-84 lilKKKI.AND. I' I IK NnKWKI.IAN Al'KnKA 1'oI.AKIS KXI'I :l)ll ION, I gOl> [903. 



EARTH-CURRENTS IN LOWER LATITUDES. 



15(5. In the preceding pages, \ve have tried to obtain by theoretical considerations a general 

 idea of the \vay in which the earth-current conditions develope in the vicinity ot the auroral /one. 



In order to conic to a better understanding, however, it will be necessary also to consider the 

 conditions in lower latitudes somewhat more closely. 



This seems to be all the more neccssarv from the tact, already mentioned, that the views on the 

 subject of earth-current phenomena in these regions, held by those scientists who have studied them, 

 are verv conflicting. 



For the purpose of undertaking an investigation such as this, Mr. Krogness. with the aid of a 

 grant from the University, went to Germany in the summer of 1910, in order to study the original 

 curves from Professor VVeinstein's material, and compare them with simultaneous magnetic curves from 

 \Vilhelmshaven or Potsdam. An investigation such as this, based upon the points of view maintained 

 above, would be of peculiar importance, especially as Professor Weinstein himself, after similar studies, 

 had arrived at a result that appeared to be at variance with our view of the phenomena, A great part 

 of this material proved to be accessible, but unfortunately, there were only a few days on which there 

 were simultaneous observations ot the two earth-current components. The one component, however, as 

 we shall presently see, seems to be sufficient tor our investigation. 



Through the kindness of Professor IS. \Ycinstein and Professor Ad. Schmidt in Potsdam, where 

 this material is at present preserved, Mr. Krogness obtained the loan of a number of original curves 

 with copies of simultaneous magnetic curves trom Wilhelmshaven. 



In the spring of 1911, Krogness and I, as already mentioned, made an expedition to Egypt and 

 the Soudan for the purpose of studying the xodiacal light. On the way home, we spent a few days at 

 Pare St. Maur and Greenwich, in order to go through some of the original earth-current registerings 

 made at these observatories. Krogness had the opportunity of making photographic copies from 

 a series of characteristic perturbations. The observatories further had the kindness to send us copies 

 of a number of other selected storms. 



Finally, we have had sent us from Pawlowsk a couple of photographic copies of the earth-current 

 registerings made at that station. 



As the working up of this material is inseparably connected with the investigations of the earth- 

 current conditions in the polar regions described in the preceding articles, Krogness has kindly handed 

 over the material he collected, so that the whole can be studied together. 



In order to obtain as comprehensive a view as possible of the connection between earth-current 

 and magnetism, we will here produce a number of copies, principally photographic. The magnetic 

 curves from Wilhelmshaven are the only one's for which drawing on transparent paper has been em- 

 ployed. For the sake of the reproduction, however, we have had to darken with Indian ink those parts 

 of the curves that were faintly reproduced; but this has been done as little as possible, and always 

 on the photographic copy itself. We thought that in this way the curves would best preserve their 

 character, which is here of importance, as it is often in the small details that the greatest resemblance 

 is found. 



EARTH-CURRENTS IN GERMANY. 



157. \Ye will first consider the curves from Germany. 



Two earth-circuits were employed here, namely, Berlin to Thorn (V. \\'|, and Berlin to Dresden 

 (X S), and the scale-value was determined daily by the interpolation of known electromotive forces, as 

 more fully described by Weinstein in his treatise (I.e., p. IT). 



