38 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION igO2 1903. 



"At these four Norwegian stations the three magnetic elements will be registered photographically. 

 To this effect registering instruments will be employed like those used by the contemporary Antarctic 

 Expeditions. The three elements will also be determined absolutely. The term observations stipulated 

 by the Antarctic Expedition will also be carried through at these stations. 



The special subject prosecuted by our expedition, and for the fulfillment of which we solicit your 

 kind support are : 



The determination of the cause and progress of different magnetic perturbations, as discussed by 

 me in my report: "Expedition Norvegienne de iSyy 1900 pour I' etude des aurores borcales. Resiiltats 

 des recherches magnetiques" . 



Some information was added as to the best way of making the observations for the purpose desired; 

 and the times for the rapid registerings were fixed. 



As it would have been impossible to have material sent from all the observatories for the whole 

 of this period, it was necessary to confine ourselves to a few fixed days. As soon as we had observa- 

 tions from two of our stations, I sent out a new circular from Christiania, to the same observatories, 

 dated June, i903( 1 ). Part of this was as follows 



"After comparing photograms from Bossecop with corrresponding ones from Potsdam, I selected 

 thirty days, on which general magnetic disturbance was great, as those which most suited my purpose 

 and I have, consequently, determined to adopt these as the basis of my investigations. 1 now take the 

 liberty of asking all those who are in the position to do so, to give or lend me copies photographic 

 preferred --of photograms of magnetic disturbances that may have occurred on those thirty days, and 

 urge them, in the interest of science, not to mind facing the considerable amount of trouble which must 

 be undertaken in order to fill such a request; and, if required, I am willing to refund any expence 

 necessarily incurred in connection with it. In the work that I intend to publisch, I shall reproduce so far 

 I can by photography, a very large number of such photograms after they have been reduced to a uni- 

 form scale as regards time, so that any one may be able to check the results arrived at, by me, from 

 my manipulation of the materials to hand. The variations of most value for my work, are those of the 

 two horizontal elements. In respect to the thirty days in question, when the vertical intensity shows 

 marked variations, it will be, likewise, very important to me to obtain copies of photograms relating to 

 vertical intensity." 



We have in this way, in response to our request, received numerous photographic reproductions 

 of magnetograms and tables of magnetic observations for comparison with simultaneous observations 

 from our 4 stations, from each of the following 23 observatories: Honolulu, Sitka, Baldwin, Toronto, 

 Cheltenham, San Fernando, Stonyhurst, Kew, Val Joyeux, Uccle, Wilhelmshaven, Munich, Potsdam, 

 Pola, Pawlowsk, Tiflis, Jekaterinburg, Bombay, Dehra Dun, Irkutsk, Batavia, Zi-ka-wei, Christchurch. 



We have further received observations of occurrences of cirrus bands -- these being made, while 

 the expedition lasted according to a common plan -- from the meteorological observatories at Valencia 

 (Ireland), Falmouth, Aberdeen, Kew, Aix-la-Chapelle, Von der Heydt-Grube (b. Saarbrucken), Bremen, 

 Uslad, Celle, Brocken, Christiania, Potsdam, Grunberg, Schneekappe, Neustettin, Budapest, Konigsberg. 



For this extreme readiness on the part of my honoured confreres to give their assistance, I would 

 here offer them my warmest thanks. 



It is my hope that the importance of this material to our work will be fully apparent from the 

 subsequent treatment of the subject. 



To one man more particularly, if he had lived, this expression of gratitude would have been 

 addressed, namely the late Geheimrath VON BEZOLD. It was especially through his valuable aid that I 

 succeeded in obtaining such ready response from observatories all over the world as I finally did. 



(') Terr. Magn. and Attn. Electr. June, 1903, pp. 74. 



