— 243 — 



= 12'' 40"' m.t. of Götting-en has been inscribed at the place 

 of each station and from that point the successive hourlj' 

 values along the parallel of the station at distances of 15" 

 from W to E. Fiirther the lines of equal vertical intensity 

 have been drawn. 



In the plate the field of force constructed in this luanner 

 is reproduced. 



The arrows indicate the direction of the horizontal vector, 

 but not by their lengtli the magnitude as is usual, because 

 these magnitudes vary largely for the arctic and tropical 

 stations. 



Accordingly, if we give the vectors for the tropical regions 

 a practical length, it is necessary to use very long arrows 

 for the arctic stations, which would inevitably canse confusion 

 in the aspect of the plate. 



Only in case the vector nearly vanishes, the arrow has 

 been substituted by a small circle, the direction being very 

 doubftul in such a case. 



The map makes it evident, that the lines of equal vertical 

 intensity enclose different foei, of which two may be said 

 to be doublé. The eastern arctic one, which shows two 

 maxima over 50 7, {7 = 0.00001 C.G.S.) owes this feature 

 perhaps to the fact that for these regions the field depends 

 on the values of two stations, Kingua Fjord and Jan Maijen, 

 differing much in longitude. It seems not improbalde that onlj' 

 a single focus exists, which, ho wever, suffers some change 

 during the daily rotation. 



The two western foei on the parallel of Greemiuch owe 

 their existence to the values of this station only; notwith- 

 standing it seems better to consider both as the two centres 

 of a double-focus. 



From the foei in southern latitudes the eastern one is 

 partly shown on the map, but the western one is only 

 indicated; the existence, however, of two antarctic foei, 

 corresponding to the arctic ones, may safely be accepted. 



Considering' the directions of the arrows it is obvious, that 



