Very little is known of the surfaces of Uranus and Neptune. Indications of the existence of belts resembling those of Jupiter have been found in the case of both planets. There are similar belts on Saturn, and as they seem to be characteristic of large, rapidly rotating bodies of small density, it was to be expected that they would be found on Uranus and Neptune.
The very interesting opinion is entertained by some astronomers that there is at least one other great planet beyond Neptune. The orbits of certain comets are relied upon as furnishing evidence of the existence of such a body. Prof. George Forbes has estimated that this, as yet undiscovered, planet may be even greater than Jupiter in mass, and may be situated at a distance from the sun one hundred times as great as the earth's, where it revolves in an orbit a single circuit of which requires a thousand years.
Whether this planet, with a year a thousand of our years in length, will ever be seen with a telescope, or whether its existence will ever, in some other manner, be fully demonstrated, can not yet be told. It will be remembered that Neptune was discovered by means of computations based upon its disturbing attraction on Uranus before it had ever been recognized with the telescope. But when the astronomers in the observatories were told by their mathematical brethren where to look they found the planet within half an hour after the search began. So it is possible the suspected great planet beyond Neptune may be within the range of telescopic vision, but may not be detected until elaborate calculations have deduced its place in the heavens. As a populous city is said to furnish the best hiding-place for a man who would escape the attention of his fellow beings, so the star-sprinkled sky is able to conceal among its multitudes worlds both great and small until the most painstaking detective methods bring them to recognition.
Very naturally the moon has always been a great favorite with those who, either in a scientific or in a literary spirit, have speculated about the plurality of inhabited worlds. The reasons for the preference accorded to the moon in this regard are evident. Unless a comet should brush us--as a comet is suspected of having done already--no celestial body, of any pretensions to size, can ever approach as near to the earth as the moon is, at least while the solar system continues to obey the organic laws that now control it. It is only a step from the earth to the moon. What are 240,000 miles in comparison with the distances of the stars, or even with the distances of the planets? Jupiter, driving between the earth and the moon, would occupy more than one third of the intervening space with the chariot of his mighty globe; Saturn, with broad wings outspread, would span more than two thirds of the distance; and the sun, so far from being able to get through at all, would overlap the way more than 300,000 miles on each side.