CHAPTER I. 

 POLAR MAGNETIC STORMS 18821883. 



81. The Treatment of the Observations from the Polar Expeditions of 1882 & 1883. 



In the discussion of the magnetic storms in Part I, it was frequently pointed out that we obtained 

 only an imperfect knowledge of the conditions round the auroral zone, owing to the fact that, 

 with the exception of our four arctic stations, all the stations from which we had observations were in 

 southern latitudes. We have frequently drawn conclusions as to how the phenomena up there might 

 naturally be assumed to have developed, if the perturbation-areas that appeared in southern latitudes 

 could be explained by the previously-mentioned simple points of view. 



We will therefore, in this part of our work, subject these conditions to a closer study, and will 

 then be able to see whether the actual conditions round the auroral zone prove to be in accordance 

 with our previous conclusions. 



It is the polar storms in particular that will make an interesting subject of study; and it will then 

 be especially necessary to investigate the movement and formation of the various systems of precipitation 

 in the course of the twenty-four hours. 



It will be remembered that in the compound storms of 1902 03, we arrived at a very simple 

 interpretation of the occurrence of the polar storms, and of the changes in their main features. This 

 interpretation we now have the opportunity of verifying, and even supplementing on various points. We 

 will here recall to the reader's mind the more important of the main features. 



In the first place, we divided the polar storms into two kinds, namely, the negative polar storms, 

 during which we found negative values of PI,, in the district of precipitation round the auroral zone, and 

 the positive polar storms, during which we found positive values of PI, in the district of precipitation 

 (see Art. 69. Part I). 



The negative storms had, as a rule, an extensive area of precipitation on the night-side of the earth, 

 and also on the day-side in high latitudes (Axeleen). The positive storms had a more limited district of 

 precipitation, and as a rule appeared on the afternoon-side of the earth. 



It further appeared that during the great magnetic storms, these areas of precipitation seemed to 

 move, the movement to some extent following the sun in its apparent daily course round the earth, and 

 being dependent upon the sun's change of altitude above the magnetic equator (see Art. 71, Part I). 



In the material we are now going to study, these conditions can be investigated far more thoroughly. 

 In the reports of the international polar expeditions of 1882 and 1883, we have a material carefully 

 worked up, that will prove to be of the greatest interest to us in this study. It is the term-days observa- 

 tions that are of special importance for our purpose. We have at our disposal observations from ten 

 stations scattered round the auroral zone, namely, Godthaab, Kingua Fjord, Fort Rae, Uglaamie (Point 

 Barrow), Ssagastyr, Little Karmakul, Sodankyla, Bossekop, Cape Thordsen and Jan Mayen, and also 

 from Fort Conger, a station situated in the vicinity of the magnetic axis of the earth, and from some 

 more southerly stations, four of which have been employed, namely, Christiania, Pawlowsk, Gottingen 

 and Kasan. 



