If the Moon is a vessel how can the vessel itself wax and wane?

And inasmuch as the Moon seems to be made for the numbering of thirty days, and consists altogether of these parts., when the thirty days come to an end, it (itself) ceases to exist. For it is not one thing and its Light another thing. And because "the Moon is a vessel into whose midst the Light is poured," even if that Light were lacking, the vessel itself as [P. 20, l.9.] regards its own nature with (i.e., in proportion to) the aforesaid Light, would not be able to come to an end or increase, since all vessels give evidence that they themselves exist in their natural size, and if there falls into them a greater amount the vessels do not grow larger, and if less falls into them, they do not shrink. And if anything that is in them is emptied out and vanishes, those vessels themselves do not vanish. And since they call the Moon the Ship of Light, let a demonstration come forth from a ship to refute them, (namely), when it is filled or emptied it remains in its proper size, that is to say (in the real proportion) of its length and breadth and height. But in the case of this Ship of Light, which, they say, is in the heavens, the Light which is poured into it or emptied from it is visible to us, but the Ship itself is not visible ; either let them then tell [P. 27.] us the nature of the vessel, that we may know that for this purpose it was arranged that it might be filled and emptied as they say ; or let them tell us if that vessel itself is filled and built up and rises, and is completed and demolished and comes down. It is evident even to blind men who do not see that the Moon is made for the numbering of the months, and is not for a Refining.