SEVENTH MOON OF SATURN 177 



tage of the slightest lifting of the curtain which con- 

 cealed a world of wonders from view. 



As soon as his great mirror was finished, he turned 

 it on Saturn, and " the very first moment he saw the 

 planet, on August 28, 1789," he was presented with a 

 view of six of its satellites, "in such a situation and so 

 bright as rendered it impossible to mistake them or 

 not to see them." Five of these satellites had been 

 known for more than a century: a sixth was thus 

 added. Constantly continuing his watch on the planet, 

 he was rewarded, three weeks after, with discovering 

 a seventh so close to the planet that the telescopes, 

 previously in use, had failed to find it. 1 Even in his 

 great mirror " it appeared no bigger than a very small 

 lucid point," and it lies so near the planet and its ring 

 that " except in very fine weather, it cannot easily be 

 seen well enough to take its place with accuracy." 

 But he learned from experience, and taught others the 

 lesson, that it is easier to find a small body which has 

 been once seen, and whose place has been marked, 

 than to detect it for the first time amid a crowd of 

 other heavenly bodies. 2 The heavens teach wisdom 

 even in the littlest things, but the lessons they teach 

 are sometimes forgotten as soon as learned. He found 

 also that the time of a sidereal revolution round the 

 planet is 22 hours, 37 minutes, 22 seconds. Both it 

 and the other moon he discovered revolve so near and 

 so parallel to the ring, that he had " repeatedly seen 



1 One discovered by Huyghens in 1655, and four by Cassini in 1671 

 and onwards. 



2 Compare the ease with which observers detected the small companion 

 of Sirius, and the "crape " ring of Saturn after they were once detected 

 (Ball, Story of the Heavens, p. 387). 



12 



