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178 from the sun, and revolves round it in 29 years. A revolving luminous ring, consisting of three distinct portions, one within the other, surrounds this most remarkable planet, and eight satellites revolve round him. Uranus was, up to Adams’s, Leverrier’s, and Galle’s recent discovery of Neptune, considered the most distant planet from the solar centre of the system; the distance being calculated at 1,800,000,000 miles, and the period of revolution, 84 years. The diameter of Uranus is 35,000 miles, and the bulk about 80, the mass about 20, times that of the Earth; at least four satellites are known to revolve round him, and several more undoubtedly exist. Neptune, now the most distant known planet from the sun (2,800,000,000 miles), revolves round the latter in 165 years; the diameter of this planet is 37,500 miles, the bulk about 107 times that of the Earth, the mass about the same as that of Uranus. Among the lesser planets, we have to mention Mercury, the one nearest the solar centre, being distant from it only 37,000,000 miles; the period of his revolution is 88 days. His diameter is about 3200 miles; from the close proximity of this planet to the sun, it is conjectured that the mean heat in it is above that of boiling quicksilver, and even near the poles water would always boil. Its mass is about one-twelfth that of the Earth, the mean density rather greater than that of our planet. Venus, next to Jupiter the brightest and most important and interesting of the planets, has a diameter