384 SPECIAL RESULTS IN THE URANOLOGICAL 



phical miles. The mass of the rings is, according to Bessel, 

 -i4 T of the mass of Saturn. They present some ( 625 ) in- 

 equalities, by means of which it has been possible to observe 

 approximately their time of rotation, which is exactly equal 

 to that of the planet. Irregularities of form shew them- 

 selves in the " disappearances of the ring," when one of the 

 anses usually becomes invisible sooner than the other. 



The excentric position of Saturn in respect to its ring, 

 discovered by Schwabe, at Dessau, in September 1827, is a 

 very remarkable phenomenon. The body of the planet is a 

 little to the west of the place which it would occupy if it 

 were truly concentric with the surrounding ring. This ob- 

 servation has been confirmed by Harding, Struve ( 626 ), John 

 Herschel, and South (partly by micrometric measurements). 

 Small, apparently periodical, differences in the amount of 

 the excentricity, which have been found from series of cor- 

 responding observations by Schwabe, Harding, and de Vico 

 at Home, are perhaps due to oscillations of the centre of 

 gravity of the ring round the centre of the planet. It is a 

 curious and striking circumstance, that so early as the end 

 of the 17th century, an ecclesiastic of Avignon, Gallet, 

 attempted without success to call the attention of the 

 astronomers of that period to the excentric position of 

 Saturn ( 627 ). With a density diminishing towards the sur- 

 face, and so exceedingly small, perhaps scarcely f of that 

 of water, it is difficult to make to ourselves any represen- 

 tation of the molecular state, or material quality or consti- 

 tution of the body of the planet ; or even to decide whether 

 this constitution should actually suppose fluidity (i. e. mo- 

 bility of the smallest particles inter se), or rigidity, (accord- 

 ing to the often adduced analogies of deal, pumice, cork, or 



