and Nature of the Cosmic Electric Rays. 79 



of 3*5 . 10" 3 cm. of gold. These numbers, give an air equi- 

 valent 1*5 mm. The air equivalent of hydrogen rays of 

 this velocity should then be of the order 1 mm., and if 

 no gas lighter than nitrogen were present in the higher 

 strata of the atmosphere to any appreciable amount, we see 

 from Table X. and from the nitrogen curve (fig. 7) that 

 a ray of a penetrating power of this magnitude would 

 just suffice to bring the ray down to a height of about 

 105 km., or to the very interval where we find the bottom 

 edges of most auroree. 



Jb'or the present I think we ought to be somewhat cautious 

 in laying too much stress on this coincidence. There may 

 be great errors in the calculation of the pressure of nitrogen 

 in these higher strata of the atmosphere, because the pressure 

 we deduce for these regions will greatly change with the 

 assumptions we make with regard to the variation of tempe- 

 rature as we pass upwards from the ground. If, e.g., 

 the mean temperature above 10 km. were put equal to 



— 100° instead of —55° C, the nitrogen curve w T ould 

 nearly coincide with that given for oxygen in fig. 7, or 

 points with the same air equivalent would now lie about 

 20 km. lower. 



§ 9. The Luminosity Distribution and the Nature of 

 the Cosmic Electric Rays. 



If the explanation previously given with regard to the 

 variation of luminosity distribution is the right one, we shall 

 be able to draw some important conclusions with regard to the 

 magnetic deflectibility of the ra}^ producing Aurora Borealis. 

 If the diameter of the cross section of a ray streamer is d, 

 then the radius of curvature p of the orbit of an electric 

 ray moving perpendicular to the lines of force cannot be 



greater than -. Now at places near the auroral zone 



we may put the intensity of the total magnetic force equal 

 to about 0'5 CG.s., and from the well-known relation 



— = Hyo we conclude that the cosmic rays must fulfil the 



, . . . mv d 



condition — < 7 . 



e 4 



Now, many times we observe extremely thin ray-streamers 



of the nature which keep a fairly constant luminosity from 



near the bottom edge to 200-300 km. up in the atmosphere. 



In a number of such cases we have measured thicknesses ol 



rays less than 1 km., or — < 5/2 . 10 4 . 



J e 



