1 52 Todd — Optical Resolution of the Saturnian Ring. 



Art. XIX. — Optical Resolution of the Saturnian Ring; 

 by David Todd. 



Observational research upon the ring of Saturn may be 

 embraced in ten stages : 



(1) Galileo (1564-1642) represented the Saturnian system 

 triform. " Ultimum (altissimum) planetam tergeminum 

 observavi" he announced and he drew the ring as two separate, 

 equal, and lesser spherical bodies on either side of the planetary 

 ball. 



(2) Scheiner (1575-1650) connected these two bodies with 

 the planet, making it appear like a head with large ears, or a 

 circular plaque with ansae (handles) as they were called, and 

 still are. 



(3) Riccioli (1598-1671) and Hevelius (1611-1687), with 

 larger and better telescopes, came very near the real ring form 

 and all but guessed the true shape of the puzzling anomaly. 



(4) Huygens (1629-95) was the first who divined the ring as 

 such, and he gave a full and accurate description of it as fol- 

 lows : "Anulo cingitur tenui piano nusguam cohaerente ad 

 eclipticam inclinatoP His characterization of the ring first 

 explained all the appearances that had baffled his predecessors : 

 how the ring might disappear and reappear 2 and in about 30 ' 

 years could pass through a complete cycle of phases, from abso- 

 lute invisibility to the amplest widening. 



(5) Cassini (1625-1712), with a better telescope, showed that 

 the ring had symmetric dark markings on it which divided it 

 into two parts though unequal in breadth, the inner one the 

 brighter and broader. 



(6) Eocke (1791-1865) discovered a similar division of the 

 outer ring into two parts, though he found it impossible to trace 

 the dark dividing line all the way round. In fact, it is often 

 invisible at the present day. 



(7) Bond (1789-1859) and Dawes (1799-1868) discovered a 

 broad, dusky ring inside the inner Huygenian ring, and 

 seemingly joined to its inner edge. 



(8) Barnard (1857- ), by observing with the Lick telescope 

 the transit of Japetus through the shadow of ball and rings, 

 found the satellite readily visible in passing the crape ring, 

 fainter by the bright ring, while it disappeared completely in 

 the shadow of the ball. 



(9) Keeler (1857-1900) photographed the spectrum of the 

 ring, and measured the displacement in spectral lines of the 

 inner and outer edge of the bright ring. This displacement 

 he found exactly what it should be if the ring were not solid, 

 but made up of clouds of particles revolving round Saturn, 

 as shoals of satellites in full accord with the Keplerian har- 

 monic law. The ring might still, however, be gaseous. 



It only remained to visualize the separate particles of which 

 the ring is composed. There are many telescopes powerful 

 enough to make this observation possible ; and the highly unfa- 



