

888 SPECIAL RESULTS IN THE URANOLOGICAL 



and by Flamstead, in 1690, established with admirable 

 promptitude the elliptical orbit and all the planetary elements 

 of Uranus. Its mean distance from the Sun is, according to 

 Hansen, 19-18239 distances of the Earth from the Sun, or 

 3 9 6^- millions of geographical miles (1586 millions English 

 geographical miles) ; its sidereal period of revolution is 84 

 years, 5 days, 19 hours, 41 minutes, and 36 seconds; its 

 inclination to the ecliptic 046' 28"; and its apparent diametei 

 at its mean distance from the Earth 9"' 9 . Its mass, which the 

 first observations of its satellites had given at l ^ 1 8 ,is derived, 

 by Lament's observations, as only 24 a 05 : according to 

 this, its density would be intermediate between those of 

 Jupiter and Saturn ( 633 ) . Ellipticity of figure, or com- 

 pression at the poles, of Uranus, was suspected by William 

 Herschel from observations in which he employed magni- 

 fying powers from 800 to 2400 : according to Madler's 

 measurements, in the years 3842 and 1843, its amount 

 would seem to fall between -^.y and i. T ( 634 ). That the at 

 first supposed two rings of Uranus were merely the effect of 

 an optical illusion was acknowledged by the discoverer him- 

 self, ever so ready to apply due caution, and to continue 

 perseveringly to test the reality of all newly acquired data. 



Satellites of Uranus. 



" Uranus," says the younger Herschel, " is surrounded 

 by four, or probably by five or six, satellites." They pre- 

 sent a remarkable peculiarity, in a feature to which nothing 

 similar has yet been found in any part of the solar system : 

 viz. that whereas all other satellites (those of the Earth, 

 Jupiter, and Saturn), as well as all the primary planets, 



