67 



3. 



The variableness of the magnetic state 

 of the earth. 



The above delineated magnetic state is however a such 

 that the force is variable to its direction and intensity. The 

 changes are of two kinds periodic or variations and occa- 

 sional or disturbances even called magnetic storms. The 

 former are daily, yearly and secular in all the three ele- 

 ments. The daily and yearly variations are characterized 

 by relatively slow movements about an equilibrium-position 

 which however varies every year. The disturbances again 

 possess another character. They consist of vehement re- 

 inovals in the magnetic force both to its direction and in- 

 tensity and are almost, not always, spread över the whole 

 earth. They have been observed simultaneously on widely 

 different places. The both kinds of variations have the com- 

 mon propriety that theyr magnitude increases in a high de- 

 gree, the more we approach the polar-regions and in these 

 regions they present, at least in the more northern, a course 

 opposite to that in the temperate zones. 



It is now clear that this variableness of the magnetic 

 state can not agree with a view of the earth as a perma- 

 nent magnet but on the contrary very well with the appre- 

 hension of it as an electro-magnet viz, as a magnetic body 

 which is kept in the magnetic state by electrical currents. 



Out of the above mentioned theory of Gauss it re- 

 sults that the seat of the earths magnetisme must be with 

 in the Globe and as we knovv with certainty that the solid 

 earth-crust contains at least 2 °/ magnetic matter, we can 

 without doubt regard the earth as a body which can be 

 magnetised for instance by electric-currents. But now rises 



