45 HIKKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 1903. 



ADAM POULSON('). As far as I know, no one has, however, studied this phenomenon in connection with 

 simultaneous magnetic registrations at the same place. This we had the opportunity of doing, and 

 the very interesting fact came out, that the formation of these clouds was always accompanied by 

 simultaneous magnetic storms and earth-currents; and there thus appears to be no doubt that these are 

 direct cloud-forming effects of the same rays that occur in the auroral phenomena. From this it seems, 

 that these cirrus-clouds are directly formed by the corpuscular rays which we suppose to be the cause 

 of magnetic storms and aurora. The first hypothesis that one naturally might form as to this phenomenon 

 is, that the clouds are due to water-vapour brought to condensation by the ions formed by the impact of 

 negative rays. It is however also a probability that some of the observed auroral clouds are not real 

 clouds, but merely a very strong concentration of corpuscular rays, which in the case of darkness might 

 appear luminous; in the daytime the concentration of corpuscles should have the effect of making the 

 places where they occur less transparent, and able to diffuse light,- and thus become visible. In such a 

 way also possibly certain faint polar bands observed in the polar regions might be explained. According 

 to circumstances these concentrations may disappear or give rise perhaps to real clouds. 



(') Met. Zeitschrift 12, 161 (1895). 



