( 788 ) 



earth-currents, but more observations under other circumstances will 

 undoubtedly be necessary. 



It seemed important to me (o investigate whether that great 

 difference in earth-current is always incidental to difference in amplitude 

 of the magnetic variations. 



For, Buitenzorg lies on the edge of the volcanic Southernpart of 

 Java, and Batavia lies in the Northcoastplain ; moreover simultaneous 

 registrations of the magnetic component are for both places available. 



I have used the registration of the X-component at Batavia on the 

 earth-current diagrams and of the TöPFER-Uni filar of the X-component 

 at Buitenzorg. 



In January, February, March, July, August, September the magnetic 

 variation-instrument registered on the earth-current diagrams the mag- 

 netic component perpendicular to the direction Batavia — Anjer, i. e. 

 N4°E. The difference in direction with that on ïöpfer's instrument 

 with which the X-component was registered, can be neglected. 



On each diagram I compared the amplitude of a variation of short 

 and of long duration, as much as possible at an ecpial distance 

 from the basis. In this way I was independent of differences in values 

 of the scale division and other differences. 



I got as average case in 30 cases in the months of January — 

 March '07 and 24 cases in the months of June — September '07 : 



Average Amplitude of the 

 Variations of Variations of 



short duration. long duration. 



Buitenzorg Batavia Buitenzorg Batavia 



1.44 m.m. 13.21 m.m. 2.68 m.m. 21.27 m.m. 

 1.01 „ 8.71 „ 2.93 „ 24.03 „ 



1.25 m.m. 11.21 m.m. 2.79 m.m. 22.49 m.m. 



22.49 

 Whilst thus the longer variations give a proportion -y— = 2.01, 



2.79 

 the short pulsations give — - = 2.24. 



1 .Z Ü 



That difference of J0 7„ 1 believe must be ascribed to the following 

 circumstance : 



According to the image of the earth-current diagrams, on which the 

 pulsations are large and easy to see, the points of reversion are 

 pointed. On the Buitenzorgdiagrams on a ± ten times smaller scale 

 those sharp points are blunted and we obtain a too small amplitude. 



That shortening can be estimated at a tenth millimeter^ i. e just 

 10 7o of the amplitude. 



