the centre of the sun's disc for each month. \Ve notice that the main feature 

 of the variation of S follows that of the absolute value of L; but the maxima and minima of S T seem 

 to occur somewhat later than the corresponding ones for L. 



It thus seems as it tin- annual inequality may be explained by assuming that the intensity of this 

 electric radiation on an average is weaker at the sun's equator than at some distance from it; for if the 

 radiation leaves the sun perpendicular to its surface, and if the sun's magnetic axis forms an insignificant 

 angle with its axis of rotation, the rays which at any time shall reach the earth must start from points 

 having about the same hcliographic latitude as the centre of the sun's disc. It must however also be 

 taken into account that the pencils consisting of diverging rays from the solar spots of radiation are 

 probably somewhat bent towards the magnetic equator of the sun. We shall return to this question 

 in the chapter on the results of the experimental investigations with a magnetic cathode-globe in 

 vacuum-cases. 



A resume of the above investigations on "Storminess" at our four polar stations has already been 

 published in a communication to the Congres de Radiologie in Brussels, 1910. See also Arch, de 

 (ieneve XXXII, August, 1911, pp. 97 116. 



Since writing the above, I have seen a paper by Ur. BIDLINGMAYRR, published by the Kaiserliches 

 Obscrvatorium at YVilhelmshaven (Berlin, 1912), in which the author has introduced the idea "terrestrial- 

 magnetic aetivitv", which has certain points of resemblance to that of "storminess" introduced here. 

 I >r. Bidlingmaver has employed the idea for observations from Wilhelmshaven in the year 1911. 



It is a highly interesting fact that Dr. CIIRFJ: in his most valuable "Studies in Terrestrial Magne- 

 tism", London, 1912, Chap. XVII, makes some reflections concerning sunspot relations that agree well 

 with the results obtained by our analysis. 



Our results on storminess here given were printed as early as 1910, and only the last two pages 

 have been reprinted in 1913, two lines having been removed and a few lines added in conclusion. 



