PART II. POLAR MAGNETIC PHENOMENA AND TERREI.LA EXPERIMENTS. CHAP. Ill 547 



The result for Kaafjord of the separation of small and large storms is the most remarkable. 

 If 33 'u of small storms are removed, the quantity v becomes infinitely large, that is to say that out of 

 the 67 "' u of storms greater than a certain value, no oiif appears during the calm period. 



For the other three stations .1' has a finite value. The reason for this is partly the fact that the 

 percentage of small storms taken out is smaller for these stations. 



For Matotchkin-Schar has the large value of 10.7, although the small storms removed only make up 

 2 3 % f tne whole storminess. If we were to increase the upper limit for small storms so as to 

 make the percentage a little greater, we might expect to find perfectly calmness. 



Also for Dyrafjord and Axeloen 2 increases rapidly with the percentage of small storms taken out 

 but not quite so fast as for the two former stations. 



The rapid increase of .T for great storms shows that the storminess of the calm period is almost 

 entirely due to comparatively small storms showing a diurnal distribution somewhat different from that 

 of large storms. 



The two maxima for Sf, at AxelOen, one four hours before, another four hours after, midnight, 

 follow the group of large storms. Thus in spite of the fact that these storms are so limited in their 

 sphere of action that they produce practically no effect at Kaafjord, they appear at Axeloen as fairly great 

 storms. I think this will clearly show that the current-systems causing the disturbances carry a compara- 

 tively small amount of energy, so that they can only produce the great effect at AxelOen by passing 

 near to the station. 



THE DISTRIBUTION OF STORMINESS AND THE SOLAR ORIGIN OF POLAR STORMS. 



106. The existence of a well marked diurnal period of polar storms was already shown in my 

 previous work "Expedition Norvegienne 1899 1900". See p. 16, and PI. II. The type of variation is 

 tumid for Hossekop for the period 1899 1900, and for a number of other stations for term days during 

 the polar year 188283. The diagrams are in good accordance with the present results found from a 

 more complete statistical treatment. 



From the study of the occurrence and motions of the perturbing fields, I was led to the conclusion 

 that these fields followed the diurnal motion of the sun (See: "Exp. Norv. etc." p. 29), a result which 

 has been brought to full evidence through the present investigation. 



The diurnal distribution of perturbations shows immediately that some part of the storminess, in 

 some way, must be connected with the sun. 



One of the most interesting features of the diurnal variation is the existence of a well-marked 

 calm period. I think this is a property of the storminess which may serve as an important test for an}' 

 possible explanation, and we shall subsequently see how far it is in agreement with our own theory. 



The properties of the diurnal distribution of storminess for a certain interval of time can be ex- 

 pressed in the following simple way: At any moment there is a region of the earth with great distur- 

 bedness. This region is not symmetrical with respect to the axis of the earth, but is mainly restricted 

 to the night and evening side, and extends from places near the magnetic axis to places some distance 

 to the south of the auroral zone, where the storminess rapidly diminishes. At the night end of the 

 disturbed area we have negative, at the afternoon end positive storms, and nearest the pole we have an 

 area of very local disturbances. On the evening side, between the two types, there is no calm region, but 

 the two types will to a certain extent overlap. 



From the diurnal distribution we can draw some interesting conclusions regarding the amount of 

 storminess which is a direct effect of the sun. 



Suppose part of the storminess was produced by something showing a period different from 24 

 hours; the storminess from such a cause would be evenly distributed over all hours of the day. 



