( 518 ) 



Notwithstanding the imperfection in these measurements, the double 

 annual period and its correspondence with that of the magnetic 

 component is so distinctly expressed that doubt is not possible. 



Variations of short duration. 



The second period of registration, November 1905 — October 1907, 

 was chiefly devoted to the study of the connection of the vibrations 

 of short duration in earth-current and magnetic component. 



The usual ^•elocity of registration was here 1 mm. a minute, 

 which with sharp photographic lines allows the measurement of 

 variations with the duration of half a vibration of 0.2 to 0.3 minute, 

 but in numerous nights the velocity was enlarged to 4 mm. a 

 minute, when it was possible to measure accurately differences of 

 time of O.'J minute. 



By the continued registration of the earth-current along different 

 lines, each one accompanied by that of the corresponding magnetic 

 component, an extensive material of curves was collected, from which 

 in general the following could be gathered. 



For the earth-current along about east-west lines ^) to each vibra- 

 tion answers a similar one of the magnetic component. For that 

 of the nearly north-south lines that correspondence seems also to 

 exist in part, but it is greatly disturbed by the circumstance that 

 the earth-current keeps following more or less the vibrations of the 

 east-west line. 



So also near the equator ^ve find complicated phenomena, but 

 only in part, for as far as the east-west current is concerned we 

 meet with such a striking correspondence that it is possible to deduce 

 simple laws; the two same laws, which were found for the daily 

 variation : 



1. the vibration in the earth-current precedes that of the magnetic 

 component ivith a certain difference in phase; 



2. the ratio of amplitude of earth-current and magnetic component 

 decreases ivhen the duration of the vibration increases; 



1) The east- west lines were: The north-south lines were: 



Direction Distance Direction Distance 



Bat. — Anjer W 6° N 106 K.m. Bat. — Billiton N 13^ E 392 K.m. 



, — Poerwakarta E 40 S 78 „ , — Buitenzorg S 5 E 46 , 



, — Gheribon E 18 S 200 , , — Soekaboemi S 9 E 84 , 



, - Semarang E 12 S 406 , 

 , - Soerabaja E 10 S 665 , 

 . - Makassar E 5 N 1486 , 



