PART 1. ON MAGNETIC STORMS. CHAP. II. 



I2 7 



This circumstance, together with the fact that the effect at the side, at right angles to the current- 

 arrows, ceases before very long, can only be explained by the assumption of a comparatively low-lying 

 horizontal part of the current, which passed between Axeleen and Kaafjord, and a little to the south of 

 Dyrafjord. This horizontal part of the current forms the connection between the upward and downward 

 flowing vertical currents. Perhaps at about o h 28 m , the current has passed south of Kaafjord, but has 

 then turned off over this place to take up the above-named position. The curve for P, at Kaafjord seems 

 to indicate the transverse passage of the current over this place at the beginning of the polar perturba- 

 tion. We have seen, moreover, that the field may always be assumed to have been produced by a 

 system such as this, which, in order to explain the variation of the field with time, must be supposed 

 to be moving eastwards along the auroral zone (see the perturbation of the I5th December). 



We have mentioned the remarkable fact of the maximum occurring earlier in Central and Western 

 Europe and the United States than at the arctic stations. This is a necessary consequence of our 

 assumption, At o h 30, when the perturbation is at its height on the continent of Europe, these stations 

 lie considerably to the east of the point of convergence, which, on account of the direction of the forces, 

 must be looked for in the region of the North Atlantic. Owing, however, to the movement of the system, 

 the stations on the mainland of Europe, at the time the perturbation in the north is at its height, will be 

 situated in the neighbourhood of the neutral area. This same movement of the system will also cause 

 it to withdraw farther and farther from the American stations. This again will cause the maximum of the 

 perturbing force at these stations to occur before the time at which the current-strength of the system 

 has reached its maximum. This displacement must be greatest at those stations which lie nearest to 

 the current-system; and this we also find to be the case. The displacement, as will be seen from the 

 table, is less at Sitka than at Toronto ; and at Honolulu it is imperceptible, as the time of the maximum 

 coincides with that at the northern stations. 



While this perturbation was going on, remarkable aurora was observed, and earth-currents were 

 registered at Kaafjord. These will be discussed under the special treatment of these phenomena. 



THE PERTURBATIONS OF THE 22nd MARCH, 1903. 



(PI. XX.) 



44. The perturbation of the 22nd March is in reality, like that of the 3151 March, composed of two 

 principal phenomena, an equatorial perturbation and a short, well-defined, comparatively powerful elemen- 

 tary polar storm. As the equatorial one is rather slight, it will not have a greatly disturbing effect 

 upon the polar storm, of which the properties can therefore be fairly accurately determined. As it is 

 the polar storm to which, on account of its simple course, we have especially turned our attention, we 

 have thought it best to class it among the polar elementary storms. 



THE EQUATORIAL PERTURBATION. 



45. This perturbation begins quite suddenly at 12'' 58, with an oscillation that is noticed simultane- 

 ously all over the world. In the equatorial regions, this sharp deflection is uniform in direction, and 

 appears principally in H. About the auroral zone the curve oscillates, and the perturbation is notice- 

 able both in D and H. This first oscillation is shown on 



Chart I, at ij h 4, 



which is the time when it reaches its maximum. About the equator the arrows are comparatively large, 

 and run about parallel with the magnetic equator. In the south and centre of Europe, the current-arrow 

 points considerably towards the north, as compared with what is generally the case during these 



