Fig. 17. 



Amount of extrapolation, in gammas, from last surrey-yalue per 30° -tessera to epoch 

 1945, magnetic horizontal intensity, basis isopors 1920-1925 



Fig. 18- -Amount of extrapolation. In gammas, from last survey-value per 30° -tessera to epoch 

 1945, magnetic vertical intensity (positive downwards), basis isopors 1920-1925 



58 



