1 76 HERSCHEL AND HIS WORK 



Messier, viewing the planet in 1766 with what he calls 

 "an achromatic reflector of 10 feet 7 inches focus," 

 " perceived on his globe two darkish belts, extremely 

 faint and difficult to be discerned, directed, however, 

 in a right line parallel to the longest diameter of the 

 ring." 1 However, till Herschel applied his 40 - feet 

 reflector to its system, discovery may be said to have 

 reached its limits. To " the liberal support, whereby 

 our most benevolent King has enabled his humble 

 astronomer to complete the arduous undertaking of 

 constructing this instrument," Herschel writes, was 

 due the discovery of other two moons or satellites, a 

 fuller knowledge of the nature of the ring, and, in 

 short, a new era in our knowledge of that wonderful 

 system. An object so engaging drew Herschel's 

 attention as early as the spring of 1774, long before 

 he was known to fame. On the 17th of March that 

 year, with a 5 J-feet reflector, he saw the ring " reduced 

 to a very minute line," and the planet looking like a 

 ball with a knitting-needle projecting through it on 

 both sides. About a fortnight after, the ends of this 

 axis had vanished, and a dark band or shadow crossed 

 the planet's equator from side to side. In the follow- 

 ing year he saw the ring gradually open out, with a 

 " dark zone contained between two concentric circles," 

 as if there were two rings with an open space between 

 them. For ten years he continued watching the planet 

 with telescopes of various powers, suspicious that it 

 had not told astronomers all the story of its ring and 

 satellites. The ten years' watch lengthened out to 

 twenty, and the twenty to thirty or more, but this 

 eager watcher still kept guard, ready to take advan- 



1 Phil. Trans., 1769., vol. lix. p. 459. 



