4 
CARL STORMER. M.-N. Kl. 1917. No. 3. 
4) The lower boundary of 80—g0 km. for the computed heights of 
2500 chosen points of Aurora Borealis during my expedition in 1913, 
proves that the auroras observed cannot be due to such penetrating 
and rigid negative rays as Prof. BIRKELAND alleges are the cause ot 
Aurora Borealis. 
Prof. BIRKELAND does not, as it seems, fully appreciate the utility of 
the mathematical theory concerning the trajectories of electric cor- 
puscles in the field of an elementary magnet. He does not seem to 
know the methods developed by me, which permit a discussion of 
whole classes of orbits, without having previously found the coordi- 
nates as explicite functions of the time. In opposition to Prof. BIRKELAND, 
who considers the importance of this mathematical theory to be very 
slight indeed, I maintain that it is of a great significance not only 
for the prediction of experimental facts, but also as a guide to 
research and the thorough discussion of the experiments thus 
performed. 
Printed Aug. 27 1917. 
"ind 
