( 532 ) 



Ad. Schmidt (Met. Zeitsch. 1902 p. 94) brings the supposition 

 forward that the current can be generated in the wire by induc- 

 tion onl}^, thereby supposing: the wire to be closed by the earth. 



Then putting the case very simply we arrive by application of the 

 rule of Ampère at : 



dX d^Z 



Ae—\v =^ — y - — + d" . 



dt difdt 



This gives the difference with respect to the above that the 

 variation Z makes its appearance. 



The Z, however, changes but little in equatorial regions, so it 

 cannot make the theory correspond to the observations. 



The slow increase of the earth-current when the frequency increases 

 does not point to induction, but rather to direct connection wiih 

 the primary current. 



The quantity has indeed, compared to — , rather a slow 



1 -|~ ^ ^ 



course. 



That difference in phase is according to Schuster-Lamb rather 

 decreasing for quicker vibration whilst for the earth-current it proves 

 to be constant. 



But whence the difference in phase? 



The differences in the intensity and the difference in phase of the 

 earth-current for the lines to Anjer, Cheribon, Billiton and Buitenzorg 

 can be explained also by the difference in conductivity of the ground 

 between those places and Batavia. 



For instance between Anjer and Batavia lies the volcano Karang 

 and therefore the conductivity is probably greater than between 

 Batavia and Cheribon, and the fact that the earth-current is four 

 times as strong can be attributed to it. 



The great intensity of the earth current for Buitenzorg — Batavia 

 may be partly attributed to the same reason and moreover to the 

 difference in height ( 280 M) ; that between Batavia and Billiton to 

 the well conducting seawater. 



For the lines Semarang — Batavia and Soerabaja — Batavia we find 

 however for the ratio of amplitude a distinct difference for vibra- 

 tions of short duration. Each attempt at explanation of the connection 

 between earth-current and magnetic variation will be in vain as 

 long as this has not been confirmed and expounded. 



To explain it out of the loss by isolation is impossible, as the 

 difference would have to appear less for the lines Anjer-Batavia 

 (106 K. M.) and Cheribon-Batavia (200 K. M.) which is not the case. 



