1 8 Wilde, Origin of Conietary Bodies and Satunis Rings. 



The thickness of the rings is difficult to determine on 

 account of the great distance of Saturn from the earth, 

 and has been estimated by Herschel as not exceeding 250 

 miles. Assuming this value to be approximately correct, 

 the vent in the crust of the planet through which the 

 matter of the rings was ejected may not have been larger 

 than those from which it is assumed the outer satellites 

 of Saturn and Jupiter were also ejected. 



The polar compression of Saturn is well determined 

 by the photographic method when the edge of the ring 

 alone is visible, and is in the ratio of 10 to 1 1 of the equa- 

 torial diameter. The value of the compression from good 



observations varies between and 



9"02 1 01 9 



Turning now to the times of revolution of Saturn's 

 rings respecting which there are wide differences of 

 opinion, arising from the fact that there are no distinctive 

 marks on their surfaces from which their rotations can be 

 determined. 



Laplace and also Herschel were content to consider 

 the rings as one body, and both assigned the period of its 

 rotation to be 10 hours 32 minutes, as being the time of 

 a satellite revolving at the same distance as the middle 

 of its breadth. 



Later investigators have, however, found it necessary 

 to recognize, from the discrete constitution of the rings, 

 the different times of revolution of their outer and inner 

 circumferences, but have still treated them as one body, 

 and assigned a period of 12 hours 5 minutes for the outer 

 circumference, and 5 hours 50 minutes for the inner edge 

 of the dusky ring C. 



From the fact that the ring A is separated from the 

 inner ring B by a clear space of 2,585 miles, the time of 



