150 BIRKEI.AND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 1903. 



curvature. Two things might now be possible; either the curvature might continue to increase, when 

 we should obtain a spiral, or it might decrease, and the lines pass westwards through the South Atlantic, 

 and thus form elliptical paths. We may conclude from the rapid decrease of the perturbation out 

 towards the sides, both eastwards in Europe and westwards in America, that the current-system must 

 appear both in the neighbourhood of the American stations and in that of the stations in the west of 

 Europe; or to speak more precisely, the bulk of the system ought to lie at a distance from the West 

 European stations that is small in proportion to the distance between Pola and Tiflis, or between Wil- 

 helmshaven and Pawlowsk, as the perturbation at Pawlowsk is only a fourth part of that at Wilhelms- 

 haven, and the perturbation at Tiflis is almost imperceptible. 



It will be seen that the effect over the district Wilhelmshaven, San Fernando, Stonyhurst, Pola, is 

 of about the same magnitude. As this constitutes an area that has a section almost equal to the distance* 

 between Pola and Tiflis, we should be able to conclude that the current-system itself has its greatest 

 density in this district. 



In order to draw conclusions from the vertical intensity at Pawlowsk, which is directed downwards, 

 they must be electric currents above the earth's surface, with which we have to do. 



These currents would then have to be sought at a height that was small in proportion to the earth's 

 dimensions, small indeed in proportion to the distance between Pola and Tiflis. 



We can draw similar conclusions for the stations in the western hemisphere. 



On account of the convergence of the forces, it might perhaps be natural to seek an explanation 

 of the system in the effect of a south pole situated in their point of convergence. But the 

 effect from this point would not be able to account for the properties of the field. While this pole 

 should be acting strongly, both in America and in Europe, we see that the force from Pola to Tiflis 

 passes from a value that lies near the maximum of the values observed, to an almost imperceptible 

 amount. The bulk of the current itself must thus pass over the place in about the direction given by 

 the current-arrows. 



If we assume the current to be of a cosmic nature, and consisting of electrically charged particles 

 in motion, we see that it is deflected in just such a manner as would result from the movement of the 

 current in the magnetic field, as in the northern hemisphere we must get vortices with a movement 

 contrary to that of the hands of a clock. 



The simple course of this perturbation enables it to be very carefully studied. The form of field 

 also exhibits conditions of a simple nature. The perturbation cannot be referred either to the equatorial 

 or to the polar storms, but is of a special type. Its chief characteristics are that it is as great in medium 

 as in high latitudes, and that the current-lines are vortical in form. For this reason, we have called 

 these perturbations cydo-mcdian. 



The perturbation of the type now under discussion, does not, however, appear as a free current- 

 vortex. 



However the system may be constituted, it is almost stationary all through the time of its appear- 

 ance, the relative strength of the perturbation remaining constant all the time. 



With the material at our disposal, it is impossible to draw any certain conclusions as to the com- 

 position of the current. 



From the stability and immobility of the system, it must necessarily follow that it is ruled by 

 higher laws. 



It is difficult to suppose that such a system might arise and be maintained only by means of pro- 

 cesses on the earth, as in that case other more variable and compound forms would be brought into 

 action. It is probable, on the contrary, that the current-systems in question are produced by the emission 

 from the sun of very stiff rays of electric corpuscles ; for then all the corpuscles that reach the earth will have 



