( 246 ) 



If we suppose, that a difference of potential rises between Cheribon 

 and Batavia, when a certain variation of the magnetic force occurs, 

 and supposing the gradient of potential to be 1 Volt per K.M., we 

 are able to calculate the potentials rising at the different stations. 



For convenience, sake we may assume the potential at Cheribon 

 to be zero. We find : 



From these and formerly found values we deduce the following 



gradients. 



Potent. 



Between gradient Geological formation. 



Anjer and Serang b.'i Neo-volcanic 



Serang and Tangerang. 1 "> Quaternary 



Rangkas Betoeng and Tangerang 4.1 Quaternary 



Tangerang and Bekassi k 2.1 Quaternary and alluvium 



Bekassi and Kravvang 

 Krawang and Cheribon 

 Cheribon and Semarang 



0.4 Alluvium 



1 .0 Quaternary and alluvium 



0.9 Quaternary and cretaceous 



Semarang and Soerabaja 1.1 Quartenary, cretaceous a. alluvium. 



The geological formations encountered on the different passages, have 

 been borrowed from the geological atlas of Verbeek and Fennema. 



It is not to be denied, that a certain connection seems to exist 

 between gradient and formation, such that the gradient is least in 

 alluvium, greater in quaternary and greatest in the volcanic layers; 

 and neither may it be said, that this succession is improbable. 



Also for the volcanic province of the Preanger in southern Java 

 I found a high value, viz. 3, but here the proportion of amplitudes 

 for current and force bears the other type, which involves the 

 gradient to be small, viz. 1, for oscillations of longer duration. 



The formations given by the geological atlas are those met with 

 at the surface of the earth, and the outlines of the deeper layers, 

 no doubt, will differ much from those of the superficial ones. 



Thus when we find a connection between the strength of the 

 current and the outlines of the superficial layers, this points out that 

 the currents measured are the superficial ones too. 



