Eight-Year Cycle in Relation to Physical Cause 133 



will be of incalculable value in the solution of the 

 problems that interested him, and the contemplation 

 of his courage in thought and expression and his de- 

 votion to science will always produce an emotional 

 elevation. 



In the theories of Birkeland cathode rays, or /5-rays, 

 play an unportant role. It is to these negative particles 

 which are shot off by the Sun and gathered in by the 

 Earth along its magnetic lines of force that he attrib- 

 uted the aurora borealis and the simultaneous varia- 

 tions in the magnetic needle. For a while Birkeland 's 

 theory stood a chance of wide acceptance, but doubt was 

 created by the dissent of his pupil Vegard and his mathe- 

 matical colleague Carl Stormer both of whom had at 

 first accepted his explanations but later attributed the 

 phenomena to a-particles. He was fortunate, however, 

 in the character of the men who opposed him, and in 

 view of what has just been said about Birkeland 's 

 personality, his love for science and his unswerving 

 fidelity in its pursuit, one cannot fail to have a lively 

 satisfaction in the most recent utterance of his critics. 

 Both Vegard and Stormer have modified their dissent- 

 ing views and have taken a position much nearer 

 Birkeland's original hypothesis: 



"Dans son dernier ouvrage publie pendant la re- 

 daction definitive du present memoire, M. Vegard a 

 abandonne sa theorie, que les aurores sont causees par 

 des rayons a; en effet, en etudiant la distribution de la 

 lumiere le long des rayons auroraux, il arrive a la con- 

 clusion que cette distribution ne pent pas etre explique 

 par sa theorie; il faut supposer que I'aurore est causee 

 par des rayons cathodiques, des rayons |3 ou bien 



