PART I. ON MAGNETIC STORMS. CHAP. III. 



195 



as these are very frequent in these regions. This impression is also confirmed by a study of the copies 

 of the curves. 



At Matotchkin Schar the current-arrow maintains the characteristic direction, making oscillations 

 about the main direction. 



Up to the chart for 2o h , the force is almost as strong at Dyrafjord as at Matotchkin Schar; but 

 on the next chart, that for ao h i5 m , the field in the north shows that the storm-centre has moved east- 

 wards. The force at Matotchkin Schar has increased, while that at Dyrafjord has diminished. At the 

 same time the current-arrows for Axeleen and Kaafjord have acquired a distinct divergence. 



In southern latitudes the field is decomposed. The dotted arrows represent the field as it is before 

 and after the polar storm. As regards this field, we will only state that it has on the whole the same 

 character as that in the previously-mentioned perturbation from 9'' to n h . The current-arrow in the 

 eastern hemisphere is directed westwards, and that in the United states towards NNW. 



That which here especially interests us, however, is the field in so far as it is connected with the 

 storm in the north. The current-arrows to represent this force are drawn with broken lines. The field, 

 as we see, may be characterised in a few words by referring to the previously-described polar elemen- 

 tary storms e. g. of the i5th December, 1902, and the loth February and the 22nd March, 1903. This 

 holds good, at any rate during the time when the storm is at its height, and the perturbing forces can 

 be most accurately determined. There is a distinctly-marked area of convergence in the eastern hemi- 

 sphere, and a distinct area of divergence in the western. In Europe the direction of the current- 

 arrows is at first south-west; but between ig h i5 m and ig 11 46, they turn a little counter-clockwise. They 

 then, however, turn back, a turning that is in accordance with the eastward movement of the field, which 

 we deduced from the conditions at the Norwegian stations. Simultaneously with this, there is also a 

 clockwise motion of the arrow at Sitka. 



Although the conditions in the main are similar to those found during the usual polar elementary 

 storms that appear at this time of day, there are also certain deviations from the typical conditions. 

 The force in Europe, for instance, at about 2o h and 20'' 30, seems to be comparatively small, while at 

 Sitka at the same time it is comparatively great, and turns, as we have said, in a positive direction. 

 The distribution of force cannot here be explained by the assumption of a single elementary system. 

 The comparatively great force at Sitka indicates that there is a simultaneous precipitation on the day-side ; 

 and it seems as if in Europe at this time 2o h o m there are possibly two systems counteracting one another. 



We will look more closely into this peculiar variableness of the conditions in Central Europe. 



While the direction varies greatly from place to place, the force is small. There is no doubt 

 that the direction of the force, especially during lengthy perturbations, becomes uncertain, when the 

 absolute value of the force is small, as the unavoidable error in the placing of the mean line with small 

 forces will have a great influence; but nevertheless when we look at the curves, there is a very notice- 

 able change from place to place. This difference is especially evident in the //-curve. Here there are 

 three types of curves; the first is found at the stations Stonyhurst, Kew and Val Joyeux, the second at 

 Wilhelmshaven and Potsdam, and the third at Munich and Pola. Within each type the form of the 

 curve is very similar. 



It has been already said that this storm exhibits many points of resemblance to the storm of the 

 1 5th February, 1903, and in this respect also, there is now a complete accordance between the two days. 

 On that day also the //-curve showed exactly similar differences in the European field; and the stations 

 were separated into exactly the same three groups, a circumstance which strongly confirms our opinion 

 that this is not a chance resemblance. 



