Cometary Bodies and Saturn's Rings. 753 



The velocity with which a body is ejected from the interior 

 o£ a planet, as I have said, determines whether it shall be 

 designated a comet, a cometary satellite, or a cometary ring. 

 If.' the latter, it will be obvious that, from whatever part of 

 the circumference of the planet the discharge takes place, the 

 ejected matter will necessarily move in the same direction as 

 the axial rotation. Moreover, if the discharge continued 

 without interruption during one or more rotations of the 

 planet a complete ring of discrete bodies would be formed in 

 accordance with the accepted theory and observations. 



It will be further evident from the three orders of 

 cometary discharge specified above, that the formation of the 

 outer ring A preceded that of the next inner ring B, as 

 shown by the interval of 2585 miles of clear space between 

 them. 



That the second ring was formed some time subsequently 

 to t\ic first, is highly probable from the long period of inter- 

 mittent discharges observable in terrestrial A T olcanoes, and 

 also in celestial explosive action, of which there are abundant 

 instances in planetary volcanoes and variable stars. 



That the third and dusky ring C of Saturn represents its 

 last and final effort of cometary evolution is shown by the 

 with 1 separation of the discrete bodies of which the ring C 

 is composed, and further indicated by its semitransparency 

 through which the body of the planet is distinctly visible. 



I have not included in the table of distances the now well- 

 recognized subdivisions of the exterior ring A and of the 

 dusky ring C, so distinctly seen in the photographs, but they 

 are sufficiently definite for a measurement to be taken of 

 their width, which is approximately 230 miles. 



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 bv 

 the photographic method when the edge of the ring alone 

 is visible, and is in the ratio of 10 to 11 of the equatorial 

 diameter. The value of the compression from good obser- 

 vations varies between ^-^ and - .^.^ « 



Turning now to the times of revolution of Saturn's rings 

 . . . . . 



respecting which there are wide differences of opinion, arising 



