22 THE SATURNIAN SYSTEM. [§ 31 



E (,.»,=^+^-f.[A.(^) 5 i^m 



z(<') = -^-, i2 ('•')■ 



?■ — a 



The values of Z in these equations are only applicable when 



z>b; 

 but when 



2<b, 



they must be multiplied by -r. 



31. The following tables contain the value of the potential and attractions of thin 

 rings computed by the formulae of §§ 27 and 30. In the first table, the ring is narrow 

 as well as thin, and in the second table, it is continuous to the centre of the ring. The 

 values of r and r" are the same in both tables for the same value of i. 



(284) 



