In the revolutions of the moon we find anew proof of what we have advanced.  When it stops and grows less it does not consume itself in all its body, but in the measure that it deposits or absorbs the light which surrounds it, it presents to us the image of its decrease or of its increase.  If we wish an evident proof that the moon does not consume its body when at rest, we have only to open our eyes.  If you look at it in a cloudless and clear sky, you observe, when it has taken the complete form of a crescent, that the part, which is dark and not lighted up, describes a circle equal to that which the full moon forms.  Thus the eye can take in the whole circle, if it adds to the illuminated part this obscure and dark curve.  And do not tell me that the light of the moon is borrowed, diminishing or increasing in proportion as it approaches or recedes from the sun.  That is not now the object of our research; we only wish to prove that its body differs from the light which makes it shine.  I wish you to have the same idea of the sun; except however that the one, after having once received light and having mixed it with its substance, does not lay it down again, whilst the other, turn by turn, putting off and reclothing itself again with light, proves by that which takes place in itself what we have said of the sun.