Uranus.
Uranus was discovered by Herschel in 1781, and has been called after its discoverer, and sometimes the “Georgium Sidus.” It revolves at an enormous distance from the sun—viz., 1,753,000,000 of miles. It takes about eighty-four of our years (30,686 days) to go round the sun, and possesses four moons. It is very much larger than the earth—about four times the diameter, and forty times its volume. We can only speculate concerning its physical constitution, which is assumed to be similar to that of Jupiter, while the changes of temperature and seasons must vary immensely. The names of the moons are Ariel, Umbriel, Titania, and Oberon. The outer pair can be seen without much difficulty.
Neptune.
The existence of this planet was determined by calculation before it had been seen at all. Uranus was observed to be disturbed in his orbit, moving sometimes faster than at others; and even before Uranus had been discovered Saturn and Jupiter had been seen to be affected by some body in the system. M. Leverrier determined to ascertain the cause of this, and came to the conclusion that some other planet was influencing Uranus. The Newtonian theory here received a most convincing proof. While Leverrier was calculating, Mr Adams of Cambridge leaped to the same conclusion, and wrote the result of his calculations to Professor Airy, and the planet was seen, but not reported upon. Meantime Leverrier published his calculations, and the observers at Berlin detected the new planet in September 1846.
Fig. 595.—Neptune in field of view with stars of 6th, 7th, 8th, and 9th magnitudes.
Very little can be said concerning Neptune, as its distance is too great for observation. It is at 2,746,000,000 of miles from the sun, and takes 164 years to go round it (60,126 days). It is about the same size as Uranus. It has one moon, which moves round the planet in 5d 21h, and is of great size.
