[ 47 



IV. Recent Results of Northlight Investigations and the 

 Mature of the Cosmic Electric Rays. By L. Vegard, 

 Professor of Physics at the University of Christiania *. 



[Plate II.]. 



§1. IN a series of papers t previously published I have 

 JL discussed the problem of determining the physical 

 properties of the solar electric rays which produce the aurora 

 polaris. 



It was found that a number of the most typical features 

 of the auroraB with regard to their structure, form, geo- 

 graphical distribution, and position in space, would indicate 

 that the cosmic rays had properties similar to those of the 

 a-rays, and I put forward the hypothesis that the aurorse 

 were produced by some kind of positive electric rays. 

 With regard to details I must refer to my previous papers. 



An account of the various ways in which we might get 

 information about the question was given in a paper pub^ 

 lished in Jahrbuch der Radio aktivit bit und JElektronik, 1917 J. 



As the investigation of the problem has proceeded, and as 

 through the examination of a more extensive observational 

 material we have gathered more knowledge about details 

 and peculiarities of the phenomenon, it appears that the 

 problem of finding out the nature of the cosmic electric rays 

 is not so simple as we might at first think. 



During the later years a considerable material has been 

 collected and treated. After Professor St0rmer in the year 

 1910, by using very sensitive plates and lenses of a high 

 light power, had succeeded in bringing the time of exposure 

 of an aurora down to the order of magnitude of one second, 

 a possibility was given of taking pictures which show even 

 minute details of the auroral structure. The photographs 

 have usually been taken from two stations simultaneously so 

 as to make it possible from the pictures to determine the 

 position in space of the auroral display. Besides, the pictures 

 have enabled us to study — in a more objective way than 

 before — the structure and luminosity distribution of any 

 aurora. 



After Stunner's first expedition to Bossekop in the year 



* Communicated by the Author. 



t L. Vegard, " On the Properties of the Rays producing- Aurora Bore- 

 alis," Phil. Mag. Feb. 1912. " Nordlicht Untersuchungen," Ann. d. Ptos. 

 vol. 50, 1916. 



X L. Vegard, " Bericht iiber die neueren Untersuchungen am Nord- 

 licht," Jahrbuch d. Had. und Elektr. xiv. 1917. 



