PART I. ON MAGNETIC STORMS. CHAP. III. 175 



As regards Europe and Asia, the circumstances on the whole justify the decomposition of the per- 

 turbing force. In America the forces act the whole time almost in one direction, so that decomposition 

 there cannot be effected. 



THE PERTURBING FORCES. 



58. In giving a detailed description of the field of force, we will divide the subject into three 

 separate sections, viz. 



(1) from the commencement of the perturbation up to i6 h 15, 



(2) i6 h I5 m to i7 h i5 m , that is, during the powerful intermediate storm, and 



(3) T 7 h I 5 m to its termination. 



The conditions during the first section are shown on the Charts I, II, III, and IV for the hours 

 I4 h 30, 15'' o m , i6 h o m , and i6 h 15. 



During this period the field of force in southern latitudes, and also at Dyrafjord and Kaafjord, 

 remains fairly constant. At Dyrafjord the current-arrow points along the auroral zone, but in an easterly 

 direction. At Kaafjord its direction is SE and E, and at Pawlowsk SSW. At the stations in Central 

 and Western Europe their direction is WSW, and in the United States WNW. 



We thus see that the current-arrows in these districts during this period maintain the form of a 

 positive vortex, which means that there is here an area of divergence for the perturbing force. 



It will be seen that the arrows at Dyrafjord and Stonyhurst are in opposite directions, indicating 

 that the point of divergence must lie between these stations, that is to say somewhat to the north-west 

 of Scotland. In the vicinity of the point of divergence, P\ = o. We find moreover that the arrows in 

 the district between Pola and Stonyhurst decrease throughout, and even at Wilhelmshaven are compara- 

 tively small. In accordance with our theory, the vertical arrows at Kaafjord have downward direc- 

 tion. The arrows at Ekaterinburg and Irkutsk indicate further that there is also an area of convergence 

 for the perturbing force with a storm-centre lying in the north-east of Siberia. During the first part, 

 hardly any perturbation is noticeable at the equatorial stations, the force on the charts at 14'' 30 m and 

 I5 h being either zero or very small. 



In the district about Dehra Dun, distinct perturbations do not begin until about I5 h , and at 

 Honolulu half an hour later, indicating the existence of a perturbing force directed almost due south, 

 along the magnetic meridian. 



It appears from the curves, as also from Charts III & IV, that the perturbations at Dehra Dun and 

 at Batavia are very similar both in magnitude and course. 



The current-arrows moreover are very different in direction from what one would expect if the 

 direction were to harmonise with the field farther north, that is to say if it were a direct effect of polar 

 systems. For this reason it seems probable that it is not exclusively polar systems that we have to do 

 with here. On looking at the charts (III & IV), we receive a very decided impression that in addition 

 to the polar system, which undoubtly exists, there is an equatorial system, or more correctly speaking 

 a system of which the greatest effect is to be looked for in low latitudes. The fact that the system in 

 north has lasted for a appreciable time before anything is noticed at the equator also goes to prove that 

 the perturbation in the south is due to something relatively independent. 



The conditions at the Norwegian stations, Dyrafjord and Kaafjord, have been already mentioned. 

 The perturbation there is rather slight, and the curve quiet in character. The conditions moreover are 

 closely connected with those farther south. 



As regards Matotchkin Schar, the current-arrow is at first eastward in direction, along the auroral 

 zone, that is to say in direction similar to that at Dyrafjord. At i6 h o m the force has already changed. 



