OF AN EIGHTH SATELLITE OF SATURN. 285 



19th of August, 1787, but was prevented by other researches from 

 verifying his observation. The final discovery may be stated in his 

 own words : — " In hopes of great success with my forty-feet spec- 

 ulum, I deferred the attack upon Saturn till that should be finished ; 

 and having taken an early opportunity of directing it to Saturn, the 

 very first moment I saw the planet, which was the 28th of last Au- 

 gust (1789), I 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. The retrograde motion of Saturn amounted 

 to nearly 4^ minutes per day, which made it very easy to ascertain 

 whether the stars I took to be satellites really were so ; and in about 

 two hours and a half, I had the pleasure of finding that the planet 

 had visibly carried them all away from their places. I continued my 

 observations constantly, whenever the weather would permit, and 

 the great light of the forty-feet speculum was now of so much use, 

 that I also, on the 17th of September, detected the seventh sateUite 

 when it was at its greatest preceding elongation." * 



Of the two satellites discovered by his father. Sir John Herschel 

 thus expresses himself : — " The two interior satellites, which just 

 skirt the edge of the ring and move exactly in its plane, have never 

 been discerned but with the most powerful telescopes which hu- 

 man art has yet constructed, and then under peculiar circumstances. 

 At the time of the disappearance of the ring (to ordinary tele- 

 scopes), they have been seenf threading like beads the almost in- 

 finitely thin fibre of light to which it is then reduced, and for a short 

 time advancing off it, at either end, speedily to return, and hasten- 

 ing to their habitual concealment." t 



* Transactions of the Royal Society, 1790, p. 10. 



t " By n)y father, in 1789, with a reflecting telescope of four feet aperture." 



f Sir John Herschel's Treatise on Astronomy, § 468. 



