66o 



BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 1903. 



with our hypothesis, if the very natural assumption be allowed, that the small particles, molecules 

 gaseous or vaporous atoms thrown off, separated by comparatively great distances from one another 

 have come in the course of time to perform their mean rotation about the planet in obedience to Kepler's 

 law. We return to this question further on. 



If, after all, future investigation should confirm BARNARD'S previously-mentioned suggestion that the 

 rings are auto-luminous, it would probably in a great degree strengthen the electrical theory here brought 

 forward of the genesis of Saturn's rings. 



It appears that of late other scientists have also felt unconvinced of the correctness of MAXWELI'S 

 purely mechanical view of the nature of Saturn's rings. My colleague, M. GUILLAUME at Meudon, writes 

 in a letter to me: 



"On the subject of Saturn's ring, I draw your attention to an interesting publication by Mr. A; 

 SCHMIDT, the most distinguished meteorologist of Stuttgart, who, on the basis of the extreme thinness of 

 the ring, puts forward the idea of a directing force, and he found this force, as a suggestion in a mag- 

 netic field centred on the axis of the planet, and acting on diamagnetic matter. You will understand 

 what value there may be in a quotation of this anteriority to which, however, Mr. SCHMIDT attaches 

 importance only as a preposterous hypothesis". 



