and Sature of tJie Cosmic Electric Rays. 59 



comes out greater than 90°. Now it might seem as if this 

 fact should force upon us the assumption of a negative 

 charge of the cosmic rays. But although it gives an argu- 

 ment in favour of this assumption, we must remember that 

 the directions of bands are subject to considerable varia- 

 tions, which are probably to be regarded as an effect of 

 perturbing influences, and it is also quite possible that these 

 influences might change the mean direction of the bands. 



Indeed, our results from the Haldde Observatory give 

 indications in this direction, for we see that the draperies 

 which usually appear during the interv.il of the most violent 

 magnetic disturbances give a greater magnetic azimuth than 

 the arcs. 



§5. The Variation of Light Intensity along the 

 Auroral-Streamers. 



As pointed out by the writer in previous papers*, the 

 investigation of the distribution of luminosity along the 

 ray-streamers, which constitute an auroral form, is of con- 

 siderable interest in connexion with the determination of 

 the properties of the cosmic electric rays. 



On certain assumptions with regard to the constitution 

 of the upper strata of the atmosphere, I calculated t the 

 luminosity-distribution that would be produced by «-rays, 

 and it was found that the distribution found would account 

 for some auroral forms, which end very abruptly and which 

 have a maximum of light intensity near the bottom edge. 



It was also shown that a luminosity distribution of this 

 type was not to be derived from the calculations of Lenard J 

 and St0rmer § of the absorption of the electron-rays in the 

 atmosphere. 



In a previous paper I pointed out, however, that the 

 exponential law of absorption on which the calculations of 

 Lenard and Stunner are based, does not necessarily hold under 

 the conditions present in the upper strata of the atmosphere. 

 Thus we have to take into account that the absorption takes 

 place in a magnetic field, and it was mentioned || as a possi- 

 bility that if the effect of the magnetic field was taken into 

 account, the assumption of electron-rays might come into a 

 better position. 



* L. Vegard, "On the Properties of the Radiation producing Aurora 

 Borealis." Phil. Mag. 1912. 



t L. Vegard, Vid. Selsk. Skr. Kristiania, 1916; Ann. d. Phys. vol. 50, 

 p. 853 (1916). 



t P. Lenard, Sitzungs-Ber. d. Heildelberg«r A/cad. d. Wiss., L911. 



§ C. Sto-rmer, Arch. d. Sc. Phys. et Nat'.. 1911. 



I| L. Vegard, Jahrbuch d. Had. u. Elehtr. xvi. p. 46] (1917). 



