546 BIBLIOGRAPHY OF HERSCHEL's WRITINGS. 



Hersehel, W.: Synopsis of the Writings of— Continued. 



A. D. Tol. r. 



this, and also llie hanging of the satellites on the limb ; the time 

 of hanging on the limb for Mimas has actually amounted to 20 

 minutes. This would denote a refraction of about 2" [provided, 

 etc.]. 



1790 80 16 The second conclusion is that Saturn turns on an axis perpendicular 

 to the ring. The proof depends on the position of the belts which 

 for 14 years have been [nearly] always equatorial. 



17 Another reason is that Saturn, like Jupiter, Mars, and the earth, is 



flattened at the poles, and therefore ought to be supposed to turn 

 on its axis. [Observations 1776, July 22, to 1789, Sept. 14, given.] 

 On the last date equatorial diameter 22".81 (4). 

 polar diameter 20". 61 (4). 



18 The equatorial is to the polar diameter nearly as 11 to 10. 



18 One beautiful observation of the transit of [^Titan'] over the disc I 

 must add, of 1789, November 2. 



William Herschel. 

 [Dated] Slough, near Windsor, November 3, 1789. 



1790 80 427 On the Satellites of the planet Saturn and the rotation of its Ring on an 

 Axis. By William Herschel, LL. D., F. R. S. Read June 7, 1790. 



427 The observations to be given extend from July 18 to Dec. 25, 1789. 



On calculating the appearances of bright luminous points on the 

 ring, I found that all of them could not be accounted for by satel- 

 lites. 



428 The question, then, is, what to make of these protuberant points? 

 428 To admit two or three more satellites appears too hazardous. And 



yet a suspicion of at least one more satellite would often return. 



428 The observations of each satellite have been separated, and at least 



one observation of each has been calculated for each night. 



429 Fig. 1, Plate XIX, p. 494, gives a scheme of the orbits. Explanation 



of this figure and of the tables, 



432 Observations on the fifth satellite of Saturn [Japetus']. 



438 Observations on the fourth satellite of Saturn [Tt/rtH]. 



441 1789, Nov. 2. Transit of Titan's shadow. 



444 Observations on the third satellite of Saturn [Bhea'\. 



447 1789, Oct. 16. The color of Rhea is inclining to blue. 



450 Observations on the second satellite of Saturn [T)ione'\. 



17S9, Sept. 25. Probable occultation of Dione by Tethijs. 



456 Observations on the first satellite of Saturn lTethys'\. 



403 Observations on the sixth satellite of Saturn \_Encelad'ds'\. 

 1789, Oct. 16. Occultation by Saturn. 



473 Ohsa'vations on the seventh satellite of Saturn l_Mimas']. 

 1789, Oct. 16. Occultation by Saturn. 



478 The motions of these 7 satellites are so well known that no shape of 

 lucid spot, protuberant point, or latent satellite can be occasioned 

 by any one of them without our knowing it. I found that the ob- 

 servations to be given presently could not be explaiued by any of 

 the known satellites. 



478 The first idea was of another satellite interior to the 7th ; and if a 

 revolution slower than about 15J hours could have been found to 

 account for most of the places where the bright spots were seen, 

 I should have believed these to be caused by an 8th satellite. This 

 being impracticable, I examined what would be the result if these 

 bright points were attached to the plane of the ring. 



