Uranus revolves round the sun at a distance from him of about 1,780,000,000 miles, in an orbit which takes eighty-four of our years to complete. Barnard gives his diameter at 34,900 miles, and if this measure be correct, he is the third largest planet of the system. Other measures give a somewhat smaller diameter, and place Neptune above him in point of size. Subsequent observers have been able to see but little more than Herschel saw upon the diminutive disc to which even so large a body is reduced at so vast a distance. When near opposition, Uranus can readily be seen with the naked eye as a star of about the sixth magnitude, and there is no difficulty in picking him up with the finder of an ordinary telescope by means of an almanac and a good star map, nor in raising a small disc by the application of a moderately high power, say 200 and upwards. (Herschel was using 227 at the time of his discovery.) But small telescopes do little more than give their owners the satisfaction of seeing, pretty much as Herschel saw it, the object on which his eye was the first to light. Nor have even the largest instruments done very much more. Rings, similar to those of Saturn, were once suspected, but have long since been disposed of, and most of the observations of spots and belts have been gravely questioned. The Lick observers in 1890 and 1891 describe the belts as 'the merest shades on the planet's surface.' The spectrum of Uranus is marked by peculiarities which distinguish it from that of the other planets. It is crossed by six dark absorption-bands, which indicate at all events that the medium through which the sunlight which it reflects to us has passed is of a constitution markedly different from that of our own atmosphere. It was at first thought that the spectrum gave evidence of the planet's self-luminosity; but this has not proved to be the case, though doubtless Uranus, like Jupiter and Saturn, is in the condition of a semi-sun. Like the other members of the group of large exterior planets, his density is small, being only 1/5 greater than that of water.