[From the Proceedings of the Royal Society of Edinburgh, Vol. IV.] 



XVIII. On Tfieories of the Constitution of Saturn's Rings. 



THE planet Saturn is surrounded by several concentric flattened rings, which 

 appear to be quite free from any connection with each other, or with the planet, 

 except that due to gravitation. 



The exterior diameter of the whole system of rings is estimated at about 

 176,000 miles, the breadth from outer to inner edge of the entire system, 

 36,000 miles, and the thickness not more than 100 miles. 



It is evident that a* system of this kind, so broad and so thin, must 

 depend for its stability upon the dynamical equilibrium between the motions of 

 each part of the system, and the attractions which act on it, and that the 

 cohesion of the parts of so large a body can have no effect whatever on its 

 motions, though it were made of the most rigid material known on earth. It 

 is therefore necessary, in order to satisfy the demands of physical astronomy, 

 to explain how a material system, presenting the appearance of Saturn's Rings, 

 can be maintained in permanent motion consistently with the laws of gravitation. 

 The principal hypotheses which present themselves are these 



I. The rings are solid bodies, regular or irregular. 

 II. The rings are fluid bodies, liquid or gaseous. 

 III. The rings are composed of loose materials. 



The results of mathematical investigation applied to the first case are, 

 1st. That a uniform ring cannot have a permanent motion. 



2nd. That it ia possible, by loading one side of the ring, to produce 

 stability of motion, but that this loading must be very great compared with 

 the whole mass of the rest of the ring, being as 82 to 18. 



