( 529 ) 



variations of the magnetic component might be explained by the 

 passage of electric current vortices. 



Following this explanation we should have to conclude for Batavia 

 to the passing of vortices whose centre remains far from Batavia, 

 so that only the outside slightly bent pieces of current pass by. 



So as a first approximation we may assume that the extra-terre- 

 strial current is almost rectilinear at Batavia and when varying in 

 intensity has but slight oscillations in direction. 



The average direction must be WSW — ENE for almost without 

 exception an increase of the iV-component is accompanied by a 

 weakening of the ^-component and so AX"^ AY. 



That current we really find back in the diagram of the equipo- 

 tential lines of the daily variation according to Schuster- von BEZoiiD, ^) 

 which equipotential lines follow at first approximation the current-lines. 



Also for the explanation of the phenomenon found by me of the 

 earthiiiagnetic after-disturbance, it was a matter of fact to take a 

 current encircling the earth and this current too had to have a 

 suchlike direction as was mentioned above, but the angle with the 

 equator was at Batavia much smaller than is found now. 



Each varying extra-terrestrial current will induct an intra-terrestrial 

 one and the magnetic variation observed at the surface is the sum 

 of the influence of the two. Lamb (see the paper quoted above of 

 Schuster on the daily variation) proves that the ratio of the potential 

 of the primary and the secondary field is complex and that therefore 

 difference in phase exists. The horizontal component caused by the 

 extra-terrestrial current is in advance compared to the one generated 

 by the inducted currents; so the resulting component will be in 

 retardation compared to the extra terrestrial current. 



By Schuster however no difference of phase is found for the 

 vertical force and Lamb has pointed to the fact that this can be the 

 consequence of increasing electric conductivity of the earthstrata 

 towards the depth. The results of the uqw seismological observations 

 point to an iron nucleus of the earth and therefore to a very great 

 increase. 



We may therefore probably assume that the difference in phase is 

 very little, at any rate that difference in phase is slight for variations 

 of short duration. 



The magnetic force observed consisted of a primary and of a 

 secondary part, which have the same sign as far as the horizontal 

 component is concerned. 



1) Sitz. Ber. der Berliner Akademie fur 1895. 



