78 Prof. L. Vegard: Results of Nortliliglit Investigations 



of hydrogen. The spectrum analyses rather suggest that 

 there is practically do hydrogen above the auroral niveau. 



Even helium should according to Wegener form a con- 

 siderable part o£ the atmosphere at the height interval of 

 maximum auroral light-emission, and it seems from the 

 evidence given by spectrum analysis that we are justified in 

 concluding that also the values found for helium are by far 

 too large, [f there is no such hydrogen and helium zone 

 as Wegener supposes, and no hypothetical gas, it will be 

 a nitrogen atmosphere that characterizes the atmosphere 

 above the auroral niveau*. Now we see that a-rays which 

 at the presence of a hydrogen atmosphere would have been 

 stopped at the height interval from 246-315 km., in the 

 absence of this atmosphere will penetrate down to an 

 interval between 78-85 km., and if also helium is absent 

 to an interval between 76*5-82 km. If the a-rays were 

 moving in the directions of the magnetic lines of force, 

 and not making turns round them, the a-rays would have 

 a too large penetrating power to explain the height of the 

 lower limit of most aurorse. 



§ 8. Absolution of other Positive Rays. 



It might also be of interest to consider the absorption 

 of positive rays of the type produced in vacuum dis- 

 charge. We have not many experimental determinations 

 of the penetrating power of these rays, but \\ e have some 

 estimates by K. Glimme and J. Koenigsberger t, who 

 measured the penetrating power of " Kanalstrahlen " in 

 aluminium. Further, Kausch von Traubenberg % has 

 measured the penetration in gold foil. We will suppose 

 that the air equivalent of " Kanalstrahlen " can be cal- 

 culated in the same way as for ordinary a-rays. In the 

 case of Al, Grlimme and Koenigsberger found that hydrogen 

 rays with a velocity 



v = 2*7 x 10~ 8 cm. 



were just able to penetrate an Al foil with a thickness of 

 3*5 . 10" 5 cm. These numbers give an air equivalent of 

 0*5 mm. Rausch von Traubenberg finds that hydrogen 

 rays with a velocity 2'6 . 10 -8 cm. can penetrate a thickness 



* This would also involve that the green auroral line— as earlier 

 suggested by the author — should be a nitrogen line. 



f K. Glimme & J. Koenigsberger, Sitzungsber. der Heidelberger Akad. 

 der Wiss. Abt. 3, A 3 Abh. p. 6 (1913). 



X Rausch von Traubenberg, Naehrichten der K. Gesellschaft der 

 Wi&senschaften zu Gottingen, Matli.-Phys. Klasse, 1914. 



