ON AN AURORAL EXPEDITION TO BOSSEKOF 

 IN THE SPRING OF 1913. 



By PROFESSOR CARL STORMER, 



(University of Christiania). 



The following is a short account of a new auroral 

 expedition which I made to Bossekop in the spring 

 of 1915 for the purpose of completing the results of 

 my expedition to the same place in 1910.* 



My assistant was the meteorologist, Bernt Johannes 

 Birkeland, who also went with me in 1910, and is 

 going with Roald Amundsen's expedition over the 

 North Polar basin. 



The purpose of the expedition was mainly to 

 obtain more accurate and a greater number of 

 auroral photographs for the determination of the 

 form of aurora and its height and situation in 

 space, and, further, to experiment with prism- 

 objective photographing and the taking of cinemato- 

 graph films. 



Our preparations and equipment were, on the 

 whole, the same as in 1910 ; but the following 

 improvements, based upon experience gained on 

 that expedition, were carried out. 



The cameras were furnished with an arrangement 

 whereby a photograph of an illuminated watch-face 

 was taken on the plate simultaneously with the 

 aurora. The time could then be read from the 

 photograph, and also the exposure by the sector 

 described by the second hand. This improvement 

 I had already employed in photographing aurora in 

 Christiania in the winter of 1910-11. 



In order to avoid the waste of time in changing 

 plates in a dark room, each station, in addition to 

 forty cassettes, was furnished with changing boxes 

 in which the plates could be changed in the open 

 air. Thanks to this improvement, it was possible 

 on some evenings to take more than eighty simul- 

 taneous photographs at the two stations. 



In order to have the arms at liberty the following 

 improvement in the telephone arrangement was 

 made. The microphone and receiver were fixed to 

 the chest and head and connected with the field 

 telephone apparatus by a cord four metres in length. 

 In this way it became possible to utilise more 

 fully the brief moments during which the aurora 

 displayed its greatest intensity. 



F"or the purpose of obtaining reliable parallaxes a 

 base of twenty-seven and a half kilometres was 

 chosen, as against four and a half kilometres in 1910. 

 The station at which Birkeland took up his quarters 

 was Store Korsnes, the other was Bossekop. As 



assistant at Bossekop I had engaged Sergeant Ottem. 

 The direction from Bossekop to Korsnes was almost 

 due north. 



Through the courtesy of the Telegraph Depart- 

 ment the State telephone line from Bossekop to 

 Korsnes was placed at our disposal every night 

 from 7.30 p.m. 



Thanks to these arrangements, we succeeded in 

 one month in taking the following pairs of simul- 

 taneous auroral photographs at Bossekop and 

 Korsnes : — 



On the six best evenings, the 11th, 14th, 15th, 

 29th, and 30th March and 1st April, the weather was 

 clear and the aurora vivid and continuous, so that we 

 were able to make use of every chance. 



The parallaxes, thanks to the large base, were very 

 distinct, as a rule between five and fifteen degrees, 

 and the large number of photographs — four hundred 

 and forty-seven pairs as against forty-four in 1910 — 

 gives very much more certain and complete results 

 than on that occasion. If we reckon about ten 

 measurements to each photograph, these will give 

 more than four thousand reliable determinations of 

 height. All important forms of aurora were photo- 

 graphed, and there are long series of developments. 



: 'See Bericht iibcr cine Expedition nach Bossekop zwecks photographisclie Aufnahmen unci Hbheninessuitjieti von 

 Nordlichtem, mit 57 Figuren itn Text und 88 Tafcln. Videnskabsselskabets Skrifter, MathNaturv. Klasse 1911, 



No. 17, Christiania. 



263 



