BIBLIOGRAPHY OF HERSCIIEL'S WRITINGS. 545 



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



1790 BO 5 The mass of tlie planet, as determined from the satellites, includes 

 that of the ring; and the ring produces irregularities in the mo- 

 tions of the satellites, as does also the oblateness of tlie ball of the 

 planet. 



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



given.] 



6 The ring is extremely thin for — 



1789, July 18, ITethys'] was thicker than the ring; 



, July 23, [I)ione'\ was twice as thick as the ring; 



J July 27, lEnccladns'] was thicker than the ring; 



^ August 29, IMimas'i was thicker than the ring ; 



1789 Oct. 15: the ring was barely visible in the 40-foot reflector, 



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



arm. 

 1789, Oct. 10: I followed IMimas and Enc4:ladus'] 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 square, 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 be rough, owing to 



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

 supposed luminous points was kind enough to venture off 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 [Enceladus-i I find its 



sidereal revolution 1" 8" 53™ 9^, and by computation its distance 

 35".058. Its light is considerably strong, but not equal to that of 



12 The seventh satellite [Mimas} makes one sidereal revolution m 2. 



40™ 46^; its distance (computed) is 27".3C6. 



12 It is incomparably smaller than lEnceladus^ and even in the 40-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 from April 9, l/7o, to 



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

 15 We may Araw two conclusions from these : First, Saturn has probably 

 a very considerable atmosphere. The changes m the belts show 

 S. Mis. 31 35 



