UHANUS. 525 



phenomena, also observed that the luminous intensity de- 

 creased considerably in proportion as stronger magnifying 

 powers were employed while in the fixed stars (6th and 7th 

 magnitude) it remained nearer the same. 



When Herschel first announced the existence of Uranus he 

 called it a comet, and it was only by the united labours of 

 Saron, Lexell, Laplace, and Mechain, which were considerably 

 facilitated by the discovery made by the meritorious Bode in 

 1784 of the previous observations of the planet by Tobias 

 Mayer (1756) and Flamstead (1690), that the elliptical orbit 

 of Uranus and the whole of its planetary elements were deter- 

 mined with admirable celerity. According to Hansen, the 

 mean distance of Uranus from the Sun is 1,918,239 or 

 15 86 million geographical miles ; his period of sidereal revolu- 

 tion, 84 y. 5d. 19h. 41m. 36s.; the inclination of his orbit to 

 the ecliptic, 46' 28" ; his apparent diameter at the mean dis- 

 tance from the Earth, 9"- 9. His mass, which was determined 

 as yy^y-g- from the first observations of the satellites, is, ac- 

 cording to Lament's observations, only -jjioT ? consequently 

 his density would be between those of Jupiter and Saturn. 89 

 A flattening of Uranus was already conjectured by Herschel 

 from his observations with magnifying powers of from 800 to 

 2,400. According to Madler's measurements in 1842 and 1843, 

 it would appear to fall between y^.y and -g.-g. 90 The original 

 supposition that Uranus had two rings was found to be 

 an optical illusion by the discoverer himself, in all cases so 

 cautious and persevering in confirming his discoveries. 



88 William Herschel, Account of a Comet in the Pliilos. 

 Transact, for 1781, vol. Ixxi. p. 492. 



* 9 Cosmos, vol. iv. p. 446. 



90 Madler, in Schumacher's Astr. Nadir. No. 493. (With 

 regard to the flattening of Uranus, compare Arago, Annuaire 

 for 1842, pp. 577-579.) 



