RECENT INVESTIGATIONS ON AURORA 



BOREALIS. 



By OUK r.KRLIX CORRESPONDENT. 



According to a hypothesis suggested by Professor hypothesis. He also worked out a new inetiiod of 



Birkeland of Christiana University, auroras are due aurora investigation bv photographic records, 

 to cathode rays given out from the sun, and which In view of the inadequate luminous intensity and 



on their way through the cosmic space would great mobility of auroras, it had so far been cOn- 



converge towards the magnetic poles of the earth, sidered impossible to fix the phenomenon photo- 



FlGURE 1. 



Figure _'. 



The Aurora Borealis. 



thus producing a bright fluorescence in the 

 surrounding air. 



In fact, when arranging below a Crooke's bulb a 

 ver\' strong magnet, the cathode ra\s are seen to 

 converge towards this, like light ravs converging 

 towards the focus of a lens. This phenomenon 

 Professor Birkeland denotes bv the name of " suction 

 effect" of the magnetic pole. 



\\'hen a discharge bulb with a minute "magnetic 

 earth " suspended in its interior is lined with a 

 layer of platinum-barium c\anide. any spot struck 

 by the cathode ravs becomes distincth' visible. 



By varying this experiment, there are obtained 

 the most manifold fluorescent forms reminding in all 

 details of auroras. In order to test his theory, 

 Birkeland also undertook three vo\ages of discover\- 

 to polar regions, from which he brought home man\- 

 valuable data on the aurora borealis and the 

 concomitant magnetic disturbances. 



His colleague, Prof essor CarlStormer.of Christiana, 

 in a memoir recently submitted to the Fourth 

 International Congress of Mathematicians, then 

 established a theor}- of the phenomenon, showing all 

 its details to be perfectly accounted for on the above 



graphicallv. Professor Stormer, however, realized 

 that bv choosing a proper combination of objectives 

 and photographic plates, sufficient sensitiveness 

 could be insured. B\- means of a cinematographic 

 objective one inch in diameter and two inches in 

 focal distance and violet-labelled Lumiere plates, he 

 then succeeded, on a voyage to Bossekop (Finmarken), 

 in Februarv and March 1910. in obtaining four 

 hundred satisfactorv aurora photographs out of a 

 total of eight hundred, with exposures var\-ing 

 between a fraction of a second and twenty 

 seconds, according to the luminous intensity of 

 the phenomenon. 



One of the most valuable uses these photographs 

 can be put to, is measuring the altitude of auroras 

 and ascertaining their accurate position in the cosmic 

 space. To this effect the position of the aurora in 

 regard to the surrounding stars should be compared 

 on two photographs taken simultaneously from two 

 stations connected by telephone. A systematical 

 application of this method (a report on which was 

 recenth- presented to the French Academy of 

 Sciences) will doubtless gi\-e the most \-aluable 

 results. 



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