596 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 1903. 



of gigantic magnets. I shall soon have at my disposal a 3o-tons magnet, with which, for a distance of 

 from 1.5 to 2 metres. I can hold a field strength of 20,000 C. G.S.; and with this I shall try if it j s 

 possible to deflect rays such as these. 



From the equations given, we obtain 



JL. JL,p,4l.i M< 



H a Q O m 



Further by the aid of the values for -=- and > we obtain - 1.82 X 10 3 



ti a y m a 



If we now assume that our corpuscular rays are formed of ordinary electrons, and that we may- 

 venture to employ LORENTZ'S formulae (') for the extreme case we have before us, then 



m 1 



from which we obtain 



/J = -jJL= = 1.82 X 10 3 . 

 ': m ^ yi_ pz 



If we here say that fi = 1 - .we obtain approximately 



X 



x = 1.82 X 10 3 or x = 6.7 X 10 . 

 2 



We thus find that the velocity of the corpuscular rays should be u p . c c < i. e. only 45 



metres less than the velocity of light. The transversal mass of the corpuscular rays, m, equals 1.82 X io :l /, 

 and is thus of an order one thousand times as great as the mass of an electron with small velocity (-). 



Recently LsNARD( 3 ) has also treated this very important question, and has arrived at similar conclusions 

 as to the stiffness of the cosmic corpuscular rays. 



Although we may probably take it for granted that LORENTZ'S formula in this extreme case no 

 longer holds good, we may nevertheless conclude that the corpuscular rays from the sun, which should 

 be capable of giving rise to such precipitation-phenomena upon the earth as are manifested in aurora 

 and magnetic storms, must be extraordinarily penetrating and exceedingly inflexible to magnetic forces- 

 As, on this earth, we are not acquainted with any rays possessing such properties, the above result 

 must at first sight seem discouraging; but if we look into the matter, we soon find several observations 

 that are in complete harmony with it. 



We know, for instance, that in the polar regions aurora very frequently descends to within 

 50 kilometres of the earth, indeed there are good observations of its descending to within 10 kilo- 

 metres and considerably lower. Auroral rays may sometimes be seen with a length of 30 kilometres. 



It is thus clear that the rays which produce auroral phenomena, and which we assume to originate 

 in the sun, must be capable of penetrating considerable strata of our atmosphere. They must be sup- 

 posed capable of penetrating a layer of mercury more than 100 millimetres in thickness, if the rays follow 

 the law, Equal penetrability for equal masses. This moreover agrees with the idea that these same 

 rays, before reaching the earth, have been obliged to penetrate a certain stratum of the solar atmos 

 phere, since they issue from the regions in the vicinity of the sun-spots. 



(') A. H. LORENTZ, The Theory of Electrons, 1909, p. 212, equation 313. 



( 2 ) BIRKELAND, Sur la deviabilite magnetique des rayons corpusculaires provenant du Soleil. Compt. Rend, de 1'Academie 

 des Sciences, Paris, le 24 Janvier, 1910. 



( 8 ) LENARD, Ueber die Strahlen der Nordlichter, Heidelberger Akademie der Wissenschaftcn, Jahrgang 1910, 17. Abhandl. 



