The Polar Aurora

angle Atmos aurora belts Aurora Borealis aurora stations auroral arcs auroral forms auroral zone bands base line Birkeland Bossekop bundle calculated cathode rays Chapman cloudlike aurora colour corona corpuscular corresponding cosmic cosmic rays curtains curve diffuse arc direction distance earth echoes electric corpuscles electrons equations equatorial plane explain formula frequency Gartlein Geneva paper Geofys geomagnetic geomagnetic axis geomagnetic equatorial plane give Harang homogeneous arcs horizon hydrogen lines infinity intensity interesting ionosphere lower border magnetic field magnetic storms maximum motion negative night nomograms northern Norway numerical integration observed obtained origin Oslo photographs plates polar polar aurora pole protons Publ R₁ ray structure region q remarkable researches Rz-plane seen in Fig simultaneously solar southern Norway space spectra spectrograph Störmer sunspot surface taken Terr terrella theory trajectories Tromsö upper atmosphere values Vegard velocity y₁ yellow-green zenith