and Nature of the Cosmic Electric Rays. 67 



than the other forms without assuming any difference ivith 

 regard to the penetrating poiver of the cosmic electric rays. 



It should also be borne in mind that the angle between 

 the ray and the lines o£ force — and thus the number of turns 

 per unit length of the streamer — may be changed from the 

 effect of perturbing magnetic or electric fields, and it is in 

 this connexion of interest to remember, that the ray- and 

 drapery-forms usually appear and are most prominent during 

 the time intervals, when the accompanying magnetic storm is 

 at its highest. 



It should be remarked that in order to explain the varia- 

 tion with regard to distribution of luminosity it is not 

 necessary to suppose that the electric rays return into space, 

 it is merely necessary to assume that the ray bundles consist 

 of rays which may form different angles with the lines of 

 force, and when the rays get sufficiently far down into the 

 atmosphere before the number of turns per unit length 

 becomes large they may be completely absorbed, but it is 

 clear that sometimes they may become perpendicular to 

 the lines of force so far up in the atmosphere that they are 

 not absorbed, but return into space. 



In fact the study of the relation between the aurorse and 

 the magnetic disturbances* has led to the assumption that 

 only a small fraction of the electric rays which form the 

 perturbing current systems penetrate into the atmosphere 

 so as to make themselves visible in the form of an aurora. 



Thus we must assume that in certain cases the rays are 

 turned out into space from the action of the magnetic field, 

 and it is then very likely that also some of the rays which 

 penetrate into the atmosphere are not completely absorbed, 

 imt return to space with a somewhat reduced velocity. 



It should also be remembered that the probability that the 

 rays shall return into space will be increased by perturbing 

 magnetic or electric fields. It is thus possible that the 

 variations of luminosity distribution in many cases may 

 result from a combined action of electric and magnetic forces. 



The fact that we may have a variation of the heigbi of 

 aurora produced only by the action of the magnetic field of 

 the earth, does not of course signify that all aurorse are 



* See L. Vegard, " Nordliclltlmtersuchll.ng•en. , ' Ann. </. Phys. vol. 50, 

 p. 853 (1916) ; Vid. Selsh. S/er., mat.-nat. KL 1910, No. 13, Uhristiania. 

 The same matter will also be treated in a subsequent paper on the basis 

 of observations from the Haldde Observatory. Preliminary reports are 

 given by Krogness in some lectures and in a paper read before tin 

 Geophysical Congress at Gottenburg 1918. See " Forhandlingar " etc 

 p. 48. 



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