794 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 1903. 



Thus the earth-current moves principally in the direction given by this earth-circuit, i. e. from N'VV 

 to SE and vice versa, that is to say, on the whole as in Germany. 



The deflections that occur in the other two curves Paris Nancy and Paris Bar-le-Duc, and 

 that show a somewhat different course, seem therefore to have to do only with details in the 

 phenomenon. 



As it is very difficult, if indeed possible at all, to find sufficiently distinct points of agreement 

 between these last curves and those from Germany, it would seem probable that the variations here 

 observed might be contingent in a comparatively greater degree upon the local geographical conditions 

 in this country. 



But in all essential phenomena we find a satisfactory agreement between the conditions in Germany 

 and those in France. 



In England too, in the various curves, we can to some extent find the same peculiarities as those 

 here pointed out. The principal deflection in the earth-current here, however, is not nearly such a good 

 example as in the material previously dealt with, but seems to be of a similar character. The deflec- 

 tions, however, are considerably smaller, and comparative!}' strong effects of wandering currents evi- 

 dently break in and efface many of the smaller deflections with their characteristic peculiarities. 



The first and most powerful deflection, simultaneous with an increase in the deflections in D, is 

 here too, exceedingly distinct in both components, while the last, most marked bend during the time 

 when Pd is diminishing, is extremely inconspicuous. 



As regards the details, there can be seen, especially in the magnetic curves, a number of the same 

 small, characteristic jags as in the two previously-considered regions; and they are also exceedingly 

 typical here. 



They can also be observed in the earth-current curves, but only sometimes distinctly, on account 

 of the small degree of sensitiveness and the great local disturbances. 



In all the other cases here brought together, in which we have simultaneous registerings from two 

 of the three districts, exactly the same conclusions may be drawn as here, namely, that the earth- 

 currents behave in all cases, in the main, uniformly throughout the district. Characteristic deflections- 

 both large and small, are followed, as a rule, synchronously, and the magnetic influence of the earth- 

 currents upon the magnetic elements has its outcome in the exact uniformity in all the details, especially 

 of the course of the horizontal intensity curve, at the various stations within the district under con- 

 sideration. 



The fact that the course of the declination-curve is so strikingly similar at the various stations 

 should be accounted for, according to what has been said, by the almost identical effect of the com- 

 bined extraterrestrial and intraterrestrial current-systems upon this magnetic element at the various places 

 within the district. Concerning this, I need only refer the reader to the various comparisons of curves 

 given in the plates. 



162. In the preceding pages, we have principally considered the conditions during polar storms, 

 and throughout have found our former precisely-defined view of the phenomena confirmed. 



We have, however, also included a number of examples of positive equatorial storms. 



The chief peculiarity of these storms consisted, it will be remembered, in the rather sudden ir 

 crease in the horizontal intensity all over the earth, the deflection thus obtained remaining more c 

 less constant for a period of varying length, until, as a rule, other forces of a more polar nature 

 interfered. 



At first, also, a deflection in the //-curve to the opposite side was very frequently found. 



