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Geophysics. — " Registra tio7i of eartli-cuvvents nt Batavia for the 

 investigation of the connection between earth-current and force 

 of earth-magnetism." By Dr. W. van Bemmelen at Batavia. 

 (Communicated by Mr. J. P. vam der Stok). 



(Communicated in the meeting of December 28, 1907.) 



Notwithstanding the j^reat progress in our knowledge of the phe- 

 nomena of earth-magnetism, the desired improvem-ent has not yet 

 been noticed in the explanation of these phenomena. 



That the different variations to which the magnetic needle is liable 

 are the consequence of the changes of electric currents has become 

 highly probable and the place, too, where in that case the currents 

 are to be found is no longer entirely unknown to us. 



So Schuster-) has proved that the daily variation is in general 

 caused by extra-terrestrial currents, whilst I myself have indicated') 

 that this is likewise the case for that part of the magnetic disturb- 

 ances which shows a regular daily variation. 



Suchlike electric currents have, howcN'er, not been shown experi- 

 mentally and their indication in those unapproachable regions is for 

 the present not to be expected. 



Only one part of the earth is accessible to us, viz. the outer crust 

 and numerous are the investigations on the electric currents circuiting 

 in that crust. 



However, all these investigations have but poorly advanced our 

 knowledge about the connection between those currents and the 

 magnetic variations. 



The reason is not only to be found in the great experimental 

 obstacles and the lack of cooperation in the various investigations, 

 but especially in the complicated relations of the system of currents 

 in those zones of the earth where those investigations have been 

 made, viz. between 40^ and 70° latitude. 



My supposition that in the equatorial zone, just as for other 

 geophysical phenomena, simpler relations must exist, has been proved 

 to be right by the investigations which I wish to communicate here. 



The annotations of the earth-cun-ent executed by me these last 

 three years at the observatory of Batavia can be divided into two 

 series. 



Daring the first period, March — November 1905, I registered the 



1) Phil. Trans. Vol. 180, p. 667. 



2) Natuurk. Tijdschrift voor N. I. Dl. 63, p. 227. 



