Eight-Year Cycle in Relation to Physical Cause 135 



in atmospheric electricity. Birkeland also, as I have 

 remarked in the account of Halley's comet, attempted 

 to connect meteorological phenomena with variations 

 in the supply of ionizing cathode rays. It would seem 

 ob\aous, therefore, that if Venus is the source either of a 

 magnetic or an electrostatic field, its approach to, and 

 recession from, the line of radiation from the Sun t6 

 the Earth and its interposition in the direct line of 

 radiation must produce disturbances in terrestrial 

 meteorology. If that be true, then, since the conjunc- 

 tions of the Sun, Venus, and the Earth are periodically 

 reproduced, meteorological disturbances should tend 

 to show the same recurrent cycles. 



The reasons for assuming that Venus may be the seat 

 of a magnetic field have already been given. Likewise 

 the proofs of the defiectibility of the ionizing rays have 

 been reported. Supposing that Venus carries a mag- 

 netic field comparable in intensity with that of the 

 Earth, what ground is there for believing that the 

 trajectories of the corpuscles shot from the Sun would 

 be so altered by the magnetic field of Venus as to affect 

 materially the electric phenomena of the Earth? For- 

 tunately we have the very best authority for making a 

 positive statement. 



After Birkeland advanced his hypothesis that the 

 aurora borealis is due to cathode rays emanating from 

 the Sun and taking a course in the Earth's atmosphere 

 that is determined by terrestrial magnetic lines of force, 

 Stormer undertook to subject the theory to a mathe- 

 matical treatment. His primary problem was to devise 

 mathematical ways of computing the probable trajec- 

 tories of the electric corpuscles starting from the Sun 



