TART 111. EARTH CLJKRK.NTS AND KARTH MAGNETISM. CHAP. 



7 8 7 



As the main direction of the earth-currents very nearly coincides with the direction of the mag- 

 etic meridian, it will be easily understood that the effect of the earth-current is more distinct in D 

 mn in //. 



We have also in the case of H attempted to determine the relation between synchronous deflec- 

 :jns in the earth-current curves and the //-curve and found the following: 



TABLE CXXV11I. 



It is doubtful, however, whether any special significance should be attached to these figures, parti- 

 ilarly as the deflections have not always themselves the same direction. 



Sometimes distinct induction-phenomena may also be found in //, e. g. on 



Nov. 28 29, Sept. 4, March i. 



In these storms we also find a peculiarity similar to that in the D-curve, namely a more or less 

 iirked bending-out of the curve simultaneous with the reversal of the earth-current curves. In such 

 <ses we can distinctly see the effect of the earth-current also in the //-curve; and the amplitude of the 

 i flection harmonises well with the figures found in Table CXXV. 



Finally I may here draw attention to the fact that in cases where this bending-out is distinct, we 

 m infer directly from the course of the curve the effect of the earth current, without at the same time 

 1 ving registerings of the earth-current. This is immediately apparent from what has just been said. 



In the storm of the loth February, we found that the greatest effect of the earth-currents at Kaa- 

 f rd amounted to about V 6 of the greatest effect of the outer current-system. By the aid of the out- 

 \ird bends shown by the magnetic curves in southern latitudes, it is now easy, in accordance with the 

 iovc, to estimate the greatest effect of the earth-current. If we compare this with the greatest effect 

 c the outer system answering to the magnetic force at the time about the characteristic bending-out, 

 c rather perhaps at the beginning of the latter, we find 



H ma* 



p 



Hi max 



Potsdam 0.53 



Wilhelmshaven .... 0.52 



Pawlowsk 1. 1 2 



Tiflis 0.64 



* H ronx 

 "at max 



Kew 0.50 



Stonyhurst 0.54 



Val Joyeux 0.44 



Munich 0.40 



If we compare this with the values we found in the theoretical argument in Art. 154, we see that 



ft the first extreme case the relation -=-- ' varies when one moves away from the storm-centre to a 



f if.- ~. 



dtance of about 20 from it, on an average from 100 to 20, or if preferred from 5 to i, that is to 

 the effect of the earth-current at the last place should be comparatively about 5 times as strong as 

 a the first place. 



