Science has made such progress, and common sense has so far kept pace with it, that the old idea that this was the only inhabited sphere in the universe is now completely exploded. There is no reason to believe that our planet is the only one in our solar system which is devoted to a useful career; nor is there any ground for imagining that our sun is the only one, of the myriad of suns we see every night, which gives light, and heat, and happiness to human creatures. On the contrary, the supreme wisdom of the Deity affords a fair presumption that this little planet of ours is but as a grain of sand among the worlds which have been created for the glory of God, and that each planet after its kind is fitted for the habitation of creatures whose office and purpose it is to thank and bless Him for their existence. Moons may be an exception for a time. Of all this we know but little, and can only conjecture vaguely. As science advances, we may have telescopic instruments so superior to those now in use that we shall be able to decipher the moon's surface as plainly as a distant shore on our own planet. But visits thither must ever remain as impossible as they are at present. The story of Hans Pfall will remain a brilliant imagination to the end of time. "In consequence of the moon having no atmosphere, or but a very thin one, all celestial objects must be seen with very great distinctness. The earth, when full, appears to an inhabitant of the moon thirteen times as large as the moon appears to us; that is, its diameter is about 3-6/10 times as large as our apparent lunar diameter. It is always on the same part of the heaven, when seen from the same part of the moon. M. Quetelet, in his _Astronomie Elémentaire_, Paris, 1826, a very good work, which ought to be translated, has the following remarks on the appearance of the earth at the moon, which we would rather quote than vouch for, though they may possibly be well founded. "Our vast continents, our seas, even our forests are visible to them; they perceive the enormous piles of ice collected at the poles, and the girdle of vegetation which extends on both sides of the equator; as well as the clouds which float over our heads, and sometimes hide us from them. The burning of a town or forest could not escape them, and if they had good optical instruments, they could even see the building of a new town, or the sailing of a fleet." The lunar day, as we shall afterwards see, is equivalent to our actual month of 29½ days: though the rotation of the moon on her axis is performed in the sidereal month of 27 days 8 hours nearly. Hence the inhabitant of the moon sees the sun for 14¾ of our days together, which time is followed by a night of the same duration. Of course the existence of any animal like man is impossible there, as well on this account as on that of the want of an atmosphere.