548 BIBLIOGRAPHY OF HERSCHEL's WRITINGS. 



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



A. D. Vol. P. 



The telescopic milky way is probably composed of this sliiniiig fluid, 

 whicli must commence somewhere about the range of the stars of 

 the 7th magnitude, and extend to the regions of the 9th, 10th, 11th, 

 and 12th. 



1791 81 85 The shining fluid might exist independently of stars. The light of 



this fluid is no kind of reflection from the star in the center. If this 

 matter is self-luminous, it seems more fit to produce a star by its 

 condensation than to depend on the star for its existence. 



86 List of diffused nebulosities and planetary nebuhe ; both better ac- 



counted for by the hypothesis of a shining fluid than by supposing 

 them to be distant stars. 

 Regeneration of stars from planetary nebulae. 



87 How far the light-coriiuscles emitted from millions of suns may be 



concerned in this shining fluid it is not necessary to inquire. We 

 need not know the origin of the luminous matter whose existence 

 is rendered evident by means of nebulous stars. 



W. Herschel. 

 [Dated] Slough, January 1, 1791. 



1792 82 1 On the Ring of Saturn and the rotation of the fifth satellite upon its axis. 



By WiLTjAM Herschel, LL. D., F. R. S. Read December 15, 1791. 



1 In a former paper (Phil. Trans., vol. Ixxx, p. 4) I spoke of the sur- 



mise of a division in Saturn's ring with proper doubts. My late 

 views of the southern side of the ring and the discovery of its quick 

 rotation enable me to speak decisively. 



2 The black division is always of the same breadth if we leave out of 



account certain very small variations which I have occasionally 

 observed. 



3 Observations on the Ring of Saturn (from 1790, Sept. 7, to Oct. 24). 



4 From these and fonner observations I think myself authorized now 



to say that the planet Saturn has two concentric rings. * * * 



5 The relative dimensions of the rings and spaces are given in a table. 



5 This opening in the ring (which is some 2,513 miles in width) must 



be of considerable service to the planet, in reducing the space that 

 is eclipsed by the shadow of the ring. 



6 It becomes a question if both rings revolve in the same time. The 



period formerly given (Phil. Trans., Ixxx, p. 481), belongs to the 

 outer ring. The former observations indicate that the inner riug 

 revolves with great velocity on its axis, but are not sufficient to 

 determine the period. 



7 It is quite probable that there should be a small difference in the 



periods of the two rings. 



7 A memoir (in Histoire de V Academie Royale des Sciences de Paris, 1787, 



p. 249 — ) refers to observations of many divisions of the ring of 

 Saturn. 



8 My own observations of Saturn since 1774 contain only four where 



any other black- division upon the ring is mentioned than the one 

 I have constantly observed. These 4 observations were in 1780 — 

 (see Plate I, figs 1, 2, 3.) 



9 Saturn was then in the very best situation for viewing the plane of 



the ring, but I have hitherto set these observations aside as 

 wanting more confirmation. 

 9 Observations have been made by M. Cassini, Mr. Short, and Mr. 

 Hadley [and are referred to]. 



