BIBLIOGRAPHY OF HliRSCHEL's WRITINGS. 545 



Herschel, "W.: Synopsis of tiik Writings of— Continued. 



A. D. YvL P. 



179U tiO 5 The mass of the planet, as determined from the satellites, ineludes 

 that of the rint;; and the ring jiroducea irregularities in the mo- 

 tions of the satellites, as does also'tho oblateness of the ball of the 

 planet. 



5 The light of the ring is brighter than that of tlie planet. [Proof 



given.] 



6 The ring is extremely thin for — 



1789, July 18, [Tcthi/s] was thieker than the ring; 



, July 23, [Dione'i was twice as thick as the ring; 



, July 27, lEnc(Iadus'\ was thieker than tlie ring; 



, August 29, lAIimas'] was thicker than the ring; 



1789, Oct. 1.5: the ring was barely visible in the 40-foot reflector, 



but lEnceladus'] was visilde about the middle of the preceding 



arm. 

 1789, Oct. IG: I followed [^[mas and Enceladns'\ up to the very 



disc of the planet. 



7 A suspicion arises that by a refraction through some very rare atmos- 



phere on the ring the satellites might be lifted up and depressed so 

 as to be visible on both sides of the ring. 



8 The edge of the ring is very probably not squan;, but spherical or 



spheroidical. 

 8 The ring cannot possibly disappear on account of its thinness. 



8 I formerly supposed the surface of the ring to l)e rough, owing to 



9 luminous points like mountains seen on the ring, till one of these 

 supposed luminous points was kind enough to venture oft" the edge 

 of the ring and appear as a satellite. As I had noted all such in- 

 equalities I could calculate all such surmises, and I have always 

 found these appearances to be due to satellites. 



9 Upon the whole, I cannot say that I had any one instance that could 

 induce me to believe the ring was not of a uniform thickness; that 

 is, equally thick at equal distances from the centre and of an equal 

 diameter throughout. 



10 Strong suspicions of the existence of a sixth satellite I have long en- 

 tertained. I saw it 1787, August 19. I was then busy with the 

 Georgian satellites. 



10 In 1788 my 20-foot speculum was much tarnished. 



10 The very first moment I turned my 40-foot telescope on Saturn, 1789, 



August 28, I saw six satellites, and on September 17 I detected the 

 seventh satellite. 



11 From many observations of the sixth satellite [7w(«7arf«.'*] I find its 



sidereal revolution l*" 8'' 53'" 9", and by computation its distance 

 35". 058. Its light is considerably strong, but not e(]ual to that of 

 LTf%s]. 



12 The seventh satellite [J/tmfl.s] makes one sidereal revolution in 22'' 



40"' 46^; its distance (computed) is 27". 366. 



12 It is incomparably smaller than \^EuceJaduii'\, and even in the 4fl-foot 



reflector appears no bigger than a very small lucid point; to which 

 the exquisite figure of the speculum not a little contributes. 



13 The orbits of these two satellites are exactly in the plane of the ring. 

 13 Observations of the belts and figure of Saturn froni April 9, 1775, to 



Sept. 8, 1780, and reference to [rough] figures arc here given. 

 15 "We may draw two conclusions from these: First, Saturn Has probably 

 a very considerable atmosphere.. The cliang»;a in the belts show 

 S. Mis. 31 35 



