[ 9J?D ] 



XOII. On the Periodic Times of Saturn $ Rings. 

 By Henry Wilde, D.Sc., D.C.L., F.P.S. 4 



IN my paper on the " Origin of Cometary Bodies and 

 Saturn's Rings," read beFore the Society in October 

 lastf a new determination was made of the periodic times of 

 the rings, based on the commonly accepted distance of Mimas, 

 3*36 Saturnian units. This element of the orbit was derived 

 from observations made by Herschel and subsequently 

 adopted by all astronomical writers. 



Recent observations of American astronomers with more 

 powerful telescopes and under more favourable conditions, 

 have reduced the distance of Mimas from the planet to 

 3'1G units, with the consequent increase in the times of 

 rotation of the rings. 



The difference between the older and later determinations 

 is sufficiently large to induce me to place on record for com- 

 parison the results computed from both observations and 

 Kepler's third law, as shown and demonstrated in the 

 following tables : — 



Distances of Mimas = 3*36 and outer edge of ring A =2*3. 



(1) 3'36 3 : 2'3 a :: 22h. 37 2 m. : #=12h. 48 2 m. for A. 



Distances of Mimas = 3*36 and inner edge of ring C = 1'27. 



(2) 3-3G 3 : 1-27 3 :: 22h. 37 2 m. : #=5h. 15 2 m. for 0. 



Distances of Mimas = 3'16 and outer edge of ring A = 2'3. 



(3) 3-16 3 : 2-3 3 :: 22h. 37 2 m. : ?=14h. 4 2 m. for A. 



Distances of Mimas = 3*16 and inner edge of ring = 1*27. 



(4) 3-16 3 : 1-27 3 :: 22h. 37 2 m. : a? = 5h. 45 2 m. for C. 



The unit distance, 3*lf), for Mimas necessarily involves the 

 correlative reduction of the distances of the other Saturnian 

 satellites, as now set forth in the tables of these elements 

 published by American astronomers. 



That Saturn's rings are ejectamenta from the interior of 

 the planet is further evident from the fact that no causal 

 connexion subsists between their times of rotation and that 

 of the planet itself, as the inner edge of the ring has a 



* Communicated by the Author. From the Manchester Memoirs, 

 vol. lv. 1910-11, no. 14. 

 t Manchester Memoirs, vol. lv. 1910-11 ; Phil. Mag. November 1911. 



Phil. Mag. S. 6. Vol. 22. No- 132. Dec. 1911. 3 R 



