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.

CHAPTER VIII

THE MOON, CHILD OF THE EARTH AND THE SUN

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.

In consequence, of course, of its nearness, the moon is the only member of the planetary system whose principal features are visible to the naked eye.  In truth, the naked eye perceives the larger configurations of the lunar surface more clearly than the most powerful telescope shows the details on the disk of Mars.  Long before the time of Galileo and the invention of the telescope, men had noticed that the face of the moon bears a resemblance to the appearance that the earth would present if viewed from afar off.  In remote antiquity there were philosophers who thought that the moon was an inhabited world, and very early the romancers took up the theme.  Lucian, the Voltaire of the second century of our era, mercilessly scourged the pretenders of the earth from an imaginary point of vantage on the moon, which enabled him to peer down into their secrets.  Lucian’s description of the appearance of the earth from the moon shows how clearly defined in his day had become the conception of our globe as only an atom in space.