78 



of potential between a given point in the atmosphere and 

 the earth in a certain moment and thus we know the EMF 

 of a current from this point to the earth if they would be 

 united by means of a conductor in the same moment, but 

 we do not know what a EMF will occur in the next mo- 

 ment. The same is the case if we determine by electrome- 

 ter the difference of potential between two points in the 

 atmosphere, situated for instance in vertieal direction. We 

 know in a given moment the EMF between them if they 

 are united with a conducting wire, but we do not know it 

 in the next moment. Such a difference of potential, is a 

 necessary condition for an electrical current, but it does not 

 include that the potentials itself must undergo changes, for 

 instance by time of polarlight, but only that a difference 

 always exists. 



An electric air-current can therefor flow, without beeng 

 detected by the electrometer. 



The studies of the magnetic perturbations have shown 

 a fact which speaks in a striking manner for the existence 

 of an el. current from the atmosphere to the earth. This 

 remarkable fact was discovered by M:r Wijkander, who 

 among others made magnetic observations in Polhem at 

 Spitsberg 1872 — 73. Comparing observations on magnetic 

 perturbations from polar-regions with such from observatories, 

 situated in more southern latitudes he received the follo- 

 wing results. 



Dividing the perturbations of declination in West and 

 East perturbations we shall have: 



West perturbations East perturbations Stations in middle 

 Max. Min. Max. Min. latitudes. 



