I<«l Prof. E. Ekllund on Atmospheric Electricity 



not possess the force to render the air luminous. The electric 

 fluid is driven into the air, by forces incessantly active, from 

 every point of the earth from the equator to the localities 

 where the downflow is effected ; and that fluid is at the same 

 time conducted from the lower to the higher latitudes. We 

 must therefore admit the incessant passage of currents from 

 the equator towards the poles, while the electric fluid circu- 

 lates in the opposite direction within the earth. This does not 

 mean that the direction of these currents is entirely north and 

 south, many causes contributing to make them deviate from 

 that direction. We picture to ourselves the atmosphere cut by 

 a plane parallel to the equatorial plane and situated between 

 that plane and the auroral ring. The electric fluid driven by 

 the active forces of the earth into the atmosphere between the 

 equatorial plane and the plane in question must then pass 

 through the latter. The sum of the currents passing through 

 a plane of this kind will therefore be greater in proportion as 

 the latitude of the plane is higher ; consequently the intensity 

 of the currents increases from the equator towards the poles. 

 Although the electromotive forces to which these currents are 

 due are always the same, yet their intensity must be subject 

 to incessant variations, seeing that it of course depends also 

 on the resistance they meet with in their course. This resist- 

 ance must depend in great part on the constitution of the air 

 in its lower strata : when these are saturated with humidity, 

 the electric resistance is much less than when they are rela- 

 tively dry. As, for this reason, these primitive currents often 

 vary in intensity, induction currents will result, of a sort to 

 complicate still more the system of currents we are here con- 

 sidering. 



It is obvious that these currents must act upon a declina- 

 tion-needle placed at the surface of the earth ; but to calculate 

 the intensity and direction of the action is not so easy. In the 

 first place, the currents in question act directly on the declina- 

 tion-needle almost in the same manner as the current which 

 passes through the circuits of a galvanometer acts on the 

 needle of that instrument ; and, in the second place, it must 

 be remembered that the earth contains a quantity of magneti- 

 zable materials, the magnetic condition of which is modified 



the zone of maximum of aurone boreales shifts so as to be found more 

 northward during the winter and summer than at the periods of the 

 autumnal and vernal equinoxes. If this be confirmed by future observa- 

 tions, the annual variation ascertained at lower latitudes may be accounted 

 for by this displacement. (See XordUchtbeobachtiivgen der osterreichisch- 

 ungarischen arktischen Expedition 1872-1874, bv 0. Wevprecht : Vienna, 

 1878. 



