— 228 — 



H (D,-D J 

 determined hy tg y. = ~^^ — ^p - e(iuals the magiietic azi- 



miith of this difterential vector, wliiih inay l»e called a 

 disturbing vector. 



A first result of these calcidations was that this angk' x 

 was found to be fairlj' constant for each station; and a 

 second result, obtained by means of deriving this azimnth 

 for 28 stations distributed over the earth. that generally 

 speaking this distnrbing vector is directed perpendicularly 

 to the isochasnis (lines of equal frequency of aurora polaris), 

 pointing away from the pole of aurora borealis. 



As it is always allowed to suppose magnetic foi-ce to l)e 

 caused by an electric current directed perpendicularly to 

 the vector, this result led to the hypothesis of a system of 

 electrical currentrings compassing the earth parallel to the 

 isochasms; the strength of current being increased during 

 disturbance, and decreasing at a greater or smaller rate 

 afterwards. 



As S("H^nI)T ') has made it plausible, that tlie more qnickly 

 expiring disturbances are caused by wandering currentrings. 

 we are lead to the following supposition: A system of electrical 

 currents compasses the earth; at every magnetic disturbance 

 not only the strength of current is increased, but numerous 

 current-vortices are originated and wander over the earth. 



This system offers a strong analogy to that of the general 

 circulation of atmospheric air, as it lias been rccently described 



by HiLDKHHAM) HiLDKI'.HAXDSON "j. 



There also we meet the lai-ge polar-cyclone and snmllei' 

 depressions wandering within it. 



It being obvious to suppose, that such a system of cur- 

 rentrings, which has its axis not in the axis of rotation but 

 in a direction differing at aboiit lo degrees from it, must be 

 inflnenced in some manner by tlie terrestrial rotation. the 

 investigation was extended as folldws: 



1) Meteorol. Zeitsehr. l«Vt!», j). 'AH'i. 



'^) Les bases de Ia uieteoroloyiv di/nainiqxe No. ü, 1903. 



