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. "Especially did it occur to me to laugh at the men who were quarreling about the boundaries of their land, and at those who were proud because they cultivated the Sikyonian plain, or owned that part of Marathon around Oenoe, or held possession of a thousand acres at Acharnae. Of the whole of Greece, as it then appeared to me from above, being about the size of four fingers, I think Attica was in proportion a mere speck. So that I wondered on what condition it was left to these rich men to be proud."[14] [Footnote 14: Ikaromenippus; or, Above the Clouds. Prof. D.C. Brown's translation.] Such scenes as Lucian beheld, in imagination, upon the earth while looking from the moon, many would fain behold, with telescopic aid, upon the moon while looking from the earth. Galileo believed that the details of the lunar surface revealed by his telescope closely resembled in their nature the features of the earth's surface, and for a long time, as the telescope continued to be improved, observers were impressed with the belief that the moon possessed not only mountains and plains, but seas and oceans also. It was the discovery that the moon has no perceptible atmosphere that first seriously undermined the theory of its habitability. Yet, as was remarked in the introductory chapter, there has of late been some change of view concerning a lunar atmosphere; but the change has been not so much in the ascertained facts as in the way of looking at those facts. But before we discuss this matter, it will be well to state what is known beyond peradventure about the moon.