CHAPTER V 



THE EIGHT-\^AR GENERATING CYCLE IN RELATION 

 TO ITS PHYSICAL CAUSE 



"You ask a rational question, and answering to the Objection, 

 I say: That although Astronomy in the courses of many ages hath 

 made a great progress in discovering the constitution and motions 

 of the Celestial bodies, yet is it not hitherto arrived at that height, 

 but that very many things remain undecided, and haply many 

 others also undiscovered." 



— Galileo. 



"Dans revolution du systeme du monde, les forces electriques 

 et magnetiques semblent jouer un role comparable a celui de la 

 force de gravitation." 



— Kr. Birkeland. 



The preceding chapter closed with the suggestion 

 that the eight-yearly interposition of Venus between the 

 Sun and the Earth may be responsible for the eight- 

 year generating cycle. Reasons were given for assum- 

 ing that Venus may be in a state of vast meteorologi- 

 cal conmiotion, and the conjecture was offered that her 

 interposition between the Sun and the Earth produces a 

 disturbance in the interplanetary mediiun which af- 

 fects the solar radiation on its way to the Earth. 



WTien this theory was first advanced a distinguished 

 man of science wrote me that the eight-year cycles 

 appeared to be established but the alleged cause was 

 "hard to digest" for the reason that one could not 

 conceive how Venus might produce the effect. The 

 criticism recalls the attitude of Galileo when he as- 



