PART I. ON MAGNETIC STORMS. CHAP. II. 117 



We here distinctly see that except as regards the arctic stations, one circumstance is very conspi- 

 cuous, namely, that the perturbing force is strongest in the equatorial regions, and decreases towards 

 the poles. Honolulu is an exception to this; but, as mentioned under the perturbation of the 26th 

 January, this may be ascribed to local conditions. The arrows point along the magnetic parallels from 

 west to east. 



In the arctic regions, especially at Dyrafjord, the conditions are different, owing to polar distur- 

 bances. In these regions, indeed, there is hardly ever calm. The distribution of force, and the pertur- 

 bation as a whole, are of exactly the same character as that of the 26th January; we therefore refer 

 the reader to the description of the latter, for its most probable explanation. 



At about 23 h I2 m , after this equatorial perturbation has ceased, comparatively normal conditions 

 appear to supervene, at any rate in latitudes lower than 60; and these are maintained for three quarters 

 of an hour. At the stations nearest to the equator, however, there is now a distinct deflection in H to 

 the opposite side. There is thus now for a time a slight equatorial perturbation, corresponding to a 

 current-system resembling the previous one, but in the opposite direction. 



THE POLAR PERTURBATION. 



42. The storm about the auroral zone is very powerful and well-defined, especially at Dyrafjord, 

 where it appears very suddenly at o h 24, and concludes almost as suddenly at 2 h i6 m . 



At Axeleen the perturbation is observed a little earlier, but the really powerful storm nevertheless 

 commences later here than at the other arctic stations. 



At Kaafjord the perturbation begins very much earlier than at the two previously-mentioned stations, 

 especially in H. As early as 23 h , the deflections in H begin to increase continuously. At o h 24, 

 that is to say at the same time as the storm at Dyrafjord begins, the point of light swings out of the 

 field, to return no more. The reason of this great deflection must partly be that at this hour the sen- 

 sibility was made very great, the magnet being suspended by a thread with small moment of torsion. 

 But if otherwise, on this occasion, the apparatus acted properly, it would at any rate appear that the 

 perturbation began with a low-lying current about Kaafjord, which then developed further into a more 

 extended system, at the same time moving northwards. That the system really moves in a northerly 

 direction seems also to be shown by the very interesting vertical intensity curve at Kaafjord; for at 

 about o h 36, P v , from being directed downwards, turns upwards, corresponding to the flowing of the 

 horizontal portion of the current past the place from south to north. The curve exactly resembles that 

 in the lower diagram in fig. 40. 



The fact that the point of light does not return - i. e. that the magnet goes round to another 

 position of equilibrium prevents our concluding very much from this circumstance; for it is not 



impossible that the enormous deflection is partly due to the almost neutral equilibrium of the apparatus 

 over a large area. 



At about 23 h 50, the effect of the polar perturbation is noticed at all the southern stations 

 throughout the world. At 2 h io m , the normal conditions have reappeared in these latitudes. 



In this, as in so many other instances, Christchurch occupies a peculiar position, inasmuch as con- 

 ditions appear there, which have no parallel in the northern hemisphere. A distinct perturbation is also 

 observable there, however, which to some extent coincides with the perturbation in the northern hemi- 

 sphere, which it also resembles in its course. At the three American stations, Toronto, Cheltenham 

 and Baldwin, a peculiarity is observable, namely, that the perturbation apparently lasts longer in H 

 than in D. 



