[Footnote 22: We have a convincing proof of the light reflected from the earth at this time, in the dusky light perceived on a part of the moon that is not enlightened by the sun. Astron. Art. 1412.] Enough--said the Marchioness, in her lively manner; I shall easily learn the rest when I like: let me stop a moment, and trace the moon through her monthly circle. I see that in general that planet and the earth have very different degrees of light, and I imagine that when we have the full-moon all the luminous side of the moon is turned toward all the part of our globe which is obscure; and that, at that time, the inhabitants cannot discern us at all, but say they have _new-earth_. I should not chuse to be obnoxious to reproach for obliging you to enter into a long explanation of any thing so easily understood, but the eclipses--how are they effected? You could guess it without difficulty, I replied. When we have a new moon, and she, being between us and the sun, presents her dark side to our luminous half, the shadow of this obscure part falls on the earth; so that wherever the moon is in a direct line under the sun, she hides that luminary from our sight, and darkens a part of the enlightened side of our globe; this, then, forms an eclipse of the sun to us during the day-time, and an eclipse of the earth to the moon during her night. When the moon is at the full, the earth is between her and the sun, the shaded side of the earth towards the light side of the moon. If the earth's shadow fall directly on the moon, it darkens the luminous half that we see; 'tis then we have an eclipse of the moon in our night, and the moon, an eclipse of the sun in her day. What prevents an eclipse every time the moon is between the sun and us, or the earth between the sun and moon, is this; it often happens that these three bodies are not placed exactly in a line, in which case the one that would occasion the eclipse throws its shadow on one side of the other and consequently does not obstruct its light.