Fig. 6. Isoporic chart for vertical intensity (lines of equal annual change), approximate epoch 1920-1925 

 (Position of isopors in high latitudes, especially near the magnetic poles, very uncertain) 



Fig. 7. Isoporic chart for total intensity (lines of equal annual change), approximate epoch 1920-1925 

 (Position of isopors in high latitudes, especially near the magnetic poles, very uncertain) 



Fig. 8. Isoporic chart for north component (lines of equal annual change), approximate epoch 1920-1925 



52 



