7G 



variations of the earth-currents are the primary causes 

 to the magnetic perturbations. It exists however in the 

 earth-current variations which do not correspond to any 

 magnetic variation and vice versa. The first are either too 

 small to exercise an influence or consist of alternat currents, 

 which annul the effect of each-other. 



That this explanation is right results i. a. from a com- 

 parison between the earth-currents in two lines, the earth- 

 plates of which are advanced a length of about half the 

 distance between them in each line; (see fig. 7) it shows 

 cleaiiy the local nature of the phenomenon in exceptional 

 cases. In general the gal vanometers in each line follow 

 each-other as closely as it can be expected, but exceptions 

 occur. The deviations are then often in opposite directions 

 and of different intensity, showing that the potential in the 

 earth increases and decreases very rapidly in a relatively 

 short space. We must hence conclude that only one part 

 of the earth-currents are going around its axis and the other 

 part flowing in closed curves on its surface. Their effect 

 on the earth-magnetism in such cases must be very little 

 or none. 



The magnetique perturbations, which do not correspond 

 to those in the earth-current, can have their cause: either 

 in earth-currents which appear in other regions of the earth 

 or in the currents from the atmosphere as above mentioned. 

 The deviation in the last named case depends on the po- 

 sition of the magnetic needle to the space in which the 

 current is flowing and on its direction. 



A comparison between the simultaneous observations 

 in Pawlowsk and Sodankylä shows that a nearly perfect 

 concord exists in many cases, but well pronounced une- 

 qualities appear also, proving that the phenomenon can be 

 of local nature. It is however probable that the greatest 

 perturbations appear över the whole globe. 



A comparison between the simultaneous observations 

 in Sodankylä and Kultala offers a special interest. It results 

 from them i. a with high probability that, as it exists in the 



