HIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 1903. 



Current-Arrows for the 9th December, 1902; Chart VI at 17k 15m. 



Fig- 35- 



THE PERTURBATION OF THE 23rd OCTOBER 1902. 



(PI. III). 



30. This perturbation does not belong to those mentioned in the circular, and is therefore from 

 only a small number of stations. 



It is especially developed about the equator, and is there characterised as a positive equatorial 

 perturbation. It commences suddenly at ig h u m , simultaneously all over the earth. The curve is 

 serrated in character, and appears only in H, in which it occasions an increase. 



About iV2 hours later, a polar storm, not, indeed, violent, but characteristic, simple and well- 

 defined, appears around the Norwegian stations. It is especially distinct at Matotchkin Schar. This 

 storm has at the same time the properties that characterise the polar elementary storms. The current- 

 arrow points westward along the auroral zone, indicating that the storm-centre, which is situated in the 

 region about Matotchkin Schar, now lies on the midnight side. 



The field of force is shown on a chart, which represents the conditions at 19 h i6 m and 22 h 



22 n 22.5 ' 



At the first-named hour, the field exhibits a typical equatorial character; at the last-named, it is 

 the effect of the polar system, which, at any rate in somewhat more northerly latitudes, is most conspicuous 

 (see the polar elementary storms). 



