[Footnote 20: When the moon is viewed through a telescope its spots bear no resemblance to the human face; but on contemplating it with the naked eye, it is easy to imagine that form; and it is become so common to talk of the face on the moon, that even an astronomer can hardly divest himself of the idea.] [Footnote 21: The earth always answers to one side of the moon, but not the same point in the sky.] All the planets, said the Marchioness, are like us human beings, who always attribute to others what belongs to ourselves. The earth says; _it is not I who turn, it is the sun_. The moon says; _it is not I who vibrate, but the earth_: there is error throughout. I would not advise you to attempt making any reform, answered I; you had better consider the remaining proofs of the resemblance which the earth and moon bear to each other. Figure to yourself those two globes suspended in the heavens. You know the sun always enlightens one half of a circular body, whilst the other half remains in the shade. There is then one half of both the earth and the moon, which is enlightened by the sun, or in other words, in which it is day, and the other half in which it is night. Observe likewise that as a ball moves with less force and celerity after it has struck against a wall from which it flies off to an opposite place, so the light is weaker when reflected to us from a body that only receives it. The pale light of the moon is in reality the brilliancy of the sun, but as we receive it merely by reflection, in coming to us, it is deprived of its strength. Of course, it shines with much greater splendour on the moon, and for the same reason the dazzling light received by our globe, from the sun, must appear faint, when reflected back to the moon. That part of the moon which to us appears luminous during the night, is the side which has day-light; and the part of the earth which is illuminated by the day, when turned toward the dark side of the moon, affords equal light to her. All this depends on the mutual position of the earth and moon. During the first days of the month, when the moon is not discernible, she is placed between the sun and us, and proceeding in the day time with the sun: the luminous side is therefore necessarily turned to the sun, whilst the dark part is towards the earth. We are unable to see the unenlightened side of the moon, but this dark half viewing the part of our globe in which it is day, is assisted by our light, and though invisible to us, has the advantage of seeing the earth as a full moon: it is then to the lunar inhabitants _full-earth_, if I may so express myself.[22] After this, the moon advancing in her monthly round, and no longer between the sun and earth, turns towards us a small part of her enlightened half, and that we call the crescent. At the same time that part of the moon which is involved in the obscurity of night, ceases so see all the luminous side of the earth, and finds it continue to decrease.