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tromagnet. Its magnetic state or its magnetic moment must 

 in consequence of it be submitted to changes by electrical 

 currents on its surface. The earth constitutes a core of a 

 eoil with a feeble current represented by the earth-currents. 

 The influence exercised on our magnetic instruments of 

 variation would hence be double: a direct influence of the 

 earth-current being beneath the instrument and an indirect 

 influence through its effect on the moment of the earth as 

 a magnetic body. 



When a current is going in E — W direction beneath 

 the magnet it will exercise the same effect in both cases. 

 that is to say a reinforcement of the horizontal component. 

 manifesting itself by an augmentation of the directing force 

 of the magnet. A current in the S — N direction will remove 

 the declination magnet to the east and change the magneti- 

 cal moment in the same sence. The direct effect is much 

 smaller in most cases, but it attains the magnet in the same 

 moment as it removes the magnet in the galvanometer. The 

 indirect effect cannot be manifest in the same moment: it 

 requires the time necessary to make its effect on the core 

 (the earth). The interval increases with the greatness and 

 other properties of the core, but it is not yet well deter- 

 mined. 



From this point of view the interval between the varia- 

 tions in the earth-currents and those in the earth-magne- 

 tism is easily explained and is to find in the time required 

 of the earth-current to make its influence on the earths 

 magnetism. 



Besides these two forces \ve must add the current 

 from the atmosphere, which is going on principally above 

 the maximum belt of the auroras and exercises an effect on 

 our magnetic instruments 



Mr Wild finds in general the conclusions of Airy con- 

 firmed and is inclined to regard the earth as a magnetic core 

 of a coil, represented by the earth-current. 



The observations at Sodankylä show that the conclu- 

 sions of Airy are in general confirmed, namely: that the 



