PART I. ON MAGNETIC STORMS. CHAP. IV. 



39 



Fig. 139- 



Our calculated current will lie, for instance, at C (fig. 139), whereas in 

 reality the current may be gathered at a lower level A B. 



In this way the height of the current will be rather an indefinite con- 

 ception; but we believe the values found will at any rate give an approximate 

 determination of the heights at which the greatest density of the current in 

 each separate case must be looked for. 



We will now, in conclusion, see how far the conditions at Dyrafjord 

 and Matotchkin Schar agree with the values found. Assuming the strength 

 of the current to be the same, we will calculate the height at which a 



horizontal current must pass in order to produce the magnetic disturbances that occur at the two 

 stations. If we call the distance from the station to the nearest point in the current r, we obtain 



r= 5P' 

 where P is the total perturbing force. 



If we assume the current to be horizontal, we obtain 



h r sin <p , 



where 



p 



tan = -W- 



TABLE XLVI. 



These calculations show that if the current were horizontal, it would lie especially high above the 

 two stations, Dyrafjord and Matotchkin Schar, particularly during the latter part of the perturbation. 

 Our assumptions for these calculations can only, as we have already said, be regarded as a first approxi- 

 mation; but it is most probable that the erroi will be in the same direction in all the calculations, so 

 that the relative proportions will be fairly correct. If the current were to continue with the same average 

 strength, it could not do so at the same height as between Kaafjord and Axeleen, but would curve 

 upwards. 



This harmonises well with our view of the current-system, which maintains that the system would 

 curve upwards. The actual circumstances at Dyrafjord and Matotchkin Schar could also be explained, 

 however, if we assume that the current there is spread over a large section. Moreover the assumption 

 that the average strength in the advancing current would preserve its value unchanged, owing to the 

 undoubtedly cosmic nature of the current, can by no means be regarded as safe, as the paths of the 

 separate electric corpuscles will be very numerous. The constancy of the average current-strength can 

 therefore only be regarded as a very rough assumption. 



A comparison of the current-strengths found for this perturbation, with those for the perturbation 

 of the I5th December shows that the former are about three times as great as the latter. At the same 

 time the effect of the force at corresponding places in the field outside the arctic regions is much smaller 

 on the 1 5th December -- only about one third. 



