SCIENCE-GOSSIP. 



99 



SATURN'S RING SYSTE^I. 

 By Frank C. Dennett. 



nPHIS wonderful object, as seen through a good 

 instrument, is perhaps the most beautiful in 

 the heavens. Ever since its discovery, it has 

 proved itself to be a grand puzzle to those who 

 have studied it. The outside diameter of these 

 rings reaches about 170,000 miles, and the inner 

 diameter of the bright ring about 106,000 miles. 

 Notwithstanding this immense area the total thick- 

 ness is probably not over about 100 miles. The 

 first problem to consider is how can the rings be 

 stable? Kepler's laws show that it is necessary 

 for the inner portion to travel much faster around 

 the planet than the outer portions. This demon- 



rings which tend to prove this contention. Some- 

 times the principal, or Ball's, division appears 

 hard and sharp, and black, whilst at others, not- 

 withstanding beautiful definition, the edges of this 

 division refuse to appear hard, and at times are 

 even jagged — vide Trouvelot's observations, very 

 specially, December 30th, 1874 — and the division 

 itself has frequently been observed by many 

 observers, including the writer, to be very far from 

 black. Usually a large instrument brings out the 

 Encke division of the outer ring about three-fifths 

 from its inner edge, sometimes as a black division 

 and at others only as a pencil-line. Often, how- 



Saturn's Rings. 



strates that it is quite impossible for the ring to be 

 a solid continuous surface. 



Perhaps some reader points out the fact that the 

 rings are not continuous, but that divisions separate 

 the surface into concentric rings. The problem, 

 however, is not ended here, because as early as 

 1821 Kunowsky noticed that the rings, though so 

 close together, were not in absolutely the same 

 plane, and Coolidge, Secchi and others have made 

 similar observations. But this is not all. The 

 ball is not placed in the centre of the rings, but a 

 little on one side, making the eastern, or /, ansa 

 a little the largest. The consequence of this 

 eccentricity would be to make the different parts 

 of the same ring travel at different rates, faster on 

 the western, slower on the eastern side of the ball. 

 These considerations render untenable any idea 

 of the ring being solid. 



Variations are constantlv being noted in the 



ever, it is only visible on one side of the planet, 

 whilst at times it seems to be quite invisible. 

 Again, it seems sometimes to sHghtly vary its 

 position on the ring, whilst occasionally it has been 

 seen accompanied by two or three other divisions 

 on the same ring. M. L. Trouvelot has sometimes 

 seen the outer ring apparently partially broken into 

 fragments at the ends of the ansae, and very 

 occasionally this has been confirmed by other 

 observers. 



yi. E. Antoniadi, of Juvisy, on April iSth, 1S96, 

 made a most interesting observation of Saturn. 

 His beautiful drawing is here reproduced from the 

 " Bulletin de la Societe Astronomique de France " 

 for May, and which has kindly been forwarded by 

 the observer. Here, not only are the mottlings of 

 the outer ring visible, but the divisions are absent, 

 whilst the middle bright ring has three divisions 

 which are very rarely seen. It appears that the 



