Fig. 13 Variation with longitude of AH/H (annual change averaged without regard to sign), of the 

 distribution of the proportion of land and water areas, and of secular-change activity approxi- 

 mately determined by the density of the distribution of isoporic lines 



Fig. 14. Distribution of foci of rapid annual change of the magnetic declination, inclination, 

 and horizontal intensity, approximate epoch 1920-1925 



56 



